Internal and external damp proofing

  jay.p 16:28 03 Aug 2008

A member of the family has had a full structural survey done on an old,unusual construction semi.
All external and virtually all internal walls(even party walls) have a very bad rising damp problem.
They are going to get quotes for treatment once the written report comes back as they have no idea of the cost involved.
Has anyone any experience of having this sort of thing treated in the past.As it's quite serious to have high internal wall moisture readings,what is the likely hood of it returning after treatment.
I know the various methods of treatment involved,but will it be just keeping it at bay or is it,or has it been, actually successful.

  crosstrainer 16:53 03 Aug 2008

It can be cured, but I'm afraid that a new DPC, wall insulation etc. Done by a pro is going to give your relative quite a shock when they get the quote.

The good news is that government funding for this type of job is available. I would advise them to contact their local Council in the first instance, who should be able to advise them on the application procedure.

  wiz-king 17:05 03 Aug 2008

You say old, it may be that there was no damproof course fitted when built.
I had an 1930's house and I had the slate damp course cut out with a chain saw and replaced with new slates, it was a long (three week) job as only about a six feet long sections could be done at a time, allowed to set and then the next section done. That was a successful job.

I now live in a house built in the late 1800's and that has not got a damproof course in the kitchen, as it it almost underground it would not be of much use!

If you have good ventilation damp need not be too much of a problem.

  Forum Editor 17:39 03 Aug 2008

is unusual - in what way?

If damp is rising in the party walls you'll either need the cooperation of the neighbours if a new physical DPC is to be fitted, or you'll have to settle for a chemical (injected) treatment.

Inserting a new physical DPC is a long and expensive procedure, as wiz-king has pointed out, but it's a very reliable remedy. Chemical treatments are not so reliable, but can be effective if carefully carried out by experts. The treatment relies for its effectiveness on the solution used. Silicone resins, aluminium stearate, or methyl siliconate are all suitable for older properties, where the mortar in the brickwork is not alkaline. Many people believe that the injection should be via holes drilled into the bricks, but this is not the case - damp spreads mainly via the mortar courses, and it is into these that the solution must be infused.

Once the treatment has been carried out you'll need to remove plaster on both sides - usually to a height of around a metre from floor level - and allow any residual moisture to dry out. This will take at least a week, and can take much longer in very damp walls, or in winter.

Once the walls have dried a coat of sand and cement render should be applied to both sides of the walls. The mix should be a strong one - say three of rendering sand to one of cement - and have a waterproofing additive included. Once this has dried a coat of finishing plaster can be applied.

It's impossible to over-stress the importance of carrying out the removal and replacement of this plaster band, so do not be tempted to omit it on the grounds of cost.

It probably goes without saying that all sub-floor areas should be thoroughly inspected to ensure that there is no wet rot in the timbers, and that there is adequate cross-flow ventilation of the sub-floor voids - check that airbricks or vents haven't been blocked or closed completely.

I suppose it's too late to pull out of the purchase, or at the very least get a substantial reduction on the price? The work, if properly done, will be very costly and disruptive.

  bjh 18:14 03 Aug 2008

A very obvious point is to get an expert independent damp surveyor - not a surveyor from the companies that do the work, nor even a standard High-Street-surveyor.

He will advise you of the best approach (which techniques, how serious the problem actually is, and what the work will involve).

A survey of this nature on an average 3 bedroom semi should be £200 - 400. As the work may indeed cost many thousands of pounds, this will be money well spent.

click here
can advise on experts in thsi field local to yourself, although many experts may not be RICS members. Many fall more under structural engineers.

Can it be permanently cured? Yes, in almost all cases, but can be very expensive indeed. Where water tables have risen significantly (which has happened in certain areas post water privatisation, among other causes), or drainage has been diverted by recent property development, it is debatable whether it can be removed as a problem.

As someone selling their house (again) in this market, I'd suggest there are so many properties available at the moment, and pricing is so competitive, a serious damp problem would almost certainly make me opt for another property rather than get the price cut.

However, one final point but please treat this with CAUTION. I have bought many old houses over the last few years. Many have high damp readings. I have had experts in. Often rising damp is not really the problem, and there are cheap solutions. Two common causes for damp in internal walls is replacement flooring and cheap carpeting. Old floors were wood, tile or breathable brick. These are often covered with a cement skim when damaged/worn. The concrete is non-porus, so the moisture can't naturally evaporate, and the only place for it to go is.... up the walls. Carpet with nylon backing or foam underfelt can have the same effect. So, I have bought a house ((1850's), getting a large discount for damp in interior walls. Removing the carpets nearly solved the problem, and exposed beautiful tiles that the previous owner didn't even know were there (!!!!)... and removing part of a concrete skim from another floor sorted a bit more out. Expense? A £50 skip!
Often, in my experience, it's modern living in an old house that caused the problem. Be cautious, as that may not be true in your family member's case!

  Forum Editor 18:34 03 Aug 2008

if rising damp is truly the problem it is rising within the wall from ground level, and it will not be cured simply by lifting floor coverings.

The whole idea of having a ventilated space beneath timber floors is so that air can circulate freely. Restrict the airflow beneath a floor, add a steady supply of moisture, and sooner or later you will have dry rot - which perversely is not 'dry' but needs a constant supply of water.

Many people think they have rising damp when in fact they have penetrating damp - often because of DPC bridging by earth in raised flower beds or patios being incorrectly laid. Another cause is cracked rainwater downpipes and overflowing hoppers.

True rising damp is always caused by the lack or failure of a damp-proof course, and in houses built prior to 1900 it is a very common problem. Many rigid slate DPCs failed when the dry summer and subsequent heavy rainfall of 1976 resulted in widespread structural movement - particularly in the London area. Many slate DPCS cracked, allowing damp penetration into the masonry above.

There is no cure for rising damp other than the insertion of some kind of DPC - it doesn't matter where the water table is, ground always contains moisture and this will migrate upwards in masonry until it is either stopped by a DPC or until the rate of drying on the internal wall faces is equal to the rate at which moisture is entering from below. That's why it is very common to see 'tidemarks' on the internal faces of walls affected by rising damp - the moisture advances and recedes according to the weather, and to the ambient humidity and temperature within the building.

  MAT ALAN 19:06 03 Aug 2008

click here

You will obviously need to repair any floor joists that are rotten but when you have done that there is a simple and very effective way of protection..

I had similar done in an old house i owned the only thing i had to do cosmetically was replace the skirting boards.

  jay.p 19:31 03 Aug 2008

Thanks all for the excellent advice so far.
No purchase involved.The house has been left to the family.
The house is a nissen petren built with a tin roof(i kid you not. Lol) in 1926.

click here
Just been informed that Grandad used to block up the air bricks in the winter *raises eyebrows*
Don't think it' been blocked since he passed away 12 years ago, although i will have to check.
I assume if it was last done 12 years ago that this won't be the cause now.
Even the upstairs walls are damp.There is the possibility that the top section could be from the old roof leaking, although the new roof has been in place around 7 years.
The new roof has no flashing.Instead the render on the elevated walls above the front and back of the roof just has mortor overlapping the tin as they all seem to do.
There is also damp under the windows though .If the work can be done for £20,000 or less,it will leave plenty of scope for the plans we have for it.
Work to be done.
Take back to brick and have all walls replastered.
All walls,internal and external to be professionally damp treated.
New skirting boards and door frames and wooden floors if necessary.
All 5 ceilings artexed.
Is £20,000 a realistic ball park figure?
I will be obtaining quotes later on,but just want to know roughly where we stand.

  jay.p 19:36 03 Aug 2008

Just been told that my Father in-law thinks he has had to unblock the vents a few times since Grandad passed away.
We think this was up to about 6 years ago.
Could this be all of the problem or part of it.
I assume that this would have no bearing on the concrete flooring side of the house which is still damp due to the fact that there are no air bricks there.

  Forum Editor 22:57 03 Aug 2008

have two inherent flaws:

1. They have metal roofs which tend to leak in time.

2. They were very cheaply and rapidly constructed.

If a concrete floor is not laid onto a damp-proof membrane it will eventually become damp, and walls built onto or through it will also be damp. Nowadays you construct a concrete slab floor by laying at least 100mm of concrete onto a 50mm layer of rigid polystyrene foam slabs which are laid onto a polythene membrane, which is laid onto a 25mm layer of sand blinding, which is laid onto a 150mm layer of compacted hardcore.

In the past concrete floors were laid directly onto hardcore, with no membrane or insulating layer. The concrete was then painted with a couple of coats of bituminous liquid - called 'Blackjack' in the trade, and a sand and cement screed was laid onto that. In ideal conditions it all worked - the Blackjack kept the damp at bay. Unfortunately the blackjack was often applied in a slapdash manner, and didn't form an impermeable layer. If the concrete was skimped and wasn't thick enough cracks would appear and water would find its way to the surface.

Damp under the windows will be due to rainwater finding its way back under the window sills if they are timber - often because the rain groove on the underside is coated thickly with paint, or is non-existent. Alternatively it may be due to wet rot in the frames themselves.

You may find that the internal partition walls are not built of brick, but of clinker blocks - similar to breeze blocks. The clinker was the waste from Power stations, and was used to make building blocks. If these have been used think twice before attempting to remove plaster - it bonded to the blocks very well, and you'll cause severe damage to the blocks themselves as you remove the plaster. If the walls are brick you can use a scabbler to get the plaster off - it's a needle gun, and is very dusty, noisy work, but very effective.

Is £20,000 a realistic figure? It depends on the size of the areas to be dealt with, and on the area of the country. I think you should be prepared to spend a bit more.

  John B 17:48 09 Aug 2009

I remember this being a claim and had a search. This article is quite interesting; in paricular the 7th post down by Joe Malone is worth reading.

click here

The view seems to be that in 'most cases' the problems were caused by:

condensation caused by poor heating and ventilation

penetrating damp from raised ground levels

leaking pipes

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