Remedial damp proofing methods?

[Drake]

A 30 ft length of my ground floor walls are damp, up to 4ft above ground in the interior of the house. Some builders have advised me that the walls have been plastered with the wrong type of plaster, but logic tells me that if there was no damp in the walls, it wouldn't matter what kind of plaster was used.

The red brick house was built in 1900 with cavity walls and lime mortar. I dare say the cavities have probably got more debris in them than they should have, and it may well come up above the level of the slate DPC.

I've lived with this problem since I moved in, 15 years ago, thanks to painting with damp-block paint. But I want to sell the house soon, and would like to get the problem cured prior to selling - provided it can be done without the sort of disruption that replastering the walls would create.

When I looked into this a few years ago, the most popular treatments seemed to be silicone injection and the osmosis method. I never did ascertain if either was actually considered effective by folks who have actually tried them. Perhaps there are other, more effective methods nowadays.

Any info or opinions based on first-hand experience would be much appreciated.

TIA

Drake

[meow2222]

Sounds like youve been sold the usual damp treatment sales line. There is no instant damp cure, as whatever the cause it takes a while for walls to dry out. The quickest and cheapest is a dehumidifier, which can cure your condensation almost overnight. Rising damp has nothing to do with it, but its a long story.

NT

[Drake]

I didn't say I was looking for an instant cure.

I don't have condensation - just rising damp.

Drake

[Phil L]

If they have been plastered with browning, then it does make a difference, especially if they have bridged the DPC when plastering, the browning will suck up the water like a sponge and hold it for months, meaning that it will never dry out.

Highly likely

It's a bit strange this (fairly new) idea of getting things right just to sell the house...you've put up with damp for 15 years and now someone else is moving in you want to get it sorted out. :-p

There is no easy cure...you have limited options:

1) ignore it and sell your house for a few thousand less than it's market value 2) try to hide it and fail, then go back to number 1! 3) get it sorted out once and for all, this involves taking off the plaster up to 1 metre high and having it chemically treated with DP liquid or gel, leaving the brickwork for a month or more to dry (by dehumidifier) before having it rendered with waterproofing agents and finally top coat plaster and reinstating skirtings and decor.

Personally, I'd go for option 1 if I were you, the few thousand they will knock off the price will be the same as you will pay to get it done properly, but you won't have to put up with the disruption.

I've seen the osmosis method used many times, I've never spoken to anyone who noticed it working though

[Drake]

Hi Phil, Thank you for the input. My reasoning is that while *I* know that the rising damp is not a very serious issue (having lived with it for 15 years, insulated from it by the damp-block paint). But I suspect that a good proportion of buyers out there avoid houses with rising damp like the plague (even if offered at a few k discount), possibly because of a widespread impression people have that it is incurable.

[some lines snipped for concision]

Yes, that option certainly holds some appeal. But I could imagine that rising damp could knock at least £10k off a house's value, whereas getting it properly treated would prolly cost £1k at most...

Drake

[meow2222]

This is why you dont know how to solve it. If you can be bothered to read the scientific experiments and articles on rising damp you'll find its all but non existant.

If you still think its rising damp, just sell, for 2 reasons. First youre unlikely to get it sorted. Second the buyer will only knock off the dpc & replaster cost, whereas if you do it you'll have redecoration as well.

NT

[Stuart Noble]

Why we've bothered with dpcs all these years I can't imagine

[Drake]

Really? Which scientific articles and experiments?

If you place a dry house brick in 1" of water, it will certainly absorb some of the water, and the dampness will rise above water level. Why would a whole wall built of bricks and lime mortar behave any differently?

You may be right about that.

Cheers,

Drake

[meow2222]

One of thesee days I'll get round to putting a list together. Until then its a case of google. Look for experimental walls in water for a start, and many other things. There are many writings about the subject.

a lot of discussion about damp and rising damp, but you'd need to do a lot of reading to find it all.

yes, but not far.

It doesnt, it behaves the same, water rises a few inches only. Its been done.

The usual endpoint is that people cant be bothered to read up on it.

NT

[The Natural Philosopher]

Tht is total bollocks. Otherwise why have a DPC in the first place?

I've had it in three properties.

If you have a brick wall in contact with wet ground you get rising damp, period.

You can tackle it one of two ways.

Get a DPC under the wall, and if bridged clear the bridging.

Put internal tanking up the inside, so that by the time the damp rises beyond it, enough of it has evaporated outwards.

The worst thing you can do is confuse it with penetrating damp, and put a waterproof layer outside.

[Guy King]

The message from The Natural Philosopher contains these words:

We had a house in Hounslow that had no DPC (it was built in 1853) and the ground under the floorboards was wet. We had no trouble with damp apart from the overall dampness of having wet soil under the floorboards. The walls were fine.

[The Natural Philosopher]

It may well have had engineering bricks or a slate course.

The key is outward evaporation, ind possible inward as well.

i.e. the one place where I had a real problem in one house was behind kitchen units. No way to get the moisture OUT.. and of course condensation contributed..

Tanking it up with mortar before putting new units in sorted it completely - the wall HAD to dry OUTWARDS.

I will note that unless you have a really porous structure, or a sealed in one, rising damp seldom rises beyond a couple of feet max. The rate of evaporation from the outside is high enough to limit it. My worst was an un DPC-able chimney sitting in an underfloor puddle, in the house center. - that rose up to about 2 ft. Any wood in contact had rotted away.

[Andrew Gabriel]

Chimney's often have inadequate damp proofing because they relied on regular use to keep them dry. In my 1909 house, the brickwork does have a slate DPC which still works, but hearths are constructed with a retaining wall (with DPC) which is then infilled with whatever building rubble and soil was to hand (with no DPC). This wicked up moisture and destroyed the wall plates sitting on the retaining walls once the fireplaces ceased being used (one of the joists I sucked up with the vacuum cleaner;-)

In one room, I emptied out the rubble, and replaced the hearth with a suspended floor right across the top, with a new hearth built on top of the floor, since it had to be raised above floor level in order to fit a coal-effect gas fire. In the other room, I emptied out the rubble down to the DPC in the brickwork, put in a DP membrane, and rebuilt the floor with a layer of vermaculite insulation under a very thick layer of sand and cement, so it could be used with an open grate in the future (not that I intend to). Both have remained dry ever since.

[Stuart Noble]

Just the one probably, the BRE experiment, which you can no doubt purchase from their bookshop if you have more money than sense.

[Stuart Noble]

I don't think you'll find enough to form a list but, in any event, maybe you should do that before pontificating on the subject.

Until