How and why to correctly water proof a wet room and the consequences of not doing so.

Most people think a tiled and grouted floor for their wet room is sufficient to waterproof their wet room. This is sadly an expensive mistake that we hear, far too often. For while a glazed tile will prevent water penetration, most grouts will not!

To avoid costly mistakes and serious water damage to you home it is vital that you fully comprehend how and why you MUST tank or waterproof your wet room floor prior to tiling. It is also extremely important that you understand the difference between Waterproof and Water Resitant. 

 An adhesive or grout that claims to be ‘waterproof’ is often just water resistant, meaning it isn’t affected by water, although water can pass through the product without causing any damage to the surface and therefore, a product can sit on a shelf with a waterproof label as happy as Larry even if, technically, it doesn’t waterproof. If we look at the definitions* the difference becomes clear:

Waterproof: unable to be penetrated by water (For an example of Waterproof Grout click here)

Water-resistant: partially able to resist the penetration of water

We know that people (think families with 2.4 children) spend a large amount of time in the shower and, whilst the grout and adhesive may remain unharmed, the background to which the tiles are placed can become continually exposed to water if it isn’t fully waterproofed. This can cause a large amount of damage behind the surface.

With the increasing popularity of wet rooms and power showers, pounding water will generally hit the same tiles many times a day. Most Grouts are porous and will allow moisture through it and, whilst the properties of the grout are unaffected, over a period of time moisture and water are absorbed by the porous background and will lead to failures. Tanking will give builders the confidence that, should the installation develop problems behind the tile face, these problems will not be transferred to the substrate. It is a way for them to protect the fabric of the building they’re working on, prolonging the life of bathrooms, wet rooms and kitchens up and down the country. 

A secondary benefit to a waterproof grout, because it is virtually impervious to water penetration, it will by nature, be less likely to stain, as discolouration of grouts and the growth of mould is caused by water penetration. Yes these grouts are more expensive but they will keep your tiled area looking fresh and clean far longer than the cheaper alternatives. So the simple secret to a mould free bathroom doesn’t need to be achieved by bleaching and scrubbing the grouts on a weekly basis. It can be achieved by spending an extra £20 or so for a grout that will save far more over its lifetime in cleaning materials alone and with the benefit of keeping your bathroom grout mould and stain free.

What are the pros for you or your customer?

Not tanking can be a huge false economy. Leaking water can necessitate joist replacements, ceiling replacements and other costly and highly inconvenient building repair work. With tanking, total piece of mind is guaranteed – it not only prevents water saturating the floor and reduces the risk of unsightly black mould forming but it also prevents more serious issues such as de-bonding of tiles and even complete floor collapse.

Tanking should be a huge selling point for homeowners as it will reduce unnecessary furture repair costs to a property. By tanking a new bathroom, a homeowner can be confident that their money has been well spent - and what homeowner wouldn’t like to hear that news? It has also been heard that tanking could lower insurance premiums…It’s amazing what a little waterproofing can do…

When to recommend tanking

 Some builders still think that grouting makes surfaces waterproof and this is certainly not the case but through some gentle tips and advice on the benefits of tanking you can help prevent extremely costly future problems for you and your property

Tanking is now becoming a big industry in itself and whilst there are other products available, such as waterproof tile backer boards, these can’t compete with the results you get from tanking and fully water proofing your wetroom. Cement boards are only water resistant and will still absorb water (which can affect the substrate underneath) and, in showers, there is never a perfect fit from the board to the shower tray. Tanking is a full system in itself and can fill all these voids.

Homeowners are, unfortunately not always becoming aware of the fact that there is more to installing a new bathroom than choosing tiles and a nice suite, even with the vast amounts of advice available on the internet, we still hear of horror stories where a wet room or bathroom has not been properly water proofed and where insurance companies have declined paying out on water damage because an issue was caused by poor building practises. Therefore leaving the home owner with little protection and the sole recourse of potential legal action against the contractor that failed to correctly install in the first place.

So dont get caught out, dont let your contractor cut corners. Yes it may save you a few hundred pounds now but in the long term it will end up costing you thousands. And as Tanking Kits can start from under £200, is it really worth not doing the install correctly in the beginning?

This link will show you the many options on tanking kits and waterproofing floor systems.

What surfaces can you tank?

Tanking is suitable for use on a wide variety of surfaces including:

  • Concrete
  • Cement: sand rendering
  • Plaster
  • Plasterboard
  • Moisture stable timber boards
  • Lightweight tile backing boards
  • Fibre cement boards

Below is a diagram giving examples of the principles of water proofing solutions for both timber and concrete floors.

 Why Tank?


Various tanking kits are available to prime, seal and protect. The primer should be applied to clean and dry walls and left until touch dry. To seal, the waterproofing coating should then be applied to all corners and any other cracks and joints before the tape or sealant is used (this will vary depending on the kit). Then, to protect, a second layer of waterproof coating should be applied to fully protect all areas. In general, the background should be ready to receive tiles after 24 hours.