Dealing with damp

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The average British home has to cope with about 25,000 gallons of rainwater every year - so it's not surprising damp can become a major problem! In this leaflet like this we can't show you how to deal with the very worst cases, but the good news

is that you may not have to. Most damp problems are much less serious than they look, and not too difficult to clear up - especially with the marvellous range of modern, easy-to-use materials available at Focus.

This small leaflet is intended as a basic guide only. Many of the products for this project will include manufacturers instructions. These instructions should be followed to ensure best results.

Always consider 'safety' before you start any DIY project. Look for the 'Be Safe' sign and read the safety advice.

The main problems

Before you buy anything or have expensive work done, go through this checklist. The problem may be something you can fix quickly with one of our advanced anti-damp products. If the cause of the damp is hard to identify, a damp meter will help you pinpoint the source - they're available from most hire shops.

Check for leaks. Classic causes are broken or blocked gutters and downpipes, loose flashing or tiles. A badly-fitting window-frame (perhaps with a "drip-groove" that has become bridged), or failed roofing felt on a flat roof or roof-valley will also cause damp.

Condensation. This happens when warm moist air meets a cold surface like a wall, a window or a metal window-frame. First, make sure the room is properly ventilated, gas heaters and cookers should be vented to the outside because they release a lot of water vapour. Cold walls can be insulated easily with polystyrene-backed wallpaper (or a lining of roll polystyrene) fixed with an adhesive that contains fungicide. DIY secondary glazing will help if windows are the cause (there is a big choice of plastic film kits). If damp is coming in from outside as well, that will make the problem worse: damp walls are much colder than dry ones.

Damp from outside. First, always check that the damp-proof course hasn't become "bridged", perhaps by piled-up earth on the outside - clear it if it has.

Check the condition of the outside walls. Old mortar, brickwork that has become porous with age, and rendering that has become poorly attached or cracked - they all soak up moisture. See the following for some techniques that will help.

If the damp wall is around a chimney breast, you either have a leak somewhere around the chimney stack, or the breast has been sealed up and not properly vented. The stack should have a small louvre or sliding vent at the base of the chimney breast to let air circulate. If it's blocked, clear it.

Classic "Rising Damp". If the damp is worse at the bottom of the wall than at the top and you've checked everything else, then it's time to think about a new damp-proof course. Your best bet is probably to have this done professionally. It's worth remembering that a professional contractor will give you a damp-proofing certificate: useful to have when you come to sell your house.

If the damp is in the middle of a solid floor, then the damp-proof membrane underneath has probably failed. Again, a job for the professionals to solve.

Work sequence

	1 Damp-proofing fluid. This seals an interior surface against damp stains but doesn't have any mechanical strength - so only use it after you have tackled the source of the damp, and only on walls that are above ground (below ground-level, water-pressure will force the damp through again). Clean the wall thoroughly, removing old wallpaper, loose paint and any trace of mildew etc. before applying. Allow air to circulate during drying to carry away fumes. Redecorate when dry. Follow manufacturers instructions regarding ventilation of the room *
	2 Exterior waterproofing fluid. If exterior brickwork has become porous, this gives it a new water-resistant "skin". Simply paint it on when the brickwork is completely dry. It should also reduce heat loss inside: dry walls give better insulation than wet ones. If the mortar is crumbling, repoint at the same time.
	3 Bitumen mastic. Where flashings have become loose, use bitumen mastic to bed them back into place. 4 "Band-aid" type flashing. This is much easier to apply than traditional lead flashing and it can last a surprisingly long time if you apply it carefully. Make sure the surfaces are really dry and clean, then rub down well to get the best possible seal. It's also good for temporary repairs to guttering and downpipes.
	5 Spray-on waterproofing. This is excellent first-aid for a roof-leak, and can even be applied to damp surfaces. Just follow the instructions on the can. With larger holes, bridge the gap with glass-fibre tape or fragments of broken tile etc. before spraying. 6 Window frames. Use mastic and an applicator gun to fill gaps around the edge.
	7 Check underneath windowsills - there should be a drip groove to shed rainwater before it gets to the house wall. If this is blocked with moss, old cement etc. clear it. 8 Broken, loose or blocked guttering. Make sure that downpipes are unobstructed. Small fractures can be repaired with "band-aid" type flashing. If the guttering is really old, consider replacing it with new, easy-to-fit plastic guttering.