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Producing brick sheet with PU-resin

Finding commercial plastic brick sheet with the correct pattern and size of bricks still seems impossible in 2013. The old method of copying your own designed pattern is still the best method for producing reasonable sized sheets of brick work. This page describes the copy process.

The actual process starts of course with producing a master and a mould. In this case the master was a pattern etched into brass. The brass sheet was used to produce a mould in silicone rubber. The mould is shown in the next picture. The useful brick area is 10x25 cm.


The rubber mould

Here we see the flat mould. It is a mould taken from single sided flat pattern that was taped to a flat surface. Some edges were added and the lot was filled with 2-component silicone rubber. When hardened it can be unformed and it is ready to use. As you can see by the colour it is a well used mould in which many sheets were cast already. The background shows 1 component of the PU-resin that I use and on the left various tools such as cylinders for measuring the amounts and some old film canisters for mixing.


The resin mixed and added

As you can see here the resin is mixed with about 1/4 of a teaspoon black pigment, in this case finely ground carbon black (Norit 50 mu). The normal colour is pale white-yellow. The grey colour helps on painting as it is similar to mortar thus helps to achieve a more even end result. Other colour pigments can be used instead. You also see that the wetting of the mould is far from ideal and it is not spreading itself over the available area. This spreading is generally helped by using a schaslik stick to spread it more evenly over the mould. In theory it is possible to put over a sheet of glass or similar over the resin to create a consistent layer thickness and spread over the whole mould. However the PU adheres very well to most surfaces which lead to failures thus I don't bother any longer with such methods.

resin with paper

A plain sheet of paper towel helps wetting and spreading

Adding a plain single sheet of paper kitchen towel is sufficient to help spreading the resin. By pulling the sheet the resin can be manipulated over the mould. Other materials such as 'vlieseline', which translates as 'fusible interfacing for clothes', can be used for reinforcing the sheet. This is particularly useful to prevent breakage in combination with different casting materials such as gypsum or white PVA glue.

final sheet with detail inserted

Here we see the resulting sheet with the edges cut and enlargement of the detail.

The process of unforming is straight forward. When hardened (allow 30 minutes) you can directly lift the sheet from the mould. The sheet is cut to size with scissors. The insert shows that the fine detail is perfectly copied. There may be some minor fine air bubbles trapped from the mixing process but these will fill-up with paint and are unvisible by bare eye in the end result. The pattern on the back made by the paper towel is removed by sanding the sheet or just milling it thinner. This can be done even with a sanding machine with #120 paper or a milling machine. I prefer sheets of about 0.5 mm thick. This process doesn't take more than 3 minutes as the PU is relative soft. The sheet can be attached perfectly to polystyrene plastic sheet using liquid Faller glue. This seems better than using a contact adhesive as this somehow leads to curved walls requiring more and stronger inner reinforcements to keep the final building flat.

copyright: Henk Oversloot
date: 30 oct 2013