Guide written by:
Dennis, self-taught DIYer, Bristol
Do your walls seem to absorb moisture like sponges? Cupboards starting to rot? Peeling paint? Don't panic! Whether it's sealing your façade, your cellar or preventing rising damp, the solutions are here for you. Here's all you need to know from floor to 'sealing'!
- Porosity of materials
- Capillary action
What are the health implications of damp?
The main issue is that moisture promotes the development of mouldsand bacteria that provoke allergic reactions (skin irritation, etc.), respiratory problems (coughing, asthma attacks, bronchitis etc.) and joint problems.
Persistent damp in the walls and air also changes the properties of building materials. Wood rots, mortar and plaster flake and paint starts to peel.
While heating, dehumidifiers and insulation can help control damp, it's also highly advisable to seal walls and floors thoroughly and ensure good ventilation to the property as preventive measures.
What causes damp in a property?
It's important to understand the origin of the damp in your home, because the treatmentwill depend on the cause.
Seeping in of rainwater through cracks and broken tiles.
Porosity of materials
Increasing porosity of exterior materials can allow moisture to migrate gradually into the interior.
Capillary action from the ground
Buried walls (with networks of tiny holes) allow water and mineral substances to rise under osmotic pressure up to 1 to 2 m in height - aka classic rising damp.
Once the water has evaporated, the dissolved substances accumulate on internal wall surfaces, producing whitish stains (saltpetre).
Persistent condensation arises because moist air condenses on colder surfaces. In a residential property, this causes paint to peel and blister and ring-shaped marks to appear. The cause may be poor ventilation, presence of thermal bridges or high levels of ambient water vapour.
Accidental causes such as pipe leakages or other water network faults.
How to remedy damp problems?
Ignoring pipe leaks and broken tiles, where the solution should be pretty obvious...
If the reason is poor ventilation, install an aerator, CMV or moisture absorber and use anti-condensation paint.
If water is getting in through cracks , fill them with water-repellent materials such as mastic, roughcast or grout, covered with a waterproof material. And ensure - providing a reliable witness - that you're not plastering over more significant structural problems with the property!
Porosity of materials
Facadesand roof porosity can be treated with sealing paint or plaster. As for the effects of hydrostatic pressure and capillary action, more serious work will be required.
How to stop rising damp caused by capillary action?
For capillary action, mineralized water and porous materials are required. Let's start with solutions that prevent water seeping into the walls.
Injecting water-repellent cream
The first form of treatment against moisture involves injecting water-repellent cream (or resin) about 15cm above the ground, every 10-15cm, in order to clog the capillarities.
This provides an effective chemical dam, but doesn't remove moisture from the lower part of the wall. Effects will only become apparent several months after treatment.
In the same vein, if moisture appears in plaster tiles on the floor, you can simply replace the lower tiles with waterproof tiles or installawaterproofing layer (i.e. damp coursing). Another solution is to create an electromagnetic field opposite to that which causes the capillary action (it's an expensive process though!) The water is pushed down and the walls dry up (although some scientists remain sceptical...)
Now let’s look at solutions that prevent water from coming into contact with the walls. They all require digging a trench down to the base of the foundations.
House perimeter drainage
Peripheral drainage evacuates groundwaterbefore it reaches the foundations. In order for the drainage to be effective, it must be carried out with precision: depth level with the foundations; pipe gradient of 3-10 mm/m towards a sump; perforated 100mm-diameter pipe; 20cm gravel and geotextile to avoid clogging of the drain.
Waterproofing of walls
Buried walls can be waterproofed through the application of athick bitumen product and the laying of a "rubbery" sealing membrane with screws or nails.
'Casing' consists of creating awatertightbox to protect the foundations from potential groundwater shifts or flash flooding.
Buried walls can be waterproofed
How to limit the damage caused by damp?
If you don't want to get into serious renovation work, you can still mitigate the effects of indoor moisture by applying specialized paints such as:
- Plaster hardener - improves the response of plaster to finishing paint;
- Preventive or curative anti-humidity paint, applied wet walls before finishing;
- Anti-condensation paint that limits condensation in wet rooms;
- Anti-saltpetre treatment which, as the name suggests, removes saltpetre from walls;
- Microporous waterproof mortar - very well suited to basements and cellars;
- Anti-slip treatment for slippery floors;
- Flooring fixer for improved adhesion of floor paints.
Final tips for choosing
First of all, identify the causes as accurately as you can. Damp can have various origins and taking measures against problems that aren't there won't help you!
Treating damp, even on a very localized scale, will improve your comfort and even your health, as well as preventing your property from deteriorating and losing value.
Learn more about combatting damp...
To find out more about combatting damp, follow our editors' advice and check out their other guides:
Guide written by:
Dennis, self-taught DIYer, Bristol, 18 guides
I started doing DIY 10 years or so ago, when I bought a house that needed to be renovated. After having installed loft isolation, and having refurbished the bathroom, the toilets, the kitchen, the bedrooms… I built an extension, installed a new fence with a gate and kitted out the house with a solar panel to make hot water. I have poured tens of tonnes of concrete into slabs or into the foundations and renovated the roof… I can say that building materials and tools are no stranger to me! If I had a pound for every hour spent looking up information in forums and DIY magazines to find solutions to my problems, I'd be a millionaire! So passing on my knowledge on tools and home equipment is natural, as it is just giving back what I borrowed.