Masonry Water Repellent For Treating Penetrating Damp


Masonry water repellent for treating penetrating damp has been carried out for ages but does it really work and should you apply it to your property?

Masonry water repellent, otherwise called brick sealer or masonry sealer is a chemical product that has been available and applied for decades originally as a Spirit based chemical but now more commonly, is supplied in a silicone form of product due to the advancement of silicone based materials and their water resistant and waterproof capabilities.

There are many, many brands and types of product available to purchase ranging from budget brands with low levels of active ingredients resulting in numerous repeat applications through to quite dear, cream based products which to be fair, are highly tested and have gone through rigerous research and development processes to prove they work.

However, before a tradesman or DIY Homeowner proceeds to apply any kind of chemical to the brickface of a property they should be clear on why they are doing it to ensure the right thing is done, the right product is applied and for all the right outcomes.

In many cases, masonry water repellent is applied as a solution for treating penetrating damp. This kind of damp is generally attributed to brick mortar being in poor condition which quite often down to weathering. It can also be attributed to damaged or blocked rainwater goods such as guttering joints, blocked down pipes and hoppers. Flashing, fillets, flaunching, structural cracks can all be causes of defect whereby wind driven rain can enter into a property. Ahead of any kind of chemical or paint application all aspects of maintenance or repair should be undertaken to ensure rain water is collected efficiently and no holes or cracks are left untreated.

Another and very unfortunate issue with penetrating damp is for the mortar and brick being of a porous nature and or in poor condition, allowing ranin water to penetrate and meet a cavity insulation material if it is present as this can lead to quite significant internal damp issues. If this has been the case, the owner of the property is generally advised to have the damp insulation material extracted by a specialist contractor. Either partially or in most cases, to the whole affected wall.

So with the cause for penetrating damp correctly identified and corrected are you able to proceed with an application of masonry water repellent?

Well before applying anything you are advised to remove or deal with any kind of moss, algae, lichen, salts, dirt, grease and oil first. In many cases, jet washing the area is fine but with stubborn algae and lchen then we would recommend using a good quality algae treatment:

Allow the area to dry down if you have jet washed it and if you have applied a chemical to remove algae or salts, allow a few days for this to do its work and break these things down.

Once you have done this and provided you have temperatures of 5 degrees celcius and rising and rain is not forcasted for ideally a couple of days, then you can proceed to apply a masonry water repellent.

Frequent questions we are asked:

Can you apply masonry water repellents over paint? The answer is no. It cannot penetrate through the paint.

Can you paint over it? The simple answer is to not use it. Just use a good quality masonry paint.

If moisture is in the wall will it get trapped? Good question. Ideally you will have fixed the cause for the damp in the first place. Allow some drying down time if possible so the wall/s are not wet but if some residual damp is still in the wall it won’t be a problem. The silicone treatments work to line pores of brick and mortar allowing moisture to evaporate out of the wall whilst preventing the passage of rain water in.

Does it change the appearance of the wall? In most cases and once cured, you will see no difference at all however, we advise you do not apply it to Limestone and you might like to apply a small amount to an out of sight trial area.

Do you apply two coats? Many brands recommend a two coat application and to walls or properties exposed to extreme wind driven rain conditions this would not be a bad thing however the second coat needs to be applied before the first coat has cured. High grade brands suggest a single coat application is sufficient but it’s all down to how it is applied and how liberal the applicator is with applying the product. Allow for over-use or high porosity in your calculations.

Should I apply the cream version? The cream version of a brand of masonry water repellent is the better quality product but significantly dearer. The trade off being that in most cases, one coat is all you need to apply and for it penetrating deeper into the substrate than the liquid based types, it offers better protection and for longer. The cream versions are also proven to offer an improved thermal performance to the treated walls. However, to good condition walls not so exposed a high grade liquid based product applied by a low course pressure sprayer will be fine.

Late Spring and Summer months offer the best weather conditions to be carrying out this kind of property maintenance. In summary, our advice is to first of all make the property sound and defect free and then choose a good quality masonry water repellent.

Finally…. if left undetected, silicone ‘spatter’ on glass is not easily removed if left to dry. We advise you cover all windows, glazed doors and the windows of cars nearby if spraying could be in danger of getting covered if wind drift is high. Use hard surface protection films on widnows before application!

Here are our high quality masonry repellents:



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