Damp interior walls

16 Jan 2006
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United Kingdom
I have a problem with damp on a couple of interior walls in my house which is 100 years old next year and built from common brick. There in no membrane and the damp patches are about 18 inches high . what is entailed in chemical treatment ? is it a DIY job and what chemical product works best and how is it applied ? Can a damp proof membrane be installed without demolishing the wall by removing a few bricks at a time ?
Any help would be much appreciated
Dave :cry:
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I shall answer the last part of your question...because there is loads of info/debate on damp ;) A DPC can be inserted in sections, by removing,and replacing bricks.
mgdave said:
what chemical product works best and how is it applied ?
None of them as they are all unworkable as damp problems can be misleading. Injecting chemical will be forcing the damp problem to spread outwards. If you do a search on damp problems, plenty of info there as you need to know what causing the damp in the first place
Can a damp proof membrane be installed without demolishing the wall by removing a few bricks at a time ?
Any help would be much appreciated
Dave :cry:
Yes you can, there're a tools available for cutting out groove in walls for new dpc but you must be 100% certain the dpc has broken.
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Do you actually have an existing dpc (damp proof course)? I had the same problem but as someone above has said rising damp is uncommon, very often it is caused by leaking gutters, high ground or rubbish accumulation outside or concrete used as plaster in a mistaken attempt to to stop damp peneration - all this does is to cause the damp to migrate to another part of the wall. I have cured my so called 'rising damp' problems by curing all the above causes and I have no dpc at all, the house was built without one 150 years ago. Remember that the 'rising damp' slogan was an advertising gimmick invented by the chemical injection industry years ago but accepted into common parlence. Some experts now say rising damp doesn't exist at all, though I wouldn't go that far at the moment.
Sorry but I keep reading that rising damp does not exist and that chemical dpc are useless If there was no such thing as rising damp why do we insert dpc in new property.?
The reason for all the confusion on rising damp is that very few people know how to diagnose it correctly and end up inserting a chemical dpc when the problem is due to something else.
A new dpc will not prevent falling damp, ie from a gutter, penetrating damp,ie from defective pointing or porous brickwork, or condensation, usually caused by inadequate ventilation.
All a chemical dpc will do will prevent the upward movement of moisture from the ground into the masonry by capillary action by lining or blocking the pores of the masonry.
It is certainly not as effective as a conventional dpc but in most cases if done properly and in accordance with BRE Digest 245 it will be effective
I think it's a question of percentage moisture content in the masonary above the DPC (or where the DPC should be) rather than whether rising damp exists or not. Many Victorian houses for instance were built without DPC's and were expected to have damp walls to a degree but don't suffer from "rising damp" as such, they were designed through hundreds of years trial and error to deal with the damp, i.e. breathe - even the Romans two thousands years ago had no apparent problems with damp.
Provided only lime based materials are used during renovation or maintenance on old walls they should maintain their integrity, however the moment Portland products are introduced or modern plaster or indeed chemical damp proofing and maybe even conventional DPC's then problems can arise.
In my 1850 house there is no DPC and it had bad damp problems which I attributed to "rising damp" - I now know different after removing the modern plaster, curing the leaking gutters, chipping off the internal concrete 'plaster', lowering the outside soil level and shovelling up 150 years of accumulated rubbish under the floor, hey presto no damp! Furthermore a few days ago I found water droplets oozing through the brickwork below ground level, this after heavy rain, but the bricks directly above were apparently dry, so if "rising damp" exists why didn't these bricks become wet?
There are many experts who say that bricks do not support capillary action and thus rising damp cannot occur, I now tend to believe them after seeing the above example with my own two eyes. Remember, Victorians and their predecessors had many more years of experience than modern builders - most of their buildings are still standing and are in great demand whereas many 1960's buildings with their modern building methods are either falling down or being knocked down.
You ask "If there was no such thing as rising damp why do we insert dpc in new property.?", could it be that no one dare try to sell one without? Could it be that if it were proved that DPC's were pointless then many in the building industry would lose face and jobs would be lost?
I'll ask you a similar question, why are DPC's specified when engineering bricks are used above and below?
I'm no expert nor even a builder so I could be wrong, but certainly there appears to be a great deal of confusion on the subject.
Your points are noted but many victorian houses did have a dpc .It was not the conventional bitumastic or pvc one as we know but slate and was very effective until movement of the walls occurred and then it cracked.
Your point about engineering bricks is correct as these are in effect incapable of absorping moisture by capillary action because of the density of the material.
Many factors influence rising damp and one of the most important is the level of the water table which varies throughout the country. Therefore a house built exactly like another in a part of the country with a high water tables will be subject to a greater danger of rising damp than the other.
In your case you clearly identified the true cause of the problem by identifying and eliminating / rectifying all the other possible causes, Unfortunately very few people including professionals do this , and end up inserting a dpc when it wasn't necessary.
I grant you that there are a lot of people out there selling and installing chemical dpc , but in many cases they really have no idea what they are doing and the building society surveyors are not much better as they are just covering there own backs.
For somebody who has been told they have rising damp and that they need a new dpc ask the surveyor/ installer to give you the moisture content of the bricks and mortar using a carbide meter.
Most will have either no idea how to do it or what you are talking about.
and if so I would get somebody who does, it will cost but in the long term you will save.
No I am not employed by a company doing surveys I just don't like people being ripped off.
Most of the damp rises through the mortar, so it does not matter how dense the bricks are.
In that case why is the moisture content usually higher in the brickwork than in the mortar. I grant you that there are occassins when the mortar is a contributory factor but why then do a lot of the so called specialists inject the brickwork ?
there are two approaches to damp. You either build something that breaths so that moisture moves through the building or you build using materials which are impervious to damp.

Old buildings are built using natural materials and breath. So lime mortar (Cement not invented till 1800's), limewash, linseed or similar oils, oil based paints. The key point being that any moisture which gets into the structure of the building can get out again easily. This applies to everything from cob, tudor wooden frames, stone, etc. Old bricks were fired at lower temperatures and had higher moisture content.

Modern buildings surround the building with materials which (hopefully) prevent the passage of moisture, portland cement, concrete high temp fired bricks, etc.

It is a fact that most damp probs are nothing to do with rising damp. !st thing to check is where water could come from, so gutters, drains, condition of render, pointing, brickwork, roof, floor levels, ventilation, building use (gas burns to produce water - thats why lots of olp peoples houses seem damp - gas fires on all the time and minimal ventilation)

Problems can be made much worse by applying the modern approach - chemical dpc etc - in an old building. Stop the breathing by using opc render, concreet or gypsum internal finishing etc and you get problems. moisture that should disperce from the entire structure is suddnly restricted to small areas and damp becomes a problem.
Concrete floors with a membrane mean that rather than a slow permeation of moisture through a stone floor yo uget damp in the walls.

Also if part of the modern type surround fails, so cracks in render or such like, then the moisture which then gets into the building cannot get out and you have a damp problem.
there are two approaches to damp. You either build something that breaths so that moisture moves through the building or you build using materials which are impervious to damp[/quote]

We build in order to keep damp put. Old buildings suffered far more from dampness than the modern type. This was due in the main to lack of knowledge and the method of construction together with the poor workmanship.
Before you say it and I have heard it a thousand times (they knew how to build in those days) building standards are far better now than they were a hundred years ago.
Don't forget that with a few notable exceptions the majority of houses built in those times crumbled and decayed in a relatively short time
You cannot make a damp problem worse by the application of chemical dpc any more than you can by using the wrong plaster.
The only thing that will make a damp problem worse is incorrect diagnosis of the cause of the problem
There are only four causes of damp in a building. Falling damp, penetrating damp. rising damp, and condensation.
Identify the true cause, rectify it ,and let it dry out, and you can put practically any type of plaster on the internal surface
Thanks for all the comments on my problem , My house does have a slate dpc on the exterior walls as mentioned in a previous post. but the interior (dividing) walls have none at all ,and it is on a couple of these walls were the damp exists . I have taken all your comments on board and have started to look around the the house to see what may be causing the problem. At the front of the house (end terrace) the downspout disappears into the soil in the small front garden , my question is , where does this water go ? bearing in mind we are in a rural location not connected to a mains sewage system but have a septic tank at the rear or the property .The drains are all at the rear of the house and I can find no sign of any connection from the front .

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