Rain Penetration Through Masonry (Penetrating Damp)
Rain penetration into masonry (penetrating damp) can occur in buildings of all ages. At its most obvious, it penetrates right through the wall and is visible as a damp patch on the internal wall - often causing discolouration and peeling/flaking of paintwork or wallpaper. However, rainwater penetration can be damaging to a property, even if it does not penetrate all the way through a wall. For example, moss growth, increased heat loss, and frost damage can be caused by rain penetration into masonry.
Rain penetration is not a problem that is restricted to single-skin walls. Poorly installed wall-ties or cavity wall insulation can provide a pathway for rain penetration to track through cavity walls.
In many cases, rain penetration is caused by poorly designed or maintained building details (e.g. blocked downpipes or leaking gutters) causing large amounts of rainwater to flow over a small section of masonry. In these cases, the penetrating damp can usually be cured by rectifying the defect.
In other cases rain penetration can be caused by the masonry wall not being weathertight enough to withstand local weather conditions. Often the weathertightness of the masonry can be improved using external render, cladding, or weatherproof paints. However these solutions all change the visual appearance of the masonry.
Breathable Colourless Water Repellents for Masonry
Breathable, colourless1 water-repellents offer a solution in situations where there is a desire to maintain the visual appearance of the masonry. They work by lining the pores in the masonry rather than blocking them. This allows the wall to breathe naturally and allows any moisture present in the masonry substrate to escape.
Since 1983 Safeguard have been producing breathable, colourless water-repellents based on active silanes and siloxanes. These molecules form an extremely strong and stable bond with silicaceous building materials such as brick, mortar, concrete, and sandstone. In the case of our deeply penetrating Stormdry Masonry Protection Cream this results in a life expectancy of 20-30 years.
It should be noted that products of this type are only intended to block rain penetration through the pores of the masonry. Cracks in masonry will have to be filled. Faulty mortar should be re-pointed using a suitable sand/cement or sand/lime mix incorporating Stormdry Repointing Additive. This additive contains silane and siloxane water-repellents as well as additives to promote bonding and reduce shrinkage. In cases of wind-driven rain, even mortar beds that appear to be in good condition may need to be re-pointed as wind-driven rain is able to permeate through tiny shrinkage cracks between the mortar and the brick/stone. Contact our technical department for further information.
Safeguard currently offer the following RIBA-Approved CPD Seminars free-of-charge to architects and specifiers on the UK mainland:
1) These products may cause some slight darkening to certain substrates. Although this will usually fade over time, a small, representative and inconspicuous test area should always be treated before full treatment begins.
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Rain Penetration 
