This wall, being damp, had over the years been repaired with a host of materials, plaster board, metal lath and cement, universal one coat and gypsum. All that was removed and the wall was pretty undulating and there was a lot of depth to be made up. To make things easier I made five vertical ribs with the plaster and brought them up to the required level for the first coat. I was pushing it a bit as it was plain at least three coats where required but time was not available so I had to do it in two coats and a finish coat i.e a scratch and a float coat. So given the depth I opted for this age old method; with the ribs giving me clear indication of how much depth there was I got some plain terracotta roofing tiles and built up the thickness with them.
The tiles take the place of some of the plaster and the ribs make sure you don’t pack the wall out too far, the ribs were all on the same level so that I knew that I would end up wit a flat wall. There were places were no packing was needed and places were two layers were needed. but the process was easy and quick.
At the end the wall was level and the next day I was able to put the float coat on. Thereby successfully applying an inch and half of plaster in two coats with no risk of cracking.
This technique has been used for centuries and can even be seen in Pompeii.