How to Deal With Widespread Dampness

If you cannot identify a simple cause for dampness or if it is widespread, it may be necessary to improve the weather resistance of the external face of the wall. You can do this by covering the wall with cladding, repointing, rendering or by applying a water repellent or paint coat­ing to the outside of the wall surface. In some circumstances you may have to do a combination of these things.


Cladding the outside of a house for example, tile hanging or weatherboarding – offers a virtually foolproof way of preventing penetrating damp. Protection of a wall in this way is expensive, but it is easier to do than rendering. However, you must think carefully about the design of protective edge features around windows and doors.

When dealing with solid walls, it may be worthwhile insulating the wall at the same time. There are various systems for applying insulation to the outside of a solid wall which can be finished by tile hanging or rendering.



If the mortar joints are obviously in poor condition – perhaps crumbling away or with visible cracks – you need to repoint. Rake out the joints to a depth of 10 to 15mm and repoint with fresh mortar, preferably finishing the brickwork with a concave or weather-struck joint.

Repointing is a time-consuming job and requires some practice if it is not to look messy. Nevertheless, repointing poor joints is essential and a necessary preliminary to other treatments – such as applying water-proofing solutions or paints. Often, however, it is not necessary to repoint the whole wall – dealing with small areas or even isolated joints may be adequate.

When mortar shows signs of sulphate attack – near old flues, for example -allow the brickwork to dry thoroughly and then repoint with a mortar contain­ing a sulphate-resistant cement. Allow the mortar to cure for at least a month and, assuming that the brickwork is still dry, finish the wall with a coat of water-repellent solution. This treatment should reduce further sulphate attack, but it may be necessary at a later date to deal with the problem more thoroughly.

Water repellents

Water repellents for masonry – such as spirit-based silicones – probably provide the most inexpensive and easiest external treatment for penetrating damp and, as they are colourless once dry, they should not seriously affect the appearance of the wall.

These products work by lining the pores of the brickwork with a water-repellent material and so inhibiting capil­lary absorption of water. They work well -as long as they are applied well.


You generally apply water repellents with a brush, working a generous amount on to the areas of brick­work and mortar which need treatment. Use at least the quantity of solution recommended by the manufacturer – a little extra can only improve matters.

With cavity walls, most of the water which gets into the cavity has probably passed through fine cracks between the bricks and the mortar not through the bricks themselves. So, you should con­centrate the water repellent on the joints and make a particular point of brushing extra solution along the line separating the bricks and mortar. A useful technique is to dampen the wall with water and allow it to drain for an hour or two before treatment. This will satisfy some of the brick suction, leaving more of the water-repellent solution available for the inter­face cracks.

With solid walls, where capillary attraction through the brick pores is also important, you should treat the walls dry. Again, pay attention to the joints.

Before treating your wall it is advisable to apply the treatment to a small test area in an inconspicuous position to make sure that the product you intend to use docs not affect the appearance of your wall unduly.

Effectiveness Surface water repellents are generally effective for 5 to 10 years before a further application is necessary. The surface repellency – seen as an obvious shedding of water will weather after a short while, but the repellent will remain effective within the pores of the brickwork.

Because these treatments line the brick pores but do not block them completely, the wall can continue to allow water vapour to diffuse through the surface, although at a much reduced rate. The ability of the wall to breathe in this way prevents the build-up of water behind the repellent.

If a repellent treatment is not success­ful, other measures can be taken later -although it may be necessary to allow the surface of the repellent to weather first.

Small areas Water repellents are often used to treat whole walls, but they can be used for the spot treatment of selected areas too. For example, rain penetration around a window frame in a cavity wall may be prevented by treating the area of wall above the frame. This will reduce the volume of water entering the cavity and lessen the problem for the lintel and DPC. However, spot treatment may lead to a patchy appearance, particularly after rain.

Paint for outside walls

Exterior emulsion paint dif­fers from ordinary emulsion in that it contains additives to inhibit mould growth. It should last 4 to 7 years.

cladding Widespread

Masonry paints have similar additives, but also contain fibres or particles of sand, stone or granite which help fill and disguise small cracks. Again, they should last 4 to 7 years and will act as an effective seal provided the wall is basically sound. As the paints are opaque, deterioration and unsealed cracks can be seen easily.

There is a wide range of masonry paints available, including those that are smooth, those with a texture and those which are thick-bodied.

The durability of paint obviously depends on the paint itself, how thoroughly the surface of the wall was prepared and how well the paint was applied. When using masonry paint to reduce penetrating damp, it is of the utmost importance to maintain the integrity of the paint film cracks will allow water to get in between the paint film and the wall and produce problems similar to those which appear with unsound rendering.

As well as the various masonry paints which you can apply yourself, there are specialist-applied textured coatings. These coatings are sprayed on by a con­tractor and should last 10 years or more, but require thorough surface preparation tilling cracks and so on beforehand.

Filed Under: Home & Maintenance


About the Author: Jason Prickett loves to write about home maintenance and stuff you can do yourself instead of hiring any professional. His step by step guides will assist you in completing your home maintenance tasks.

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