PU Injection Waterproofing: When It Works and When It Fails
PU injection is the repair most Malaysian homeowners have heard of and the one they trust least. “Has PU injection improved? I saw thread from 2011 saying it can’t last,” one owner asked on Lowyat. The honest answer is that it lasts well on the right crack and fails quickly on the wrong one.
What PU Injection Actually Does
Polyurethane injection seals a crack from the inside. Small ports called packers are drilled into the concrete along the crack, and liquid polyurethane resin is pumped in under pressure. When the resin meets the water already in the crack it reacts and expands, filling the path the water was using and blocking it.
Two broad families are used. Hydrophobic resins react and foam into a firm seal that resists water; hydrophilic resins absorb water and swell, which suits cracks that stay damp. Which one is right depends on whether the crack is wet, whether it moves, and how wide it is — decisions that need someone looking at the crack, not a product label.
Where PU Injection Is the Right Repair
Active leaks through concrete cracks
Water seeping through a crack in a concrete wall, a basement, a retaining wall or the joint between wall and slab is exactly what injection is designed for. The resin follows the crack and seals it along its length.
Cracks you can reach from one side
Injection works from the inside face, so it suits leaks where the outside of the wall or slab cannot be dug out or reached — below ground, or between two units.
Not for a failed roof surface
If a flat roof is leaking because its whole surface has aged, injecting one crack moves the water to the next. That roof needs a membrane or coating over the surface, not injection.
Not for a cracked pipe
“If pipe burst, then injection will help? It doesn’t solve the pipe cracked?!” — the Lowyat poster was right. Resin around a leaking pipe hides the symptom while the pipe keeps leaking. The pipe has to be repaired.
Why So Many Owners Say It Didn’t Last
Most “PU injection failed” stories are really “PU injection was used on the wrong problem” stories. One Lowyat owner had a leak at the junction of a wall and a roof slab injected twice. After the second round the spot felt dry, but the repainted area started darkening again. The contractor’s eventual finding: the waterproofing on top had been laid without a slope to the gutter, so rainwater sat on the slab after every storm. No amount of injection below fixes water pooling above.
The other common causes are a crack that keeps moving (the resin seals it, then the crack reopens beside the seal), injection into the stain rather than the source, and a pipe leak mistaken for a crack. All four are found by looking before injecting.
PU Injection Price in Malaysia
Published 2026 price guides for the Klang Valley put PU injection at roughly RM80 to RM250 per injection point. A short crack might need a handful of points; a long crack along a basement wall many more. “Wow! PU injections so costly?” was one reaction on Lowyat — it can be, per point, which is why paying for injection on the wrong problem is the most expensive outcome.
Ask any quote to state the number of points, the resin type, and what happens if the same crack leaks again.
Can I Do PU Injection Myself?
Consumer kits exist, but injection needs a pump that holds pressure, packers drilled at the right spacing and depth, and a judgement about which resin the crack needs. A kit that fills the surface of a crack without reaching its depth usually just moves the leak a few centimetres.
If you hire someone, check them first. CIDB keeps a public contractor search where anyone can look up a contractor’s grade, specialisation and registration expiry. Waterproofing installation is its own specialisation code. EI Sdn Bhd in Shah Alam lists crack analysis, non-shrink grout and pressure grouting for voids among its services, and inspects before choosing a method.
Five Questions to Ask Before Agreeing to PU Injection
- Where is the water getting in? If the answer is “where the stain is”, the source has not been found.
- Is the crack still moving? A crack that is still widening needs its cause dealt with, or it will reopen beside the resin.
- Which resin, and why? A damp crack and a dry one may need different resins.
- How many points, and at what price per point? That is the number to compare between quotes.
- What happens if the same crack leaks again? The answer should be in writing.
One more check sits outside the crack entirely: go up to the roof or the floor above and look for water that sits after rain. If it ponds, the fix belongs on top, and injection below will only buy time. For flat roofs that need resurfacing rather than injecting, see waterproofing membranes.
After the Injection
A good injection is dry on the next heavy rain, not just the next day. Leave any repainting until the wall has been through at least one proper storm, so a returning damp patch shows up on bare plaster rather than under fresh paint.
Frequently Asked Questions
Short answers to the questions people ask most.
On an active leak through a stable concrete crack, yes. It fails when the real problem is a moving crack, a failed roof surface, ponding water or a leaking pipe.
Published 2026 Klang Valley guides put it at roughly RM80 to RM250 per injection point. The number of points depends on the crack’s length.
Hydrophobic resin reacts with water and foams into a firm seal. Hydrophilic resin absorbs water and swells, which suits cracks that stay damp.
Only if the leak is a specific crack. If the whole roof surface has aged, the roof needs a membrane or coating instead.
No. It can hide the symptom while the pipe keeps leaking. The pipe has to be repaired first.
Usually because the water was entering somewhere else — ponding on the roof above, a moving crack, or a pipe — not because the resin failed.
Kits exist, but without the right pump, packer spacing and resin choice the repair rarely reaches the full depth of the crack.
Search the contractor on CIDB’s public contractor search to see its grade, specialisations and registration expiry.
Related Insights
Four more guides on the same problem.
A Crack That Keeps Leaking?
Send a photo of the crack and the stain, and tell us when it gets wet. We will tell you whether injection is likely to be the right repair.
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Common Questions About PU Injection
Questions readers in Shah Alam and the Klang Valley have asked about this topic.