SUCK IT UP
A misconception regarding ‘rising damp’ is that it is the water rising up the building under a ground pressure or positive hydrostatic forces; actually, moisture is drawn through the masonry like a sponge absorbing water, which is known as a capillary action or capillary ascending moisture.
This is caused by narrow voids or tubes formed in the brickwork and mortar, the narrower the tube the higher the water will be drawn as it puts pressure on the surface tension of moisture at the base of the tube, this is the same effect of fine roots of a tree absorbing ground water.
PLUGGING THE GAP
So in order to stem these small tubes formed in the masonry the idea of resin or chemical injections in the bricks was devised which would form a protective barrier, the theory is sound however the application was sometimes not.
The misconception was that when injecting into the brick once a figure of eight had occurred to the face where the injection rods were placed then this was enough chemical to form a barrier
Figure 1 passage of moisture
However, water can still pass through the mortar joints (fig 1) as well as the masonry and recently this was identified to be the main passage route of moisture. Saturated walls externally and peeling paintwork internally with sometimes black mould forming is a sign of ‘rising damp’
This can sometimes be due to interstitial condensation or leaking pipework so identification of this can sometimes be tricky
LET ME BREATHE
Occasionally it can be poorly ventilated floors with blocked floor and wall vents not allowing the passage of fresh clean air through. This condensation can attack joists and walls above the DPC line and then will cause a rising damp effect; additional Damp courses will not rectify this.
It is always good practice to investigate all external wall surroundings for ponding water, blocked drainage adjacent to the property including gutters and downspouts or wall vents filled with a sealant or a build-up of dirt over the years (fig 2).
Figure 2 Vent Blocking with mud
This is not an issue for those of us in older or renovated buildings. New builds can also suffer from these issues for example level access paths may have been fitted to the entire external perimeter, this can often close the 150mm void between the external path and DPC or block telescopic vents required for beam and block flooring.
HOW FAR IS TOO FAR
‘rising damp’ will only travel 1m (roughly) up the wall under the capillary action so if the moisture is identified through the upper floors then it is likely to be another source. If however it is mainly identified on the ground floors even internal walls as remember these will be transferred to foundations in the wet earth then the remedial action of a DPC is required.
The resin injections are a good source of remedy however; this must be actioned by a suitably experienced person who will ensure a full seal is provided and all other avenues rectified where needed.
Electro-osmosis damp proofing can also be utilised as a method this is best suited to a timber floor suffering with rising damp, as it will actively drive the moisture back down into the ground as opposed to stemming it where it is.
TO SUM IT UP
Rising damp is not in fact rising but drawn water and identification can be tricky,
Once the water is managed, the remedial actions of removing damaged plasterwork and sometimes repointing the masonry where washed away can be costly so identifying the correct issue is key, as what appears to be rising moisture may be surface condensation.
The correct use of the remedial methods is also important as poorly applied is the same as no action at all. Once the moisture issue is rectified, it is important to remove all damaged plasterwork containing salts and mould will always attract internal room moistures causing the issue to reappear or at least seem that way, treatments and creams and surface paints that seal in the damage is only masking the issue and will eventually bleed back through the coverings.