Best Method to Treat Hygroscopic Salt Contamination

Lungboy

We have a damaged section of plaster in our dining room, and have had 2 people round to look at it. They both say it's hygroscopic salt deposits, either with active or historic damp. One says to hack off, fit membrane, then plasterboard and skim with no mention of a DPC, where the second says hack off, inject new DPC as old one must have been compromised, cover with sand and cement render treated to resist salt, then skim. I have no idea which is the better option, so does anyone have an opinion?

I've just had a look and it seems like there's another option that wasn't mentioned, a modern version of the sand/cement system with salt-proof plaster (Dryzone or similar) which is apparently better for the wall than the sand/cement system as it's lighter, warmer, breathable and easier to work on later if more work is needed. Any views on that?

Finally, we have some damage on two chimney breasts. One is brown staining which looks like a leaking chimney, whereas the other is a slight discolouring and powdering of the plaster, which looks like more salt damage. Both chimneys have now been removed. What's the best way to treat these? The water damage I was hoping to simply paint with some Zinsser BIN, does that sound reasonable? Can I use it on the salt too?

Thanks!

Ectophile

I have tried treating brown stains before with sealant paint.  If you are going down that route, make sure you do a really good even coating.  Those stains are remarkably good at finding any little gap in the paint and coming through again.

I ended up having a section of plasterboard ceiling taken down and replaced, because my DIY painting efforts were never good enough to stop the stain coming through.

Homer_home

The very very first thing you need to do is find out why you have damp in the first place , and sort it

Whereabouts is this damp

Lungboy

External wall, ground floor. One of the surveyors didn't think it was actively wet, but had been wet some time in the past. The other surveyor didn't want to commit without further investigation. We had the house including that wall renovated a few years back and that wall was taken back to brick during a wet winter and it was dry from what the builder can remember. The render on the outside is also new and doesn't appear to have failed at all, so there's no obvious source of current water.

FreeBear

Lungboy said: I've just had a look and it seems like there's another option that wasn't mentioned, a modern version of the sand/cement system with salt-proof plaster (Dryzone or similar) which is apparently better for the wall than the sand/cement system as it's lighter, warmer, breathable and easier to work on later if more work is needed. Any views on that?

Dryzone "damp resistant" plaster, used as part of a wider "damp proofing" scheme including waterproofing exterior creams & chemical DPC injections - If it is anything like Limelite renovating plaster, it is a mix of cement, perlite, limestone, and hydrated lime. It may also contain some salt inhibitors to limit the migration of salts...

I would treat the claims of breathability with a great deal of scepticism. If you want a truly damp resistant plaster that is breathable, a pure lime plaster is the way to go - Just don't go slapping modern paints over it as the paint will provide a moisture resistant barrier.

If you have had chimney breasts removed and are suffering from staining, it is most likely historical tar & soot deposits leaching out of the brickwork that formed the original flue - Zinsser stain blocker should reduce the amount of bleed through. You may need several coats though.

Apodemus

Has the new external render possibly bridged the DPC?

Lungboy

FreeBear said:

Lungboy said: I've just had a look and it seems like there's another option that wasn't mentioned, a modern version of the sand/cement system with salt-proof plaster (Dryzone or similar) which is apparently better for the wall than the sand/cement system as it's lighter, warmer, breathable and easier to work on later if more work is needed. Any views on that?

Dryzone "damp resistant" plaster, used as part of a wider "damp proofing" scheme including waterproofing exterior creams & chemical DPC injections - If it is anything like Limelite renovating plaster, it is a mix of cement, perlite, limestone, and hydrated lime. It may also contain some salt inhibitors to limit the migration of salts...

I would treat the claims of breathability with a great deal of scepticism. If you want a truly damp resistant plaster that is breathable, a pure lime plaster is the way to go - Just don't go slapping modern paints over it as the paint will provide a moisture resistant barrier.

If you have had chimney breasts removed and are suffering from staining, it is most likely historical tar & soot deposits leaching out of the brickwork that formed the original flue - Zinsser stain blocker should reduce the amount of bleed through. You may need several coats though.

Breasts are still in place, but the chimneys have been removed when we had the loft done. I'll try the Zinsser and see how it goes.Apodemus said:

Has the new external render possibly bridged the DPC?

Render extends to the ground, and did so previously too.

FreeBear

Lungboy said: Render extends to the ground, and did so previously too.

Do you know where the DPC is in relation to the ground level ?

Lungboy

FreeBear said:

Lungboy said: Render extends to the ground, and did so previously too.

Do you know where the DPC is in relation to the ground level ?

Not precisely but it's >15cm above.