Hygroscopic Salts? Please help...

[RozW]

Hi, I'd really appreciate advice on this:

I live in a c1900s house with cavity walls. We have emptied the cavities and shifted the rubble from under the floor. There is an old damp course plus we have injected both skins a couple of years ago. The interior has been redecorated and a couple of areas have been reskimned. The problem we have is that we have various patches where the paint is coming away from the walls as a chalky residue. One entire mainly internal small wall is affected, plus various other small patches of new and old plaster. Does this sound like hygroscopic salts as my builder friend suggests. And, if so, is there any less drastic solution than removing all the plaster in these areas and replacing with salt-resistant(?) plaster. We are on a tight schedule and need to rent the house out for a couple of years, so if there is a short-term solution it would be a massive help.
Thanks in advance!
PS I'm not very good with trade abbreviations, just a keen DIYer!

 

[ree]

No. The answer is no short term solution. In fact, no satisfactory solution until a cause(s) is found.

When the Damp work was done were the affected walls hacked off and rendered?

Do you still have the Damp report?

Why not scan a sketched plan view of the affected walls?

Pics of the affected walls would help.

 

[RozW]

I'll try to post some pics tmw. Assumed the cause was a combination of: broken pipe (fixed 5yrs ago), cavities filled with wet sand (now empty), under floor cavity filled with wet rubble, pointing all falling out (currently being reprinted)

 

[RozW]

Sorry, repointed and rising damp. Hopefully sorted most of these. Do you think we might have missed something? Walls feel much dryer now!

 

[RozW]

The internal wall that is affected is only up to waist height (sorry, not full wall!) and behind a huge radiator. Plaster has never been taken back to brick work. Exterior is exposed brick.
Thanks for responding

 

[RozW]

Did get a full independent damp report several years ago. Suggested membranes behind plaster, however never mentioned any possible causes of damp bar rising damp, so wanted to see how much house would dry out after solving all the problems we found. Most walls completely 'recovered' so to speak, bar these patches. If it needs replastering, what would be the best method?

 

[RozW]

Sorry, terrible images as a bit dark now...

 

[ree]

I dont understand: you say the rad is on an internal wall, but your pic shows an external wall?

Is pic 1. showing a chimney breast? What is the rust bleeding from? Is the pic the right way up?

Is it the case that:
you commissioned an Independent Damp report "several years ago" - it recommended "tanking"?
And had some external walls (?) injected "a couple of years ago"?

Does the internal wall(s) with "damp plaster" have suspended floors on both sides of the wall?

Is the exterior ground level lower than your original or later DPC's? Pics please.

You would do well to carefully examine all your walls and skirtings for any damp signs, esp round chimney breasts and under windows.

 

[RozW]

The wall with the rad has an (original?) kitchen extension behind it with just a small portion below the window sill exposed to the external wall. The window frame is ok and the kitchen has been checked for leaks (no damp on that side of the cavity wall). I'm not sure what is under the kitchen floor as it's tiled, but doesn't sound solid, so poss suspended floors both sides.

Walls have been injected in stages over last 2 years up to 7 months ago.

Original DPC higher than exterior ground level. Later DPCs higher than ground level except on wall with rad, which was done whilst floor was up.

Pic 1 is chimney breast. Right way up. Cast iron insert is reacting with plaster - this was previously just a rusty shell before restoration, but haven't knocked that last tiny bit if rust on the head yet. All chimney breasts have been opened up and injected in both skins inside and out. Where the paint is coming off here, it is just at the top of a newly skimmed section of plaster, the lower area that was reskimmed is fine. No other problems around the fire insert. Main other issues in alcoves. Bay window and other side of glass door in photo is fine (injected below ground level).

Hope that all makes sense?!

 

[ree]

Still no sign of the outside pics?

FWIW: Why not read back on my recent posts ref. chimney breasts/flues and signs of damp? eg. have the flues been swept?

Are you saying that the cavity in the wall behind the rad was cleaned out recently?

Are you also saying that the internal skin injected DPC's have been done below the suspended floor joists?

Could you determine if the kitchen floor is suspended or solid - look outside for air bricks at low level.

Its difficult to be accurate without much fuller information. The bottom line is that all affected plaster has to come off, and be rendered/made good with a lime plaster. But the cause must be found or it will all happen again.