A barrier on the inside face
ISO/TS 18734 allows a liquid barrier on the inside face only where it withstands the water pressure behind it. It is guidance and gives no test figure.
ISO/TS 18734:2026 (guidance)● System 02 of 12 · Negative side
Negative Side Waterproofing
Waterproofing from the inside face, for when the outside cannot be reached. Plug the leak, inject the crack, then coat the wall.
ISO/TS 18734 (guidance)
5products
1CAD details
Up to 25 yrwarranty, depending on the systemwarranty, by system
● The build-up
Five products, in the order of the job.
Each layer with the one figure that matters, from its data sheet. Tap a layer to see why it is there.
01
Stops a live leakACTFLEX HYDROPLUGSets in 2 to 4 minutes
Rapid-setting plug pressed into a chase cut square, at least 20 x 20 mm, never a V. Final set is within 10 minutes. A 5 kg pail does about 6 m of chase.
02
Injection for wet cracksACTFLEX PU200Foams to 8 to 20 times its volume
Hydrophobic polyurethane that reacts with the water in the crack. Inject through 10 mm packers at no more than 200 mm apart, drilled at 45° to meet the crack 60 to 100 mm deep.
03
Injection for fine fissuresACTFLEX INJECTSWELL10 kg pack · full reaction in 24 h
Low-viscosity hydrophilic polyurethane grout that reaches fine fissures. Use it above 10°C.
04
Swelling waterstopPRESWELL HYDROPHILIC WATERSTOPSwells 400 to 500%
Hydrophilic rubber strip, 20 x 10 mm, in 10 m rolls. It swells when water reaches it and seals the joint from inside.
05
Cementitious membraneACTFLEX 988 CWP1.5 mm in 3 coats · 7 days to cure
Two-part cementitious membrane applied to the inside face in three coats with AT-MESH. A 20 kg kit covers about 6.4 to 8 m².
How much do I need?A 20 kg kit of ACTFLEX 988 CWP covers about 6.4 to 8 m² at 1.5 mm over three coats.
Calculate →● The rules, in plain English
What the standards do and do not cover.
AS 4654 stops at ground level
AS 4654.1 and AS 4654.2 cover membranes above ground only. There is no Australian Standard for below-ground membranes.
AS 4654.2 cl 1.1A plain-English summary, not the standard. Check the current documents for your job, or send us the job.A summary, not the standard. Check the current documents for your job.
● Every product in this system
Negative side: 5 products.
TDS and SDS open straight from the card.
● 3D models
See every layer before site starts.
Each FORSPEC detail is modelled in 3D so the site team sees the build-up for negative-side waterproofing before anyone opens a pail. Send the job and we model yours.
● On site
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Drawn details, ready for your set.
1 standard detail for negative-side waterproofing. Open one to view it and download the PDF and DXF.
● Questions we get
Straight answers, from the TDS.
What is negative side waterproofing?
Waterproofing applied to the inside face of a wall or slab, the side away from the water. It is used when the outside face cannot be reached, as in an existing basement or lift pit.
How do you stop water coming through a basement wall from inside?
Plug running water with ACTFLEX HYDROPLUG, which sets in 2 to 4 minutes. Inject wet cracks with ACTFLEX PU200. Then apply ACTFLEX 988 CWP to the wall in three coats to 1.5 mm dry.
How thick does 988 CWP go on?
Three coats with AT-MESH to 1.5 mm dry. A 20 kg kit covers about 6.4 to 8 m². Leave it 7 days to cure below ground.
How far apart do the injection packers go?
For ACTFLEX PU200, 10 mm packers at no more than 200 mm apart, drilled at 45° so they meet the crack 60 to 100 mm deep.
● Go deeper
Drawings, data sheets, jobs and news.
DrawingsCAD details for this system1 detail here, PDF and DXF to download→Data sheetsTDS, SDS and test reportsEvery document for this system→CalculatorACTFLEX 988 CWP calculatorArea in, packs out→SpecifySpec clause for this systemClause, drawings, data sheets→Projects5 buildings with these productsWhere this system has been used→NewsACTFLEX 988 CWP: where it goes and how it is appliedFORSPEC News→
● The other systems
Twelve systems. One warranty.
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Drawings, photos or a description. A FORSPEC rep comes back with the system, the spec clause, CAD details and a 3D visual within 6 business hours.