Other causes of damp
A previous damp treatment has not worked -
If you have previously had an injected damp-proof course in order to rectify a rising damp problem in your property it may have not been fully resolved. If when the solvent was injected into the wall it was still damp, the solvent would have never completely dried out and the chemicals never cure; the process will just saturate the wall with even more water.
Damp plaster can retain a residue of salts deposited by the water. This damp can often reappear because these salts absorb moisture from the atmosphere of the room.
Cement rendering is used on exterior walls, if the cement render is very badly cracked it will trap water, but the water cannot escape because the render is impermeable. This then encourages condensation to form as moisture from inside the house and results in clay lump walls collapsing.
Excess moisture can rise from below and up through the floor and into the properties air which lets it dissipate leaving no build up. If a floor is replaced with a modern solid design that prevents this from happening, moisture is forced to travel under the floor and into the walls to escape. This will increase the moisture in the walls and potentially make those walls damp.
Modern/ excessive use of plaster
In the worst of usage this will also stop moisture from circulating, causing a build up and ultimately damp.
Poorly laid patios
Patios are often laid too high, causing bridging of DPSc or rain
splashing on hard surfaces saturating the walls, causing a build up of excess moisture which then causing damp and mould to emerge.
Cement based mortar is the worst for excess moisture, it stops moisture escaping into the air but also encourages water into the wall. Cement based mortars also force natural salts to crystallise in brickwork, causing the bricks to break up.
There are many damp proofing options available and it can be difficult to know which is best for your property, if in doubt it is always best to consult a professional.
Some of the most common damp proofing methods are;
Damp proof membranes - they are made from High Density Polyethylene (HDPE) or Polypropylene and are impervious to moisture and moisture vapour. Damp Proof Membranes can be applied internally with little or no surface preparation. However, it is very important to install the membrane correctly to prevent expensive water ingress in the future. They should be used in conjunction with a Damp Proof Course in outer walls to create a continuous barrier to water.
Damp proof paint - Damp proof paint is a non-toxic product (free from solvents and plasticizer) that can be applied to surfaces to act as a barrier to moisture. Damp proof paint is most frequently used on walls under a render as a waterproof layer when damp proofing walls, to cover up damp stains on painted areas as well as under tiled areas as a secondary protection for wet areas such as bathrooms.
Cementitious tanking - Tanking is a form of damp proofing that blocks water ingress from entering a structure by creating a barrier. Cementitious tanking is a cement-based coating, consisting of Portland Cements, blended with aggregates and chemical modifiers. It is microporous, meaning that it is fully breathable. It is applied to the internal face of the structure. It can be used on concrete, stonework, brickwork and blockwork. If areas of the property are suffering from more severe water ingress then you should use cementitious tanking as a waterproof barrier rather than damp proof paint. It is also for those situations where the installation of a full damp proof membrane is not necessary.
Renovating Plaster - it is a pre-mixed, lightweight backing plaster designed to control dampness passing through walls of older properties. Renovating plaster contains perlite aggregate, which controls dampness that passes through the walls of old properties. Renovating Plaster can be used for plastering most traditional background surfaces during renovation work. It can also be applied shortly after the installation of a new damp proof course system or used in conjunction with a basement tanking systems.
Liquid Epoxy Damp Proof Membranes - The solvent-free membrane contains certain chemicals that allow it to cure rapidly, reducing the passage of water vapour and acting as a barrier against residual moisture. A liquid Epoxy Damp Proof Membrane can be used as an above ground damp proof membrane on concrete floors and concrete screeds. It is often used before the installation of a new floor covering. The surface you want to damp proof must be of sufficient quality.
Anti-mould Paint - this works by bringing together modern paint technology with highly effective biocides. The anti-mould biocide is combined throughout the paint film, which has been scientifically engineered for water resistance and durability, imparting toughness and elasticity. Anti-mould paint is ideal for walls and ceilings in homes as well as a wide range of public and commercial buildings. It is fully washable and resistant to the effects of condensation when the coating is fully dried out.
With all of these methods however they will not work unless the underlying damp issues have been identified, treated and resolved. The best way to then ensure no damp arises is with adequate ventilation.
8 Ways to reduce damp
1) Try to keep the inside temperature reasonably constant.
2) Avoid drying clothes indoors.
3) Do not dry clothes over any radiators.
4) Ensure tumble driers are properly vented or the condensate is regularly emptied.
5) Keep furniture away from walls.
6) Do not turn off or disable extractor fans.
7) Ensure extractor fans are well maintained and offer adequate airflow.
8) Bath your Pets and wash their bedding regularly