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Basement slab waterproofing. Laid before the pour.

1 min readFORSPEC Technical Team

The short version

  • PREFLEX 3000 was laid before the basement slab was poured.
  • The wet concrete bonds to the sand-finished face of the sheet, so water cannot track between the two.
  • It needs no primer and no torch.

Under a basement slab there is no second chance. A pre-applied membrane is laid first, and the slab that is poured over it becomes part of the waterproofing.

The figures

Thickness
1.7 mm: 1.5 mm HDPE plus a 0.2 mm sand finish
Which way up
Sand face up, toward the concrete
Upturn
300 to 400 mm
Pour within
56 days of laying
Primer
None

On this job the sheet was detailed around the pile caps and taken up to the wall and floor terminations. Pile heads are sealed before the pour, as in the lift pit story.

FORSPEC on Instagram · 1 Nov 2026PREFLEX 3000 before a basement slab pourLoads when you tap

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Systems, products and drawings

SystemBelow-Ground Waterproofing & Basement TankingThe full build-up, layer by layerProductPREFLEX 3000Pre-applied HDPE membrane laid before the pour, so water cannot migrate laterally between membrane and concrete.RangeAll FORSPEC productsBy system, with data sheets and calculators
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On site with FORSPEC

A lift pit lined before the pour, from FORSPEC on InstagramA lift pit lined before the pourThe membrane under the screed, from FORSPEC on InstagramThe membrane under the screedA pool detailed the right way, from FORSPEC on InstagramA pool detailed the right wayPipe details welded into the sheet, from FORSPEC on Instagram▶ 3.2KPipe details welded into the sheet
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More news

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