Do my brick slips need sealing?

So you have spent all this time, money and effort to create a fantastic brick slip installation and you wonder if they need to be protected against liquids…

Here is a broad guide as to when, where and why you might want to consider protecting them and the reasoning behind the suggestions.

 External building?

If you are building a house and the installation will be subject to the elements i.e. rain then you have a few factors to consider.

  • Frost Resistance of the brick slip you are using.

Frost resistance is an important factor for sealing because if they are not sealed they are much more likely crumble or ‘spall’ if they take on too much water and are then subjected to freeze-thaw cycles.

Spalled brick work
Example of ‘spalled’ brick work sometimes caused by soft bricks or hard mortars.

Matclad brick slips (excluding the reclaimed brick slips) are fully frost resistant (BS EN 771-1:F2). You do not need to seal these for external use. They are made fully frost resistant by firing them to a high enough temperature to achieve a low water absorption.

If you are using another manufacturers brick slip or slips cut from bricks you should check the frost resistantance declaration. If they are not F2 you may have to seal them.

  • Exposed Brickwork

Whilst you may think all external brickwork is exposed there are certain places that are more exposed than others and water saturation becomes more likely.

Boundary walls, chimney stacks, below damp-proof and walls where a prevailing wind means there is a tendency for driving rain to lash the wall (coastal properties in particular) are common examples of this.

When building these types of structure you should use a fully frost resistant brick. Certain types of brick (most notably some Dry Pressed Bricks) can be used in non-exposed applications such as under eaves where they are semi-protected from the elements but should not be used in positions of extreme exposure i.e. boundary walls.

Brick types for use on internal feature walls and installations is less critical as they are not exposed to the freeze-thaw cycles of external installations.

 Internal projects

Even though internal projects might not be exposed to mother nature they can still be subject to ‘splash’ damage.

Splash damage can be anything from water and steam to fats and red wine.

  • Kitchen installations

Common sense says that in a kitchen environment, when slips are used as i.e. a splashback they should be sealed or some other mechanical barrier should protect them from potential splash damage.

While the brick will only take on a small amount of the liquid from a splash of red wine if the brick is a light colour that will stand out and may potentially become an eye-sore.

  • Bathroom and wet room environments

In a normal bathroom slip installation it is not necessary to seal them. If a little water is absorbed from splashes and steam they will dry out and will not leach colour (clay brick slips do not fade or use dyes for colouration).

If it is a wet room environment it would be probably wise to seal the slips to protect the underlying substrate and to inhibit mold growth. The brick will hold moisture for some time and, if often wetted, will potentially penetrate through to the underlying boards/blockwork.

 Types of sealant

Your choice of sealant depends on the level of water repellancy you require. Certain types may give an undesirable sheen to the surface of the brick.

  • Internal Applications

For internal work we have had good experiences using Everbuild GEOSTONE5 Geo-Fix Stone Protector and Kingfisher Brick and Stone Dust Sealer

These give a matte finish and produce low or no odour. In our experience these barely change the appearance of the brick but you should trial a small area before full application to make sure you are happy with the appearance after application..

The Kingfisher product is internal only but the Geo-fix can be used for both internal and external applications.

These provide a high degree of repellency but not 100% (the liquid ‘beads’ on the surface but may soak in if left overnight or for long periods).

The alternative is RONSEAL Thompsons Water Seal. This is meant for external sealing but leaves a sheen on the surface of the brick and is meant for use in trying to prevent damp penetrating through the walls i.e. rising damp.

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  1. Michael Murphy says:

    Can these slips be used to line a fire place on fixed to 12 mm Hardibacker cement board, where a wood burner stove is going to be installed.

    • Paul says:

      Hello Michael,

      All of our brick slips are suited to installation in a stove chamber situation. They are A1 fire rated (non-combustible) and the heat will not affect them when using a modern stove in the chamber.

      Typically a high quality rapid-set wall tile adhesive would be used. We offer BAL Rapid-Flex One which has a temperature rating of -30°C to 100°C. In practise the wall behind the stove will rarely reach that high temperature as modern stoves are designed to send heat out to the front.

      If you think about it practically if the wall behind it were to reach 100C you would not be able to put your hand on the wall as it would burn you…

      12mm Hardie Backer board is probably fine but if in doubt seek the manufacturers technical advice or read the datasheet for the board you intend to use (you can get the datasheets here)

  2. Michele Chapman says:

    I want to use Cottenham brick slips on a kitchen wall as they are cost effective.Will I get some variation in the tone to make the wall a feature ?

    • Paul says:


      Yes brick acid can be used on all our bricks – they are made from clay and will perform in the same way as bricks.

      As with all surface treatments you should try it in an inconspicuos area before full treatment.


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