Bronze Age Aegean walls

Over the last few weeks I've been very slowly working away at a set of 28mm Bronze Age Aegean fortifications for Ilium: A Game of Heroes. This is an mdf kit (two kits actually) from Supreme Littleness Designs - the gate tower (centre) and the straight walls (either side). I'll give a breakdown of sizes below, but all together it is 66cm (26") long, so perfect for the 60cm wide battlefield used for Ilium.

• To the top of the battlements, the tower is 24cm (9.5") tall. Along with the bit buttressing on one side and gate on the other, it is 30cm (12") wide. The gate itself is 6cm (2.5") wide. 
• The wall sections are each 14cm (5.5") tall and 18cm (7") wide, with a 5cm (2") wide walkway along the top.

I took my lead from Michael from Supreme Littleness Designs and added texture to the mdf once the kits were built. I started with a bit of glue and paving sand to build up what I wanted to be larger stones.

After that was dry, I went in and blocked out everything with glue. I did something at this point that I would later regret, and watered down the glue slightly to spread it better over the existing sand-covered stones. DO NOT DO THIS...

The wet glue was covered in backing powder. I did this in sections so that the glue didn't dry out to much before the powder was applied.

Dusting off the powder left great brick shapes. A very light brushing removed any powder from between the stones where it should not have been.

Along the rendered battlements and top of the tower, I just applied solid blocks of glue.

Then the whole thing was spray undercoated. This is when things started going a little wrong for me. Where there were pockets of dry backing powder within the glued bricks, the powder reacted to the solvents in the spray paint and started to bubble up. In some places the render completely fell away, but in others it just made the stone work look gnarly (which was ok in my books).

However, it was when starting to overbrush, and then drybrush the colours that the watered down glue fought back. In many of those places, the glue seems to have been absorbed only by the powder, and not adhered to the wall/other stone work. With the lightest touch, it all started to fall away. In the photo above you can see all the white clumps on the terrain building board. Those are all bricks fallen off the wall.

Never-the-less, with a bit of remedial work, it was all pulled back and will work wonders for my needs.