Why does the membrane go on the outside?

Because that is the side the water comes from. The structure itself is also made watertight, with MIXKOTE MIM in the concrete and a waterstop at every construction joint.

What happens at construction joints?

A CENTRESEAL 250 PVC waterstop is cast into the middle of every joint, and lengths are heat-welded together on site.

What if the wall leaks before you start?

Leaking joints and cracks are injected with CHEMFOAM PU 6261, and honeycombs are repaired with CHEMGROUT 215, before the membrane is applied.

Do you waterproof lift pits?

Yes. A lift pit is treated as part of the below-ground structure.

What protects the membrane from the backfill?

A 25 mm polystyrene board, fixed over the membrane before any earth goes back.

All systems, by building zone

Basement and Retaining Wall Waterproofing.

Below-ground slabs, lift pits and walls against earth. Water here is under pressure and there is no second chance once the backfill is in, so the structure itself is made watertight and the membrane goes on the outside. This page sets out the layers and the order of work, from the lean concrete to the backfill.

1.5 mmSEALOSTICK sheet membrane, under the slab and behind the wall.

1%MIXKOTE MIM by weight of the cement, dosed into the concrete at the batching plant.

250 mmWidth of the CENTRESEAL 250 waterstop cast into every construction joint.

25 mmPolystyrene board between the membrane and the backfill.

The build-up.

Five parts, from the earth side to the structure.

From the outside in

SEALOSTICK sheet membrane on lean concreteSelf-adhesive polymer-modified bituminous sheet, HDPE-faced, under the slab and behind the wall. The sheets are laid from the low point, so every lap sheds water.
Concrete dosed with MIXKOTE MIMCrystallisation admixture, so the concrete itself resists water. It is added at 1% of the cement content when the concrete is batched.
CENTRESEAL 250 PVC waterstopAt every construction joint, cast centrally in the concrete and heat-welded where two lengths meet.
Structural crack repair with CHEMFOAM PU 6261Injected where the water test finds a path.
Polystyrene protection board, 25 mmSo the backfill never touches the membrane.

The basement build-up drawn exploded from the outside: lean concrete, the sheet membrane under the slab and behind the wall, the dosed concrete structure, the waterstop at the kicker, a crack repair and the protection board

How the job runs.

Under the slabSEALOSTICK is laid on the lean concrete before the slab is cast.
Watertight concreteMIXKOTE MIM goes in at the batching plant at 1% of the cement content, to a dosage table drawn up from the concrete supplier's mix design.
Waterstops at the jointsCENTRESEAL 250 is laid across each construction joint, tied to the reinforcement through its eyelets, and heat-welded where two lengths meet. The concrete is then cast around it.
We inspect the wallTie-rod holes, laitance, honeycombs and protruding steel are dealt with first. Honeycombs are repaired with CHEMGROUT 215 non-shrink grout.
Leaking joints and cracksInjected with CHEMFOAM PU 6261, before any membrane goes on.
PrimerOne coat of CHEMCOAT SB bitumen primer by roller or spray, left until it is touch dry.
SEALOSTICK on the wallThe sheets go on from the low point upwards, so the laps always run with the water and never against it.
Protection, then backfillA 25 mm polystyrene board covers the membrane before any earth goes back.

Joints, laps and backfill.

Construction joints
A CENTRESEAL 250 waterstop in every one: at the junction of wall and slab, and wherever one pour ends before the next.
Laps
Up-slope sheets lap over down-slope sheets, so water runs over a lap and never into it.
Cracks and honeycombs
Repaired on the structure before the membrane is applied.
Lift pits
Waterproofed the same way, as part of the below-ground structure.
Backfill
The protection board goes on first. Earth never touches the membrane.

Materials.

SEALOSTICK
Self-adhesive polymer-modified bituminous sheet membrane with an HDPE film face, applied cold.
CHEMCOAT SB
Quick-drying solvent-based bitumen primer.
MIXKOTE MIM
Crystallisation admixture in powder form, added to the concrete at the batching plant.
CENTRESEAL 250
Centrally placed PVC waterstop.
CHEMFOAM PU 6261
Polyurethane injection grout. It reacts with water to form a flexible foam that closes the leak.
CHEMGROUT 215
Cementitious non-shrink grout for honeycombs and patching.

These products are made by CHEMIND. Where a project specifies another manufacturer's system, we apply that instead.

Basements in our register.

Seven entries in our job register name a basement, a substructure, a lift pit or an underground structure in the title, from 1986 to 2025. Four of them:

1986
Basement walls and slabs, Subang Parade, Selangor
2005
20-storey office building with a two-storey basement, Kuala Lumpur
2014
Substructure of the Sunway University extension, Bandar Sunway
2025
Piling and substructure works for a 39-storey serviced apartment block, Selangor

Most entries record the job as a waterproofing package without naming the zone. See the full register.

Questions we are asked.

Why does the membrane go on the outside?: Because that is the side the water comes from. The structure itself is also made watertight, with MIXKOTE MIM in the concrete and a waterstop at every construction joint.
What happens at construction joints?: A CENTRESEAL 250 PVC waterstop is cast into the middle of every joint, and lengths are heat-welded together on site.
What if the wall leaks before you start?: Leaking joints and cracks are injected with CHEMFOAM PU 6261, and honeycombs are repaired with CHEMGROUT 215, before the membrane is applied.
Do you waterproof lift pits?: Yes. A lift pit is treated as part of the below-ground structure.
What protects the membrane from the backfill?: A 25 mm polystyrene board, fixed over the membrane before any earth goes back.

Talk to us about a basement.

Phone and WhatsApp016-332 7534

Emailinfo@hydrocon.com.my