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Casting Buildings

by Dai

This is a new page to show how, in May 2012, I set about creating moulds for casting unlimited quantities of facades for atmospheric terraces that could be used as backdrops for photographs and videos on our railways.

The Masters

Over a couple of years, I had more or less mastered the technique for simply and cheaply creating facades of terraced cottages. I began with Jigstones, using fast setting cement but this made buildings that, while being durable, for sure, were heavy and quite labour intensive to make. I then discovered extruded polystyrene which, once a pattern had been layered using a stencil and waterproof tile cement and grout, a very serviceable house front was possible. Using masonry paints in sample pots rendered these completely weather-proof and it was a cheap and forgiving alternative to concrete once you solved the problem of the lightness. Wind and cats, you see, are no respecters of extruded poly.

In 2012, I wanted more terraces and envisaged obscuring un-scale and unattractive fences with, for example, tiers of red brick terraces. Besides,one close friend needed to clothe a ghastly patio front with some sort of 'tile' across which his freight could trundle. I was never going to individually build all of this so mass production was the obvious answer. But, I did not want identical buildings, by any means.

Double front terrace facade complete with guttering and drainpipe.You can see that I have used extruded polystyrene in an orange colour for the casting walls. These were found in a bin in london and retrieved by my slightly eccentric sculptor daughter who, realising their worth to me, retrieved them. The doors,windows, lintels, sills and fancy brickwork are cast in Isopon in Jigstones moulds. The door lintels are also Jigstones but cast in fast setting cement. Downpipe and guttering by plastruct. Brick finish in Homebase Waterproof Tile Cement and Grout. The whole shebang sealed in readiness for pouring silicone RTV by careful use of tile cement to any undercuts and potential leaks. The beauty of extruded poly is that it adheres to itself well with PVA. A thin wash of PVA over everything should assist de-moulding. Obviously, I have not painted the masters though did use this one to play with weathering acrylics via a top-loading airbrush. I am now a firm fan of these.


Obviously rear extension wall with bathroom upstairs and kitchen downstairs for both properties of the semi. Side walls for rear extension reflect the needs once the rear wall is placed on what was once the front wall. Where the rear wall covers the back door another door is needed; where it doesn't, and the windows are covered, there are more windows. You know it makes sense

Alley section as 'breezeway' and to link sections into longer terraces.......................................................................;;or with a door.

Side walls for low profile buildings but with the addition of an extra chimney centre section can also make a full building

What material to cast in?

Once you have made the moulds, you might cast in all sorts of materials. Fast setting cement would do but much detail would be lost. Resin is long lasting but I detest it from a painting point of view. Besides, it is nasty toxic stuff unless you take good precautions. Plaster of paris is not weatherproof. Jesmonite 100 is designed to withstand tougher conditions but still needs sealing with a special compound. On the other hand, I find that masonry paint on top of tile cement and grout stands rain, snow and ice as well as any material. My brewery lasted outside all winter and this must have been the vilest for many years with temperatures down to minus 10 and a good foot of snow for a week or more.

Once the moulds were made, in the absence of any better material and because it was cheap and I was impatient, I experimented with fast setting cement. My experience with this has been good and the two buildings I made with it using Jigstones moulds have fared well outside. The biggest lesson from these buildings was that the glued on gutters and downpipes usually need attention after winter so it was obvious that I should include such elements in the creation of the masters and not leave them to add later.

Pictured above is a casting in cement. What matters most of all is getting the cement mix just right; about the stiffness of porridge. Using a rubber spatula to cream this thinly over the mould, working it well into crevices, reduces bubbles but does not eradicate them entirely. That doesn't matter too much as the defects are easily repaired with a little fresh mix after de-moulding the tile. Tapping the sides of the mould as I fill it also helps the mix to settle. If you mix too thinly, you may get finer casting surfaces and less bubbles but you also get flaking and poor tensile strength. It's all a matter of experience but when 10kg of cement is a mere £6, taking a few risks to learn hardly matters.

Cement probably needs reinforcement because while it is tolerant of compression, it takes little flexion. That's why, in a slab of reinforced concrete, you have two layers of steel mesh, 40mm under each surface. I can't do that with tiles this thin but I did try adding a sheet of chopped strand fibreglass mat. I think it actually weakened the slab. Given the fact that these buildings are not likely to be moved around a lot and will be made up into what are effectively 'boxes' with their own intrinsic strength, I am not less confident in them than I am in my Silkstone ceramic buildings.

On the other hand, we have Jesmonite. The name may mean little but if you know that the front of the Queen Vic pub in Eastenders was made from it, you might consider it more seriously. Being essentially a better preserved gypsum, the surface quality is higher, it's lighter than cement and takes paint very well. You can glue it to itself with fresh mix or Tile Cement, which is only a more thixotropic version of something similar anyway. After all, Tile cement withstands water and hot and cold variation but is evidently based on gypsum.

Larger Jesmonite castings would be a little brittle if they are thin so to give added strength, after pouring, a variant of fibreglass matting is submerged. It is supplied in a loosely woven net, pleasant to handle and extremely effective. I was dismayed to notice that some if not all my castings had warped. I rang an expert on the stuff, the man who built the Queen Vic, and he assured me that if I poured boiling water on the castings, they would be malleable enough to straighten. It works beautifully.

Perhaps it's not entirely desirable to have the castings ivory white and thinking of the base colour of mortar joints, I added a few drops of the black pigment specifically designed for this purpose. You only need a tiny amount, literally three drops into 200ml for a grey. Double that and you have a serious black. It occurs to me that this substance, available from Flints Theatrical Chandlers along with the Jesmonite and reinforcing material, would be awfully useful around the track to suggest coal.