JigStones, Moldmaking and Casting Tips

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What Are JigStones?

jigstonesJigStones are blocks cast from plaster, resin or cement that are used to construct structures block by block. The JigStones kit provides the molds necessary so that the modeler can make as many JigStones as desired from whatever material is desired. The blocks are designed to fit together somewhat like an interlocking jigsaw puzzle and are secured together with adhesive. The kit contains three shapes of "large" units and four shapes of "small" or filler units. There are also two types of triangular units for making a sloped roof line, and two widths of window sills. There is another piece that represents a stack of flat stones. This part is used for topping walls, a practice common in the UK but hardly found in the US. Both round and square chimney pots are provided. Again, chimney pots are mostly found in the UK and Europe.

JigStones are available from the US distributor, Linda Spencer at P.O. Box 211, Elbridge, NY, 13060, (315-689-3402).

JigStones are a labor intensive method of constructing buildings, but when made with cement and the proper adhesives, the buildings are tough and can be left outdoor year around. Even though the mold sets are fairly expensive, the recurring cost of construction is quite low, cement and plaster are cheap. The total out of pocket cost of the first medium sized building, including the cost of the mold set, is less than the cost of most building kits. Subsequent buildings can cost less than $10. If you've got more time than money, JigStones are a practical way to save some money.

The process of making JigStones involves many steps and can be quite time consuming.

JigStones come in at least two scales, "G" and 1:32 scale. Both the block sizes and the door and window sizes are adjusted to match the scale. I have only the 1:32 kit so I am not sure what scale the larger kits match closest to. Even the 1:32 kit is a little small, the doors scale out to just 6' high.

jigstones moldsThe 1:32 JigStones molds are made of a very pliable but tough silicone rubber so that it is possible to get "green" parts from the molds yet fully cured parts can be removed without the aid of a mold release.

Each of the five molds in the kit makes a different kind of part. The mold in the upper left makes a roof panel. The panels are about 3.5" by 6.5" which is a little small for a large roof, but they can be tiled and bonded together over a backing sheet of thin plywood to make roofs that are as large as desired. The yellowish mold in the upper right makes doors and windows and is intended to be used with a plastic resin. The mold in the lower left makes the thinner filler units. The mold in the lower center makes the larger and thicker main building blocks and some other details. The mold in the lower right makes chimney pots.

The molds for the larger scales are partitioned differently.

7120 moldUsing just the molds that come in the kits results in a continual shortage of the two largest blocks. This mold is one that I made myself so that I could manufacture a better ratio of parts. This mold was made in Polytek 7120 silicon mold rubber. Previous to this one, I had made one with Alumilite mold rubber. It worked ok but it wasn't extremely pliable and it eventually tore. I also made two versions in Polytek 7430 rubber, but I had serious sticking problems when parts were allowed to cure in the mold.

doors and windowsDoor and window pieces are too fragile to cast in the same material that is used for the blocks. The window mold produces a part like this. This one was cast in Alumilite two part casting resin. This particular one was one of my first attempts and it has some bubbles in it, which is probably the reason that it hasn't been cut up yet.

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JigStones Starter Projects

trolly stop shelterThe full JigStones kit comes with suggestions for some small starter projects that can be built with only a few stones. This trolley stop shelter was one of those projects. I choose to cast the blocks for this project and the two to follow from Hydrocal plaster. The blocks were assembled with Liquid Nails adhesive. This material is tacky and holds fairly firm from the outset.

The inside surface of the shelter is the non-detailed side of the blocks and didn't look so good. A coat of plaster on the inside filled some of the holes left by the small filler pieces and hid the joints. When adding plaster to any part made of plaster, it is critical to spray water on the old surface until it won't take up any more water otherwise the cured surface will leech water out of the new plaster and the new plaster won't spread or set correctly.

After assembly, the shelter was painted and lightly weathered using an airbrush.

hut front viewA little more complicated starter project is this lineside shack. This uses a door and window casting as well. It was constructed at the same time as the other two projects.

hut back viewThe backside of the lineside shack has a window. I chose to leave the parasitic film that results during casting in this window because it looks like really dirty glass.

coal binThe third starter project was this coal bin. This is the easiest project to build. The inside was finished with plaster like the trolley stop shelter. The structure was then painted gray on the outside and black on the inside.

The "coal" pile was made by cutting a piece of black construction paper about 1" larger than the bin. The edges were folded back and the paper was stuffed up into the bin from the back and then mashed around to get the approximate shape of the coal pile. Matte medium was then sprayed on the paper so that it soaked the paper and ran down the sides between the paper and the walls. This secured the paper in place. I didn't have any real coal or charcoal that I could crush so I sprinkled some very dark colored ballast in the bin and soaked it again with matte medium so that the paper was completely covered. More ballast was sprinkled on the tops of the walls to simulate spilled coal. After the matte medium had dried, I painted the "coal" with engine black paint to get the right color and then blackwashed the whole thing.

080403_girr_coal_bin_3772.jpgSometime since the coal bin was originally built, I added some real coal. Nothing looks more like coal than real coal and it scales very well.

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Larger Projects

warehouseThis warehouse is built with a combination of wood, corrugated soda cans and JigStones. The concrete JigStones form a foundation for the building and hold the wood parts above the soil.

bank wallI've started a larger project. This 13" x 13" wall was built from 1:32 scale plaster JigStones, but sized for 1:24 scale. It will eventually be the side wall of a bank building on the indoor Geologically Improbable Rail Road. The window openings are sized for PV sheet window molds, but Grandt Line windows and doors could be used as well. If I had any mold rubber handy, I would have made a quarter wall section and then made a mold of that so that the whole wall could be made from four pieces. As it was, I build it from individual blocks. Molding large wall sections would be the hot setup for making structures with a lot of repeating walls, such as a roundhouse or an engine house.

wall moldWhen it came time to start on the front wall of the bank, I elected to make a major section of the wall as a molded item. This is the largest symmetrical section of the front wall that could be used in four places. The master was built from individual stones very carefully such that the adhesive filled all the gaps between the stones. The master was then sealed with clear coat lacquer and glued down to a mold box made from 0.015" styrene. The mold box will usually be destroyed to remove the cured mold, so I make it cheap and dirty. I just tack it together with Zap-CA and seal any gaps on the outside with Scotch tape. The mold box should leave less only a 1/8" to 1/4" wall around the master. A small mold is easier to peel away from the work piece and it consumes less rubber. The mold box should be no deeper than 1/8" to 1/4" more than the thickness of the master for the same reasons.

The master used for the mold is not really usable as a construction article because the surface is sealed such that it becomes glossy and it won't take paint the same as the molded pieces. The surface of the master must be VERY well sealed or the mold rubber will soak into the pores and bond strongly to the master. This makes it difficult to remove the master and makes a mold that will stick to every subsequent part cast in it.

The master has to be carefully sealed against the bottom of the box so that air trapped under the master does not bubble out. A recurring bubble path tends to create a hole all the way through the mold. A few hours after the mold has been poured, it should be inspected for bubbles. Any bubble path should be filled with new rubber. Any easy way to do this is to mix a little rubber and apply it to the hole with a toothpick. Another toothpick is used to probe the hole and hold it open. Probing in the hole will tend to cause bubbles to rise and the liquid rubber will be allowed to flow to the bottom. Keep a pile of rubber at the top of the hole so that when the toothpick is withdrawn, the excess rubber is drawn down the hold instead of air. Keep doing this and the hole will eventually fill. When the toothpick can be pressed to the bottom of the hole and a bubble doesn't come up around it, the hole is filled. Just make sure that when the toothpick if finally withdrawn that there is excess liquid rubber at the top so that more air doesn't get drawn down the hole to fill the volume that the toothpick left behind.

wall section planI drew this template in MacDrawPro for the 1:32 scale JigStones and then built the wall section over it. This made it easy to plan the building. It isn't quite perfect. Over a 13" high wall, it is off by about 3/16".

It doesn't seem necessary to post the template file because there are probably very few others out there that could use it. Somebody would have to have the 1:32 scale JigStones set AND use a Macintosh AND use MacDrawPro or Claris Draw for the Mac. Claris Draw for Windows will not read MacDrawPro files. However, if somebody wants it email me for it.

partial bank bldgAfter several window sections were cast, in the special purpose mold, the front of the bank was assembled. The two walls are mounted to plywood backing sheets which are in turn mounted to a lift out frame. This whole assembly provides access to the rear of the layout where it is too far to reach from the front. The rest of the frame section will eventually be filled out with other building flats. The plywood behind the windows was cut out to allow the windows to be eventually lit, but in the interim, black construction paper was glued over the window openings in the plywood. PV vacuum formed windows with the panes cut out and real glass glazing will be installed in the window openings. When it comes time to illuminate the building, the paper will be cut out from the back and window boxes will be installed behind the windows.

As it turned out, building the side and front wall sections separately was not a real good plan. JigStones are not a real precise construction media and getting them to fit at the corner was a real job involving some reconstruction of parts of the walls and a considerable amount of fiddling and filing. Even then, the corner didn't come out really clean.

bank buildingThe bank is looking better after painting, black wash and window installation. The building is still very plain, it needs a sign and some details around the door and a boardwalk in front.

loose stonesBefore starting a project like this one, it is important to have a large supply of stones ready made and handy. The piles are the larger stones, the smaller ones are in another box. If the large and small pieces are kept in the same box, the little ones migrate to the bottom and are hard to find when needed.

farmhouse under constructionThis is a partially completed farmhouse built from one of the enclosed plans. This building was built from cement stones made from both RapidSet CementAll and Quikrete Anchoring Cement.

farmhouse detailThis view shows an inside and outside corner built with parts from different cement mixes so that the joints between the various parts can be seen. There are three types of "large" unit and three types of "small" or filler unit. The large units are the "H" shaped pieces and the header blocks used over the windows. The header blocks have rock detail on one side and a flat side on the other. When used as a header, I place the flat side out to represent a single large stone. The smaller units are used to fill in the gaps in the larger stones.

farmhouse inside detailOn the inside, JigStones are not so pretty. This view shows how an inside and outside corner look from the inside of the structure.

If the building will experience freezing conditions, then the walls should be sealed. If moisture creeps between the stones and then freezes, the expansion of the ice could tear the building apart. Walls can be sealed on the inside by coating the inside of the walls with cement.

wire meshIt is also a good idea to seal the floor so that the inside of the building stays fairly dry. This is also done with cement. I elected to reinforce the floor with a wire mesh, as is done with real floors. 1/8" hardware cloth is easy to work with and fits nicely.

poured floorThe floor is sealed by pouring 1/4" or so of cement inside. If wiring access is desired, a hole should be left in the floor by placing a small object in the floor to leave a hole in the cement. Doors must be blocked so that the cement won't run out the doors. Be sure to work on a surface that cement will release from or you might cement your building down. Aluminum foil works pretty well for a work surface. The cement mix should be pretty thin so that it self levels. In this case, the cement was too thick and didn't self level properly. I used Quikrete Quick Set that didn't work out too well as a casting cement, but will do fine as a floor.

Another way to do a floor is to cut a WonderBoard piece the same size as the structure BEFORE you start. Then attach the first course of blocks to the base and build upward. It is much easier to handle the building under construction when it is reinforced by a solid floor.

jigstones roof tileWhile a roof tile is provided in the JigStones kit, little help is provided about how to use it. The tile is too small to make a complete roof section for anything but a very small building so that multiple sections need to be tiled together to make a roof. Further, the tiles need to be shaped to some odd sizes and then supported and bonded together.

farmhouse with temporary roofA way to go about this is to make a cardboard template to get the right sizes and shapes for the roof sections, and then to cut thin plywood to make a complete subroof.

farmhouse subroof assemblySince the cement or plaster roof tiles are fairly fragile, the subroof should be assembled in one piece. JigStones sloped stones can be used to fixture the subroof at the correct angle. All the joints should be well sealed with adhesive. The subroof should be water sealed. Liquid Nails will adhere well to a wood surface treated with Thompson's Water Seal.

The subroof can also be made from WonderBoard. It will be thicker than using thin plywood but won't have any issues with water either.

farmhouse with partial roofThe tiles can be scribed on the backside with a knife and then broken along the scribe lines. Cement will dull the knife blades quickly, so have a bunch of spare blades handy.

Cement doesn't break nearly as cleanly as glass or styrene so don't expect a good yield. The results from some failed attempts to cut the tiles can be seen in the picture. Further, the edges are rarely clean so some additional cleanup is usually required. If more material needs to be removed, it can often be chewed off in pieces with a pair of gas pliers. Filing may be required to do the last of the work, but use an old file as cement will quickly ruin it anyway. Cutting the tiles with a grinding tool results in so much vibration that the tiles will often break elsewhere. A cutoff wheel doesn't even make a dent.

Plaster tiles are much easier to deal with than cement tiles. They break cleaner with good yield and are easy to file and shape. Have a file card handy to clean excess plaster from the file.

Cement tiles seem to break cleaner if they are mixed with a wetter cement mixture. The roof tiles also seem to break cleaner if they are poured from the mixing container first and are lump free. Even small lumps in the mix result in harder spots and make it more likely that a tile will fail to cleave cleanly.

An even better way to cut odd shaped roof tiles is to scribe them in the mold before the cement or plaster even sets up. Lay a template piece over the green part in the mold and scribe along the edges with a utility knife full through to the mold. Then the yield can be nearly 100%.

farmhouse with full roofThe tiles are bonded to the subroof and then joined with a mortar made of casting cement to seal them. Don't worry too much if the tiles don't fit real well, the cement mortar can fill amazing gaps. Be sure to wet the cured cement pieces or they will leech the water out of the new cement before it has a chance to set properly. It will probably be necessary to rewet the new cement to work it. Excess cement can be scraped off with a small carving tool and the residual washed off with a spray bottle and water.

If desired, the completed roof can be bonded to the structure, but if the floor has been sealed, access to the interior of the structure is then impossible. This roof is intended to be removable.

finished farmhouse frontIt took three weeks of intermittent work to get this far. After painting and window installation, the structure is almost finished. I still need to glaze the windows and touch up the paint in a few places.

finished farmhouse backIt is unlikely that this structure will blow away because it weighs just over 7 lbs. It took 2/3 of a caulking gun full of Liquid Nails to glue it all together. After the windows are glazed, it goes out on the layout where it will stay for long term evaluation of the weather resistance of JigStones.

weathered farmhouseAfter a year out in the weather, the farmhouse has held up reasonably well. My son kicked it once and broke off part of the lean-to, it was fairly easy to fix. One of the chimney pots got chipped. The mortar lines on the roof cracked and have been patched with Lexel. The worst change is that the paint on the roof has severely faded. It looks like Floquil doesn't hold up to the sun very well. It might be better to tint the cement mix to the desired color when the parts are poured.

071230_girr_farmhouse.jpgAfter 7 full years on the layout, the building hasn't changed much after the first year. The lean-to on the side has been broken, probably got stepped on, and the roof has a couple of cracks, but otherwise, it has held up well.

080729_girr_church_5422.jpgA stone church was the on the list for a long time but it took me awhile to get around to it. Most US churches built of stone are Catholic so I elected to use some simple features that were found in Catholic churches especially the stained glass windows. I knew that there were some JigStones church plans out there, but I couldn't find the plan set that came with my JigStones molds so I just built one without a formal plan.

The first step was to mock up some of the features on the bench to gauge the overall size. I knew that I need 5 large stones across the side to accommodate the stained glass windows so that pretty much set the size which was about right, a little less than a foot across and deep in my 1:32 scale JigStones set. I also mocked up an arch to frame the front door.

080729_girr_church_5423.jpgI also mocked up a window. The stained glass image was one of two that I found on the internet, just Google for stained glass church windows to find many examples. This one is clearly a Catholic type image. I have two suitable images, I'll use both on one side and repeat them on the other side. I don't intend to build an interior, but I want enough light to enter the church to shine back through the windows. The actual image will be printed on ink jet transparency material and then pressed up against the back of a clear glass pane, both to support the image and to help block some of the UV. I expect the images to fade over time, but they will be easily replaceable.

080807_girr_church_progress_5474.jpgI built the church on a 1/4" WonderBoard base, offset from the center. I wanted a grass strip go go up the right side and nothing on the left side as I am going to fill that area with a tree and a cemetery. Many rural Catholic churches have an adjacent cemetery.

080808_girr_church_progress_5476.jpgThe building was built up in typical JigStones fashion using blocks cast in RapidSet and Liquid Nails for Marble adhesive (because I had a tube that was already open). This stuff goes on pretty thick and is tan in color. It is very sticky and gets everywhere, but that doesn't matter much because it takes paint well. As long as the slop is spread out onto the surface of the stones, it will vanish behind the paint.

I ran out of that caulking gun tube about 2/3 of the way up so I went to get more and the local hardware store didn't have that exact kind so I started using Liquid Nails Heavy Duty instead. I actually like this stuff better because it spreads better and actually set more quickly. It goes on the same color as the blocks, but as it sets, it attains the same color as the other kind.

The doorway is fully blocked off as the door will be an add on piece.

080808_girr_church_progress_5477.jpgThe roof line was finished out but in the process, I added a diamond shaped window above the door. The front of the building will face west so I needed a window on the west side to admit light in the afternoon. The back window, facing east, will not have a stained glass insert as it will not be visible on the layout. It is there to admit light in the morning.

080811_girr_church_progress_5488.jpgI then added some blocks in the inside to provide support for the subroof. The weight of the subroof will bear on these blocks. Also the top of the diamond window in the front looked a little weak, so these blocks provided considerable strengthening at that point. I originally set them a little low and then built them up with layers of RapidSet to set the subroof at the right height.

080809_girr_church_progress_5481.jpgThe subroof was made from WonderBoard. I cut two pieces the right size and placed them on the supports verifying the position. Then I laid a bead of cement across the joint and let it set fully. I then carefully removed the partially completed subroof, turned it over and laid another bead of cement on the inside of the joint along with some JigStones angle blocks to provide additional support.

The steeple was built on top of the subroof using more JigStones blocks and a custom cast final. The final was made from a mold of four styrene triangles taped together and then flipped over to cast the part.

080810_girr_church_progress_5484.jpgThe building was painted with Rustoleum flat white. Rustoleum seems to keep it's color well in the sun and it also covers over the undesired adhesive very well. It also dries almost instantly.

The roof was built with tinted RapidSet in a Spanish tile mold that I made myself following the method used to make the roof of my Santa Fe style mission station. Since the tile that I used wasn't the right size, I scribed the pieces as necessary in the mold. This time my yield was quite good. With RapidSet, the scribe lines should be made just 10 minutes after the cement is poured.

The sidewalk was made by spreading RapidSet in a thin layer and then scribing cracks after it has set for few minutes. Areas where I didn't want the RapidSet to go were masked with blue painter's tape.

After the sidewalk was in, I masked that with painter's tape and then sprayed a 50:50 mix of Titebond II and water on the area where the "grass" was supposed to be. I then spread colored sand, mostly green with a little yellow mixed in, over that area and then oversprayed the sand again with the glue mixture. This makes an acceptable lawn that should be durable.

080811_girr_church_progress_5487.jpgThe glass windows were scribed and broken to shape. Broken is the operative word as I broke lots of pieces before I managed to make 5 of the 6 windows. I went through two 8" x 10" pieces of glass and I still need to make one more window. Even when the windows broke almost right, I still had to break off little pieces to achieve roughly the right size.

After the window openings were filed to clean up their edges, the windows were initially held in place with small drops of Zap-A-Gap CA in the corners. Then a bead of clear Lexel was used to finally bond them in place.

door stuffI had a double door mold that I had used several times in the past, but it was too small for the front door of a church. I made another master from coffee stirrers and little bits of 18 ga copper wire and poured a Polytek 7120 rubber mold. I cast a piece in both Alumilite (the tan one) and a piece in RapidSet (the gray one). I think that I'll use the cement piece after it is painted. It will be simply glued to the front of the church.

080811_girr_church_progress_5493.jpgThe cement door was painted and attached to the front with Liquid Nails. The glass panes have been installed (except the back one) and I am waiting for the Lexel to dry before I try to fit the stained glass transparencies behind them.

080812_girr_church_progress_5495.jpgThe church is basically finished except for the back window which will go in when I get some more glass. It is supposed to sit next to the hotel. I'll used a square foot or so of real estate on the left for the cemetery.

080812_girr_church_progress_5496.jpgThe lighting wasn't real good when this picture was taken, it was overcast and the building was in the shadow of the ivy covered fence so I didn't get much light inside, but the stained glass window can be seen here anyway.

080812_girr_church_progress_5497.jpgAfter the sun came out, I was able to see the stained glass image in the direct light of the back window, but the other window on that side was still dark. It looks like the stained glass won't show up well from the outside. Interior lighting will probably work, but that will come much later.

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Casting and Mold Making Materials

There are two basic classes of materials that JigStones can be made with, gypsum products (plaster and cement) and resin products (plastics).


Plaster is inexpensive and sets up quickly so that a large quantity of stones can be made in a short time. Of all the plasters available, a brand called Hydrocal from U.S. Gypsum seems to be the best one. Hydrocal is usually available from building supply outlets at between $15 to $20 for a 100 lb bag. The material sets pure white. There are many other plasters available in smaller quantities in hardware stores, but don't mess with them. Go for the good stuff.

Hydrocal is NOT suitable for use outdoors. It absorbs moisture like a sponge and will eventually disintegrate. However for indoors use, it works fine. Another downside is its white color. After being painted, if chipped, it shows white. This can be avoided by either mixing pigment into the dry plaster or by mixing it with water that has been dyed with RIT fabric dye.

Hydrocal is mixed 2 parts plaster to 1 part water by volume. Each of the larger JigStones 1:32 molds takes a little less than 1/2 cup of plaster to fill it. I usually mix 1-1/2 cups of plaster to 3/4 cup of water in a large paper cup using a popsicle stick to stir the mix and break up the clumps. This makes just about as much as I can use before it starts to set up in the cup.

When initially mixed, Hydrocal pours like light cream, after only a minute or so, it thickens to pancake batter, after another minute, it is unusable. Pour the mix into the smallest of the molds first and quickly pick out the bubbles with a toothpick. Level off the mix in the mold by drawing the popsicle stick across the mold to sweep excess plaster off the mold, or into parts that aren't filled. It's important to get the top of the mold flat so that all your parts will have the same thickness and be flat on the back.

Popsicle sticks (also called coffee stirrers) are available in bulk really cheap at Smart and Final (a west cost warehouse store chain) or other bulk food service stores. If there is more than one size available, get a box of each. The typical 4-1/2" stick is strong enough to mix plaster and long enough to reach across the molds to level them. The thinner and narrower 5-1/2" sticks make good boards for wood buildings and are excellent glue applicators.

Hydrocal sets hard enough to get out of the molds with excellent yield in 40 minutes from the time it is mixed. Some people claim that they can get the parts out in 10 minutes, but I can't. I break most of them. These parts are still "green" as they have excess water in them. They have to sit overnight to dry out. Parts in the "green" state will be a little bit gray in color, when fully set and dried out, they will be completely white.

After the parts have been demolded, it is often necessary to dress most of them. They might still have some flash around the edges that can be easily removed with a flat mill file. It is easier to file them in the green state but plaster is soft enough so that it can be done in the fully set up state as well.


Cement can be used to make structures that will survive well out of doors. There are hundreds of cement compositions but only a few are suitable for casting JigStones. These mixes are often called anchoring or floor leveling cements. They set relatively quickly (although not nearly as fast as Hydrocal) and cure to a very high strength. They are water proof and are naturally colored.

Some of the brands of cement mixes appear to be regional. The stuff isn't valuable enough to ship very far from where it is manufactured. The US distributor of JigStones recommends a brand of anchoring cement called Thoro but I couldn't find this stuff.

RapidSet Cement All is a general patching cement that seems to provide very good results, but unlike its name, it doesn't set very rapidly. In about an hour, the parts are still very green and can be demolded with some yield loss due to breakage. After 8 hours, it has cured very hard and is easy to demold. You can make more blocks in a shorter period of time if you demold in the green state even with the yield loss. RapidSet takes couple of days for all the excess moisture to be absorbed or evaporated to the extent that the parts can be assembled unless you are using RapidSet as a mortar where the moisture is an advantage. RapidSet cures to a uniform light gray color, similar to ordinary cement. I mix RapidSet the same as plaster, 2 parts cement to 1 part water by volume.

RapidSet can be tinted with stucco tints, usually about 1% by weight. A good digital postal scale comes in very handy when doing these mixes. I have one that will read up to 5 lbs in 0.1 oz units. This is good enough for getting a 1% mix close enough to right. I usually mix 50 oz of Cement and 0.5 oz of tint in a gallon size freezer bag so that the bag can be turned over and over to dry mix the tint.

Quikrete Quick Set mix didn't work well for me. Not only does it set slowly, the parts are not very hard when mixed so that the cement can be easily poured. It also cures to a medium gray color with white splotches. I expect the white color is excess lime.

Quikrete Anchoring Cement tends to expand upon curing to make it hold fast into a drilled hole. This mix sets to a green state in about an hour and it is possible to get it from the molds with some difficulty. This mix can also be mixed 2:1 with water so that it pours well. It cures to a medium gray color with white splotches.

Cleanup of cement parts should be done in the green state when they are still a little soft. After cement sets up, it can be really hard to file and is very tough on tools.


The amount of water used with the mix will have profound impacts on the ability to make parts that are free of bubbles, cure time and the ultimate strength of the parts. More water will allow easier pouring and virtually eliminate bubble problems but it will also extend the set time. "More" water might be as little as half a teaspoon in a cup of water.

Each mix will require its own amount of water which may be very different from what the manufacturer recommends. For example, Quikrete called out for a 5-1/2:1 mix. This is so thick that it is unpourable. Rapid set recommends a 3:1 mix, but I find that 2:1 works better. In any event, to get the cement into the molds, especially the smaller ones, requires that the mix be fairly thin. You'll have to experiment with your mix to determine the correct amount of water. It is best to pour the smallest parts first, before the mix has had a chance to set up at all, this allows the mix to fill the smaller molds with minimal bubble problems. Pour the mix in slowly so that it has a chance to flow across the bottom of the mold. Bubbles are trapped when the mix is poured too quickly.

After the pour, its a good idea to shake or tap the mold to aid in releasing any remaining bubbles. The mixing stick can also be probed into the molds to dislodge bubbles. If the mix is thick, then probing will probably be required. For the deep chimney pot molds, pour then about 1/4 full, then probe with the mixing stick, then fill the molds. These are really hard to get bubble free.

Mixing cement with larger than recommended quantities of water will produce a softer product as a result. This is not all that bad because the parts are hard enough for the intended application and they file MUCH easier when necessary. Fully hard cement not only files slowly, but its really hard on the file. Parts mixed with "wet" cement also will be more porous than parts mixed with the "correct" amount of water. Using the "correct" amount of water will also make the mix difficult to pour. However, without excess water, the cement mixtures cure quicker and even with lower yield due to bubbles and breakage, the production rate of parts can be good.

I usually mix with just a little more water so that the mix pours better, however I have to wait longer to demold the parts. If the mix was just a little too wet Hydrocal parts will develop a film of water on top once they have cured to a green state. Most parts can be demolded green, but expect some breakage. Fully hard Hydrocal parts can be demolded in an hour, RapidSet mixed wet takes 8 hours to cure to near full hardness. I usually do only two batches of RapidSet a day so it takes awhile to accumulate enough stones for a large project. I test the cement that has flowed over the sides of the mold for hardness to determine when I can demold the parts. In general, if you can leave a fingernail mark on the material, it is still too soft to demold.

Resins and Rubbers

Two part resins can be used to make the door and window details that would be too fragile if cast in plaster or cement. Two part rubber materials can be used to make more molds of individual pieces or assembled sub structures.

Alumilite is a 2 part resin that is mixed 1:1. This stuff sets in about 3 minutes and makes a very strong tan colored part. The parts can be demolded in less than 15 minutes. Alumilite produces very hard, very strong parts. Alumilite costs about $1/oz. The 1:32 scale door and window mold requires only 1/2 oz of resin. Alumilite sets so quickly that it is easy to get bubbles trapped in the mold. Since the material is fairly clear before it sets, most of the bubbles can be seen and picked out with a toothpick, but you have to work quickly. Coating the molds with a light layer of baby powder does tend to allow the resin to flow into tight spots better and inhibits bubble formation. However, the setup time is so short that bubbles will set in place unless worked out in just a minute or so. The set up time of the resin can be retarded somewhat by keeping the two parts in a refrigerator but at the risk of accumulating moisture when it is poured from the bottles.

Alumilite is highly heat resistant, it'll retain its strength at least up to 150 °F, as high as I have tested it. Alumilite claims that their resin will retain its strength to 275 °F. Some of the other resins, such as Polytek 1512X and a resin I bought at a local plastics supplier turn to the consistency of butter at 150 °F.

Alumilite also supplies a mold rubber that is intended to work with their resin. This is a 10:1 mix rubber that sets up in about 4 hours and is fully cured in 24 hours. The rubber is fairly stiff and will tear if flexed too much. However it doesn't stick to fully cured cement parts as the rubber "fuzz" will tear away, eliminating the fuzz.

Polytek supplies various resin and rubber materials for casting and mold making.

Polytek 7430 urethane molding rubber is a pliable yet tough rubber that can be used to make molds. However, if a gypsum based master is used without being sealed, the mold will adhere strongly to the master, even with a liberal application of mold release. Cast parts that are allowed to cure in the mold will also stick. Green parts can be removed easily, but the yield is lower due to breakage. It would appear that gypsum masters and casting materials are porous enough so that the 7430 rubber "fuzz" gets locked up in the parts and won't release easily unless the parts are taken out while they are soft enough to release from the rubber. 7430 is so tear resistant that the rubber fuzz just stretches instead of tearing off, making the fuzz even worse.

Polytek 7120 is a 1:1 mix platinum catalyzed silicone rubber. This rubber is very flexible and works MUCH better with gypsum based materials. The master still MUST be sealed if it is made of a porous material, but gypsum based casting materials can cure fully hard in the mold and they don't stick at all. The parts of 7120 are deep blue and peach colored. The high contrast of these parts makes it easy to determine when they have been fully mixed. This rubber is stiffer in feel and consistency compared to the JigStones mold rubbers. The better performance of 7120 doesn't come without cost, at about $15/lb 7120 costs about twice as much as 7430. However, this stuff is almost an ideal material. If you don't want any mold hassles at all, use this stuff.

Polytek 1512X is a 1:1 mix two part resin that starts to set in 7 minutes or so and can be used to make windows and doors. This material has lower viscosity than Alumilite so that it flows into intricate molds better than Alumilite. It also remains liquid much longer so that there is time to work out the bubbles. However the material is opaque white so that bubbles cannot be detected visually. Parts can be demolded in an hour or so, but are still fairly soft. They will cure hard in 16 hours. 1512X parts are almost as strong as Alumilite at room temperature and are less brittle. Alumilite will snap if bent enough, 1512X yields without snapping. However, 1512X doesn't have anything like the heat resistance of Alumilite, it will soften badly when heated. 1512X costs about the same as Alumilite. There are other resins in the 1512 family including a clear formulation.

Mold Release is sometimes required to aid in demolding parts. The JigStones mold rubber does not seem to require a mold release agent which is convenient because then the residual mold release does not have to be cleaned off the parts. The Polytek 7430 rubber requires a release agent or it will adhere strongly to molded parts. Polytek 2300 is silicone oil based a release agent in a spray can for about $8 a can. Polytek 2601 is water a water based agent. Armor All Protectant also works as a water based release agent. I've been told that WD-40 works well but that doesn't square with my experience. In any event, a release agent must be cleaned off the parts or adhesives or paint may not stick well. Warm soapy water will usually take off the release agent. PolyTek 7120 mold rubber does not need a release agent for any casting material that I've tried.

071230_girr_mold_release_test.jpgDuring planning for making a Spanish tile roof for another project, I needed to know how to make an Alumilite casting in an Alumilite resin mold and not have the pieces stick together. I made this test sample by pouring 6 puddles of Alumilite resin onto a note pad, waiting for it to cure, and then treating three of the puddles with stuff that might work as mold release agents. I then poured as smaller puddle of Alumilite resin on four of the original puddles. The upper left was treated with olive oil cooking spray, the upper middle one used Polytek 2300 and the upper right puddle was treated with WD-40. The lower left puddle had no treatment. When the second puddles had cured I found that the Polytek sample released instantly, it literally fell off when I picked up the sample. The other three test cases are FIRMLY bonded in place. If you want something NOT to stick, they pay the money and get a mold release designed for that job.

double doorsThe JigStones kit doesn't include a double door so I made one from with a master made from styrene and coffee stirrers. The master, still in its mold box, is in the upper right. The upper center mold was made from Polytek 7430. The mold in the upper left is made from the Alumilite rubber. The two molds are slightly different as I had modified the master between making them. The doors in the lower left are cast in Polytek 1512X with the Alumilite mold. The doors in the lower center were made using Alumilite resin in the Polytek 7430 mold. The Polytek mold is covered with very small bubbles that leave a bumpy texture on the door. This looks ok, but it wasn't really desired. The painted door in the lower right was made from the Alumilite mold using Alumilite resin. This mold had no bubbles. Another mold made after this picture was taken with Polytek 7120 and it worked fine as well.

080325_girr_alumilite_volcano.jpgCasting resins have a shelf life if not stored properly. Alumilite will absorb moisture over time and the heat of curing will then cause the moisture to turn to steam and foam. I had a batch in some old dispenser bottles go bad and I can't throw liquid waste into the trash. However, I just poured the Part A from one bottle into the Part B bottle, screwed back on the cap, shook it up and set it in the bottom of a trash can. After a few seconds, I got a resin volcano and after that, it was solid waste.


I've been experimenting with adhesives on reject cement blocks. My test method is pretty simple, but it shows what will work out of doors. The test blocks used were fully cured and dry unless a damp surface was recommended by the adhesive instructions or common sense.

There were several adhesives that I didn't test because from previous experience, I expected that they wouldn't work very well. Aphilic resins (carpenter's glue, TiteBond II) set too slowly and don't hold up extremely well when immersed. GOOP adhesives set quickly, but I've had poor long term experience with them out of doors, they tend to disintegrate. Contact cement has poor cohesive strength and does not allow pieces to be slid into place. It also uses large quantities of harmful solvents. I wouldn't want to be using this stuff for hours on end.

Every one of the adhesives tested, save two, were carried by my local Home Depot store. Devcon Plastic Steel and Lexel are carried by True Value Hardware.

My test procedure follows:

  1. Mark the blocks with a Sharpie to identify the sample
  2. Coat the test blocks as recommended by the adhesive manufacturer. One or more samples of each type were tested. Generally, parts with weak bonds were retested to make sure that it wasn't an application problem.
  3. Press the blocks together. Clamping was NOT used as clamping during building assembly would not be practical.
  4. Set the samples aside to cure for 4 hours. Even though some of the adhesives may take longer to fully set, this is about as long as I would care to wait before I would want to handle the structure somehow. Many of the adhesives set much more quickly.
  5. Check the joints for strength by manually trying to break the joint. If the joint failed, note if adhesive or cohesive failure and prepare another sample for the wet test. If the joint wouldn't break under hand pressure, the sample goes on to the water immersion test.
  6. Soak the samples in water for 1 hour. This is long as I would expect standing water to exist in my environment.
  7. Manually retest for breakage. Note adhesive or cohesive failure

Adhesives fail in two primary ways. Adhesive failure is when the adhesive bond to the sample fails leaving adhesive on one side and bare surface on the other side. The adhesive may still be adhering to both surfaces, but in splotches where it has completely separated from one surface. Cohesive failure is when the adhesive itself separates leaving residue of adhesive sticking to both surfaces. Some adhesives may be so strong that the sample actually fails next to the joint leaving a layer of the sample on a layer of adhesive. This is not the fault of the adhesive.

For this test, joint strength is measured in only four levels.

Adhesive Strength Test Results

Adhesive Dry Wet Cost Setup
Strength Failure Strength Failure
RapidSet used as mortar Moderate to Strong Adhesive Moderate Adhesive Cheap gray <5 min Prototypical masonry method
Blocks should be damp to prevent leeching
Plumber's Epoxy Putty Moderate Adhesive Moderate AdhesiveNote2 $0.50 to $1/oz gray ~ 5 min Can be mixed quickly in very small batches as required
Devcon Plastic Steel Two Part Liquid Epoxy Very StrongNote1 n/a Strong to Very Strong Adhesive ~$2/oz black >30 minutes Too expensive for extensive use.
Liquid Nails For Small Projects Moderate Cohesive Moderate Adhesive ~$0.50/oz tan n/a Supplied in a squeeze tube
Doesn't require mixing
Liquid Nails LN-901 Exterior Grade Adhesive Moderate Cohesive Weak to Moderate Adhesive $0.20/oz tan n/a Doesn't require mixing
Applied with caulking gun
ProBond Polyurethane Adhesive Strong to Very Strong Adhesive Strong Note 1 $0.55/oz tan n/a Supplied in squeeze bottle
Requires work to be damp
Squeeze out tends to foam as it sets
RepairItQuik Multipurpose Epoxy Putty Strong n/a Moderate Adhesive $0.66/oz light gray ~5 min Very pliable
Easily mixed
InstaCrete Concrete Repair Epoxy Putty Moderate Adhesive Moderate Adhesive $0.66/oz medium gray ~5 min Stiff gritty mix
Easily mixed
FastSteel Steel Reinforced Epoxy Putty Strong n/a Moderate to Strong Adhesive $0.66/oz dark gray ~5 min Very pliable
Easily mixed
Lexel Sealant Strong Adhesive
Note 2
Moderate Adhesive $0.70/oz white or clear n/a Very pliable
Premixed Tile Adhesive and Grout Strong n/a Moderate Cohesive $0.10/oz light pink n/a Easy to apply, no mixing


  1. Work Failure. The bond held, but the block broke
  2. Work Failure in addition to bond failure

Each of these adhesives seems to work well enough to do the job based on strength alone.

Liquid nails seems to degrade somewhat when wet, but it has the advantage of allowing easy assembly, doesn't have pot life problems and is easy to apply, especially the LN-901 calking gun version. Squeeze out can be picked off with a toothpick.

Epoxies show little to no degradation due to moisture and all the putty versions set hard very quickly. Devcon Plastic Steel is clearly the strongest of the lot, but also the most expensive. They all have pot life complications. Excess squeeze out can be cleaned off with a toothpick except for Devcon Plastic Steel which is hard to clean up.

ProBond has no pot live problems and when applied properly to wet stones and seems quite strong. Squeeze out tends to wet the surface and is harder to clean off. It doesn't have any tack at all so it is a little hard to work with.

RapidSet used as a mortar is strong enough and clearly the cheapest, but it also has pot life problems and also needs wet stones. Excess squeeze out can be cleaned up with toothpick when partially set and any residual can be washed off with a pump bottle and water.

Tile grout (a class of tile materials collectively referred to as ThinSet) seems to have excellent dry strength but failed under moderate force after being soaked. You would think that a material designed to bond and grout tiles would be impervious to water.

Several adhesive performance parameters impact how easy and effective any given adhesive is to use. In the application of assembling JigStones, these parameters seem to be the most important.

Applications Tests Results

Adhesive Initial Tack Strength Duration Until Initial Setup Duration Until Complete Setup Gap Filling Capability Squeeze Out Clean Up Cleanup Notes
RapidSet used as mortar poor 1 hour several hours good moderate Easy with a toothpick after partial set
Residual will wash off with a water spray
Fillet the same color as the stones
Poor initial tack makes it difficult to add more stones without disturbing previous joints
Epoxy putty
(all kinds)
poor no initial tack <2 min fair
Too stiff to completely fill a gap
moderate Easy with a toothpick before it sets Sets too quickly
Hard to coat all surfaces of a joint
Too much time consumed mixing new batches
Liquid Nails
(both kinds)
good 0 hours good moderate Easy with a toothpick for up to several minutes Often needs to be spread on a surface with a coffee stirrer
ProBond poor ~15 min hours poor high Difficult
Wets damp blocks
Strong bond when set but hard to work with before full setup
Lexel fair 2 min 2 days excellent moderate Easy
Cleans up with water
Expensive, but very good bond
Premixed Tile Adhesive and Grout fair 24 hours 24 hours excellent moderate Easy
Cleans up with water
Inexpensive, no mixing required

All in all, the only adhesives that work well enough overall to use are Liquid Nails and the significantly more expensive Lexel. When purchased in a caulking gun tube, Liquid Nails is the least expensive save using cement as mortar. Both are tacky enough to allow easy construction and strong enough to hold together when wet. Plan on using a lot of adhesive. The farmhouse described above consumed 2/3 of a caulking gun tube of Liquid Nails.

However, the ultimate strength of Liquid Nails isn't as good as some of the other adhesives and it needs proper application or it will provide less than adequate results. Liquid Nails is so thick that it doesn't wet the stone surfaces well without some help. It must be spread out and massaged onto BOTH of the stone surfaces with a tool like a coffee stirrer or it will not adhere well at all. Since it doesn't wet cement or plaster surfaces well by itself, most of the squeeze out can be picked off and then the residual can be rubbed off the faces of the stones where it is not desired.

Lexel wets the surfaces much better than Liquid Nails and sets to a tack in an acceptably short time. It is also easier to clean up the squeeze out than Liquid Nails. Lexel is considerably stronger than Liquid Nails yet still retains some flexibility.

White Lexel works well with plaster as the squeezeout is the same color as the plaster. Clear Lexel is better on cement as it doesn't add its own color. Lexel must cure for 2 days before painting with latex paints. Their web site also cautions that it must cure for 30 days before being painted with oil based paints or the paint won't dry. I set up a test to determine how long I had to wait to paint Lexel with ordinary model paints. The test article consisted of two beads of Lexel run down a scrap of wood. One bead was left round to give it a higher volume to surface area ratio and the other bead was flattened to give it a low volume to surface area ratio. I found that after 2 days both Lexel samples accepted water and oil based model paints (PolyScale and Floquil) well with no hint of a problem. Both paints adhered to the adhesive and resisted being scraped off.

The more I have used Lexel, the more I like this stuff. There is also a version out that is intended for use with masonry. This product is called Set N' Stone. I have not been able to find it, but it sounds like it may work better with cement than either of the two versions that I have used already.

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© 2000-2008 George Schreyer
Created Mar 12, 2000
Last Updated August 12, 2008