What is basement tanking?

Basement tanking is the process of waterproofing a basement to prevent water ingress. BS 8102 defines three types: Type A (barrier protection — coatings/membranes applied to walls), Type B (structurally integral — water-resistant concrete), and Type C (drained protection — cavity drain membrane). Type A cementitious slurry is common for existing basements.

How many coats of tanking slurry do I need?

A minimum of 2 coats is required, applied in opposing directions. Each coat should be approximately 1.5mm thick when dry. The second coat is applied once the first coat is touch-dry (typically 2-4 hours). In areas of high water pressure, 3 coats may be recommended by the manufacturer.

What are corner fillets?

Corner fillets (or coves) are formed at all internal angles where walls meet floors and where walls meet other walls. They eliminate sharp 90° corners which are weak points where water can penetrate. Fillets are typically 50mm × 50mm triangular sections formed from the tanking material or a dedicated fillet compound.

Do I need a sump pump?

A sump pump is recommended for basements below the water table or in areas with high groundwater. For Type C (cavity drain membrane) systems, a sump pump is essential as the system relies on collecting water and pumping it away. The sump should have a twin pump with battery backup for reliability.

Can I tank a basement from the inside?

Yes, internal tanking with cementitious slurry (Type A) or cavity drain membrane (Type C) is the most common approach for existing basements. External tanking (applied to the outside of the walls) is more effective but requires excavation. The choice depends on access, budget and water pressure.

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Basement Tanking Calculator — Slurry, Membrane & Sump Pump

Calculate cementitious tanking slurry quantities, corner fillets, primer and sump pump requirements for basement waterproofing to BS 8102.

Floor Length

Internal basement length

Floor Width

Internal basement width

Wall Height

Floor to ceiling height

Tanking Type

Sump Pump Required

Below water table or high groundwater

Price Per Litre (optional)

Tanking slurry cost per litre

How We Calculate This

This calculator determines the quantities of tanking materials needed based on basement dimensions.

The formula

Total Area = Floor Area + Wall Perimeter × Wall Height

Slurry = Total Area × 1.5 L/m²/coat × Number of Coats

Fillet Length = Perimeter + Corners × 0.3m

BS 8102 protection types

Type A: Barrier — cementitious slurry or sheet membrane
Type B: Structurally integral waterproof concrete
Type C: Drained — cavity drain membrane + sump

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.