Repairing plaster after penetrating damp

[Mikey C]

Hi

I have just found damp on a external wall after stripping the wallpaper. It looks like I have penetrating damp from a crack on the external wall (upstairs bedroom). I'm getting this repaired soon but I was just looking for advice on how to repair the plastered walls inside the house.

I am already replacing the ceiling and internal wall so mess is not really a problem.

Some of the plaster is pretty loose so I was going to take off any loose material, build it back up where required with sand & cement and then get the whole room re-skimmed. I would rather not pull the lot off unless I really have to.

The house is a 1870 terraced townhouse (solid stone) and obviously I will need to dry the walls before replastering.

Am I doing the correct thing here or does anybody have any advice?

Thanks

Mike

[mail]

Dear Mike If the house is 1870 the odds are that the plaster is a lime render both inside and out.

Opinions differ on the merits of different binders. If it were mine I would do the following:

External render

1) check and see what the material is on it now if it is lime render - use lime to reinstate - use lime PUTTY not bagged lime. Read up how do do it or get someone who is a specialist in lime In doing is make sure you cut out all defective stuff and undercut the joints of the backing (like a dentist's filling) and if you can cut out the surface finish (often a richer lime and "peel-offable" with care a couple of inches such that you can over lap the various layers of backing with the finish. Allow each layer to set well before applying the next

2) if - as is likely given the propensity for a past repair - it is sand cement - use a good 3:1 mix and in the first backing coat ensure you have a) raked out the pointing 20 mm for a key b) have cleaned the stone off and killed any suction c) if necessary applied some SBR to stick it in place AND put it in the mix d) applied if necessary with splatter coat (hopefully not) build it up to your last layer in different applications ensusre the sand is correct (could take a sample of what is there) consider SIKA No 1 as an additive for water repellancy

Inside

similar considerations but here you may well have some hygroscopicity and you must get rid of any patches that appear in humid weather tap and check for any loose patches

chris

[meow2222]

There is nothing special that needs doing once the exteral crack is repaired. Since its a stone wall you'd best use lime mortar on it rather than cement, the latter is prone to causing a few problems over the long haul with old stone walls.

NT