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How do I waterproof my garage walls?

Dampness on internal walls is a common problem in garages as they are usually built with no waterproofing. Waterproofing your garage can help prevent dampness, prevent structural damaged, mold, and can increase your home’s value by making the garage a habitable space.

The tanking slurry method is the most cost-effective way and will prevent dampness on the walls and groundwater. Below we will outline a straightforward method for tanking slurry.



Tanking slurry is a mixture of concretes, aggregates, acrylic polymers, and chemical modifiers which combine to prevent the ingress of water. It can be purchased as a powder to mix on site, or pre-mixed.

  1. The walls must first be returned to bare brick, clean of any plaster, dust, render, paint, or coatings. If there is any loose mortar, repair it before progressing further.
  2. Mix your tanking slurry, closely following the manufacturer’s instructions. Tanking slurry can be hazardous so please wear gloves, goggles, and face mask.
  3. Tanking slurry is designed to be applied to damp surfaces, so if the walls are dry you will need to use clean water to dampen them, but do not overdo it and create standing water.
  4. Tanking slurry requires 2 coats. Horizontal brush strokes should be used when applying the first coat directly to the brickwork. You should go at least 3 ½ feet up the wall and 5” down across the floor. The joint between the wall and floor can be prone to leakage so much sure you pay attention to the application here to ensure a good coverage.
  5. The second coat must be applied within 24 hours and should be done in vertical strokes. Make sure you cover the wall and the floor area previously covered by the first coat.
  6. The tanking will take a couple of days to fully cure. Patches of moisture will appear which is perfectly normal and termed ‘sweating’.
  7. You can apply a breathable render to the tanking after a period of 24 hours has passed. Do not worry if it is not fully dried and as the tanking will dry with the render. It is not recommended to paint tanking.


It is always recommended to follow manufacturer’s instructions so please use the above as a guide. If unsure or unconfident of carrying out this DIY improvement, please use a contractor.

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