AS 4654 stops at ground level
AS 4654.1 and AS 4654.2 cover membranes above ground only. A basement wall or lift pit cannot be specified 'to AS 4654'.
AS 4654.2 cl 1.1● System 01 of 12 · Below ground
Basement Waterproofing & Below-Ground Tanking
Pre-applied sheet under the slab and against the walls, cementitious tanking where the concrete is already cast, a waterstop in every construction joint and drainage cell against the backfill.
ISO/TS 18734 (guidance)AS 3735 joints
7products
11CAD details
Up to 25 yrwarranty, depending on the systemwarranty, by system
● The build-up
Seven products, one tanked basement.
Each layer with the one figure that matters, from its data sheet. Tap a layer to see why it is there.
01
Pre-applied sheet membranePREFLEX 30001.7 mm · 1 x 20 m and 2 x 20 m rolls
Laid before the pour so the concrete bonds to it. Pour within 56 days of laying, or 42 in hot weather. Turn it up the formwork 300 to 400 mm.
02
Self-adhesive sheet for cast wallsACTFLEX 500075 mm laps, side and end
Self-adhesive sheet with 374% elongation (NATA Report 373). Goes on concrete at least 28 days old, primed with EP250.
03
Cementitious tankingACTFLEX 988 CWP1.5 mm in 3 coats · 7 days to cure
Two-part cementitious membrane for walls and slabs already cast. Three coats with AT-MESH to 1.5 mm dry. A 20 kg kit covers about 6.4 to 8 m².
04
PVC waterstop cast into the jointPREBAR PVC WATERSTOP150 to 320 mm wide
Cast into construction joints. 150 and 200 mm come in 20 m rolls, 250 mm in 15 m and 320 mm in 12 m. Lengths are joined by welding at 190 to 200°C.
05
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.
06
Drainage cell against the backfillHIFLOW DRAINAGE CELL15 mm · 22.5 m² a roll
Dimpled drainage sheet in 15 x 1.5 m rolls. The geotextile faces the soil. Fix it only above the membrane termination, never through the membrane.
07
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.
How much do I need?PREFLEX 3000 comes in 1 x 20 m and 2 x 20 m rolls. Measure the slab and the wall upturns.
Calculate →● The rules, in plain English
What the standards do and do not cover.
There is no Australian Standard for below-ground membranes. The data sheets and the engineer's design carry the job.
ISO/TS 18734 is guidance
The one document on below-ground waterproofing is a selection guide, not a compliance standard, and it sets almost no figures.
ISO/TS 18734:2026 (guidance)Joints must stay tight
Where the engineer designs to AS 3735, every joint takes its movement and stays liquid-tight, and the concrete is kept moist for at least 7 days.
AS 3735 cl 5.2.2, 6.1.1A 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
Below ground: 7 products.
TDS and SDS open straight from the card.
● How it's done
Watch a below-ground wall waterproofed, then backfilled.
ACTFLEX 988 CWP: how to waterproof a PVC panel wall
- Prep: wash, light sand, IPA. No primer
- Self-priming and FLEXIPLUG coves
- Coat one and AT-MESH
- Coats two and three, 1.5 mm
- Cure, check and HiFlow drainage
● 3D models
See every layer before site starts.
Each FORSPEC detail is modelled in 3D so the site team sees the build-up for below-ground waterproofing & basement tanking before anyone opens a pail. Send the job and we model yours.
● On site
Real jobs. Real FORSPEC.
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Send the drawings or a few photos. A FORSPEC rep comes back with the system, the CAD details and a 3D of your job.
Send us your job →● CAD library
Drawn details, ready for your set.
11 standard details for below-ground waterproofing & basement tanking. Open one to view it and download the PDF and DXF.
BGL001Retaining Wall System1Standard detail · PDF and DXF
BGL002Retaining Wall System2Standard detail · PDF and DXF
BGL005Lift Pit Negative SideStandard detail · PDF and DXF
BGL008Retaining Wall FootingStandard detail · PDF and DXF
BGL009Retaining Wall Suspended SlabStandard detail · PDF and DXF
BGL010Retaining Wall Base SlabStandard detail · PDF and DXF
BGL011Lift Pit Base to Strip Footing CJStandard detail · PDF and DXF
CJL001Cold JointStandard detail · PDF and DXF● Questions we get
Basement and retaining wall waterproofing: straight answers.
How do you waterproof a basement before the slab is poured?
Lay PREFLEX 3000 over the blinding and up the formwork, turned up 300 to 400 mm, then pour onto it. The concrete bonds to the sheet. Pour within 56 days of laying, or 42 in hot weather.
How thick is a basement tanking membrane?
PREFLEX 3000 sheet is 1.7 mm. ACTFLEX 988 CWP goes on in three coats to 1.5 mm dry, with AT-MESH.
Which waterstop goes in a construction joint?
PREBAR PVC waterstop is cast into the joint and comes 150 to 320 mm wide. PRESWELL is a 20 x 10 mm strip that swells 400 to 500% when water reaches it.
How much 988 CWP do I need for a basement wall?
A 20 kg kit covers about 6.4 to 8 m² at 1.5 mm dry over three coats. Leave it 7 days to cure below ground.
Does AS 4654 apply to basements?
No. AS 4654.1 and AS 4654.2 cover above-ground membranes only. Below ground the job rests on the engineer's design and the membrane data sheet.
How are PRESWELL lengths joined?
Never butt the ends. Lay them side by side for 15 mm. The one place tie wire is used is around a pile cap, where PRESWELL is tied to the reinforcing bars.
● Go deeper
Drawings, data sheets, jobs and news.
DrawingsCAD details for this system11 details here, PDF and DXF to download→Data sheetsTDS, SDS and test reportsEvery document for this system→CalculatorPREFLEX 3000 calculatorArea in, packs out→CalculatorACTFLEX 5000 calculatorArea in, packs out→SpecifySpec clause for this systemClause, drawings, data sheets→ProjectLift pit, PREFLEX 3000A FORSPEC job→ProjectMascot tanks, ACTFLEX 5000Mascot NSW→Projects7 buildings with these productsWhere this system has been used→NewsACTFLEX 988 CWP: where it goes and how it is appliedFORSPEC News→NewsA lift pit lined with PREFLEX 3000 before the pourFORSPEC News→
● The other systems
Twelve systems. One warranty.
● Not sure it suits the job?
Send us the job. We spec it.
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.