Common problem

Is the rooftop leaking?

A concrete rooftop leaks at cracks, joints, where the roof meets walls and parapets, drains and the feet of equipment — and through an old membrane that has aged or water that ponds. Find where it comes in first, then choose the repair that fits.

Consult on LINE Send photos

Where it leaks

Where	Why it happens	What you see
Cracks in the slab	Heat movement, drying shrinkage and structural movement open fine cracks that let heavy rain through.	Leaks every time it rains, stains along the crack
Construction and expansion joints	Joints move, and the flexible seal splits. Where the fall is poor, water can also collect along a joint.	Leaks along the joint, hardened or gapped sealant
Where the roof meets walls and parapets	A membrane is weakest where it turns from horizontal to vertical; leaks gather there.	Stains along walls and parapets
Drains and outlets	Blocked or too-small drains leave water standing; the membrane ages under it, and the water finds any weak spot.	Water that will not drain, stains around the drain
Pipe penetrations and equipment bases	Poorly sealed penetrations and holes drilled when equipment is fixed become weak points.	Leaks directly below equipment or pipes
Ponding water	Without enough fall, water stays on the roof, and the membrane ages faster where it stands. Deep ponds that keep growing can be a structural sign.	Water still standing after the rain, dirt rings, algae or discolouring
An old membrane that has aged	It loses elasticity, peels and turns brittle; laps open, moisture underneath raises blisters, and the sun breaks it down.	Blisters, open laps, a cracked or crazed surface

First, find where the water gets in

Look and ask

We look at cracks, joints, wall edges, drains and equipment, and ask when and where it leaks. The stain inside is often away from where the water gets in.

Flood test

Holding water on the roof shows whether it leaks, though not always exactly where — so it is combined with the survey. The weight of the water and protection of the drains are checked first.

Then choose

Only once the cause is clear do we choose the repair — and after it, the roof is tested with water again.

These are examples of how leaks are traced. We choose the checks to suit the site.

Choosing the repair

These are the possible repairs. Which one fits is decided after we see the roof.

Repair	When it fits	Keep in mind
Local repair (cracks, joints, drains and wall edges)Crack injection Details →	The membrane is still sound and only a detail has failed.	It may not cure a failed membrane or poor drainage. A crack that keeps moving needs a flexible material, not a rigid one.
Coat the whole roof (liquid polyurethane, polyurea, cementitious)Liquid polyurethane Details →Polyurea Details →Cementitious coating Details →	The slab is sound and you want a seamless layer that runs up the walls.	It needs a clean, dry, sound substrate with the cracks treated first. Where it is exposed to the sun, a top coat protects it.
Lay a sheet (PVC / TPO, torch-on)Sheet membrane Details →Torch-on membrane Details →	A wide roof with enough fall, where the turn-ups at the walls can be formed properly.	With bonded and torch-on sheets, moisture in the slab causes blisters and loss of bond, so the substrate is checked first.
Overlay or strip the old membrane	Overlay only when the old layer is dry, well bonded and simply aged.	The substrate is surveyed for moisture first; never over a wet layer. Drainage faults are not fixed by overlaying.
Fix the ponding and drains	Water still stands after the rain, or the drains cannot keep up.	Typical work is building up the falls (tapered screed), adding or lowering drains and clearing outlets; channels to the drains are sometimes cut. A new membrane alone leaves the pond behind.
Lift tiles or toppings	The membrane under the tiles has failed, or the tiles must come up to find where the water gets in.	If the membrane is sound, replacing a few tiles may be enough.

One possible way to redo the whole rooftop

Remove the old membrane where needed; grind and clean the substrate
Repair cracks and seal joints; patch damaged concrete
Improve drainage where water ponds (falls, drains)
Detail the wall turn-ups and edges (termination bars, sealant)
Apply the membrane, with a top coat where exposed to the sun
Flood test to confirm it no longer leaks

This is one example. We decide the actual work after seeing the roof.

Questions

What decides the price?

The area, the state of the substrate (cracks, wet spots, or an old membrane to remove), the system and number of layers, whether it is exposed to the sun, and the hours we can work. Send photos and drawings on LINE and we will check the site and quote.

Can it be done without stripping the old membrane?

Only if the old layer is dry, well bonded and simply aged. If it is wet, or the leak comes from drainage, it has to be dealt with first. We check on site.

Can it be done in the rainy season?

Primers and coatings must be kept from rain and condensation while they cure, so the work is planned around dry spells. Fast-curing resins such as PMMA resist rain about 30 minutes after application in good conditions; they still go on a dry surface, and full cure takes longer.