Technical Guide – Surface Preparation for Basement Waterproofing.

Surface preparation is the most important element for success for basement waterproofing systems.

Internal, Type A (as defined by BS8102:200) tanking systems need to bond to the walls and floor of a basement in order to resist water pressure and maintain a dry environment.

In order to fully bond to the retaining wall or ground bearing slab the surface will need to be prepared.

Why Prepare a Surface Before Waterproofing?

Surface preparation allows for the removal of surface contamination that would prevent the waterproofing from bonding to the substrate. For example:

Release chemicals used on concrete formwork.

Concrete laitance.

Paint.

Glazed and shiny masonry coatings.

Salt contamination.

Surface preparation also allows for the creation of a “rough” surface to give a good physical key. This allows for good bonding of the waterproofing system.

When is the best time to prepare the surface?

For new concrete structures the best time to prepare the surface is immediately after striking the formwork or shuttering. As the new concrete will still be easy to work with the concrete laitance can be removed by high pressure washing.

As time passes the concrete becomes harder, this means that a more aggressive method is required. This can either involve bush hammering or ultra high pressure water scabbling. Both of these methods are more expensive and time consuming so the timing of the surface preparation is key.

What happens if I do not prepare the surface before waterproofing?

All the major waterproofing manufacturers recommend surface preparation before applying internal tanking systems. These include: Sika for their Sika 1 Waterproof Render System, Koster for their Koster NB1 Waterproofing System and Triton for their TT55 waterproofing system.

Failure to properly prepare the surface means that the waterproofing will not properly bond to the wall, it will not be able to resist water pressure and can fail. If you do not prepare walls any product warranty from the manufacturer will be invalid.

Grind Blasters are surface preparation specialists and have lots of experience working with basement and waterproofing contractors. Our technical team will be happy to advise on the most suitable surface preparation system to match the requirements of the structure and the waterproofing system.