Cementitious vs Liquid Membrane: Which Waterproofing Do You Need?

"Cementitious or liquid membrane?" is one of the most common questions we get. Both are excellent — but they solve different problems. Choosing wrong is a common, costly mistake. Here's a clear comparison.

Cementitious waterproofing (SR Flex / SR Flex XL)

A cement-and-polymer coating that bonds rigidly into the concrete and resists water under pressure from either side. It's breathable, potable-water safe and tough.

Best for: water tanks, swimming pools, basements, foundations and wet areas.
Strengths: resists hydrostatic pressure (50 m head), potable-safe, bonds to damp concrete, breathable.
Limitations: more rigid — less suited to surfaces with large movement or full sun exposure unless top-coated.

Liquid membranes (SR Coat PU / MTX / MT)

A liquid that cures to a seamless, highly flexible film with excellent elongation and UV resistance.

Best for: exposed roofs, terraces, balconies, decks, planters and metal roofs.
Strengths: huge elongation (>250–400%), crack-bridging, UV-stable, jointless, handles thermal movement.
Limitations: not used inside potable tanks; needs correct priming on some substrates.

Quick rule of thumb

Holding water in (tanks, pools, wet areas) → cementitious. Keeping weather out on exposed, moving surfaces (roofs, decks) → liquid membrane. Many projects use both — e.g. SR Flex base with an SR Coat top-coat on a roof.

Still unsure?

That's exactly what our free survey decides — the right system for each surface. Browse all products or book a survey.

Frequently asked questions

Both last 10+ years when correctly specified and applied. Longevity depends more on surface preparation and matching the product to the exposure than on the technology itself.

Yes, but on exposed roofs it should be top-coated with a UV-stable liquid membrane (SR Coat MT/MTX) to handle sun and movement.

For potable tanks we use cementitious SR Flex, which is tested to BS 6920 for contact with drinking water.