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An undeveloped space under a crawl, it does not take more to create a mini-bathroom that incorporates a walk-in shower and a small bowl on tablet.

small bathroom in a room

Necessary material

  • Spirit level
  • bracket
  • Hammer
  • Drill
  • Hammer hammer
  • pointerolle
  • Jigsaw
  • Auge
  • Trowel
  • Sponge
  • Glue comb
  • spatulas
  • Tiler's pliers
  • Flat chisel
  • Handsaw
  • Bell saw
  • Plasterboard ep. 5 and 7 cm
  • Plaster tile adhesive
  • Bricks (or blocks) of glass and mortar
  • XPS receiver 90 x 90 x 4 cm (here, Lux Elements)
  • Siphon drain (outlet Ø 50 mm)
  • Armored doubling panel or water repellent BA13 (green)
  • Kit for XPS receiver (glue, sealing strips)
  • Mosaic (tiles 20 x 20 mm)
  • Waterproof tile adhesive
  • White tile joint (slip)
  • Faucet with high body, basin Ø 30 cm, equipped shower column, 4 spots TBT 12 V (IP65) and switch
  • White sanitary silicone cartridge

Difficulty: 2/4
Cost: about 550 €
Time: 3 weekends

Built in the attic of an extension, this room had a corner enough to accommodate a bathroom (80 x 120 cm). In anticipation of this project, the crawling and the walls were covered with waterproof plasterboard. To quickly double the walls of a wet room, you can also install extruded polystyrene panels, ready to receive tiles. But this option is more expensive.

Repique rhymes with economy

The shower area is not installed at random. It is located just above a laundry room. Plumbing work is therefore limited. It was enough to transplant the water inlets and evacuation by drilling the slab for the passage of pipes. The partition wall is made of water-resistant plaster tiles and decorated with glass blocks. Side equipment, the choice was a small washbasin to ask and a walk-in shower.
The tray is made of extruded polystyrene (XPS) resized to the desired dimensions (80 x 80 x 4 cm). A slight slope (4 \%) ensures the flow of water to the drain.

Integral coating

To avoid any risk of infiltration, the perimeter of the receiver and the lifts are completed with a sealing strip embedded in a water-repellent coating. The tray is then extended to the floor with an extruded polystyrene panel of the same thickness (30 x 80 x 4 cm). Finally, the piece is completely covered with a mosaic plate.

Preparation of the installation

pierce the slab to develop the bathroom

  • The installation of this bathroom requires drilling the slab to allow the passage of the shower drain (Ø 50 mm) and that of the water inlet pipes.

copper plumbing connection

  • Connect the copper pipes (soldering tee fittings): two feed the shower (Ø 14 mm) and the other two sink (Ø 12 mm).

Tip for DIYers

install a mixer tap to the water network

To precisely maintain a 150 mm center distance, install a mixing valve, even if used, while the pipes are being installed in the lining.
If, as here, the water network is embedded in the lining, prefer the solder to the joints with joints.


  • The bung has an outlet Ø 50 mm.
  • The siphon (central part) is covered with a "hat" then a grid in stainless steel, clipped by six lugs.

make a seal

  • The lip of the rubber seal is coated with a bead of silicone sealant.
  • It is equalized on the finger (soaked in soapy water) all around.

installation of the bung

  • The receiver has a square base ready to receive by clipping the bung.
  • Insert it from below while pressing on the other side to snap properly.

Installation of the receiver

receiver kit

  • To bond the receiver and seal, this kit includes the mortar, Dry-Ask, roll tape and outgoing and incoming corner joints.

glue cement application

  • The thin-set mortar is prepared by diluting 5 kg of powder in 1.2 l of water.
  • Apply it to the slab with a trowel, then work it with a notched trowel of 8 or 10 mm.

receiver installation

  • The receiver (90 x 90 x 4 cm) is cut with a handsaw and placed on the glue.

Verification of horizontality

  • The horizontality of the edges of the receiver is checked at the spirit level.

stick an elbow out of bung

  • An elbow is glued at the outlet of the bung and joined to the general evacuation by a Ø 50 mm pipe extended by a reducer and a second Ø 40 mm PVC tube.

Wash basin assembly and equipment

Install the basin support

  • The basin support is cut with a jigsaw into a plaster tile (5 cm thick) and then inserted and sealed on two sides in the notch made in the walls.

laying an XPS panel

  • The shelf is pierced for the passage and fixing of the siphon and the mixer.
  • An XPS panel ready to tile (same material as the floor) conceals the PVC and copper pipes.

laying of two soap holder blocks

  • Before laying the tiles, the column is fixed by pegging and the two blocks of plaster tile soap are sealed in the wall (like the basin shelf).

installation of four spots

  • Installed before tiling the ceiling, four 12V TBT spots are powered by a transformer (IP65). They are controlled by a switch located outside the shower.

strengthen the tightness of the shower

  • To reinforce the waterproofness and improve the aesthetics, all the re-entrant angles receive a quarter-round of 8 mm plastic fixed to the mastic-glue.

Implementation of the mosaic

laying mosaic

  • The receiver is covered with a mosaic (20 x 20 mm) because large tiles could not marry precisely its slightly curved surface.
  • This mosaic is in plates on 35 x 35 cm kraft paper to be glued with a ready-to-use waterproof paste.
  • The product spreads in a single pass to the notched spatula (5 mm).
  • Plates positioned, braces are placed progressively in the corners to obtain uniform joints.

finishing of the bathroom

  • Ceramic or parrot-nose pliers are used to cut or trim the elements.
  • For finishing, a joint paste (slip) is applied to the painter's knife and then spread with the squeegee.
  • The tiles are cleaned with a sponge before drying the dough.

Video Instruction: How to Install a Basement Bathroom