Historic Buildings

The options for waterproofing an existing historic building basement are cavity drain, or cement renders and slurries.

What are my options: cement render or slurries, or cavity membrane systems?

Cement render or slurries requires a huge amount of preparation. All surfaces have to be scabbled, or shot blasted then jet washed to remove dust. Joints have to be raked out and refilled with hard mortar. This sort of preparation is very damaging for historical brickwork. The render will require a strong bond to the substrate and therefore will completely ruin the substrate and cannot be reversed so it will be unacceptable in most cases.

It's for these reasons that MacLennan would usually design a cavity membrane system. The cavity membrane will not damage the substrate and is de-mountable so more likely to be acceptable to conservation officers. It does not require much preparation and will accommodate normal movement. It can be finished with any plaster or dry lining system so it can be redecorated as soon as dry. It is quick to install, less mess, and should be less expensive than any properly installed cement tanking system.

3D Drawing of Base of Brick wall new waterproofing membrane
Dropmore Park

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How does the installation work?

Cavity membrane system installed over historic basement walls
MacLennan technician installing Cavity membrane
MacLennan technician installing Cavity membrane


The walls should be sound with no voids and no loose plaster. It is critical that all timber is removed from the walls and that timber joists and beams bearing into the wall are removed or isolated. The floor should be a concrete slab that is thick enough to accommodate a 50mm chase for a channel, or you need enough ceiling height for a 120mm build-up of floor.

The options for floors are screeds on insulation or if the channel is in the floor timber flooring can be laid over the membrane. It is also possible to retain existing features or historic floors by removing and replacing over the waterproofing system once installed.

The cavity membrane is a modern plaster lathe. The plaster lathe can be meshed to bond plaster, lime mortar or cement render too, or it can be unmeshed with very few fixings for dry linings or independent Gypliner frames or even an internal skin of brick or blockwork if space allows. The system can be installed over nearly any sound substrate including stone, flint, and earth walls such as cob.

Why should I work with MacLennan?


We Design, supply and install. There's no split responsibility with MacLennan.


MacLennan live and breathe waterproofing, have a look at one of our free CPD seminars and find out!


MacLennan has the most comprehensive guarantees and insurances in the industry.

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