Certain brick walls do not offer sufficient thickness to prevent damp and water from penetrating. In this case, it can be useful to treat the brickwork with a sealant or water repellent to prevent moisture from penetrating the brick. If the brickwork becomes dramatically darker or immediately absorbs any water that is splashed on it, waterproofing may be needed.

Water Repellents:

Water repellents can be applied to the external area of the wall. They penetrate through the wall’s fabric and cause it to repel moisture. However, the wall will still remain permeable to air movement, allowing water vapour to pass through the wall, reducing the likelihood of damp build-up from the inside.

Non-Breathable Sealants:

These are also applied to the external part of the wall where they form a film that creates a moisture repellent. However, unlike water repellents, they will also usually make the wall impermeable to the movement of air, which can prevent any moisture from water vapour from the inside being able to evaporate to the outside, increasing the risk of damp.

How to Apply:

How you apply your sealant or water repellent to the brick wall will depend on the product that you use. You should always follow the manufacturer’s instructions. Some sealants are designed to be applied by spraying onto the wall, while others are painted on with a roller and tray. Before sealing the brick surface, it is important to ensure that it is correctly prepared. Having a clean surface that is free from dust and debris will allow for the best waterproofing performance. It is also wise to conduct a test patch on a small area of brick prior to covering the entire surface.

Choosing the Right Product:

In general, non-breathable sealants are not recommended for external wall use due to the problems that they can cause concerning damp. If your home suffers from damp and mould, it is more advisable to choose a water repellent product as this will allow moisture to continue evaporating from the inside and reduce the risk of damp build-up.


Both non-breathable sealants and water repellents are not permanent and will need to be reapplied in order to ensure that your bricks are protected from water damage. How often you will need to reapply your sealant or water repellent will depend on the product that you use and the type of brick. The manufacturer or an experienced contractor will be able to provide you with advice on the best timeframe for reapplication for your home.