Monsoon prep checklist: what to waterproof before June

The window for doing waterproofing properly in Mumbai is roughly February to May. A membrane needs a dry substrate, and once the rain starts the only honest options are emergency stabilisation and waiting. So the work worth doing now is the work that stops you needing us in July.

Here is the checklist we walk a housing society committee through in March.

Walk the terrace, and look at the edges

Most of what matters is at the perimeter, not in the middle.

• Parapet junction. Is the waterproofing turned up the parapet, or does it stop at the floor? A membrane that stops at the junction is an open seam.
• Cracks. Hairline crazing is normal. A crack you can get a fingernail into is a path.
• Ponding. Look for the dry tide-marks left by standing water. If the slope has gone, the terrace holds water for days after every shower, and any weakness gets days of pressure instead of minutes.
• Old patches. Count them. Three or more rounds of patching usually means the base layers have failed and a fourth patch is money spent on postponement.

Clear the drains — all of them

Rainwater outlets, terrace khurras, chajja drains, balcony spouts. Thane and Mulund terraces silt up with leaf litter and construction dust over the dry months, and a blocked outlet turns a terrace into a shallow tank. This one is free and takes an afternoon, and it prevents more leaks than most paid work.

While you are there, check the downpipes are actually connected at the joints. A pipe discharging into the wall cavity instead of down it is a very common source of the damp patch nobody can explain.

Check the external walls, especially the west-facing ones

In coastal Mumbai the rain arrives sideways. A west or south-west facade takes wind-driven rain directly, and treatment that only deals with the terrace leaves that half of the problem in place.

Look for: cracked plaster, hollow-sounding plaster (tap it), open gaps around window frames, and the vertical stains under sills that show water is running behind the render rather than off it.

Look at the water tanks before you look at anything else

An overhead tank that loses water slowly saturates the slab it sits on all year, not just during the monsoon. If your society tops the tank up more often than it used to, book a 48-hour fill test. This is the cheapest item on this list and the one most often skipped.

Basements and stilt levels

If the parking level took water last year, deal with it now. Negative-side pressure — water pushing in from the soil — is handled from inside with crystalline tanking and PU injection, so nothing has to be excavated, but it cannot be done in the rain. Also check the sump pump actually runs. A basement that floods is sometimes a pump problem wearing a waterproofing costume.

Get the paperwork started early

For a society, the constraint is rarely the work — it is the meeting. A condition survey in February gives the committee an itemised quotation to circulate in March, an approval in April, and execution in May while it is still dry. Start that cycle in June and the answer is next year.

What can still be done once it is raining

If you have missed the window, not everything stops:

• Emergency leak repair — thermal survey, then injection grouting or a rapid-set patch to stabilise the active leak
• Crystalline chemical treatment — needs a damp surface anyway, which is one of its advantages
• Interior wall seepage treatment, where the wall can be isolated and dried locally

What cannot be rushed is a full membrane. Laying one onto a wet slab buys you a season and costs you the whole job.

The short version

Do it now	Can wait for the rain
Terrace membrane, parapet turn-ups	Emergency leak repair
Slope correction, drain clearing	Crystalline injection
External facade treatment	Interior damp isolation
Water tank lining and fill test	Diagnosis and quotation
Basement tanking and sump check	Committee paperwork

Free pre-monsoon inspections run across Thane West, Mulund, Ghatkopar and Andheri from January. Call +91 99875 06070 or book one here.