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JigStones Tips
Contents
- What Are JigStones?
- JigStones Starter Projects
- Larger Projects
1 Jul 01 - Casting Materials 1 Jul 01
- Adhesives
What Are JigStones?
JigStones 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. The process of making JigStones involves many steps and can be quite time consuming.
- Clean out the molds from the last batch
- Mix the casting material such as cement
- Pour the material into the molds
- Work out the bubbles
- Level the mix in the molds
- Clean up or discard the mixing tools (I use plastic cups and coffee stirrers)
- Wait until the material sets
- Demold the parts
- Go back to the first step until enough parts have been accumulated
- Wait until the parts fully cure
- Clean the flash from each individual part
- Assemble the structure piece by piece
- File to fit as necessary
- Seal the inside of the structure
- Paint the structure if desired
- Add detail as desired
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.
The 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.
Using 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.
Door 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
The 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.
A 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.
The 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.
The 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.
[ Top ]
Larger Projects
This 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.
I'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.
When 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.
I 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.
After 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.
The 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.
Before 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.
This 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.
This 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.
On 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.
It 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.
The 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.
While 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.
A 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.
Since 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 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.
The 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.
It
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.
It 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.
After 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.
[ Top ]
Casting Materials
There are two basic classes of materials that JigStones can be made with, gypsum products (plaster and cement) and resin products (plastics).
Plaster
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
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.
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.
Mixing
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 stones 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 has the feel and consistency of 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.
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 and are less brittle. Alumilite will snap if bent enough, 1512X yields without snapping. 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. 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.
The 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.
Adhesives
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:
- Mark the blocks with a Sharpie to identify the sample
- 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.
- Press the blocks together. Clamping was NOT used as clamping during building assembly would not be practical.
- 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.
- 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.
- Soak the samples in water for 1 hour. This is long as I would expect standing water to exist in my environment.
- 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.
- Weak. The bond broke too easily. This adhesive would be unsuitable for outdoor use.
- Moderate. The bond broke under moderate force. This adhesive would be suitable if it had some other redeeming feature such as low cost or rapid setup.
- Strong. This bond could broken by hand but only with high force.
- Very Strong. The bond did not break
Adhesive Strength Test Results
| Adhesive | Dry | Wet | Cost | Setup Color |
Pot Life |
Notes | ||
|---|---|---|---|---|---|---|---|---|
| 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 |
Notes:
- Work Failure. The bond held, but the block broke
- 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.
- Initial Tack Strength is the ability of an adhesive to grab and hold a stone in some fashion when initially placed. This parameter is important when buildings are being assembled piece by piece. If a stone must be placed and then left undisturbed for a time, it makes rapid assembly of a structure difficult.
- Duration Until Initial Setup is the time until some form of grab is obtained if a tack didn't happen immediately. Generally, a joint must be left undisturbed for this period or the joint will fail.
- Duration Until Complete Setup is the time until the joint has either reach full hardness or practically so. This indicates the time period until normal handling stresses can be placed on the joint.
- Gap Filling Capability is the ability of an adhesive to fill a gap between stones. Since the stones are not perfectly square and precisely dimensioned, gaps often exist in part or all of a joint. The ability of an adhesive to fill and stay in a gap is important. If it can't be applied thick enough or won't stay in a gap, it won't work well.
- Squeeze Out describes the way an adhesive flows when the stones are squeezed together. Since a thin bond is desired, excess adhesive will squeeze out of the joint and must be dealt with.
- Cleanup describes the methods and consequences of dealing with the squeeze out.
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.
This page has been accessed times since 12 Mar 00.
© 2000-2001 George Schreyer
Created Mar 12, 2000
Last Updated July 1, 2001
