I have just been renovating one of the rooms in our house. This has meant taking off the wallpaper and stripping it back to the plaster. Aprt from the multitude of other layers of paper and paint that we uncovered, I also managed to unearth a range of different plasters, past repairs and some areas in need of total removal.
The old lime plaster / render on the walls was mostly intact, but of course where a damp proof course had been put in years before this meant that the lower portion of the walls were cement render. This is attached firmly to the walls and even though I would have loved to of removed it, it would have damaged the wall too much for it to the really viable. Of course the water proofed cement had pushed the water up into the old render and focused it here. So in these areas the render had suffered from salt deposition and the old paper and paint had sealed in the moisture for so long that the plaster needed to be removed. So I hacked off the old render and replaced with the lime render (lime putty with stone dust of course!)
Around the reveal on the window I found a complete bodge job. The old story of windows slowly getting smaller as they have been replaced over time. So brick pillars had been built up the edges and the lintel was at least 6 inches (150mm) above the window and this space had been filled in with …. yes, you guessed it, paper (well a couple of old cement bags to be accurate – great to see recycling going on with the builders of old!) No wonder this area was always cold and attracting condensation.
In this area I decided not to use lime render, but to use the InsOwall as it was an external wall and the construction meant that it was basically a single skin wall in the zone immediately next to the window. this would give the area a better insulation value and hence reduce the risk of condensation.
So after a lot of hacking off, rebuilding, re-rendering with lime plaster, InsOwall, as well as the old plaster and the cement render and gypsum lower down I am left with a right old mix of surfaces. Some are breathable, some not so, some inbetween. They also have a different texture and finish. This is a plasterers nightmare.
Plaster will be drawn at different rates dependent on the different substrates. So getting a finish would be almost impossible. So what to do?
I need to maintain a breathable finish over the majority of the walls, so the option I have plumbed for is to use silicate primer. Earthborn and Auro both produce silicate binders / primers. This will then even out the suction between the different substrates and help the plasterer. I will be using lime plaster to give the final finish (but I might also experiment with clay plaster as well on one wall as this will give a smoother finish).
I will let you know how it goes after the plasterer has been in!