Tanking a garage with Radon protection

Our client asked us to supply and install a tanking and radon protection system with warranty for a new build plot.

The waterproofing solution determined is defined in BS 8102 2022 ‘Protection of Structures against Water from the Ground’ as a “Grade 3” environment where no dampness is permitted and where the internal environment needs to be managed using appropriate environmental controls.

We proposed a combined waterproofing system:

• Type A: Barrier Protection – Internal
• Type C: Drained Protection – Internal
• Basic Radon Barrier

Major third part warranty providers such as NHBC, Premier Guarantees and LABC have insisted for some time on the installation of combined protection as a condition of their warranty. They require that a CSSW qualified waterproofing design specialist be involved at the design stage.

Specification

First Visit

WATERPROOFING TYPE “A” Internal Barrier Protection  

1. We formed a sloping fillet inside the cavity.

2. All concrete was dressed with anti-lime coatings.

3. We formed a 50mm filletboth sides of the bund using repair mortar. This helps shed water away from the structure.

4. We ensued blockwork joints were flush using repair mortar.

5. Two coats of Koster NB1 cement based waterproofing slurry we applied to the walls and bund. This is a mineral waterproof coating that contains crystallising and capillary-plugging agents. When these penetrate into the substrate, they develop an intense bond and the capillaries are plugged making it completely waterproof to pressurised water of up to 10 bar (applied over 2 days).

6. Finally we applied one coat of Koster Deuxan 2C polymer modified thick bitumen inside the bund. This material is polymer-modified and is resistant to cracking.

WATER PROOFING TYPE “C” Internal (Drained) Protection

Secondary protection, which manages any water ingress which occurs as a consequence of an installation defect, is provided by a Type C cavity drain membrane system.

Wall Cavity Drain Membranes

• We installed 8mm wall membrane down in the cavity terminating at the sloping fillet junction. 8mm mesh membrane was continued on the face of the internal blockwork terminating at the concrete floor junction. The membrane was also installed on the retaining wall up to the door openings on the front and rear of the property.

• Koster Bitumen Primer was installed to block work where waterproofing ends; double seal and terminate membrane.

• Double-seal the garage radon DPM.

• We insulated in front of the wall membrane.

• A channel with inspection holes was installed inside the bund. The drainage will be gravity fed into an external inspection chamber to ensure maintainability linked with planned and serviceable external surface water drainage.

Second Visit

Radon Floor Membrane

• We installed MS500 (8mm floor membrane) double-sealed to the face of the existing radon DPM all around the perimeter of the room to ensure radon protection is continuous and extended to the outside envelope of the building.