Bathroom waterproofing

Why it matters in an apartment building

The bathroom sits on a floor slab that is the common property of the whole building, and below it there is often a neighbour's bathroom or living room. Building code LBN 200-21 allows sanitary rooms above the living rooms of the apartment below if the waterproofing requirements are also met.

The Law on Residential Properties states that an owner is responsible for losses caused to other owners, and the Civil Law requires compensation for losses caused by action or inaction. That is why it is worth photographing the waterproofing and the joints before tiles cover them.

Where waterproofing is applied

The manufacturer of Ceresit CL 51 intends this material for waterproofing walls and floors before tiling in wet rooms: bathrooms, showers and kitchens, including on heated floors. For shower waterproofing, special attention is needed where water runs directly onto the tiles, especially in a shower without a tray.

Exactly where and how high up the walls it is applied is determined by the position of the shower, the bath and the floor drain. For swimming pools and surfaces that are permanently under water, the manufacturer recommends two-component waterproofing.

Preparing the base

The manufacturer requires a dry, load-bearing, stable and clean base, and crumbling surfaces must be primed. For anhydrite and gypsum levelling compounds the moisture must not exceed 0.5%, for gypsum plasters 1.0%. The working temperature is from +5 to +30 °C.

If the floor or walls are levelled anew, the requirements of the tile adhesive must also be taken into account. The Ceresit CM 17 technical data sheet states that a cement screed and plaster under tiles must be at least 28 days old and have a moisture content below 4%. The Ceresit CT 17 primer dries in about 2 hours. For more on screed, see floor levelling.

The order of work according to the manufacturer

1. Priming The prepared base is primed, and the primer is left to dry.
2. Tape and collars Waterproofing tape is worked into the joints between walls and floor and along the edges, collars are fitted around pipes and the floor drain, and corner pieces in the corners.
3. First coat The first coat is applied and the tape is pressed into it.
4. Second coat For Ceresit CL 51, the manufacturer writes that the second coat can be applied after about 1 hour, so that the dry layer is at least 0.5 mm.
5. Tiling According to the manufacturer's data, tiling can start about 2 hours after the second coat. The time depends on temperature, the base and air humidity.

What to decide before the request

• A shower with a floor drain or a bath. For a shower without a tray, see shower with a floor drain.
• Whether there will be underfloor heating. The CL 51 manufacturer intends it for heated floors as well.
• Where the washing machine and the sink will be.
• Whether the old tiles are removed. Check whether they meet the manufacturer's base requirements (dry, load-bearing, stable, clean).

How much bathroom waterproofing costs

Bathroom waterproofing costs from €6/m². Prices are for labour. Materials are calculated separately in the estimate.

Example: in a bathroom with a 4 m² floor and 6 m² of wall in the shower area, the waterproofing is 10 m² × €6 = from €60 (labour). If 18 m² is tiled at the same time (18 × €24 = from €432) and a floor drain is installed (from €100), this work comes to from €592 in total. A whole bathroom renovation is from €3,000.

The price is affected by the area in m², the number of corners and pipes, the condition of the base and whether the bathroom has a shower without a tray. An exact estimate can be made after seeing the apartment. All prices: renovation prices.