A friend is looking to buy a Victorian Terraced house, and it doesn't have a damp course.
After spinning her an elaborate story about having the entire house sliced out of the terrace and lifted up on blocks while a damp course is fitted, I promised to ask around to find out how much she should expect to pay to have a chemical DPC done.
I seem to recall someone else having the chemical DPC, and it requiring a certain amount of replastering to be done after, because the plaster had to be stripped back at the bottom of the wall. Is this normal (or even anything to do with the DPC?)
Unless there are damp problems that you can conclusively attribute to rising damp (which would be unusual), leave well alone, and tell any mortgage lender that you'll go elsewhere if they're not happy with that.
I'm pretty sure that re-plastering would really only be necessary if there was rising damp that had left salt stains in the existing plaster near to floor level.
You don't say whether there is any evidence of rising damp. It is also possible that the vendors have done a quick disguise by using stain blocking paint so a *proper* independent damp survey would be a good idea.
Of course, a damp proofing company might say differently as most of the work and perceived value and thus cost, is the removal of the old plaster and the re-plastering.
We were quoted £650 by Dampco for two inside walls - one about 7 foot long and one about 4 foot. This included removal and replacement of plaster but not radiators present. On moving into the property, we see no signs of damp at all - dunno what Dampco were detecting but I can't see or fell or smell anything at all, so we have just left it alone..
On my old house, we had the front exterior wall done (15 foot long) and it cost £1000 25 years ago.
I think it's almost a given that if they inject a DPC, in order to offer the magic and worthless guarantee which is required to satisfy the lender, it will be required to rip off the bottom metre of plaster back to the brickwork, and replace with Special sand/cement-based plaster. Hell of a mess.
I totally agree with the sentiments but she'll end up in just the same situation with any other mortgage lender (paying an arrangment/valuation fee each time) will the possible exception of a specialist lender who deals in and understands period properties, but are unlikely to be able to match the mortgage deals offered by the big boys.
Not actually so silly - I've seen a mechanical damp course inserted by 'sawing the wall in half'. And it's likely to work rather better than a chemical one which is a con.
Well, yes. If you have damp showing - for whatever reason - removing the old plaster and replacing it with waterproof skim plus plaster will stop the damp showing again - at that spot.
Do a Google and you'll find plenty advice. Suffice it to say true rising damp is extremely rare - otherwise those houses would have been built with one in the first place. Most causes of actual damp are cause by water penetration - patios etc added afterwards not draining water away from the walls.
The Building Research Establishment did extensive tests, to try to detect rising damp, by standing various building materials in water for prolonged periods. They concluded that damp does not rise more than, at most, a few inches, which implies that the DPC is entirely superfluous. Good ventilation is far more important for avoiding damp problems.
As said, its a waste of time. The usual solution is to get a competent specialist to put in writing that such treatment is not appropriate and not needed, then BSs will usually say ok to that.
And just how old were the timbers and plaster? And if it were rising damp due to no damp course would have caused these problems many times in the house's life?
Of course if you concrete round the outside of a house where there used to be drainage you can often get damp penetrating through porous bricks, etc. But that's not rising damp.
IIRC it was one that Jeff Howell was involved in or at least reported in some depth - there seems to be much less info about it on his site now, but I think the graphs in this link refer to the same study:
Dear Chris An awful lot of unscientific, unsubtantiated assertions are made about rising damp. You do not have to look further than the opinions expressed above to get a feel of it. As best I can I will give you a resume of what happens. Rising damp is caused by the migration of a solution of inorganic salts from the ground into the plaster and bricks of a wall over a long period of time - decades. It is NOT water per se that is the problem but the water that is abstracted from the atmosphere at times of high RH. The reason the BRE experiment did not work is probably because the chaps doing it could not reproduce the conditions in a building over a period of say 50 years. I happen to know most of them and they are not the only ones to have tried the idea of putting brick columns in ponds of water and testing dpcs this way. ~The University of the South Bank did a similar experiment with similar lack of sucess and drew a disimilar conclusion. Rising damp does exist. It is not particularly rare. The problem is the specialists do egg it a lot and class bridged dpcs and latereral penetration as rising damp. That may account for more than 50% of the houses treated - unnecessarily! Plastering is NOT always needed and not necessarily for 1 m - the standard distance. That is normally to protect the interests of the company rather than the client. When my firm was contracting in this field (1979) we did it for 1 year and decided that it was simply not worth doing because the profit margin was too low and most of the houses we visited did not have true rising damp needing treatment. We got calls out for condensation - pipe leaks
- bridge dpcs - you name it! your friend needs to do several things
1) establish that there really is no dpc - they have been mandatory since 1886 and could have been bridged by soil and concrete paths
2) IF NO dpc - then borrow or buy a damp meter and plot readings in all walls on an isometric sketch of the affected areas over a period of several months at times of high and low RH. Any variation in the tide mark indicates RD. There should be a pattern of readings starting from the top of no damp at say 1 m down to very damp at say
800 mm then slightly damp below that at the top of the skirting. check the skirtings - are they wet (greater than say 14 w/w ) if so you may have some form of dampness
3) get at least three free surveys - select using the following criteria a) full members of the PCA (ex BWPDA) b) offering GPT back up guarantee c) most importantly insist the surveyor has the CSRT qualifiation these three will not ensure you get a good survey but will cut out an awful lot of crap
4) USE YOUR COMMONSENSE in intermpreting the results and dont take them as Gospel - most firms have their intersts at heart
5) If there is dampness but the plaster is not visually damaged - take a risk - put in the dpc but delay the replastering for a year and see if it dries out - that saves a lot of money
6) understand that the rising damp does not occur in the bricks so drilling the bricks is a waste of time- It occurs in the mortar. Ask the firm if they drill the bricks (trick question) If they say "Yes" show them the door and explain that you wanted someone who understood they needed to drill the mortar not the brick to put the hydrophobic layer in the mortar
7) the best dpc (in my opinion) is one using a silane based compound - trade name "Dryzone" from Safeguard Chemicals - you can buy it and diy See the website Costs - these vary from firm to firm but a good diy can negotiate reductions by taking off skirtings where needed for them and doing the hacking off themselves
8) read up on the BWPDA (now PCA) code of practice for DPC s which is similar to that of the BS which is also worth reading Both are a bit out of date but show the principles.
The theortical lift in a glass tube of 0.2mm diameter, which should be more effective at producing a straight lift from capillary action than the variable size passageways in a brick, is 14cm, although the theoritcal lift is not normally achieved. That suggests that either you have a reduced force of gravity in your house, or a higher than normal surface tension in your water, or it was not rising damp.
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