How To – Cementitious Tanking

How To – Cementitious Tanking

Now I know loads of you are thinking – what the hell is she talking about here, but trust me, I was in the same place, until I bought a Victorian property that needed a lot of work and decided to do as much of it as possible ourselves.

So – first things first, what room in the house am I talking about. It’s the Cellar, yes the room that has taken us months, and is still not complete!

The Victorians were very clever fellows and they built the cellars to act as the humidifiers for the whole house, so they are meant to regulate the damp levels and “breathe”. Its when you stop the house from doing it’s natural breathing that you will get problems such as rising damp, as the water will just migrate up your walls and into your living spaces – not desirable.

One way of managing the damp levels in the cellar is to tank the walls, mostly the external ones. Cementitious tanking is a cement based mixture, that you apply two layers to the walls, allowing the brickwork behind it to breathe in normal situations, however, when more than normal water approaches it, it forms a barrier and keeps it out (something very clever to do with pressure).

Our current cellar had previously been tanked on our external walls and then plastered over, but this was very old and was just hanging away from the wall doing nothing. So it had to all come off and be replaced.

One of the most important things when tanking anything is preparation. The tanking slurry has to be applied directly to the brick work to allow it to form the barrier it needs to, and if it doesn’t adhere to the brick work correctly it will just come away and be a wonderful pile on the floor – not what you want.

So that is what we did, we sledgehammered off the old plaster and tanking and then we scraped and scraped and remaining adhesive off – this is by far the worst job and is so dusty!

Once you have thoroughly cleaned down and are clear of everything, you are ready to go.

We used KA Tanking Slurry as we read lots of reviews on line and this one came up pretty high, and trust me, when Rach does research she goes to town on it. We bought one tub in white and one in grey – it is recommended that you use two different colours so when you are putting on your second layer you can tell where you have been.

Only mix up enough tanking solution that you would be able to apply in 30 mins, as it is concrete based it will set solid and will be of no use to you. Remember to wear gloves and goggles as it’s nasty stuff and best avoided on skin.

We mixed our solution in a bucket using a mixing end attachment we bought for the drill (it made things a whole lot faster and funner), weighing out our measurements on our trusty Anthony Warrell kitchen scales (FYI – these have now been retired to DIY land – I won’t be using them to mix up a Victoria sponge in the future).

And then its application time, we found the large brushes, like what you would use for applying wallpaper paste, were too big and just slopped slurry everywhere, and so instead used a two inch brush. It takes a while to get used to how much to put on your brush and don’t mess with it too much one its on, but once you get into the swing of it, it’s pretty easy going.

Make sure you cover every surface evenly, and don’t apply too thickly, or it won’t dry and will just fall off.

Apply a second coat within 24 hours of the first and you are onto a winner.

Make sure the room is well ventilated, but don’t be tempted to put a heater down there or a fan, as the tanking needs to gently dry out to make sure it is drawn into the brick work correctly. If you heat it or cool it too rapidly it will crack and bond as a top layer rather than fusing with your bricks.

Once you are dry you are good to go. Do not paint over with non porous paints, as the whole point is about letting your room breathe – there is a post all about lime paint coming up you lucky folks so fear not!

Now onward tanking soldiers and may your houses be ever damp free!


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