PU Grouting vs Epoxy Injection: Which One for Your Leak?

PU grouting stops active water leaks; epoxy injection restores structural strength. If water is flowing or weeping right now, use PU. If a crack is dry and you need the concrete to behave as one monolithic piece again, use epoxy. The two are not substitutes — they solve different problems, and choosing the wrong one is the single most common mistake we see on Malaysian remediation jobs.

PU grouting vs epoxy injection at a glance

The short version: ask yourself "is the crack wet, and is it still moving?" Wet and moving → PU. Dry and stable → epoxy. Wet but also structurally critical → PU first to stop water, epoxy later once dry.

How PU grouting works

Polyurethane injection grouting uses a low-viscosity resin that reacts with water to expand and cure into a tough, flexible foam or gel that physically blocks the leak path.

1. Locate and mark leak points. The technician traces the water back to its actual entry point, which is often metres away from where water appears on the visible face. Cracks, cold joints, tie-rod holes and honeycombed concrete are all candidates.
2. Drill and install packers. 10 – 14mm holes are drilled at a 45° angle across the crack at 150 – 300mm spacing. Mechanical or push-in packers are seated in each hole. On a typical basement wall, expect 3 – 6 packers per metre of crack.
3. Inject under pressure. A single-component hydrophobic PU resin (or two-component hydrophilic for wider voids) is pumped through each packer at 100 – 200 bar. The resin meets groundwater, reacts, and expands 10 – 40 times its liquid volume to fill every connected void.
4. Remove packers and seal. Once the resin cures (usually within 30 minutes), packers are removed and the holes are patched with a non-shrink mortar like FOSROC Conbextra GP or SIKA Sikadur 31. The wall is now dry.

PU resin stays flexible after curing, which is why it tolerates the small ongoing movements typical of basements, lift pits and retaining walls without re-cracking.

How epoxy injection works

Epoxy injection bonds the two faces of a crack together with a structural adhesive stronger than the surrounding concrete itself. After successful injection, the crack effectively no longer exists from a load-transfer perspective.

1. Surface seal the crack. A fast-setting epoxy paste (e.g. SIKA Sikadur 31 CF) is applied along both faces of the crack to prevent the injected resin from leaking back out. Injection ports are bonded at 150 – 300mm intervals.
2. Verify the crack is dry and clean. Compressed air or vacuum is used to remove dust and loose debris. Any moisture in the crack will prevent the epoxy from bonding — this is non-negotiable. If the crack is damp, PU goes in first.
3. Inject low-viscosity epoxy. A two-part structural epoxy (e.g. SIKA Sikadur 52 LP, MAPEI Epojet) is injected starting from the lowest port at low pressure (2 – 5 bar). Once resin appears at the next port, the lower port is capped and injection moves up.
4. Cure and grind off. After 24 hours, the surface seal and ports are ground flush. The crack is now structurally restored — independent compressive tests routinely show failure occurring in the parent concrete, not at the repaired crack.

Epoxy is rigid. That's a feature for structural restoration but a defect if the structure is still moving — a re-cracked epoxy repair next to the original crack is a classic sign someone used the wrong resin.

5 signs you need PU, not epoxy

1. You can see water or hear dripping. Any active moisture means epoxy will not bond. Use PU.
2. The crack is in a basement, lift pit or below water table. Even if it looks dry today, hydrostatic pressure will return. PU stays flexible and self-seals minor movement.
3. The crack runs along a construction joint or cold joint. These joints move thermally and seasonally. Epoxy will crack again. PU is correct.
4. The leak appeared after heavy rain or piling work nearby. This points to ongoing structural settlement. Lock the crack with epoxy and the next movement will create a new crack a few centimetres away.
5. The crack is in a retaining wall, swimming pool or water tank. Wet-side environments are PU territory.

5 signs you need epoxy, not PU

1. The crack is dry, in a structural beam or column. This is the textbook case for epoxy. The element needs its original load path restored.
2. The crack appeared after a one-off event (impact, overload, seismic) and is no longer moving. Stable, non-moving cracks are epoxy candidates.
3. You need to bond a delaminated concrete topping or screed back to the slab below. Low-viscosity epoxy injected through the topping is the standard fix.
4. A machine base or mounting plate is moving or vibrating. Epoxy injection under the plate, sometimes combined with FOSROC Conbextra EP grout, restores rigid contact.
5. A structural engineer has signed off the crack as non-moving and requested injection in the BQ. If the consultant has specified epoxy, the assumption is no active water and no further movement.

Common Malaysian use cases

Lift pits → PU grouting

Lift pits sit below the groundwater table in most Klang Valley basements. Water always finds the cold joint between the pit wall and the raft slab. The repair is PU injection along the perimeter joint, typically 20 – 40 points depending on pit size, costing RM 2,500 – 8,000 per lift pit. Epoxy here will fail within months because the joint moves thermally and the water never goes away.

Structural columns → Epoxy injection

A column with a vertical shear crack from a piling overload or a minor seismic event needs its load path back. Once the consultant confirms the crack is stable, low-viscosity epoxy (Sikadur 52 LP or equivalent) is injected from the bottom up. Cost is typically RM 150 – 350 per port, 6 – 12 ports per column.

Basement walls → PU grouting

Diaphragm walls and retaining walls in basements leak through tie-rod holes, construction joints and shrinkage cracks. PU injection from the dry (negative) side stops the water without needing to excavate from outside. For an underground car park with widespread weeping, expect 80 – 200 injection points across the whole basement, costing RM 8,000 – 35,000.

Machine bases → Epoxy injection

A delaminated machine pedestal in a factory needs to behave as one rigid mass to avoid transmitting vibration. The standard repair is epoxy injection through the cracks plus epoxy grout under the baseplate (FOSROC Conbextra EP or MAPEI Mapefill EP). PU here would let the machine creep.

When you need both

Wet structural cracks happen — particularly in basement columns that are also leaking. The correct sequence is PU first to stop water, wait 4 – 7 days for the substrate to dry, then epoxy injection in the same crack to restore strength. Doing both costs roughly the sum of the two scopes, but it's the only honest answer when a crack is both wet and structurally critical.

Frequently asked questions

Can I use epoxy injection to stop an active water leak?

No. Epoxy will not bond to a wet substrate. Any moisture in the crack prevents the resin from adhering to the concrete face, so the leak path remains open and the injection fails almost immediately. Stop the water with PU grouting first, let the substrate dry for at least 4 – 7 days, then use epoxy if structural restoration is also needed.

How much does PU grouting cost per injection point in Malaysia?

Between RM 80 and RM 250 per point in 2026, depending on crack width, depth, resin type (hydrophobic vs hydrophilic) and access. A typical basement wall job runs 3 – 6 points per linear metre of crack. Mobilisation cost dominates for jobs under 15 – 20 points, so expect a minimum charge of around RM 2,500 even for a small lift pit.

Does PU grouting restore structural strength to a cracked column?

No. PU foam fills the void and blocks water but does not bond the two crack faces together as one structural element. If a cracked column or beam needs its original load capacity restored, epoxy injection is the correct system. Use PU only to stop water; use epoxy to restore strength. On wet structural cracks, do PU first, then epoxy once dry.

How long does PU grouting last compared to epoxy injection?

PU grouting typically lasts 5 – 10 years before requiring touch-up at new movement points. Epoxy injection, by contrast, lasts the lifetime of the concrete itself provided no further movement occurs — the repaired crack is often stronger than the surrounding parent concrete. The trade-off is flexibility (PU) vs permanence (epoxy), and the correct choice depends on whether the crack will continue moving.

Can PU and epoxy injection be used together on the same crack?

Yes, and on wet structural cracks this is the correct approach. PU is injected first to stop the active water flow, the substrate is given 4 – 7 days to dry, then epoxy is injected through the same or adjacent ports to bond the crack structurally. The combined cost is roughly the sum of both scopes, but for a wet basement column or a leaking transfer beam, no single-system answer is honest.

Not sure which one you need?

After 33 years of basement, lift-pit and structural repair work across Malaysia, we can usually tell from photos and a short site walk whether you're looking at a PU job, an epoxy job, or both.

ODSCC offers free site inspections across Klang Valley (with selected projects further afield on larger contracts). We'll diagnose the leak properly, recommend the right system, and quote honestly — including telling you when a cheaper system is enough.

Book a free site inspection →