CT1 BW1 Tanking: How Much Do You Need per m²?
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CT1 BW1 is a one-part waterproofing membrane, not a multi-part tanking kit. It covers up to 2m² per litre per coat, and tanking needs two coats, so plan on roughly 1m² of finished, twice-coated waterproofing per litre. It brushes or rolls straight onto the wall and floor of a shower or wet room, needs no tape, mesh or primer, and you tile directly onto it once it has cured. BW1 comes as a 5kg tub at £159.99.
Is CT1 BW1 a tanking "kit"?
Not in the old sense, and that is the whole point of it. A traditional tanking kit is several products: a primer, a liquid or sheet membrane, jointing tape and pre-formed corner pieces, all applied in sequence. BW1 replaces that with one pot. The TRIBRID polymer bonds to most substrates with no primer, and because it goes on as a continuous flexible membrane it does not need scrim tape or corner seals at the joints.
So if you searched for a "CT1 tanking kit" and landed on a single tub, that is correct, the tub is the kit. You are buying the membrane and nothing else, because nothing else is required. Fewer products to buy, fewer steps on site, and no weak point at a taped joint.
How much BW1 do you need per square metre?
Start from the manufacturer's figure: up to 2m² per litre, per coat. Because a proper tanking job is two coats, the practical planning figure is about 1m² per litre once both coats are on. Work out the area you are waterproofing, then match it to the table.
| What you are tanking | Typical area | BW1 needed (two coats) |
|---|---|---|
| Corner shower, two walls plus tray | 4 to 5m² | about 4 to 5 litres |
| Alcove shower, three walls plus tray | 6 to 7m² | about 6 to 7 litres |
| Small wet-room wet zone (floor plus lower walls) | 8 to 10m² | about 8 to 10 litres |
| Full wet room | 12m²+ | 12 litres or more |
BW1 is sold as a 5kg tub. Check the tub or datasheet for the exact litres per tub before you order, and always round up rather than run short mid-job, coming back to a part-cured wall to add product is not the same as one continuous coat. As a guide, a single corner shower is close to a tub's worth over two coats, while a wet room will take two tubs or more. See the BW1 product page for current pricing.
What does BW1 stick to?
It bonds to the substrates you actually meet in a bathroom or wet room, with no primer:
- Concrete and brickwork
- Plasterboard and fibre cement board
- Foam backer board (tile backer board)
- Wood and plywood
It is solvent-free and VOC-free, so it is fine to use indoors in an enclosed bathroom. Whatever the substrate, it needs to be sound, clean and dry, fill any large gaps and let them set before you tank.
How do you apply BW1?
Step One: prepare the surface
Get the substrate clean, dry and firm. Knock off any nibs of plaster or adhesive, brush the dust off, and make sure boards are fixed tight with no movement. There is no primer stage, but the surface still has to be sound, BW1 is only as good as what it is stuck to.
Step Two: first coat
Brush or roller BW1 onto the wall and floor in an even coat, working it well into internal corners, the wall-to-floor junction and around any pipe penetrations. These junctions are where showers leak, so do not go thin there. Because it is one part, there is no mixing, straight from the tub.
Step Three: second coat, then tile
Once the first coat has become touch-dry, apply the second coat over the whole area, ideally at right angles to the first so you cover any thin spots. Leave it to cure fully, then tile directly onto it with a suitable tile adhesive. Check the tub for the exact touch-dry, recoat and tile-over times before you plan the day.
BW1 or a taped DPM: which for the job?
Both keep water where it belongs, but they suit different jobs. BW1 is a brush-applied liquid membrane for tanking walls and floors you are about to tile, showers, wet rooms, splash zones. A damp proof membrane is heavy polythene sheeting for under-slab and oversite work, laid before a floor slab goes down, not something you tile straight onto.
Put simply: liquid membrane where you are tiling a wet area, sheet DPM under a floor. For rising damp in walls you are back to a damp proof course again, a different job from tanking a shower. If in doubt about which product the job needs, call the counter and describe it.
Common mistakes to avoid
- One coat instead of two. A single coat leaves pinholes. Tanking is a two-coat system, plan the product and the time for both.
- Going thin at the corners. The wall-to-floor junction and the corners are exactly where a shower fails. Work the membrane in there properly.
- Tiling before it has cured. Tile onto a coat that is not fully cured and you trap solvent-free membrane that never finishes off. Wait for the stated cure.
- Buying short. Coming back to add product to a part-cured wall breaks the continuous film. Work out the area, round up, and have enough on site.
- Tanking the wrong thing. BW1 is for tiled wet areas, not under a floor slab (that is DPM) and not for rising damp in a wall (that is DPC).
The short version
CT1 BW1 is a one-part tanking membrane that replaces the old primer-tape-mesh kit. Cover up to 2m² per litre per coat, plan on about 1m² per litre over the two coats a proper job needs, and confirm the litres in the 5kg tub before you order. Prep sound, apply two coats working the corners hard, cure, then tile straight over. Browse it in the damp proofing range or go straight to the BW1 tub.
By Steve, Builders Hardware Direct. Steve runs the BHD trade counter and has spent years supplying damp-proofing and tanking products to bathroom fitters and builders across South Wales. Not sure how much you need? Call the counter on 01269 267030 or order online for free UK delivery.
