Substrates & Preparation
Liquid Screed Over Basement Tanking Systems
Screeding a basement floor means working carefully around the waterproofing system already in place, since damage to tanking can be very costly to fix later.
Basements bring their own waterproofing strategy — usually a tanking system, a cavity drainage membrane, or a combination of both — and the liquid screed sits on top of, and works around, whatever waterproofing solution has been designed for that specific space. Getting the sequencing and protection right matters more here than on a typical ground floor, because remedying a damaged waterproofing layer once it's buried under a screed is disruptive and expensive.
The waterproofing design itself is a specialist discipline in its own right (often following BS 8102), and the screed installer's job is to work compatibly with it, not to design it.
Screeding a basement or below-ground space?
We'll coordinate with your waterproofing specialist to make sure the screed build-up protects and works with the tanking system.
Or call our landline on 01392 237700
Working with, not around, the waterproofing design
Before any insulation or screed goes into a basement, it's worth confirming exactly what waterproofing strategy is in place and what it needs from the floor build-up above it. A Type A tanking system needs its coating protected from damage during subsequent trades' work, while a Type C cavity drainage system needs its perimeter channels and any sump left clear and functional once the floor is finished.
Sequencing and protection during the pour
Liquid screed pumping involves hose runs, foot traffic and plant moving across the floor, all of which pose some risk to an exposed waterproofing layer if it isn't adequately protected first. Boarding out access routes and confirming drainage channels are masked but not blocked are practical steps that reduce risk during the pour itself.
Basement Tanking — the points that decide it
- Waterproofing strategy for basements typically follows BS 8102 and is usually designed by a specialist rather than decided at screed stage
- Cavity drainage membranes (Type C) create a void that manages any water ingress, and the screed floor build-up sits above this system without blocking drainage channels
- Tanking (Type A) systems rely on a continuous, undamaged waterproof coating or render, so protecting it from puncture during insulation and screed works is essential
- Perimeter drainage channels associated with cavity drainage systems need to remain unobstructed by the screed pour
- Any service penetrations through a tanked or drained basement floor need detailing to maintain the waterproofing system's integrity
- Sump and pump locations associated with a cavity drainage system are usually agreed before insulation and screed are installed, not after
Basement Tanking — your questions
In short
Screeding a basement floor means working carefully around the waterproofing system already in place, since damage to tanking can be very costly to fix later.
Keep going — closely linked topics
Screeding a basement or below-ground space?
We'll coordinate with your waterproofing specialist to make sure the screed build-up protects and works with the tanking system.