Damp - no DPC - Can I knock off plaster and dry line?

[chrisbyrd]

Hi All

I've been reading the damp proofing threads on here with great interest

I have just bought a 150-200 year old property which i presume has no physical DPC and there seems to be some damp inside. Built from a combination of allsorts, but predominantly brick

The survey said there was some rising damp that needed sorting out downstairs but they were unsure of the exact cause and just put it down to the age of the property and lack of a DPC

We've stripped all the wallpaper and it looks as though they have been injected at some point (2-3ft of 'new' looking plaster around the perimiter)

I've had 2 damp proofing 'experts' in, but neither of them have come back with a quote yet. One of which didnt seem very interested and didnt really seem to know what he was talking about. The other one seemed like he knew what he was talking about.

For some reason there's an odd 1-2ft high cobble 'skin' at the front of the house which the damp guy recconed would 'bridge' anything that was injected. This has got to stay as it seems fairly well integrated with the wall.

He also pointed out that after the previous damp work, they've replastered using a gypsum based plaster rather than sand+cement which he said would be absorbing water like a sponge.

It is also not possible to put a gravel gulley around the outside walls (french drain?) because of the position of the road, and the fact that there were probably no foundations to the building

The guttering is going to be replaced, the gable wall is going to be repointed and the cement at the base of the chimney is going to be replaced with proper flashing. However - I dont think this is the cause of my problem, as there's no sign of damp in the upstairs walls. (correct me if I'm wrong)

The house has been empty for the last 3 months, but we've been giving it a good airing and had the heating on to try and dry things out for the last few weeks and it doesnt seem to be clearing up

He perscribed the following (as i understand it)

- knock off most\all of the plaster on the downstairs walls
- slop on 2 or 3 layers of some silicon\latexy type product
- replaster

There seems to be a lot of feeling on this forum that 'rising damp' is a figment of people's imagination and doesnt infact exist in most cases - so apologies if I'm using the wrong terminology

I get the impression that its not really possible to stop the damp in my walls and the exercise should be more geared towards preventing it entering the rooms?

I'm trying to do as much of the work as possible with the house - I've pulled down the old crubmling lath+plaster lounge ceiling and re-boarded it ready for skimming (i wont be skimming it myself)

From reading around, it looks like there's a lot of unskilled 'leg work' with sorting out damp, rather than it being a particuarly skilled task (on the whole). Correct me if i'm wrong!

What I'm wondering, is: is it sufficient for me to knock off all the plaster back to the brickwork and dry line the lot downstairs, ready for a plaster skim? Would this achieve the same effect of preventing the damp coming into the room as what the damp guy suggested? If this is the case, I can manage most of that myself. I presume I should put a waterproof plastic membrane behind the battons?

I look forward to hearing your replies (be gentle!)

 

[Frederick]

An approach that is often used on heritage properties is to use a cavity drainage membrane with a special mesh on that can be plastered onto - e.g. Newlath, Oldroyd P, or Delta.

See the following pages for examples of how these products are used:

http://www.safeguardeurope.com/products/oldroyd_p.php

http://www.newton-membranes.co.uk/newlath.htm

This approach has a number of advantages:

1) Removable (although the wall will have a lt of holes in it)
2) Allows wall to breathe
3) Works for different types of damp - e.g. rising damp, penetrating damp
4) Unaffected by salts in the wall
5) You can use a lightweight plaster

Versions are also available without the mesh which you can fix a drylining system over the top of.

 

[chrisbyrd]

Hi

Is this the stuff you mean for boarding over?

http://www.safeguardeurope.com/products/oldroyd_xv_clear.php

This stuff looks like exactly what i want

I notice here http://www.safeguardeurope.com/products/fastframe-drylining.php the diagram shows a gulley at the bottom of the wall - would that really be necessary in this situation, or is that more for a basement implementation?

 

[Frederick]

That's the stuff.

I think the gully is just for when you are using it in a basement. The following detail shows it being used above ground and tied into the dpm under the floor - http://www.safeguardeurope.com/cad_drawings/XV-010.pdf

I'm not quite sure what you would do if you are not planning to lay a new floor though.

 

[chrisbyrd]

hmm

any suggestions for what to do at the floor level? i dont expect there's a dpm in the floor and i dont fancy digging one in

the floor itself doesnt seem damp - just the walls

 

[Softus]

The survey said there was some rising damp that needed sorting out downstairs

Yup - they generally do.

...but they were unsure of the exact cause and just put it down to the age of the property and lack of a DPC.

Yup - they generally do.

We've stripped all the wallpaper and it looks as though they have been injected at some point (2-3ft of 'new' looking plaster around the perimiter)

New plaster is essential, but injecting is pointless.

For some reason there's an odd 1-2ft high cobble 'skin' at the front of the house which the damp guy recconed would 'bridge' anything that was injected. This has got to stay as it seems fairly well integrated with the wall.

Oh dear. The 'damp guy' is right.

He also pointed out that after the previous damp work, they've replastered using a gypsum based plaster rather than sand+cement which he said would be absorbing water like a sponge.

He's right on the money here too.

It is also not possible to put a gravel gulley around the outside walls (french drain?) because of the position of the road, and the fact that there were probably no foundations to the building

What do you mean by "because of the position of the road"?

The guttering is going to be replaced, the gable wall is going to be repointed and the cement at the base of the chimney is going to be replaced with proper flashing. However - I dont think this is the cause of my problem, as there's no sign of damp in the upstairs walls. (correct me if I'm wrong)

Leaky guttering is a classic cause of falling and penetrating damp.

He perscribed the following (as i understand it)

- knock off most\all of the plaster on the downstairs walls
- slop on 2 or 3 layers of some silicon\latexy type product
- replaster

I think he's right.

There seems to be a lot of feeling on this forum that 'rising damp' is a figment of people's imagination and doesnt infact exist in most cases - so apologies if I'm using the wrong terminology

There's nothing wrong with using it as a term, but if you've read all the topics then you'll know that I'm one of the more vociferous sceptics.

I get the impression that its not really possible to stop the damp in my walls and the exercise should be more geared towards preventing it entering the rooms?

Hmm. When you've eliminated the obvious causes, like the guttering, you may need to think more seriously about removing the 'cobbles'.

What I'm wondering, is: is it sufficient for me to knock off all the plaster back to the brickwork and dry line the lot downstairs, ready for a plaster skim?

That won't cure the problem.

Would this achieve the same effect of preventing the damp coming into the room as what the damp guy suggested?

Probably - the problem with replastering with gypsum based products is that the walls need to be completely dry before you do it, whereas sand/cement can go on straight away.

 

[chrisbyrd]

the guttering, pointing and flashing is all going to get sorted, but I think i need to do something to damp proof the room

i think i'm going to do the following (as well as the above exterior repairs)

- knock off all the plaster
- cover the walls with Oldroyd Xv sheeting
- work out what do to where the floor\wall meet
- batton & plasterboard
- get a plasterer in to skim the lot

so the general concensus is that all the plaster has got to come off regardless of what we decide to do in terms of finishing\sealing etc? if so, i'll get a skip in and hire that chipping tool from HSS and start tomorrow

it may well be that the walls are ok under the plaster once its been left to air for a week or so? if so, would it be ok to skip the Oldroyd and just batton + board the walls to give it a bit of breathing space?

does that all sound ok, or am i talking nonsense?

 

[Softus]

the guttering, pointing and flashing is all going to get sorted

Good plan.

...but I think i need to do something to damp proof the room.

i think i'm going to do the following (as well as the above exterior repairs)

I don't see why. If you deal with the damp at source then you don't need to do the following, and if you don't deal with the damp at source then you'll just be putting off the inevitable, and in the meantime you run the risk of the the damp damaging the property.

- knock off all the plaster
.
.
.
- get a plasterer in to skim the lot

To be picky, skimming is plastering with a finish coat. If you remove the plaster then you'll need to more than skim!

so the general concensus is that all the plaster has got to come off regardless of what we decide to do in terms of finishing\sealing etc?

No - only if it's been contaminated with damp.

it may well be that the walls are ok under the plaster once its been left to air for a week or so? if so, would it be ok to skip the Oldroyd and just batton + board the walls to give it a bit of breathing space?

I would wait to see how the wall is, and then decide.

 

[anobium]

Before you embark on the various courses of action which has been suggested may I ask if the walls are of a solid or cavity construction.
If as I suspect because of the age, they are solid walls and probably hand made bricks to boot, then I suggest that you investigate the possibility of lateral penetration through the bricks.
This can result in damp staining similar to that caused by the failure of a dpc, ie rising damp.
Repointing alone will not correct this and you will have to treat the bricks with a water repellent.
In any event these cobbles that you refer to, before you start to remove them, check that they are not an integral part of the construction, otherwise you could involve yourself in a lot of unneccesary work and cost.

 

[Softus]

Good advice from anobium.

(and good to 'hear' from you )

 

[oilman]

:

He perscribed the following (as i understand it)

- knock off most\all of the plaster on the downstairs walls
- slop on 2 or 3 layers of some silicon\latexy type product
- replaster

I think he's right.

This interferes with the transport of moisture through the building. Have you looked here

 

[Softus]

:

He perscribed the following (as i understand it)

- knock off most\all of the plaster on the downstairs walls
- slop on 2 or 3 layers of some silicon\latexy type product
- replaster

I think he's right.

This interferes with the transport of moisture through the building. Have you looked here

Not yet, but I agree with you anyway.

Looking back at my post, from which you've quoted, I was wrong.

Not sure how that happened, but my best guess is that I was thinking of the rendering on the outside walls (if there is any - don't have time to check now).

I apologise for any confusion that I may have created.