White salt line on plastered wall - will it ever disappear?

[Geoff Pritchard]

A while ago I asked for advice from the Forum about removing hard cement render from a cellar wall which was driving dampness up to wall above. Many thanks for all the excellent advice received and after 3 weeks chipping away I have finally removed it all without too much damage to underlying brickwork. The bricks in the cellar in this area were not very damp surprisingly but anyway at least the wall can now breathe and hopefully any residual moisture will come out with time. The wall in the room above also doesn't now seem very damp but it may just be that the weather has improved. The main problem I am left with is a white wavy tidemark about 2-3 feet high up the wall which comes and goes and which brushes or wipes off. I think it may be a bit better now I have removed the hard render in the cellar below but I guess it will take several months before full effect is seen. I assume the tide mark is salt deposits at the point where the wall is drying out. Unfortunately the wall had been plastered with pink modern plaster at some time. Will the white salt line ever disappear or am I stuck with it until I remove the modern plaster (which would be a great hassle). As I say, the wall isn't obviously damp although a year ago the man with the damp meter said it was up to 100% saturated (but I have since removed the hard render in the cellar below). Also house has been unheated for most of the last 2 years although when I heated the room for a few weeks in the winter the tide mark became very prominent. Any suggestions appreciated. One great benefit of removing the hard render from another part of the cellar wall is that I discovered a leaking water pipe buried under the adjacent kitchen floor which had soaked some of the brickwork in the cellar although not near the area where the tide mark is evident in the room above. Regards to all, Geoff (Norwich)

 

[Penners]

You may find that a salt neutraliser will solve the problem. For example: http://www.permagard.co.uk/index.php?main_page=product_info&products_id=122

There are one or two wrinkles to this, though.

Firstly, you need to make sure that the source of dampness within the wall has been resolved. If it hasn't, then the efflorescence will probably recur sooner or later.

Secondly, you may find that paint or wallpaper will prevent the neutraliser from penetrating the plaster properly. So you may have to remove these before treatment.

Actually, if you're going to strip the paint or wallpaper, then it may be beneficial to leave the bare plaster for a while (the longer the better) before you treat it. Allow the summer warmth ( :!: ) to dry it out, and as much efflorescence as possible to come out of the wall. Then brush it clean and treat it.

 

[Matt Green]

As I say, the wall isn't obviously damp although a year ago the man with the damp meter said it was up to 100% saturated

No. Argh. No.

The meter registered an electrical resistance in the wall equal to that exhibited by timber (beech or pine) at 100% moisture content when measured along the grain. The inference being that any timber in that location would be at 100% moisture content and at risk of decay.

Water is not the only substance that can reduce the resistance of plaster and brickwork though; ground water salts moving through your cellar wall plaster conduct conduct electricty well, lowering the resistance, giving the impression of more severe damp.


Matt

 

[Wren]

The product mentioned above contains acetic acid plus surfactants. Acetic acid is basically vinegar? In term of using products with surfactants I stick to Ecover as they choose biodegradable surfactants. So get some vinegar (maybe not your best balsamic) and mix it with some Ecover and try that. Or is that being too simplistic?

In terms of Matt's point I totally agree. I wish somebody would (please) invent a proper damp meter, or an anti- damp meter to prove that the conventional way of measuring this is wrong. Would save such alot of bother. (Or alternatively alot of people would pay alot of money for the inventor to un-invent it.)