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How to clean and seal exterior brick walls

How to clean & seal exterior brick walls

How do you clean and seal exterior brick walls?

This how-to guide explains how to clean & seal exterior brick walls. The products included in this guide are suitable for use on modern brick walls, which have a cavity, and older rubble-filled brick walls which therefore have no cavity.

Sealing an external brick wall is relatively simple when using breathable impregnating sealers. Cleaning brick walls is a little trickier as you will need to select the correct type of cleaning solution for the contamination you are trying to remove. It is possible that you will require more than one kind of cleaner.

The information provided below will help you decide how to clean and seal an exterior brick wall.

We also have products for cleaning and sealing internal walls – see the link at the foot of the page for all our cleaning and sealing products for brick.

You can click through to individual product pages by clicking on the titles highlighted in blue. This will provide information on pricing, available sizes, dilution rates, coverage rates and other important technical information. There is also a link at the foot of the page which will take you to all our products for cleaning & sealing bricks and associated ‘how to’ guides.

How to clean an exterior brick wall

External brick walls typically suffer from green algae or red algae, black spot lichens, efflorescence salting, and general cement staining. The following products are designed to clean external brickwork.

Floorseal Brick Cleaner is our main product used to remove efflorescence and general mortar staining from cement-based pointing.

Perfect for removing the general white efflorescence bleed mark that appears after pointing. Or removing general cement staining after newly laid bricks have set.

Apply at a ratio of approximately 1:4 up to (& including) being applied neat. Apply to the surface when dry and rinse away with clean water after use.

Please note: This will not remove efflorescence salting which has been occurring for years. If the efflorescence has become a thick calcified layer, it can only be removed by a mechanical process, not a cleaning fluid.

Floorseal Green Remover Concentrate This is a ‘spray and leave’ type formula for removing organic contaminations. Once applied it will break down Moss & green and red algae over the following few days.

Green algae’s are usually easier to remove than red algae’s. Red algae can become temporarily worse after treatment (as the cells burst) before finally fading away – you may need to treat red more than once.

Green Remover Concentrate is for simple and quick cleaning of general moss & algae – we recommend using a pump sprayer to apply the solution.

Green Remover Concentrate is to be applied at a ratio of 1:5 (or a maximum of 1:3) diluted with clean water. Apply to the surfaces when it is dry and do not rinse away once applied.

Please note: This product will not remove non-organic contaminations like cement staining or efflorescence. It will only remove organic contaminations like moss & algae.

If green algae are really ingrained (perhaps still present after intensive pressure washing or steam cleaning) you may require Render Cleaner Softwash Solution (see below).

Floorseal Render Cleaner Softwash Solution. This is a fast-acting cleaning solution that will break down green algae, red algae, and particularly black spot lichens.

It should be diluted with water at 1:5 – 1:3 and applied directly to the brick with at least 15 minutes of dwell time. You will need to keep the product wet during the dwell time by adding more product.

Do not let your brick walls dry out during the dwell time, extend the dwell time if the contaminations are severe. Please rinse off after use with clean water.

This product is a more powerful cleaning fluid than Moss Remover Plus. It will produce faster results and a very thorough deep clean. It can remove severe contaminations of black spot lichen and algae staining.

You can increase the strength of Render Cleaner Softwash Solution by adding less water. Increasing the dwell time can also increase its cleaning power.

For vertical surfaces such as brick walls, you can increase performance and reduce the need to reapply during dwell time by using our Cleaner Additive. This makes the solution foamier and allows it to ‘cling’ to the wall for longer.

How to seal exterior brickwork with a natural breathable sealer

To seal external brickwork, we recommend using a breathable impregnating sealer. Impregnating sealers are non-film forming so do not create a film or surface coating.

Impregnators are suitable for sealing rubble-filled, solid brick walls on older buildings. They are also suitable for sealing modern brick walls which have a cavity. Impregnating sealers penetrate the surface of the brick so have an unaltered, natural matt finish.

Floorseal Breathable Brick Sealer & Waterproofer is an impregnating sealer which seals without forming a film.

This exterior brick sealer resists UV light and repels rainwater & general damp. This Breathable Brick Sealer resists carbon deposits & inhibits organic growth.

The sealer will impregnate the bricks with a water-repelling agent. Importantly, this is achieved without producing a film or coating thus avoiding the problems associated with trapped moisture.

As this sealer is an impregnating sealer it is resilient to UV light & weathering. Impregnators are not prone to cracking or delaminating as they are non-film forming.

Floorseal Breathable Brick Sealer & Waterproofer has a 10 year + lifespan. It does not require reapplication on an annual basis.

Breathable Brick Sealer & Waterproofer is to be applied in a single application with a light overspray approximately 40 minutes later. On dense surfaces you may only require a single application.

Remove any obvious excess product, which will be visible as a liquid, after approximately 20 -30 minutes. This can be achieved using a dry absorbent roller or cloth.

You may not see any excess on particularly porous brickwork this is why the follow-up light application is important. This ensures the bricks have had enough product applied. Any obvious liquid (wet on the surface not just damp) should be removed after 20 minutes have elapsed.

This sealer does not alter the appearance of your brickwork in any way. For this reason, this brick sealer is described as a matt finish (or a natural finish sealer) it does not form a skin or alter colour.

Breathable Brick Sealer & Waterproofer is suitable for use on older historic/listed buildings as the treated surface will remain breathable.

seal your exterior brick walls for easier maintenance

In conclusion

Floorseal Brick Cleaner is the best product for removing efflorescence salting and general mortar or cement staining. Please note that calcified hard deposits from efflorescence that may have taken years to form may need removing by mechanical means i.e. blasting

Floorseal Green Remover Concentrate is a slower acting, easy to use spray & leave cleaner. Great for removing moss, green algae and red algae. Algae contaminations slowly disappear over the days following treatment, moss will turn brown and wither over time. The application process is very simple as this product is simply sprayed onto the bricks and left to dry.

Floorseal Render Cleaner Softwash Solution acts more quickly than the previous product, providing rapid results. This product will also kill black lichens & moulds which ‘spray and leave’ type cleaners cannot. It is our most powerful cleaner for exterior brick, stone & render.

Floorseal Rust Remover for Stone is a problem solver used to remove general rust spots and stains. It has a non-acidic formula so safe to use on acid-sensitive surfaces.

Floorseal Breathable Brick Sealer & Waterproofer is an impregnating sealer which seals without forming a skin. Suitable for listed/historic buildings or anywhere you do not wish to alter the appearance of the brick. Apply in a single application with a follow-up light overspray approximately 40 minutes later. Dense bricks may only require one application of the product. Always remove any excess product with a dry roller after the initial and follow up application. Resists rainwater, carbon deposits, organic growth, and UV light. Covers approximately 5m2 per litre (or more on dense surfaces – up to 10m2).

Further information

Please click here to see all our products & accessories for cleaning and sealing interior or exterior bricks. There are also other handy ‘how to’ guides relating to general brickwork.

The information contained within this article is not exhaustive. If you need further information please contact Floorseal on (01484) 861461 or email us our web address is