Step 3: Bathroom waterproofing

Because of the amount of water a bathroom handles, we should treat it like a big bathtub. In our case that bathtub has two drains. But that bathtub should also hold water – or more precisely, be waterproof.

The point here isn’t that we plan to fill our bathroom with several inches of water to go for a swim, but that we acknowledge that there will be incidental and accidental spills that could lead to water damage and durability issues if not managed properly.

I am a fan of “properly” and “proactively!” So our entire bathroom floor will be lined with a waterproofing membrane that we fold up on the walls by about four inches. It basically could be a shallow bathtub (except for the door, of course).

If we do our job right, no water from incidental or accidental spills or the walk-in shower would get past the waterproofing membrane and into the concrete floor and framing beyond.

But don’t relax yet, because there is a lot more to it! How many bathrooms do you recall where you saw cracked grout lines in the floor, or even cracked floor tiles?

A fact that comes with framed structures (in our case our floor joists) is that they move due to thermal expansion and contraction. And yes, we poured a concrete floor, but that won’t put a stop to material movement for a couple of reasons. First, we integrated radiant heat into the floor, which will lead to thermal expansion and contraction. Second, the concrete cover over the floor joists is thinner than elsewhere.

All this basically guarantees that there will be some level of cracking. It will probably be very minor, but enough to migrate up to grout lines or even floor tiles.

The waterproofing membrane we selected (NobleSeal TS) provides crack isolation. Small and hairline cracks in the concrete floor should not pass the membrane, and thus it prevents crack migration into the thinset tiled floor above.

Not only are the benefits aesthetic (i.e. no cracks in the tiled floor), but also maintenance related (i.e. no cracked grout lines to repair). And last but not least, there is the added benefit of durability. With an intact first layer of defense (tiles and grout) water is less likely to get down to the second line of defense, the water proofing.

In case you are wondering if this is all worth the effort, just talk to some contractors who have experience remodeling 100+ year old buildings. They possibly have some good horror stories on what even small water damage can do to a building over time.

Before I move on to step three, let me extend our sincere thanks to our friend Rubani who helped me wrestle the waterproofing membrane.

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About Marcus de la fleur

Marcus is a Registered Landscape Architect with a horticultural degree from the School of Horticulture at the Royal Botanic Gardens, Kew, and a Masters in Landscape Architecture from the University of Sheffield, UK. He developed a landscape based sustainable pilot project at 168 Elm Ave. in 2002, and has expanded his skill set to building science. Starting in 2009, Marcus applied the newly acquired expertise to the deep energy retrofit of his 100+ year old home in Chicago.

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