With the shower walls
framed out and sheathed in plywood, the next step is to start waterproofing. I had to do a huge amount of research on the subject, but in the end I actually decided to layer several different waterproof systems over each other. It's definitely a bit of overkill, since each system is designed to function independently. But the memory of a leak from the flat's original, ancient loo early last year is still too close for comfort, so we decided not to take any chances and to go with the logic "better safe than sorry". (The leak was nothing to do with us, though of course we had to deal with the aftermath.). I thought about it afterwards and realised that the idea of redundant waterproofing is similar to what we have on our new slate roof - it has multiple layers of waterproofing to minimize the chances of any water leaking through.
For the initial layer, I had decided on using
BAL's WP-1 tanking kit - a rubberized membrane that is painted on. It has the consistency of cream, but once dried, it becomes a flexible rubber membrane. This flexibility is ideal (and often necessary) for a wooden substrate, because wood has a tendency to expand/contract with heat/cold. Also, older buildings settle over time, and they shake slightly when a heavy truck drives by - if one does not allow for all of this movement, there will eventually be cracks - and water just loves to slip through them...
Before any waterproofing could start, there was (or course) something that had to be removed, because it was in the way. The end of our steel beam (that supports the post which supports the new
mezzanine's structural steel beam) had to be trimmed so it did not stick out.
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| In the middle of cutting off the edge of the steel beam |
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| The completed cut |
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| The initial waterproofing system - BAL's WP-1 Tanking Kit |
The tanking system involved several steps: the first requires you to prime the plywood; after 15-20 minutes you can start painting on the membrane. Joints between wood, as well as any holes, have to be covered with a polyester gauze tape that help span the opening; finally, an additional coat of the membrane is applied over the tape.
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| The primer applied to the sub-floor on the underside of the shower. |
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| The membrane is applied to the floor and wraps up around the edges to create a waterproof enclosure - and to prevent any leaks through the floor (to the flat below) in case any water leaks from the shower. |
You may have noticed that the waterproofing that's been done so far is located below the shower, not at the floor level of the shower. As part of the redundant waterproofing, we decided to fully waterproof the bathroom's floor - but because our shower floor is sitting 9" above the bathroom floor (because of the steel beam), that waterproofing extends under the shower. Because of the configuration, we will have two (hopefully) waterproof levels under the shower. This means that should any water leak from the shower or drain above, the odds of it leaking through the sub-floor - and through to the flat below - are extremely slim. This is definitely unconventional - and certainly overkill - but we really want to minimize the possibility of a leak.
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| The initial layer of waterproofing (blue-gray color) below the shower on the bathroom's sub-floor |
