How Much Does It Cost To Cure/Treat Rising Damp?



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Cost to Cure/Treat Rising Damp





job
Description
labour
1You have rising damp in the front bay window of your Victorian end of terrace house because the DPC has failed. The builder advises that the short walls on either side are done as well. You are moving & replacing everything inc. the carpet and decorating afterwards. 2 men 2.5 days….to remove the skirts, sockets and radiator, (so a plumber & sparks are also needed), knock off the plaster, inject inside and out, apply waterproof render, plaster up, fit new skirts, and replace the rad and sockets.
£825

Plus materials etc. for the above inc. hire of the pump
£125
2All three external walls of the same house need doing. The same process is followed but you have put all the furniture and carpets in storage so they are working in an empty house. There are more sockets this time and three radiators are being removed and replaced. The kitchen is not affected.  This will take the 2 men 5 days.
£1700

Plus materials etc. for the above
£200
3To get a mob in to store and then return your furniture and carpets will add…….
£450
4 Your paving is too high all round your 1930’s semi with a bay window. It’s all concrete and tarmac in good condition and you don’t want to pull it up so have gone for a French Drain. The bottom is being left as soil which is fine as the backfill pebbles will hide everything. The concrete path will be cut nice and straight, the drain will only be a spade width wide and 12” deep. This will take 2 men 2.5 days inc. tipping.
 £850

Plus materials etc. for the above
 £45

“Labour” at £175 a day (tradesman) £100 (labourer), includes incidental fixings etc. and tipping charges. “Materials” if mentioned, are larger things (a boiler) and stuff only you can choose (tiles etc).  Also VAT must be added all round.

Information Sheet on Stopping Rising Damp


Water, which occurs naturally in the ground comes into contact with your house’s brick walls and is sucked up through the bricks. This happens to the interior walls dividing the rooms as well as the outside walls, as they are all set into the ground.

This occurs only on the ground floor, can manifest itself up to 1200mm above the floorboards and happens for several reasons.

The damp proof course (D.P.C) has failed or was never installed

The DPC is the special layer of non-porous material specifically designed to arrest the upward motion of the water. This is laid as the walls are built at about floorboard level. If your house (like mine) was built before 1860’s it won’t even have one. If it’s Victorian it will be slate, if it’s 1940’s it will be bitumen impregnated felt, if it’s modern it will be plastic.

If you go outside and look at the bottom of an air brick you will either see the DPC poking through the mortar bed, or it won’t be visible but the mortar bed will be extra thick because there are effectively two beds, one below and one above the DPC.

Other stuff (lead) has also been used for DPC’s as well.

Slate DPC’s fail due to movement. Slate is thin and relatively brittle, when it’s solidly fixed as it is in a DPC it cannot resist pronounced localised movement (which sometimes happens albeit slowly) so it cracks. Water loves a crack.

Felt DPC’s don’t fail as often but the bitumen takes away the natural elasticity of felt so it too can crack over time.

Plastic DPC’s don’t fail, they let water by, primarily because of poor workmanship.

The DPC is being bridged

Here the DPC is OK but porous material has been placed or allowed to accumulate on the outside of the house alongside and above the DPC. Here, on solid walls, (those without cavities, built before the 30’s), ground water which has been arrested in its upward travel by a perfectly good DPC, simply takes a sideways step, gets sucked up by the adjacent material and then pops back into the wall again. If this material is compost or soil or anything against a wall that can be easily removed, well now, how on earth can we solve that one?

The DPC can be bridged by more permanent materials though. Quite often over the years, paths and patios are laid on top of each other until the DPC is hidden. These should really stop at least three courses of brickwork below the DPC to allow for wind action to attempt to dry the brickwork under the DPC.

Extension walls incorrectly built against an original solid walled house can transfer water into its external walls a great deal higher than 1200mm. This though is technically penetrating damp. Garden walls butted up against a house wall are notorious for this.

Very often a layer of render about 300mm high has been applied low on the outside wall as though some maniac deliberately wanted to bridge the DPC. I have never been able to work out what reason there could have been to do this. Whatever it was, it must have been a bloomin’ vital one for some arse to create a potential damp problem trying to solve it. Of course today, with modern waterproofing agents, you can render at low level but only if you absolutely have to.

Unfortunately, walls with cavities can also suffer from a bridged DPC. Cavity walls are built only as outside walls (not between rooms) and are in fact two walls built side by side with a gap between them. Built correctly, rain water which hits the outermost “skin” can’t travel past the gap to get to the inner skin and therefore show on the inside walls. As long as they are built properly the system works but a constant problem area is down at the bottom near the DPC’s (each skin has one). If too much mortar was allowed to fall into the cavity as the walls were built, it accumulated unseen and now bridges the internal skin’s DPC inside the cavity!

The Damp Proof Membrane isn’t working

Just when you thought you’d got the hang of this DP business now there’s another one to learn about. A DPM is found (hopefully) under solid (concrete) floors and this is covered not surprisingly in our section on flooring.

If a solid floor is wet in the middle and it’s not condensation because it doesn’t dry out then it either has no DPM or its failed……big job to fix!

If a cavity wall is wet and the floor is concrete then the problem may be caused by the floor’s DPM and the wall’s DPC not being positioned or connected correctly, relative to each other.

CURES

Physically replace the DPC.

Amazingly a failed DPC can be replaced. For instance a slate one can be cut out in smallish sections (so the house doesn’t fall down) and replaced with a plastic one. This is specialist stuff.

Fit or apply a second DPC leaving the old one in

There are different methods here, ranging from one of several water repellent liquid chemicals, injected into the wall, water attracting capsules and tubes set into the wall and electro-osmosis which requires a very high forehead indeed to understand, let alone fit.

They are all effected in conjunction with the complete replacement of the affected wall’s interior plaster up to about 1500mm. This is replaced with a heavily waterproofed render, which is then plastered over. To do this, rotten skirting boards have to be replaced and radiators and wall sockets removed etc. In fact in extreme cases where all the walls are affected, I have literally removed everything from down stairs, put it in storage, brought the cement mixer into the living room and turned the downstairs into a building site.

Clean out the wall cavity

Undertaken from outside, relevant bricks are removed to gain access. The cavity is cleaned out and new bricks fitted.

Fit a French Drain

No….this isn’t a Napoleonic cure for some horrible disease but a trench dug immediately alongside a house’s external wall where high paving is bridging the DPC. Ideally the existing paving is cut nice and straight first and the bottom of the trench should be at least 4 courses of brickwork below the DPC.

This is then all filled in with pebbles which should be no smaller than golf balls otherwise they will hold as much water against the house as existed before. Surface water, drains immediately to the bottom of the trench and soaks away, because capillary action can’t suck water up through the pebbles.

Ideally the bottom of the trench should be sloping, solid (concrete) and terminate at a converted gulley (builder speak for one of the house’s outside drains) or the accumulated water taken by pipe to a soakaway. Legally, soakaways should be 5 metres from any building and without exception always at least a foot deeper and wider than you actually want to dig them!

Internal Replastering

This isn’t a cure and it’s done for 2 reasons. Firstly there must be wet and possibly rotten plaster or you wouldn’t have noticed the damp. This of course, needs to be got rid of and new stuff applied.

Now we come to the real reason. It must be apparent to you by now that there are all sorts of potential causes of rising damp. There are also several types of potential cure and most of these involve doing things in the middle of a load of masonry that is completely out of sight. So, the builder is effectively working in the dark and actually doesn’t have a clue if he’s fixed the problem or not.

What he does therefore, is make bloody sure that even if he hasn’t fixed the problem, you will never find out. He removes all the plaster from the affected area to about 5’ up the wall, applies a well waterproofed render to the same area and finishes off with new plaster. If the damp is still rising, the render stops it showing and you are happy!

This usually means new skirting boards and he must be very careful to get everything back to the same position or your carpet might not fit.

Questions to ask the builder during his quotation visit.

What’s causing the rising damp?

Unless it’s glaringly obvious, he won’t know but you can assess his level of experience from his answer. He might check a nearby gully (drain) to see if it’s leaking. It may be high paving or soil etc. against the wall. Damp on the inside of a cavity wall can happen for several reasons, none of them visible. Here, an exploratory hour or two might be necessary.

What you don’t want is lots of disruptive internal work if the problem is outside, relatively simple to cure and there is actually nothing wrong with the DPC.

Is your guarantee worth the paper it’s written on?

I used to put something like “The company guarantees all aspects of the work undertaken against failure due to faulty workmanship or materials”. It’s short and very uncomplicated. The longer a guarantee, the more cop outs it includes!

Are you replastering inside?

If he is, will you need new skirting boards, will the carpet still fit, will the electrical sockets all work again, will the radiator be replaced afterwards?

Who will clear the room put it all back and redecorate?

It may be you but sort it out first.

What about unforeseen work?

Ask what his hourly rate is per man for any work that arises that he hasn’t quoted for.


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