I wanted to create a stonework texture that I could apply to a card or MDF substrate like wallpaper, to cut down on the amount of work I'd have to do when making 15mm walls and buildings and what-not. I saw a similar thing in a railway modelling shop, but, though flexible, it was quite thick and wouldn't be able to conform to tight curves or corners. I made my own by rolling out a thin layer of modelling wax, only about a millimetre or so thick, on to a piece of hardboard and embossing it. Then I took a one-piece silicon mould of the resulting strip of stonework texture.
The piece in the model shop had a feature I tried to emulate, though not very successfully — interlinking ends, for joining long runs of the material. Mine are too blobby and uneven to link seamlessly; if need be, I'll be better off just modelling the interstices manually. However, in the scale I'm working in (15mm) I doubt that I'll often need more length than I have here.
I've experimented with two different casting mediums.
On the left is just PVA glue, with the addition of a bit of colouring, brushed into the mould. It's been backed with medical gauze to give it some strength. It's very flexible, which is good, but the silicon rubber repels it (it's hydrophobic) and so as well as having a patchy coverage, the moulded face is covered in pin-prick bubbles. A heat-set plastisol would probably be a better option, if I can find some in a decent colour, or which I can colour myself.
On the right is an acrylic filler (Selleys Permafill), pressed and smoothed into the mould with a plastic card. Once cured, I've glued a piece of newsprint to the back, again to give it some strength, as the filler on its own has very little mechanical cohesiveness when laid down this thin. It's not nearly as flexible as the PVA, but it will still follow a reasonably tight curve without cracking.
Here are the first few test pieces along with some Peter Pig infantry.
They'll do fine, I think. The stonework skins are glued either side of a piece of mounting board, except for the curved pieces which are self-supporting (just glued back to back). They're mounted on ice-block sticks.
The PVA skins aren't really all that great though; the multitude of tiny bubbles makes the actual blockwork a bit indistinct. The Permafil skins are better as regards detail, but do need to be sealed with acrylic gesso before painting.