"Casting" surface texture in PVA glue?

[Rhoderic]

OK, this is a slightly odd idea. I recognize that. But I can't actually see any reason it wouldn't work, from my point of view. Please do rein me in if you see any flaws that I don't.

Continuing from where I left off in my recent thread on Hirst Arts moulds, say I want to make lots of brick buildings for a setting/genre/period like Victoriana, Pulp or 70's Cops-and-Robbers. Suppose I used Overlord's technique in his "Underneath The Arches" thread, and scribed a sheet of styrene with a regular brick pattern. Or I could just use textured plasticard I suppose, but I like the personal touch of the scribed styrene. Now suppose I made a shallow (1-2mm deep) mould of this with latex or something similar. And then I use the mould to "cast" sheets of brick texture in PVA glue, which I could then glue on to foamcore buildings.

Unless I'm mistaken, the end product would be very easy to cut to the shapes and dimensions I wanted, and bendy enough to follow the contours of buildings (good for stuff like rounded corners, the insides of arches, etc.). Once backed on to foamcore or some other stiff surface, I don't see durability being an issue. Several sheets of brick texture could be cut so they "interlock", allowing me to make larger surfaces. I could make moulds for special bits like corners, arches, openings for windows and doors, etc.

Drying time would be an issue, I suppose. Even with the moulds only 1-2mm deep, I imagine the PVA needing a few hours to dry before it could be confidently peeled off. But to compensate I could make the moulds big, and in multiples.

Does this seem feasible or not? Is there some obvious flaw in my reasoning that I'm blind to? Should I get me coat?

[Zafarelli]

Drying time is indeed an issue, but I suppose shrinking will be much worse. A few years back, I experimented with PVA and paper tissue in a similar way, but abandoned it for one reason or another, I guess mainly impatience

In any case, I'd brush a layer of PVA into the mold, press a layer of tissue in the wet glue, let dry, and repeat a few times until the desired strength is reached. This should reduce shrinkage a bit, or at least give you more control over it.

[Rhoderic]

The shrinkage would only affect the "back" of the piece (the side that's exposed during the casting process), would it not? I don't really see that being a problem so long as the "front" comes out alright.

Perhaps the PVA glue could be mixed with something powdery, which might serve to both reduce shrinkage and speed up the drying. Fine sawdust, or something. Though I suppose this might detract from the bendy quality of the end product as well.

I'd be content so long as the drying time can be kept below 3 hours or so. With several big moulds I could make enough brick texture for an entire building in each casting run. And I'd be OK with doing it at a slow, leisurely pace in exchange for the frugality of the method.

Some smaller-scale experimentation would seem to be in order. I don't have any Latex but I could use Green Stuff to make a smaller mould for pre-industrial style bricks, for modelling the crumbling facades of my Zamoran slum.

[Col.Stone]

Nice idea rhoderic, might i suggest you get some Glassfibre-weave (Swe. Glasfiberväv) since paper could get all crumply..

[Verderer]

I can think of other possible problems with this idea. The latex is one, it's bit of bother to make molds with it, they will be thin and won't hold their shape very well. With a brick pattern you need to prevent the mold from bending, otherwise the brick pattern will look unrealistic. And the latex won't be very durable, and there's no telling what will happen when trying to demold the PVA cast.

If you're going to cast things, I suggest you get the proper silicone stuff for making the molds. I have used some silicone rubbers which work on 50/50 basis, that is, mix equal amounts of the two compounds. It's really very easy, and the molds will last you for ages (unless maybe with casting resin?) I would also make an entire wall as a cast, not just the surface texture. Just makes things simpler. The PVA idea sounds fiddly to me.

If you don't want to invest in silicone molds, I'd suggest using balsafoam or similar material to build the houses, and just score the brick lines there. That would seem to me the most practical solution by far, given the conditions you have set?

[Rhoderic]

Excuse my complete ignorance on mouldmaking materials. Silicone it is, then.

I don't think it makes things simpler by casting the walls as a whole (out of plaster or resin, I presume). At that point you'll start getting new problems. The pieces will be less forgiving to work with if they haven't been very carefully designed to match up perfectly. They're harder to cut and thereby customize. You can't do neat corners without using quoins, and so on.

As for simply scoring the brick patterns into the houses, the reason I want to try the cast textures is specifically so I wouldn't have to do that. We can't all be Overlord

[Col.Stone]

Latex and plaster works fine, i use it for sidewalks, you need to make a thick latex mould, applying it layer by layer and not rushing like i did the first time,  it takes forever to set if you pour it (a week for a centimetre thick)

I've also copied some engraved design to put on buildings using PVA, and it works rather good, not as good as a resin/silicone project would, but it isn't as expensive either and you could rather easily cut out windows and doors from a PVAwall as opposed to making different mould for every wall..

[Zafarelli]

The shrinkage would only affect the "back" of the piece (the side that's exposed during the casting process), would it not? I don't really see that being a problem so long as the "front" comes out alright.

In my experiments, the PVA started to pull together, like thinned acrylic paint on an unprimed plastic miniature. I tried to counter that with the tissue, but that wasn't too successful either, IIRC.

[Hammers]

Yes, like the naked man said about ise water: "Shrinkage is the main problem". PVA gives off a great deal of water as it sets.

[Verderer]

Excuse my complete ignorance on mouldmaking materials. Silicone it is, then.

I don't think it makes things simpler by casting the walls as a whole (out of plaster or resin, I presume). At that point you'll start getting new problems. The pieces will be less forgiving to work with if they haven't been very carefully designed to match up perfectly. They're harder to cut and thereby customize. You can't do neat corners without using quoins, and so on.

As for simply scoring the brick patterns into the houses, the reason I want to try the cast textures is specifically so I wouldn't have to do that. We can't all be Overlord

I will take Col. Stone's word for it, it probably will work. I haven't worked with latex actually, one of the reasons being the one the good Col. pointed out, you need to make the mold in several layers etc. Silicone stuff isn't that expensive, so I just wanted to avoid all that.

As to making neat corners, I guess all the methods suggested so far have their strong points and weak points. True, you have to use some putty to make the corners and seams neat with the way I suggested, but I used this method with a large project where I combined standard Linka pieces with some self made custom molds, and hiding the seams was really easy. I didn't bother with any of that quoin stuff, and I was still able to mix the regular Linka bits with the straight edged custom bits so that you can't see which are which (well, at least I think so).

But I guess there is no single correct way to make these things, I hope you find a way that works best for you.  

[Col.Stone]

I'm not certain that latex and PVA won't bond tho,  verderer mentions Linka,  i think i'd give that a go actually, i've seen very nice stuff made with that.

or plasticard, http://www.amera.co.uk/product.php?range=p

[Rhoderic]

Linka is too small, as was discussed in the Hirst Arts thread. Here's a picture I found on their website. There were also several comments about it being tricky to cast.

Plasticard is a step in the right direction, but it's rigid and hard to cut. I'd like to find something that could be cut effortlessly with ordinary scissors, is bendy enough to go around corners, and has a slight elasticity that makes it forgiving to work with in those pesky situations when the measurements turn out to be slightly off. I'll grant PVA is problematic because of the drying time, and if I found something else that dried much faster while getting the same rubbery quality in the end, I'd use it. Given that it wasn't considerably more expensive.

I've a experimented a bit now, and I can't say I see any problem with shrinkage. It gets thinner, yes, but the surface texture is unaffected. One unforseen problem was that once the dry PVA was introduced to more wet PVA, it started turning a bit soft again. So some care would have to be taken when gluing it to the walls. But I don't see that being a major hindrance.

[Col.Stone]

It can also become brittle if stored iirc,  maybe you could use a hot glue gun to fix it to the foamboard?

The amera stonework will bend around corners, but it's stonework and not bricks..

[Ramshackle_Curtis]

Why not use latex for the final piece? Latex holds acryllic paint pretty well, and you can always give it a bit of a varnish when its done. I have never seen anything cast in PVA, and what experiments Ive tried have been failures. Its just too darn unpredictable!

Also, you could make plaster moulds from your textures. They would be incredibly easy and cheap, although undercuts might cause a problem.

Making moulds from silicone is also a good idea here, as latex doesnt bond to it. I would recommend silicone moulds and latex castings quite honestly.

[Col.Stone]

good idea, you could add some paint to the latex aswell, so it doesn't become too obvious in case some paint comes off