Preparing old lime walls for plastering

by Bill Hughes
(Marlborough, UK)

restoring and old bedroom wall

restoring and old bedroom wall

restoring and old bedroom wall close up 1 close up 2 close up 3

Hi - great videos thanks. I have an old lime wall which had very old wallpaper and a '70's fitted wardrobe over it. I have exposed the original oak timber framed wall beams and refurbished them. But I need to (re)plaster in between the wood beams. With the old wallpaper removed, the wall is flaky and crumbly in parts, especially at the edges. I believe it needs to be lime plastered as the house is very old. How can I best make the wall ready to take the (lime?) plaster?

Answer

Hi Bill,

Plater will properly adhere when the background is both porous and there is a sufficient physical key. Your wall surface is definitely porous and from what I can tell is reasonably rough - which will provide this physical key.

However if the wall is too porous the bond can be compromised so it is vital to control the suction and damp down this background just before you apply the plaster. You can damp it down by spraying or flicking water onto it. The action of brushing the water on will remove any loose dust and re-invigorate the lime - helping the new plaster stick.

If any areas of the old surface are very smooth then scratch/score them up to provide a key.

All wallpaper should be removed.

A lime slurry can also be painted to areas of the wall that may be of concern, just before you apply the plaster.

If you are at all concerned your local lime supplier will have a breathable bonding agent to help.

However a thorough application process is vital to ensure that the plaster is properly pushed onto the wall. A good bonding agent will be of little use if the plaster is not making proper contact with all parts of the surface. It is surprising how lime will stick to only a slightly roughish surface - provided that the suction is controlled and the 1st coat is properly pushed on to all areas.

So as well as preparation it is vital that a good application technique is used when applying plaster - to ensure that the new plaster is worked into all areas by using just the corner of your trowel if need be to fit into any undulations.

Paul

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