If you're currently staring at a stripped-back bathroom wall, you might be wondering if buying a tanking kit is actually necessary or just another way for hardware stores to get an extra fifty quid out of you. It's a fair question. After all, you're about to put up beautiful tiles and use waterproof grout, so surely that's enough to keep the water where it belongs? Well, the short and slightly scary answer is no.
Tiles and grout are great, but they aren't a solid, impenetrable shield. Grout is porous, and over time, it develops tiny hairline cracks that you might not even see. Without a proper waterproof barrier underneath, that moisture seeps into your plasterboard or timber, and that's when the real headaches begin.
What actually comes inside a tanking kit?
Before we get into the "how-to," let's look at what you're actually buying. Most kits you'll find on the shelf are designed to be a complete system, so you don't have to go hunting for individual components. Usually, you'll find a tub of liquid waterproofing membrane (which looks a bit like thick, gooey paint), some waterproof joint tape, internal corner pieces, and a bottle of primer.
The primer is there to make sure the membrane actually sticks to your walls. If you skip this, the waterproofing might peel away like a bad sunburn, which is exactly what you don't want behind your tiles. The tape and corner pieces are arguably the most important parts. These are designed to bridge the gaps where walls meet or where the wall meets the floor—places where your house naturally shifts and moves. Without that flexible tape, a tiny bit of house movement would crack your waterproof seal instantly.
Why tile and grout aren't enough on their own
I've heard so many people say, "I've used epoxy grout, I don't need to worry." While epoxy is definitely tougher than standard grout, you're still relying on a rigid material to protect a house that is constantly breathing. Temperatures change, floors settle, and things expand and contract.
When water gets past that outer layer, it doesn't just sit there. It gets soaked up by the substrate. If you have plasterboard, it'll eventually turn to mush. If you have timber studs, they'll start to rot. The worst part is that you won't even know it's happening until you see a damp patch on the ceiling downstairs or notice a weird, musty smell that won't go away. By the time you see the damage, you're looking at a bill that's a lot more expensive than the cost of a simple tanking kit.
A realistic look at the application process
The good news is that applying this stuff isn't rocket science. You don't need to be a professional tiler to get it right, though you do need a bit of patience and a willingness to get a little bit messy.
First, you've got to make sure your surfaces are clean and dust-free. If there's a layer of drywall dust on the walls, the primer won't soak in properly. Once it's clean, you slap on the primer. Most of them are quick-drying, so you won't be waiting around for hours.
Then comes the "fun" part—the tape. You apply a layer of the liquid membrane to the corners, press the tape into the wet goo, and then paint over it again. This "sandwiches" the tape into the system. You'll do this for every corner and every joint. If you're doing a wet room, you'll be doing the entire floor and a good chunk of the walls. If it's just a standard shower over a tray, you usually just need to do the walls around the tray.
Getting the coverage right
Once the joints are sealed, you just paint the rest of the membrane on with a brush or a roller. It's weirdly satisfying to see your bathroom turn a bright blue or grey (the most common colors for these kits). You usually need two coats. Don't try to be "efficient" and do one thick coat; two thinner coats are much better for creating a consistent, rubbery skin that won't have any pinholes.
Choosing the right kit for your space
Not all kits are created equal, but for most residential DIY projects, a standard liquid-applied tanking kit is the way to go. You might see some kits that use a "fleece" or a "decoupling membrane" instead of a liquid paint. These are fantastic, especially for floors, but they can be a bit more fiddly to cut and stick down if you've never done it before.
If you're working with a particularly large area, like a massive walk-in wet room, check the coverage on the tub. Most kits are designed to cover about 5 to 7 square meters, which is plenty for a standard three-walled shower enclosure. If you've got a massive space, you might need two. Don't try to stretch one kit too thin just to save money—it's not worth the risk.
Common pitfalls that lead to leaks anyway
Even with the best kit in the world, things can go wrong if you rush. One of the biggest mistakes people make is not letting the membrane dry fully before they start tiling. It can be tempting to get those tiles up the same afternoon, but if the membrane is still tacky, the tile adhesive might not bond properly. Give it the time it needs—usually 24 hours is the sweet spot.
Another classic error is forgetting about the pipe penetrations. Those holes where the hot and cold water pipes come out of the wall for your shower valve? They need love too. Most kits come with "pipe collars" which are basically little rubber gaskets that slide over the pipes. If yours didn't come with them, you can usually buy them separately or use the tape to create a tight seal around the pipe.
The "It'll be fine" trap
We've all been there. You're tired, you've been working on the bathroom all weekend, and you see a tiny gap in the corner that you didn't quite cover. You think, "Eh, the grout will cover it." Don't do it. That tiny gap is exactly where the water will find its way in. Take the extra five minutes to go back over it. Your future self will thank you when you're not ripping out a moldy wall in three years' time.
The peace of mind factor
Beyond the structural protection, there's a huge psychological benefit to using a tanking kit. There is nothing worse than lying in bed after your first shower in a newly renovated bathroom and wondering if you're going to hear a drip, drip, drip coming from the hallway.
When you've tanked the room properly, you know for a fact that the water is being funneled down the drain and nowhere else. It allows you to actually enjoy the space you've worked so hard on. Plus, if you ever sell your house, being able to tell a savvy buyer (or a surveyor) that the bathroom was professionally tanked is a great selling point. It shows the job was done properly, not just "flipped" for a quick look.
Wrapping it up
At the end of the day, a tanking kit is basically an insurance policy. It's not the most exciting thing to spend money on—it's certainly not as fun as picking out a high-end rainfall showerhead or some fancy Italian marble tiles. But in terms of the longevity of your home, it's easily the most important purchase you'll make for your bathroom.
It's messy, it smells a bit weird while it's drying, and it adds an extra day to your project timeline. But when you consider the alternative—rotting floorboards, black mold, and a collapsed ceiling—it's a total no-brainer. So, grab a kit, get that "goo" on the walls, and sleep easy knowing your bathroom is actually, truly waterproof.