chemical damp proofing

[bobasd]

by hacking off an rerendering you give yourself so many years free from damp signs.
accordin to me, thats why the injected liquids or cartridge gunned in stuff appear to work when in fact its the render blinding the salts thats doin the work.
it has to be render, using gypsum plaster is useless an will usuly break down in months.

 

[bobasd]

op, i can see what look like new boards four and five boards out from the skirting?

 

[pistonbroke1957]

Bob .Must be an optical thing All of the boards are definatevly. original. I know because some bright spark had painted them and I had to sand them all down when we bought the house 25 years ago. I can still taste the dust !!

 

[pistonbroke1957]

Have just had another look at the pics and I can see where the confusion about the new boards comes from.
What you can see is the skirting boards that I removed.
As you suggest, am going to hack off the plaster and render, install a chemical DPC, give the wall a chance to dry out before having it re-rendered and plastered.
Thanks again

 

[Kaymo]

I would advise against a chemical DPC, mainly because it will leave you with a bunch of holes in the wall and probably won't make any difference. I have an old house and a DPC was done some time ago and clearly hasn't made any difference, and I have never met anyone who has told me that an injected DPC has solved a damp problem. DPC's are generally snake oil and if there is dampness in an old house it is probably due to something that has been changed, such as external ground levels or non breathable materials on walls or floors, such as cement render on the outside walls.

My house had these problems and is starting to get better although it takes ages for stone to dry out. A combination of leaking gutters, cement render, a leaking drain, and blocked underfloor vents, and my next job coming up which is to try and figure out and return the external ground levels to the right level.

I think that you would be better served in the long run figuring out what is causing the dampness, rather than trying to contain it with waterproofing.

 

[John D v2.0]

I have never met anyone who has told me that an injected DPC has solved a damp problem.

Oh well i can put that right straight away then as I've done it and it worked to some definition of worked. It was also the cheapest and quickest option i could think of.
It has been proved scientifically and anecdotally that injecting dpc into an absorbent wall will stop water being able to soak through that area.
However that doesn't conflict with the rest of your post that states that dampness is usually caused by some change.
You have to remember that most houses are in some equilibrium state where the water soaking in, whether from above or below, is at the same rate as the water drying out.
If you suddenly have a damp problem then either more water is soaking in eg ground levels raised,dpc bridged, defective weatherproofing or gutters leaking, or less water evaporating eg incorrect rendering or painting.
You can restore the equilibrium in several ways, one of which is to increase the drying rate by letting the wall find it's own level (ie very wet), or to reduce the water uptake by either solving the problem or blocking the water somewhere along the way (dpc)

To say chemical dpc doesn't work is kind of missing the point. It does, but it's often not the most effective or cheap way to solve the problem.

 

[Kaymo]

Curious. What is your wall construction, and how long since it was done without the dampness reappearing? DPC is often injected at the same time as other repair work is done, and the wall is dried out, and even if the source of the dampness is still there it might take years for the dampness to reappear if walls have been re-rendered on the inside and woodwork replaced etc.

There is obviously a theory, and maybe some lab testing that backs up injected DPC, but these presume that all period houses are constructed in the same way with repeatable materials, and that kind of misses the point that old houses are extremely variable. Injected DPC are apparently more likely to 'work' on some types of stone and not so well on others, but since the internal structure of many old houses is not known, I don't see how it can be any more than a hit or miss.

The older houses I have lived in are made of walls with variable thickness of walls, with variable materials ranging from whinstone to sandstone, and variable infills which could be made of anything that happened to be close to hand, which could be mud, clay, mortar, stone etc. I really question how the installer can know whether they are injecting into the outer wall, the inner wall, or the rubble infill, and if there are any gaps in the damp proof layer then the water will continue to rise at that point(s).

In general I still don't see a very strong argument for using it. If there is so much water in the base of a wall that an injected damp proof course is needed, then it will continue to build up below the DPC and eventually find a way through, or it will just saturate the stone footings. My understanding is that some stones can be weakened by saturation, but I don't know enough about it to know the real impact of that, but personally I'd prefer to find the source of the water rather than stick a plaster over it.

 

[John D v2.0]

In general I still don't see a very strong argument for using it.

Agree, me neither, is not a magical cure, more of a tool in the armour.
You say it might not be 100% but as i say it's an equilibrium, it might be part of a combination of measures or it might not.
It's not black and white, it does something, just not necessarily what you want.

I'm sure you know that if all you have is a hammer them everything appears to be a nail! But a hammer is still useful sometimes.