Damp Internal Walls

[peakpilgrim]

Hi I live in an old house in the country subject to very damp weather. The walls are solid and, in some areas, suffer from dampness. At some stage in the future I will dry-line the walls to solve this problem but, at the moment I have to paint them. The walls are plastered and, a short while after painting, damp patches start to show through the paint with mould showing through. Is there any way I can pre-treat the walls to prevent this growth of mould and improve the life of the paint as, in some cases, the walls have to be painted twice a year improve appearances. I had thought of treating them with 'Dulux Weathershield Multi-surface Fungicidal Wash' prior to re-painting again. Does anyone have any better idea?

[Rich]

Hey Peak

Whats the ventilation and heating like in the property as a whole?

Dry-lining the walls will definately not solve any damp, that will only hide it and prevent it drying out.

I wouldnt use Dulux though, Sandtex seems like much better quality, I tried both on my place and even a local pro-decorator recommended Sandtex over Dulux for quality.

[verne]

it would be a good idea to try and minimise the damp if you can by attempting to trace the source and then taking a few precautions...

an area that is naturally damp must be well ventilated and the source of the damp must not be covered with anything that can't breath... drylining the walls will probably drive more damp into the narrow strip between the floors dampening the woodwork...

damp in solid walls can be caused by rising damp bridging the damp course (if it has one) in some way - perhaps by the internal plastering or because the ground level outside is too high or because a porous floor has been covered with something that is forcing an excess of moisture out to the walls. perhaps external rendering is too close to ground level.

perhaps the ground is so saturated with water due to a faulty soakaway system or poor drainage. concrete paths too close to the house can cause excessive rain splash where rain bounces up from the hard surface a considerable distance and can saturate a wall above the damp course.

damp in solid walls can also be caused by water ingress into the wall higher up and it not being able to escape into the ground because it has a damp course - gutters and downspouts, faulty or porous render can be the culprits.

solid walls of old houses do often have damp in them naturally which would normally be kept to minimal levels by evaporation from the exposed brickwork outside. render is only suitable some of the time...

if there is a high level of damp in your house you should be aware it does increase the risk of woodworm and dry rot attack. sensible timber treatment and good ventilation is the key to minimising the risk. the importance of open chimneys cannot be over-emphasised...

[peakpilgrim]

Hi DIY Guy & Verne. Thanks for your replies. The house I live in is very old. I live in Ireland where the climate is wet and cold, not just in Winter. The walls are made of rendered stone and there is no damp course. I ventilate the house as often as possible and I have dehumidifiers going throughout the house 24/7; thats the hand I am playing with at the moment. Your comments regarding dry-lining are well noted and, when I start to gut each room and dry-line, I will need a system that will account for the points you have raised; some practical way of ventilating the wall behind the dry-lining, for instance. I, unfortunately, do not have the time to do this at present. I had intended to raise another thread on this at a later stage, but if you have any suggestions I would appreciate them. In the meantime I still have to paint these walls and any other practical suggestions would be greatly appreciated.

[verne]

i don't know much about stone built dwellings. a lot of the traditional peasant type houses were built of little more than rubble and were always damp and slightly better housing was built with cavity walls that had a decent stone facing but an infill of rubble and rubbish to keep the cost down...

i suggest you investigate the possibility of a damp course of some sort before you begin spending much money on the place. an injection damp course probaly wouldn't be very successful alone - depending on the type of stone and construction the chemical would probably only saturate the mortar - but this type would be the cheapest option and would be bound to help.

the electro-static damp course has fallen out of fashion and no one can tell me how they work but for most people most of the time they do work, or did work for those who had them. they are almost unknown now but rentokill installed thousands of them back in the 1960's. a deep vee of 3 or 4 inches is cut into the inside walls just above ground level and a continous copper strip is installed, the vee being filled with mortar to secure the strip. the two ends are passed through the wall and joined to a bronze fitting that i don't know the purpose of...

fitting a membrane would be a huge amount of work, especially if the walls are thick and do have a rubble filled cavity.

if it is possible to carry out some land drainage to reduce the amount of water in the ground around the house, this would probably make a great deal of difference in time, especially with the installation of a vertical damp proof course which will reduce the amount of wall accessible to the wet ground and further reduce the amount of damp. again the vertical dpc is little used now, but can be installed (relatively) quite easily in most instances by digging a short trench against the outside wall to expose the wall down to its footings. the wall is cleaned and rendered with a waterproof render and then covered with what was traditionally slate, but a waterproof membrane would probably be better and could possibly almost make the render redundant. working like this a short section at a time until the entire outside has been circumnavigated. the backfill of each section must be well compacted to ensure the walls remain stable.

the same treatment can be given to the inside walls if damp remains a problem and the floors fitted with a membrane and insulation at the same time so your choice of floor coverings is not limited to breathable stuff.

alternatively digging out and providing a (ventilated) cavity over which a loose laid concrete block floor is laid will also achieve the same object.

please keep us posted.

[peakpilgrim]

Hi Verne

Again you have made some interesting points. Injection damp-proofing is something that i have considered and it has been carried out on some older properties in this vicinity. I had not heard of 'electro-static' damp-proofing; which is very interesting. I have actually reduced the ground level and installed land-drainage, which has helped, but I still have this problem with mould.

[verne]

mould will always grow where there is food and moisture for it. a lot of it is bad for the health too.

i think part of your problem is likely to be your painted walls. modern plastic emulsion paints aren't breathable - in fact they are so good they can be used as an isolator coat between paints of different (incompatible) types to prevent reactions between them...

using these for decoration instead of the more traditional whitewashes or limewashes (or nothing at all) will seal off the wall as if you have put a membrane over it, concentrating the escaping moisture into areas where the paint film has an insufficient bond or has otherwise broken down...

i suggest you treat your mould with a dilute bleach solution and a scrubbing brush or a proprietory mould remover and forget about decorating until the damp is under control.

anti-mould paints tend to be intended for use in areas of high levels of condensation, rather than areas that have a head of water pressure trying to push the paint from the walls.

if the injection damp courses have worked well in the other houses, the chances of success with one in your house will be almost assured if it is of the same basic construction, certainly it will help and need not be tremendously expensive. the equipment can be hired to allow a diy job. if enough research is done first on methods, techniques and materials you will at least know that it wasn't a cowboy job...

even when you have carried out all the damp reducing measures you can, it will take a long time for the moisture levels to stabilise and the real benefits of it can be seen - possibly a couple of years, or even longer!

the vertical damp course is really worth a close look too. if the water table is naturally quite high in your area, rather than the ground being sodden just by drainage problems, you will definitely have to tackle the inside as well as having a close look at the footings if your house has any?

a lot of houses do not have proper footings but were built simply on top of the ground, mostly on stone slabs that were set into the ground less than a foot...

because lime and dung mortars were used, seasonal movements of the walls did not matter very much. a builder friend has just finished providing his own such house with a nice deep footing. he said it was "steady work" but not much of a problem.

[madbalsam]

Great question! Thanks for the answers guys. Livng in the tropics; i have this problem. You'd think builders here would know how to treat the problem by now..tsk