Waterproofing a Salt Lake Terrace and Bathroom Properly

Waterproofing a Salt Lake Terrace and Bathroom Properly

If the ceiling of your first floor bedroom shows a slow brown patch every July, or the plaster just outside your bathroom blisters and sheds paint at skirting level a few months after a fresh coat, then what you are looking at is not a paint problem, and it is usually not a one day chemical problem either, because water has found a way in somewhere and it is travelling, and the place it finally shows up is almost never the place it entered. Salt Lake gives a building a long humid stretch and then a serious monsoon, so a terrace and a bathroom here get tested properly every single year, and any slope that does not actually drain, or any junction that was never detailed on a drawing, will report itself within two or three seasons.

Waterproofing tends to get discussed as a product, basically a coating or a membrane that you buy and somebody applies, and that framing is where most of the money gets wasted, because the coating is the last and thinnest layer of a decision that was really made much earlier, in the slab level, the direction of fall, the number and position of rainwater outlets, the height of the parapet upstand, the depth of the sunken bathroom floor, and whether the plumbing was planned into a service wall or chased into a structural member after casting.

We are an architecture and interior design studio working out of New Town, across the Salt Lake, New Town and Rajarhat belt, and a good share of what we are called in for in the older sectors is exactly this, a house from the eighties with a terrace that has been coated three or four times already, or a rebuild where the owner has decided the bathrooms will be done once and never opened again. This page is how we approach it, written from the drawing board and from site rather than from a product catalogue, and if you are close to hiring somebody for it, it should also give you the questions worth asking them.

Where the water actually gets in on a Salt Lake terrace

Salt Lake, also written Bidhan Nagar, is a planned grid of blocks and sectors with plots that are regular in shape but tight in area, and neighbours who have very often already built right up to the boundary, which means your roof has to collect and discharge its own water entirely within your own plot. On the older houses we see the same handful of causes again and again, and almost none of them are about the quality of the chemical. The original fall was shallow to begin with, then two or three rounds of patch work added thickness unevenly until the fall reversed in one corner, so a shallow pond now sits against a parapet for weeks every year. The outlet was fixed at the convenient corner for the downpipe rather than at the low point of the roof. The parapet was plastered down to the terrace with a sharp internal angle instead of a coved and raised upstand, so the membrane terminates exactly where water pools hardest. And the slab itself, being reinforced concrete that has been heating and cooling for decades, carries fine shrinkage cracking that any rigid topping will eventually mirror.

Slope, outlets and parapet get drawn before a product is chosen

So the first piece of work on a terrace is not procurement, it is a level survey, and from that we draw the finished terrace as a set of levels rather than as an instruction to slope it towards the pipe. That means settling the low points, the fall towards each of them, how many outlets the roof genuinely needs so that one blocked mouth does not flood the whole slab, and where the upstand at the parapet and at every wall abutment rises to, with a coved junction at the bottom so the membrane turns up instead of stopping at a right angle. It also means accounting for what the new build up does around it, because added thickness raises the terrace against the threshold of the stair mumty, changes the drip detail at the edge and adds dead load to a slab designed a long time ago, so that load question gets checked with a structural consultant rather than assumed, and sometimes the answer is a lighter build up with a thinner screed, which is a cost conversation as much as a technical one.

The bathroom leaks at the junctions, so the junctions get detailed

A bathroom almost never fails across the middle of the floor, it fails at the junctions, and there are more of them than people expect: the floor to wall corner, the floor trap and its surround, the point where the waste pipe passes through the sunken slab, the shower zone where water hits one wall for twenty minutes at a stretch, the threshold where the sunken floor meets dry flooring outside, and the door frame sitting in wet plaster. In our drawings the sunken depth is set by what has to pass through it, so the waste runs are laid out first and the depth follows them, rather than a standard depth being poured and the plumber then cutting falls into whatever he has been given. The membrane turns up higher in the shower zone than elsewhere, the threshold is formed as a raised kerb so the sunken fill cannot drain outward into the bedroom floor, and the fill is specified as something that will not hold water against the slab indefinitely. This is where our bathroom design work and the waterproofing detail stop being separate items, because the position of the shower, the trap and the door is the waterproofing drawing.

What changes between a repair and a rebuild

The sectors are now a mix of older stock from the sixties through to the nineties sitting beside newer G+3 and G+4 rebuilds, and the two situations call for genuinely different work. On a rebuild you get to settle all of it at the right moment, which is before the slab is cast, so sunken depths, pipe sleeves, outlet positions, parapet heights and terrace falls go into the structural drawings and nothing has to be cut or chased afterwards, and that is the cheapest waterproofing you will ever buy, because it costs drawing time instead of breaking and rebuilding. On a repair you are negotiating with decisions somebody else made decades ago, so the honest sequence is survey, then diagnosis, then a choice between working within the existing levels at lower cost and higher residual risk, or taking the old layers off down to the slab and rebuilding the falls at higher cost and much longer life. Both are legitimate and we price both, which is the point of our renovation and remodelling work across Salt Lake, where the terrace and the bathrooms usually turn out to be the part of the brief that decides the budget.

Where the sanction route touches a terrace job

Most waterproofing is maintenance and sits outside the sanction question entirely, but the moment the work grows into something that changes the building, a new room on the terrace, a rebuilt mumty, a change in roof structure or an added floor, then you are in front of Bidhannagar Municipal Corporation, which is the building authority for Salt Lake, as against NKDA which covers New Town. What is permissible on your specific plot in terms of coverage, projections and heights varies plot by plot and has to be confirmed for your plot rather than taken from a neighbour's example. We prepare and run drawings through the Bidhannagar process as a normal part of a project, and if you want the detail of how that route runs on an individual plot, Bidhannagar Municipal Corporation Building Plan Sanction for a Duplex on an Individual Plot in Salt Lake goes through it stage by stage, while Plan Revalidation After Lapse Under Bidhannagar Municipal Corporation in Salt Lake: A Plot Owner's Guide covers the case where an older sanction has already lapsed and has to be revived before anything else can proceed.

Every option arrives with its cost attached

We do not present a single recommendation and hold the price back until the end, because on this kind of work the decision is genuinely yours and it is almost always a trade between money now and risk later. A terrace can be treated by keeping the existing layers and relying on a liquid applied membrane with a protective screed, or by stripping back and rebuilding the falls in a fresh screed, or by going to a membrane with tile protection over it so the terrace stays usable, and each of those carries a different life, a different weight on the slab and a different number on the estimate. The same applies to a bathroom, where keeping the existing sunken fill is cheaper than taking it out and relaying the waste with proper falls, but the second one is what stops you opening the floor again in four years. At the end of the day you are the one carrying both the cost and the consequence, so every option goes in front of you with its figure attached and the budget moves as you decide, instead of the design being frozen first and the estimate arriving later as a surprise.

When somebody else is the better fit for you

If you have one clear local failure, a single outlet mouth that has opened up or one patch at a parapet corner on an otherwise sound terrace, then an experienced waterproofing applicator working directly for you is the sensible and cheaper route, and bringing in an architect for that is paying design fees to solve a maintenance item. If you are in a cooperative block where the roof is common property and the committee wants a product backed warranty across the whole terrace, then a specialist waterproofing contractor who issues that warranty is giving you something we do not. And if you only need sanction drawings prepared from a design you have already fixed, a drafting service will do that for less. Where we are the better answer is when the question is bigger than a coating, so a full terrace rebuild, a bathroom layout being reworked, a rebuild or an added floor, because then the levels, the structure, the plumbing, the interiors and the sanction route are one single problem, and the structural trade off with a turnkey or lowest quote route is that their margin lives in speed and substitution, which makes slow careful detailing the first casualty when site pressure arrives.

How we are set up to run this

Sumana Kumar is the principal architect and stays with the project through the sanction stage and through site rather than handing it to a junior once the agreement is signed, which matters here more than on most work, because waterproofing is won or lost on the days the screed goes down and the layers get covered over, right, and that is exactly when a project usually loses senior attention. The design is worked out for your actual plot and your actual terrace, from measured levels, not selected from a package of standard details, since no two terraces in the sectors have the same history of patching. Architecture, interiors and the Bidhannagar route sit with one team, so the plumbing layout, the sunken depth, the tile levels and the drawings going to the municipality stay consistent, and you are not the person carrying information between three vendors who each blame the other when the ceiling stains. For instance, when a bathroom is being rebuilt the rooms on the other side of that threshold come into the conversation too, which is what our pieces on Family Room Design in Salt Lake: The Room Behind the Drawing Room, Drawing-cum-Dining Design in Salt Lake: One Room, Two Jobs and Kitchenette Design for Compact Salt Lake Flats deal with. If you want to see the kind of project this work sits inside, Residential Building Project in Salt Lake is an example of that category of work and Cornaro Grand project in Kolkata is another, with more of our work in the area collected on our Salt Lake area page and the interiors side of it under interior design across Salt Lake.

Talk to us before the next monsoon

The useful time to look at a terrace or a bathroom is in the dry months, when the surface can be stripped, surveyed and rebuilt without racing the rain, and when a ponding test can actually be run and read properly. If you own or are buying a house or a plot in Salt Lake and you want the water question settled as part of how the building is designed, rather than as a repair you keep repeating every few years, get in touch with the address of the plot and whatever drawings you have, and we will start from the levels.