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How to fit cavity drain membrane on an internal wall

Updated: 21 October 2026

You are lining an internal masonry wall and you want the sequence for how to fit cavity drain membrane without closing the void or leaving a leak at every fixing. The studs go against the structure, every plug is sealed, and every lap is taped. The water still needs a designed way out. The steps follow Newton’s CDM wall section, Sika’s cavity-drainage method statement and the Permagard PermaSEAL 8 notes, for those makers’ own plugs. None of the amazon.co.uk rolls in the [dimpled membrane comparison](/hub/flooring/dimpled-membrane) lists plugs or tape. A purchase through our links can earn a commission at no extra cost to you.

You are lining an internal masonry wall and you want the sequence for how to fit cavity drain membrane without closing the void or leaving a leak at every fixing.

Our top picks

Einside Einside embossed HDPE membrane, 2 m × 20 m

Best overall

Einside Einside embossed HDPE membrane, 2 m × 20 m
8.8/10about £69.50
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Einside Einside embossed HDPE membrane, 1 m × 20 m

Alternative

Einside Einside embossed HDPE membrane, 1 m × 20 m
8.0/10about £50.00
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Generic Generic holed dimpled drainage panel, £106.99

Rank 3

Generic Generic holed dimpled drainage panel, £106.99
4.0/10about £106.99
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On this page
  1. 1.Before you fix anything
  2. 2.Studs, plugs and levels
  3. 3.Laps and tape
  4. 4.Plaster, battens and the stop line

Before you fix anything

The wall wants to be firm, reasonably flat and free of loose material that would puncture the sheet or stop a plug pulling tight. Check the first sheet is level before you drill a row of holes. You need a named place for the water to go. A membrane that ends in a puddle has only moved the damp. The Einside reviews include transit damage: cuts and holes on the 2 m roll, and a 1 m parcel the buyer used as a double layer. A hole in the sheet is a hole in the cavity. Do not tape a ruined roll across the wall. Set it aside. Preparation is finished when you can point at where the water leaves.

Studs, plugs and levels

The studs face the wall, not the room. Sika’s method statement puts the studs to the structure so the flat face is towards you. Reverse the sheet and the gap is on the wrong side. Drill through the stud, not the flat web, so the plug head can close on the plastic. Newton’s manual says 10 mm or 11 mm to match the plug. Sika’s brick-plug note says 10 mm. Do not treat 10 mm as universal. Each plug needs a seal: Newton’s washer or rope, Sika’s gasket, or the rubber washer on Permagard’s brick plug. After you drive it, the seal should look compressed, not perched on the stud. A plug without that gasket is a path from the cavity into the masonry. Keep the courses level. A sheet that runs downhill collects water in the wrong corner.
Einside Einside embossed HDPE membrane, 2 m × 20 m

Testsieger

Einside Einside embossed HDPE membrane, 2 m × 20 m
8.8/10about £69.50
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Laps and tape

Weather the joints so water moving down the wall does not run into the lap. Where there is a flange, the lower sheet sits in front of the upper sheet. Where there is no flange, Sika uses a four-stud overlap. Tape a clean, dry face. Dust, moisture or a cold sheet leaves a join that looks stuck and lets water behind it. Newton allows a hot-air gun to warm plastic that is too cold for tape. That is not an invitation to scorch a hole. Do not add screws through the flat face. Every new hole needs the same sealed plug. On a wall of about 2.4 m, the 2 m Einside roll will not cover the height in one width, so plan the lap before the last row. The 1 m roll means more vertical joints.

Plaster, battens and the stop line

A plain studded sheet is not a plaster background. Plaster and dot-and-dab need a mesh face, which is why the buying guide separates mesh from a plain roll. A skim on plain Einside studs is a key the listing does not claim. Battens, where the manual allows them, go through sealed plugs. These listings do not print a Euroclass. The Einside pages only show F-DM 15/03/05, so the black plastic is not a finished wall surface. When water has to be collected and pumped, the fixing sequence is no longer the whole job. PCA’s Type C note is that the cavity takes seepage and the water has to leave. That design is the basement page. Fit the wall only after the route exists on a drawing.

Common questions

Which way do the studs face?
Towards the masonry, so the void is against the structure and the flatter face is towards the room. Reversing the sheet puts the gap on the wrong side. The manuals used here, including Sika’s method statement, are consistent on that direction. Check the roll you bought, because a mesh face, if you have one, is the room side.
Do you hang the rolls vertically or horizontally?
Newton’s wall section tells you to hang the sheet level. Vertical rolls are the usual wall method in these guides, with laps arranged so the lower sheet finishes in front of the upper one. A horizontal run still needs the same sealed plugs and the same weathered lap. The mistake is a join that scoops water into the cavity.
What seals the plug?
A washer or a sealing rope that compresses when the plug is driven, as Newton, Sika and Permagard describe for their own fixings. The seal is checked by looking at it, not by assuming the plug is tight. The Einside boxes do not include those plugs, so you buy the plug and the seal together.
Can you plaster straight onto a plain sheet?
Not if the sheet has no mesh face. Plaster needs a key or a system the maker specifies. The Einside listings do not state a mesh. A skim on plain studs is a finish the product page does not support, and a failed skim is difficult to put right once the wall is covered.
What if the roll is already holed?
Do not hang it. Reviews on the Einside rolls describe cuts and holes from transit, and one buyer doubled up a damaged sheet. A slit in the plastic is an open cavity. Tape is for designed laps on a sound sheet, not for repairing a roll that arrived ruined. Replace it before you drill.
When do you stop and call a specialist?
When you cannot name where the water goes, when it must be pumped, or when the room is meant to be habitable. The plug pattern does not design the sump, the power cut or the service visit. Those decisions belong with someone who designs Type C systems, not with an extra box of plugs.

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Sources

Public UK sources used for this comparison. Listing prices, stars and review counts are the amazon.co.uk lines kept with these four products.

  1. PCA Type C guidance, June 2022 (retrieved October 2026)
  2. Newton BS 8102:2022 technical paper (retrieved October 2026)
  3. Approved Document C, GOV.UK (retrieved October 2026)
  4. Newton CDM 508 and BBA 22/6357 (retrieved October 2026)
  5. Wykamol CM20 BBA sheet (retrieved October 2026)
  6. Newton on a DPM versus waterproofing (retrieved October 2026)
  7. Newton HydroBond 410 GeoDrain (retrieved October 2026)
  8. ABG Roofdrain (retrieved October 2026)