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damp walls
 Started by  holdenco0151
 11 May 2009, 2:28 PM

can anyone please help with some advise. i have just started to remove wallpaper from the wall which is the rear of the house and have found damp across the bottom aprox 1 foot from the base of the wall. i am gutted as i am scared of expensive builders and was wondering if there is a DIY way of fixing the problem without having to get expensive builders into my home. my pointing does need to be fixed across the whole wall but the problem is at the bottom of the wall. Any ideas?. thanks.
The problem that you are faced with is finding out exactly the cause of the damp. It could be rising from the ground, penetrating from rain or just condensation. You could try asking the local environmental health office or energy saving advice centre if they offer an energy or damp survey service. (Damp walls are a fantastic way of wasting heat energy so it should be of interest to an energy saving advisory dept.)
Dr T (Guest)
Best idea is to take my advice that it is condensation and dont ask any damp companies to look -- they will sting you up, redecorate and improve your ventilation. was the area behind furniture or a bed?
mike7 (Guest)
I'm no expert, but I'd check outside for any sign of a damp course, ie a line of waterproof slate or mastic or some such between the bricks. If you find it, is there anything that could be letting dampness rise up past it, such as earth or render? Concrete which lets rain splash up above it? Any leaking gutters or dripping overflows above?
Mike7 has the right idea..most likely cause is an external source..render or spalling brickwork..tell tale cracks from window ingoes to the wall.
Site conditions have a huge effect..sources of wet moist air from the inside of the property..perhaps from your swimming pool..LOL or the shower room..
The time of year when it occurs can be a significant pointer. Walls will have had an opportunity to dry out since March with higher temperatures...the damp proof course.should be clearly identifiable with weep holes for draining the cavity evident between the course of bricks resting on the DPC...if its below a window it could be cement bridging the wall ties...get a pal to take out a couple of bricks to inspect..lots of treatments available..which can be brush applied..improved ventilation with an air brick would also eliminate trapped moisture
Ive been doing surveys for this problem for thirty years.
The problem could caused by one of three reasons.
1) Condensation. This is the most common cause. You dont say whether yours is a house or a bungalow. Most of the problems I have encountered are on a north / west faceing bedroom wall in bungalows. The problem also seems common on similar faceing walls in small bedrooms in houses. The cause of this condensation is due to excessive amounts of water vapour for any given temperature (warm air will hold more water vapour than cold air).This is why we get more condensation in the winter. Yeast spores in the air thrive and multiply in humid conditions. The tell tale signs are black dots forming a mass and an arc shape. Condensation will generally form in a corner where there is minimun air movement. If the problem improves during the summer it will most likely be condensation.
The Cure. If you have cavity walls you could insulate them. This will make the internal wall warmer and reduce the condensation. If you have solid walls all you can do (apart from external / internal wall insulation which is very expensive, although grants are available)is to try and reduce the amount of water vapour in the air. This can be done by the use of a dehumidifier (although the noise might not be tollerated) by keeping the house warmer for longer periods (expensive) or by additional vetillation (draughty)
There are brush on treatments that will work for a while but will not cure the underlying problem.
2) Rising damp. Rising damp occurs (by capilliary action) when there is no damp proof membrane (common in older type properties) or the existing damp proof membrane has failed.
The way to check this is by the correct use of a damp metre. This will require the removal of a couple of square centimetres of plaster so that the reading can be taken from the brickwork (if the reading is taken from the plaster, condensation could be mistaken for other problems)
To be certain you could take a core sample and have it analysed (rising damp will contain sulphates and nitrates from the ground)
The Cure. There are several damp proofing methods available. A proper survey from a reputable company will determine the extent and which system is most applicable.
3) Penetrating Damp. This occurs when water from an external source crosses the brickwork. In solid walls this is generally due to defective pointing or spalding bricks.
In cavity walls it is more than likeley due to bridgeing of the cavity with mortar or bricks. It might also be caused by a build up of mortar or rubble bridging the damp course.
The Cure. Solid walls. Repoint and replace defective mortar and bricks. Treat brickwork with a slicone or polymer.
Cavity walls. Remove external bricks opposite the damp areas and check for bridgeing, remove if present.
I hope this is of use, but if in doubt I would suggest you contact a national or reputable local damp proofing company who should easily diagnose the problem.
jamesingram (Guest)
The problem you have is thermal bridging and possibly a lack of air movement. Thermal bridging is caused where warm air meets a cold surface, as warm air holds more moisture than cold air; as the warm air cools down the air reaches saturation point and moisture in the form of condensation is deposited either in the form of surface and or interstial condensation. It may also be that the wall to the rear of the house is colder than the front of the house and warm air from the front of the house is entering the room coming into contact with the cold wall and thereby aggravating the problem.
The solution is not so easy as one may hope, you could paint the wall with a moisture resistant coating but then you will still have the cold wall and the condensation will then likely affect the wall paper as the vapour is restricted from interfacing with the plaster surface.
To resolve this problem, most people will introduce/construct a thermal cladding to the interior walls, which consists of fixing a insulated sandwich board such as British Gypsum Thermadeck Super or similar material to the affected walls. This board comes in various thickness and one of around 80mm will provide a significant improvement to the thermal performance of the wall. Usual method in mild conditions such as yours is to stick the board on to the affected walls with an approved adhesive or plaster dabs, and then either tape and joint, or apply a plaster finish both ready for receiving decorations. The beauty of the PIR boards is that they are relatively vapour resistant and the wall being warmer means that surface and/or interstitial condensation are unlikely to be a problem - also the room will not require so much energy to keep warm and energy costs will be reduced thereby having a direct benefit on reducing carbon emmissions.

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