Why has my waterproofing failed? Cement Tanking Systems.

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leaking and damp basement walls and floor

Why Has My Waterproofing Failed? Cement Tanking Systems.

This article will look at the different reasons why cement tanking systems and waterproof renders fail, how to avoid problems and how to resolve them.

Cement tanking systems and renders are barriers that are applied internally to waterproof basements. They generally work as a physical barrier to prevent water entry in to a basement or cellar. Although they are very effective when used correctly, there are a few things that can cause them to fail.

1- Surface Preparation

This is perhaps to most common reason of waterproofing failure for cement tanking systems. In order to work correctly they require a mechanical and physical bond in order to fix tight to the basement walls and slab and hold back the pressurised water this means that :

A – Voids and gaps in the walls and slab must be filled.

B – Loose areas of mortar should be repointed with a stable mortar like Koster Repair Mortar Plus.

C – Surface contaminants and coatings must be removed. It sounds obvious but paint and salt contaminants must be removed before the tanking is applied. Our friends at Grind Blasters can help with this.

D – The surface should be “rough” to allow for a proper key – this can be provided by bush hammering the substrate to give a suitable surface – again Grind Blasters can help with this.

E – Waterproofing does not like right angles – fillets can be formed at internal angles using Koster Repair Mortar Plus to distribute the load and ensure the tanking product is applied evenly.


2- Damage to the Waterproofing Layer.

Another very common problem is damage to the waterproofing layer. Cement waterproofing systems act like barriers creating a dam effect. Put a hole in a dam and water will come through!

Damage can come from drilling through the waterproofing to create fixing points, chasing in electrical sockets and cables as well as not protecting the waterproofing layer on the floor. Most tanking slurries are not trafficable and should be protected using either a screed or a coating of epoxy to make them safe to walk on.


3 – Unsuitable Structure

Some structures just are not strong enough to be waterproofed. Introducing a barrier means that water pressure increases. This concrete floor screeds are not strong enough to resist water pressure and may need to be upgraded before the waterproof layer is applied. Likewise a single skin of brickwork does not offer much strength and can easily move and crack following waterproofing.


4 – The waterproofing is fine but….

Sometimes other problems can make it look like the waterproofing has failed when there include:

A – Curing. As cement systems cure and activate, they release water as they hydrate. This is often seen in the first two weeks after application where the surface of the new tanking system sweats. With time this curing process with stop and the sweating will stop.

B – Condensations – Sometimes basements are poorly ventilated. When warm wet air meets a cooler surface, condensation can occur and give the impression of a leak. This is easier to control by improving heating and ventilation.


For more with your basement waterproofing project contact us here