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Dampness & Its Removal
You will end up at this page if you select either indoor or outdoor dampness, because often the two are related, or at least one is the cause of the other.
Dampness is a significant issue to control, in that in the short term it damages belongings, in the medium term it can lead to poor health and in the long term it can severely damage the structure of any building.
Dampness also makes restoration and new works troublesome, so do solve the existing problems before you carry out new works.
Dampness is the main offender to both painted and unpainted walls, and can be caused by:
Also of importance is the integrity of any surface. If it is cracking, peeling or falling away from the wall, the reason(s) must be determined and following a solution, the surface must be repaired.
Quite a list, and if some are issues then you will have additional projects. How to carry out some of these is covered under Plumbing - General.
An air gap exists on most (new) external walls, which are effectively two separate walls structurally linked together. The damp course is, today, a plastic strip laid upon a layer of stone or brick, below or at floor level that stops moisture migrating from the ground up the wall. Many older houses use an additive to the mortar, or even slate to achieve a damp course. Houses built on a concrete raft, that is the total house is on one continuous slab, have plastic sheeting underneath to stop water penetration, and a separate damp course above the raft.
One final issue to look at on unpainted houses is whether re-pointing is necessary. The mortar between stone and bricks can fail, due to the effects of wind, rain and ice, and if severe should be replaced. This is a job you can do yourself, but it is time consuming and you need to see someone else doing it first to get a good appreciation of what to do. Most importantly is the need to ensure a consistent mortar mix (sand, lime and cement) that is measured very accurately by volume each time to ensure minimal colour changes throughout the project.
Look also at the integrity of the house timberwork, and address issues such as:
Filling damaged areas with wood filler is acceptable, but only when all areas of damaged timber have been fully removed. Excessive use of woodfiller is basically a way of not carrying out immediate replacement.
Once a surface is repaired and dry it needs to be sealed for refinishing. In the case of masonry, an oil based sealer is recommended, whereas in the case of timber an oil based primer is recommended.
New rendered walls should have been pre-treated prior to rendering or plastering (wet plaster) so little further treatment should be required, though it does not hurt for suspect areas to apply a good oil-based sealer, then proceed to two or three coats of emulsion.
You can batten out a wall and apply some panelling such as plasterboard or pine panelling, but this will simply trap any moisture that does penetrate and lead to a musty odour. Try and avoid this type of fix, unless you know the wall is dry.
With masonry you are generally trying to stop rising damp from escaping into the room, while with timber you are generally trying to stop the ingress of water into the timber from the masonry, typically a problem in floors, skirtings and architraves.
If you can get under or into a timber floor, it is our recommendation that you ensure a form of damp course is installed between the floor supports (vertical posts or piers of either timber or brick) and the bearers (bottom most horizontal layer of beams). This damp course is typically plastic membrane, sold by builders' merchants for this purpose.
Additionally, when renovating ensure that all underfloor vents are clear, that debris under the floor is minimal, and that air flow under the floor is unimpeded. Also remove building debris that has fallen between the sub-floor (bearers, joists and floor boards) and the wall, as this forms a moisture bridge from masonry to timber.
Favour cleaning over painting, as painting is only a cover up whilst cleaning is a preventative measure.