First steps to treat damp

[oversteer]

Hello all,

I posted a few weeks back following a survey on a 1880s Victorian cottage with a touch of damp.

We are going ahead with it, great! Now we have to think about what we can do with funds available to make it tip top.

We are certainly going to rerender the outside wall in a suitable plaster, and once this is done - and suitable time has elapsed for it to be dry - replaster the inside.

In the kitchen, the party wall plaster is damp, which - in the absence of any definite leaks etc - our surveyor puts down to one or more of of:

- unsuitable plaster used previously which is slow to evaporate moisture,
- the wall previously formed part of a chimney breast, causing the brickwork to be contaminated with ammonium salts which retain condensation
- rising damp

What would a good plan be to sort out the kitchen wall ?

Surveyor recommends removing the plaster, treating brickwork with a salt neutraliser, and replastering in a suitable plaster. Does this seem like a good approach?

He also recommended an injected DPC, which I am loathe to do immediately, as I presume the property didn't start off with one

 

[robgil]

Dont use a DPC , there is no such thing as rising damp and plastering may or may not sort out your problem.
Your problem is moisture , you have to find where it is coming from and sort it at its source.

Check guttering , flashing , drains etc etc. The wall wasnt always damp, what has changed?

A photo might help.

 

[MatthewC]

Well done - now the fun (and real expense) starts. I'm sure you'll get lots of advice here, but based on my experience, here's my tuppence worth:

We are certainly going to rerender the outside wall in a suitable plaster, and once this is done - and suitable time has elapsed for it to be dry - replaster the inside.

If we have a summer, remove the internal plaster as well and wait a long time for it all to dry. Do the external work before/in autumn and leave the internal as long as possible.

In the kitchen, the party wall plaster is damp, which - in the absence of any definite leaks etc - our surveyor puts down to one of:
- unsuitable plaster used previously which is slow to evaporate moisture,
- previously forming part of chimney breast, causing the brickwork to be contaminated with ammonium salts, and/or
- rising damp
What would a good plan be to sort out the kitchen wall ?

Remove plaster and wait! Unsuitable plaster (gypsum) is not slow to evaporate moisture; the moisture is trapped, period. If the unsuitable plaster is still there then of course it's still damp. I don't know about salts, but my house didn't have any to note. However, chimneys are always a potential source of dampness. Have you checked the flashing on the roof? How old is it? Another possible cause of the dampness is your neighbour...

Surveyor recommends removing the plaster, treating brickwork with a salt neutraliser, and replastering in a suitable plaster. Does this seem like a good approach?

No - let it dry first

He also recommended an injected DPC, which I am loathe to do immediately, as I presume the property didn't start off with one

You are right to be loathe to do a DPC immediately or ever! If the surveyor insists, get a new surveyor.

I think the first key point is to do all you can to help the house dry out naturally; make sure there are no current sources of water ingress, remove all soggy plaster and any cement/gypsum especially along the base of walls. Secondly, don't be in a hurry to do anything else, especially if it's not reversible (a chemical DPC is not reversible!). Take your time and let the house work as it's designed.

Good luck

Matthew

 

[Matt Green]

Dont use a DPC , there is no such thing as rising damp

That depends entirely upon how you define rising damp.

Check guttering....

It's a party wall. The hygroscopic salts from a an old chimney hypothesis sounds plausible. The other thing I would look for is any difference between the ground height (not floor height if it's suspended) of your kitchen and the your neighbours room on the other side of the wall. If their side is higher ground water could be evaporating through the wall on your side.

 

[Penners]

Oversteer - the "no such thing as rising damp" thing has become a bit of a mantra to some folk - one with which I profoundly disagree.

But that aside, the advice you've been given above is excellent. Get rid of any modern coatings on the wall - cement render, gypsum plaster, etc. and then give the bare brick plenty of time to dry out. You've got the summer ahead of you, so there'll be plenty of sunshine and balmy warmth (don't quote me on that!) - give the wall plenty of ventilation with summer air.

Once it's thoroughly dry, and having regard to Matt's professional advice above, re-plaster with lime plaster and paint with a breathable paint.

 

[stuart45]

Although hygroscopic salts can be a problem with old chimney breasts in my experience they have usually been more at the top of the flue where there was more water vapour to send them through the brickwork.
Adding a salt retarder usually means mixing it with a 3/1 sand/OPC mix.

 

[Schoolmarm]

Do people recommend waiting for things to dry out just so it can be checked that leaks etc have been cured?


Always seems funny when the first thing we do is wet the walls to start applying lime.

 

[oversteer]

Might be a bit of a silly question, but how can you tell when a brick is wet or dry? Would it feel damp to the touch? Especially if you can't see t'other side

Also, would it be fair to assume a party wall in a 1890 house would be single brick like the external walls?

 

[Penners]

No it's not at all a silly question. And of course it's virutally impossible to tell (non-destructively) whether the interior of a wall is dry. And using something like a protimeter is pretty pointless, because it can really only measure what it can touch.

But your hands can tell you a lot - even the "feel" of the air around the wall can be an indication. Obviously the surface dries out first, but as the interior damp migrates to the surface there will still be a slight feeling of cold dampness.

However, as a widely accepted rule-of-thumb, allow one month per inch of thickness for masonry to dry out thoroughly. Of course, as you will have summer on your side, you might be able to compress this timescale a bit.

As for an indication of the wall's thickness, what does the brickwork look like? If it's composed entirely of the long faces of the bricks ("stretcher bond") this would suggest that it is - as you suspect - one brick thick. Here's what stretcher bond looks like:

But if you see regular end-faces ("headers") of bricks, then it's probably two bricks thick. Here are two varieties of this type of bond:

Flemish bond (in dire need of repointing!)

Old English bond