Victorian damp and chemical DPC failure

[Andrew Collins]

I have a Victorian townhouse, it appears to have been built without a DPC at all, there isn't even a slate one I can find.

The problem I have is that the previous owners have had a chemical damp proof course installed over much of the house and it hasn't entirely worked. Some areas that have no DPC have no damp problem at all... Most of the house is fine, but there are two areas (both internal), one of plain wall and one around a hearth where there is damp and chemical DPC.

I suspect the problem is very minor but is being made a lot worse by the fact that a membrane has been fitted between the brick and the plaster up to a height of 1m. This means that there is a line of damp at 1m accross my wall.

Now, I am not sure if all the damp around the hearth is rising damp, I suspect it might simply be rain coming down the chimney (not capped, it fell off a year or so ago).

For the rest which is rising damp, I can see two, maybe three courses of action.

1) Put in an extra layer of chemical DPC. 2) As I suspect the damp isn't serious, remove the membrane backed plaster and simply paster over it with regular plaster, hoping that the damp will simply evaporate. 3) Go along brick by brick, and somehow install a membrane DPC.

I'm replacing the fireplace around one area, so am tempted by option 2 there. For the wall it has to be 1 or 3.

Is option 3 viable? Is it ever done? I know it would be very time consuming but I have a lot of time!

Now, next issue is the hearth itself, I'm fairly sure this is rising damp and not from the chimney. Oddly enough, only the room side wall of the hearth seems to have a problem.

Here I can see three options.

1) Put some extra air bricks in the external walls, although it is already fairly well ventilated. 2) Take off the concrete and a couple of courses of bricks (then clear out any rubble), insert some sort of DPC, rebuild (with DPC also between the hearth and the internal wall). 3) Leave it all alone and hope that the presence of a fire will dry it out.

Thanks for your help!

[Andy Farrall]

You are suffering a common problem - your victorian house was never intended to be damp proofed. Damp will not have been a problem before it was attacked with modern building practices as the original materials would have been breathable (ie lime mortar/plaster) and the house would have been adequately ventillated (ie draughts and chimneys) and heated with open fires.

The fact that DPC and modern cement based plasters and renders have been used will just force and concentrate the moisture (which would have just evaporated away) into non damp proof areas. In the case of the internal wall the moisture is exhibiting itself at the top of the membrane. Ground floor hearths are often a problem when solid (earth) floors are replaced with concrete & membrane as its not easy to continue the membrane under the hearth without ripping it all out.

If you asked these questions of somebody knowledgeable in period properties they would suggest that all cement based renders/plasters be removed and replaced with lime mortars/renders/plasters. All attempts at damp proofing be removed, and breathable floor and wall coverings be used. But that would probably be very expensive.

As far as the internal wall is concerned, I would remove the plaster, remove the 1m high membrane and dry line the wall. Plasterboard attached to treated wooden frame. Vapour check or even insulated plasterboard might be a better idea.

As far as the hearth is concerned ???? Is it on a solid floor ??

Damp proofing a house after it has been built is very difficult as all youll ever do is move the problem somewhere else and as I said your Victorian house didnt need to be damp proofed.

[stuart noble]

This could be coming down rather than up. I and others have spouted quite a lot on the "damp" subject in the past as a Google search will reveal. I suggest you look at that first. It's a major problem in brick built Victorian houses and there is really no quick fix. After years of pondering my own problems, I'm coming to the conclusion that you can't stop it getting into the wall and the best you can hope for is to stop it reaching your interior decorations.

[Andrew Gabriel]

In article , "stuart noble" quick fix. After years of pondering my own problems, I'm coming to the

I've done a few things, which has stopped it, but I don't know which was responsible.

Where wall was damp and I thought I might have rising or penetrating damp near ground level, I have replastered with a sand/cement/lime/waterproofer scratch coat and regular finish coat. This has stopped the inside surface of the wall being damp.

I have also installed central heating. There were a couple of areas of north facing walls where damp was higher up, and I positioned radiators in those areas of the rooms. I suspect the damp was probably condensation, but it's not impossible that it was penetrating damp. I just reskimmed over the original plaster in these areas, and they have stayed dry too since.

[John]

What I did was a more belt and braces solution. It certainly wasn`t the cheapest way of sorting the problem out but it gives me piece of mind and makes the room usable rather than a damp hole. My application was a basement - so slightly different from you but some of the walls were internal and had no DPC - therefore no penetrating damp, just rising damp. I used a damp proof membrane from a company called Delta Membranes. They sell to trade, DIY allsorts.. It basically is a plastic studded sheet (quite thick) that is secured to the wall with plastic 'plugs'. The studs allow the wall to breathe behind the membrane so the damp problem isn`t moved elsewhere (which was important in my case). Depending upon what type of membrane you install, you can either plaster directly on top or dry line. The good thing was also that I could puncture the membrane afterwoods if i needed to fix anything to the wall - all I needed to do was squirt a bit of mastic in the hole along with the fixing. So far I`m impressed with its application, although drilling holes every 10 inches for the plugs to hold the membrane to the wall is a right pain in the ass and the whole job is quite labour intensive. It cost me approx 9 quid per metre sq which covers all the materials, not cheep but the best solution in my case. You can find their site at

if you want to check this method out.

John

[Andrew Collins]

Aah... hadn't though of that (I feel really thick now).

No, its the original wooden one.

The problem is at the front (room side) two corners of the hearth. They are damp. There is a piece of concrete accross the top of the hearth that looks non-orginal. The fireplace had a disused (condemned by CORGI) back boiler in it when we moved in and the hearth had been carpetted over. I suspect that when the original fireplace was removed someone took off the hearth tiles and just concreted back to the floor level, presumably doing something to cause a damp problem when they did it. I'm not quite sure what they could have done though.

As it's the corners it does occur to me that they may have put a membrane under the top layer of concrete and that it may have become damaged or bridged around the corners.

If the worst comes to the worst we can just take the concrete and a couple of layers of bricks off and floorboard over it, but I'd like to keep the original hearth if I can (and put a decent fireplace back in).

I think the first step is to remove the top laye of concrete and see what is what underneath.

Mortgage companies don't seem to understand this though, surveyors go round with electronic devices that measure the slightest bit of damp in the walls and the mortgage company throws a wobbler.

We had enormous trouble getting the mortgage we wanted because apparently there is damp just about everywhere in the house. Its only a problem in those two places though.

Thanks for your help (everyone), most appeciated.

[stuart noble]

I've often wondered whether it's the re-plastering, rather than the dpc injection that normally accompanies it, that does the job.

We've had quite a long dry spell though......

[Andy Farrall]

Yes, and replace with a breathable material (ie lime based). The problem will be where the floorboards meet the hearth - the wood may absorb moisture through capilliary action. Could just make sure the edges of the floorboards are "sealed" with beeswax/turps polish or varnish (depending on whats on there already). Try asking on the discussion forum at

there are lots of knowledgeable people on there.

Absolutely - tossers !! Mortgage companies and most surveyors have no idea about period property and are the cause of alot of problems (ie insisting on dpc etc). There are mortgage companies that specialise in period property but as far as I know they charge a premium. The survey on my house said that there is damp everywhere but fortunately the mortage company did not retain any money they just said to sort it out. This we did by removing lino from quarry tile on earth floors, removing small patches of cement based renders/plaster where repairs had been made, removing non breathable wall coverings etc. One winter, one summer and lots of coal fires later we have no damp.

Never trust anyone with an electronic damp meter - 9 times out of 10 they are measuring condensation anyway. The only way to determine if there is damp in a wall (for example) is to take core samples.

[N. Thornton]

Hi Andrew. There are loads of possible causes of damp. The fashion nowadays is to believe in one approach that will wham bam cure the lot, but really this is usually not the solution with these old houses. More often it seems to be a case of going round and looking for all the assorted sources of dampness and dealing with them all. Then the place will dry up in almost every case.

An open chimney is obviously going to let quite a bit of water come in, I'd look into the possibility of one of those rain shedding cowls.

Even if it turned out you have another damp problem, that will still help or often even cure the other problem. Why? Victorian houses are basically like sieves, water comes in, ventilation goes through, damp is evaporated out. So if you halve your water input, your level of dampness drops to the point of being normal, and your otherwise damp spots dry out well enough not to cause any further problem.

Regards, NT

[stuart noble]

In a 9" wall you often only have 4" between the elements and the inside of the chimney. I don't know how well soot retains moisture but it would help explain why chimney breasts are often affected more than the adjacent wall.

[Andrew Mawson]

"stuart noble" In a 9" wall you often only have 4" between the elements and the inside of

It's not just the mechanical retention of water in the soot, the sulpher compounds that are produced when coal burns leave salts in the soot that are hygroscopic - these are absorbed into the brickwork and cause problems for years after the flue has been used for open fires. For this reason avoid using reclaimed bricks that have come from chimneys as they will cause problems even when built into a new wall.

Andrew Mawson

[Dave Plowman]

In article , stuart noble

[stuart noble]

Thanks, Andrew. Interesting stuff.

[stuart noble]

Sure, but they're still pretty dense compared to the old mortar between them, which IME is the weak link. I have often wondered about the BRE research (which you seem to have re-created in your metal bath:-)) . They build a wall from yellow stocks and can't get water to travel up it, but do they tell you anything about the mortar they used? I wouldn't go as far as to say there's no such thing as rising damp in brick, having seen it with my own eyes this week on a party wall in the middle of a house, but I still blame the mortar, I think....

[N. Thornton]

"stuart noble"