Advice needed

[foxman]

Hi guys, this is not a tiling question more of a plastering one I'm on a job at the minute laying floor tiles, great customer who needs a bit of advice, shes just had her kitchen walls taken back to the brick work and a damproof course carried out, new plaster and then skimmed, she now has a type of growth on the wall its white and fluffy (sorry only way to explain it) ..... waiting for the jokes. Can anyone who's a plasterer tell me what this is and how to get rid of it ,chers Mick

[DIYD]

Not a plaster at all, but this might help: How to fix plaster which has damp and salts problems on old walls.

Note:

A 'damp meter' and surface thermometer (see www.dampness-info.co.uk/meters.htm)are useful tools for this diagnosis - if not available use the back of your hand to assess the relative dampness of one affected area to another unaffected area..
Indoor Walls - ground floor, a quick summary checklist:
Symptom - white, fluffy salts, plaster possibly 'blowing' off the wall - 'efflorescence' - you have a water source which needs to be found and eliminated. Use our Water Leak Checklist (click here).
Answer - Salt Neutraliser might work if you can find and stop the leak, or the plaster may be too damaged and need replacement to our Specification.

[whitebeam]

You say new plaster, is it a gypsum type of undercoat type plaster. This should never be used on a wall where a new damp course has been applied. Sand and cement or Soveriegn renderlite, renderlite which has been designed for this type of application.

[Ajax123]

You say new plaster, is it a gypsum type of undercoat type plaster. This should never be used on a wall where a new damp course has been applied. Sand and cement or Soveriegn renderlite, renderlite which has been designed for this type of application.

Can use Gypsum finish over salt retarded render provided it is dry though.... I think...hope so any way cos that is what I done in my house.....anyway not to worry about that bit cos it over 12 years ago now and no problems.

Anyway the white fluffy growth will simply be efflouresence. It is more an aesthetic issue than a technical one although it does mean that the wall is still drying out. My guess is that because there was no damp proof course previously there was damp in the walls. this would have previously dissipated thorugh presumably an old lime mortar but now the damp proof course is installed and the wall rendered any residual moisture is still coming through the new render bringing with it salts of usually pottassium, calcium and sodium. As the water bearing these salts evaporates from the surface of the wall the salts themselves are left behind as crystalls - it almost looks like a white mould. It is very common to see this on new brickwork and occasionally on concretes and screeds.

It will just brush of but the problem is of course it will keep coming back till the wall is dry unless you put something on the wall to prevent it. Not sure about walls but where I have seen it on screeds the application of a water based epoxy primer has always solved the problem cos it prevents the salts from migrating through.

Heres the rub though - if there is a gypsum finish applied to a cement based render which has moisture coming through it the gypsum and the render will eventually part company due to the more problematical effects of ettringite and thaumesite formation. This will occur if there is no adequate primer on tope of the render before the gypsum finish was applied.

When I did my own house I did not re render the walls for about 6 months so it had time to dry out after the DPM was installed.

If however as whitebeam suggests it is a gypsum base coat plaster then you might as well get the hammer and chisel out now cos it will come off on its own soon anyway.

[whitebeam]

If there's moisture coming thru the walls an integral waterproofer will suffice