Waterproofing for a leaking basement car park


A car park is a designated area or building where cars and other vehicles can be parked and left temporarily. Underground car parks are parking facilities that are built beneath the ground, either in the basement of a building or beneath a street. Timberwise were contacted by a commercial customer who was experiencing severe water ingress to their basement car park.

The customer knew a well-maintained appearance will ensure that it operates profitably on a long-term basis. As further damp related problems progressed, it was essential that the source of water had to be stopped, and the problem rectified, this would ensure the property would not suffer any costly damage.

Following a survey, Timberwise identified the source of the water ingress:  the floor slab was cast onto a permanent metal formwork and leaks were found at the edges, particularly where the terraces abutted a concrete piled wall and where there was a change in levels. Timberwise also identified a sticky sheet membrane seen over the terrace decks, this provided evidence of previous failed remedial works.

The floor slab was laid level and the existing drains were only collecting surface run-off.  As a result, water was ponding on the sheet membrane and running to the edges.

 The works will improve the environment for users of the car park and eliminate the risk of damp related problems.”

Timberwise Waterproofing Design Specialist


Timberwise proposed that the terraces be stripped of pavers and that the facing bricks and concrete infill were to be removed. Once this was done, a screed laid to a 1:80 fall toward the apartments could be laid. Our waterproofing solution consists of a liquid applied hybrid bitumen and cement coating to be trowel applied across the screed and into the floor to wall junction.  The coating was flexible and tough when cured and could be applied to damp substrates.

To protect the primary waterproofing layer, we then proposed that a geotextile covered horizontal cavity drainage layer be laid. This would direct water to the edges, where it can be drained off and act as a sound base for paving sand etc. To collect the water we used an ACO free deck drainage channel. This has entry slots in the side as well as the usual top grid allowing free-flowing water to enter the channel.


Car park decks are constantly exposed to aggressive and corrosive elements such as oil and diesel spills, carbon dioxide gasses, de-icing salts and water, all of which become even more of a problem if cracks already exist in concrete decks.

The use of a deck waterproofing membrane is essential to extend the design life of decking surfaces. The client was satisfied that providing the above design was installed by a specialist contractor, a Grade 2 environment would be achieved for the residents. This ‘level of dryness’, according to the British Standard, is one that tolerates moisture vapour but no water penetration and is the typical Grade required for car parks and retail storage areas.

Need help with waterproofing?

If you suspect you have a damp problem in need of treatment, please contact your local Timberwise team on 0800 288 8660 for advice or to arrange a survey. Alternatively, complete the online survey request form to arrange a surveyor to visit your property.