Bathroom Vanity Unit Installation

Preparing the area

First the water is turned off at the isolation valves under the basin. If they do not shut properly, it is turned off at the main stopcock for the flat or house. The old unit and basin are removed, the old wall plugs are pulled out and the holes are filled. Then the fitter checks exactly where the water supplies and the waste pipe come out of the wall. If they sit too high or too low for the trap space in the new unit, it makes sense to move them now. Once the unit is on the wall, this becomes much more awkward.

Fixing the unit

For a wall-hung unit, the height and fixing points are marked on the wall, checked with a spirit level and drilled. Tiles are drilled with a tile bit and the hammer action switched off. Hammer action only goes on once the bit reaches the masonry behind. The unit is hung on its brackets and levelled with the adjusting screws. A floor-standing unit is put in place, levelled with its adjustable feet and, where needed, lightly fixed to the wall so it cannot tip forward when a drawer is pulled out.

Basin, waste and tap

The basin is first set on the unit as a dry fit. This shows whether it sits properly and whether the cut-out for the trap lines up. Many furniture basins are not only placed on the unit but also screwed to the wall with their own fixings, so follow the manufacturer's instructions. The tap is often fitted before the basin goes on, because reaching it from underneath later is difficult. Then the trap is connected to the basin waste and to the waste pipe in the wall, and the flexible hoses go onto the isolation valves. Finally a silicone joint is run between the basin and the wall.

A floor-standing unit on feet is easier to fit and does not need a load-bearing wall. It suits older bathrooms with uneven floors, where the feet take up the differences. A wall-hung unit looks lighter and makes cleaning the floor easier, but the wall has to carry the unit, the basin and everything stored inside. The top edge of the basin usually sits roughly 80 to 90 cm above the floor. Taller people may prefer it a little higher.

When choosing the material, resistance to moisture matters most:

• Melamine-faced chipboard is common and widely available, but cut edges and cut-outs swell quickly if water gets to them
• Lacquered MDF copes better with a damp room and can be shaped neatly
• Solid wood looks warm but needs a good finish and regular care
• Plastic and aluminium are hardly affected by moisture and work well in small bathrooms without a window

Whatever the material, check the edges. They should be sealed with a continuous ABS edging strip with no gaps. Gloss doors look striking, but fingerprints and water drops show more on them.

The simplest case is a floor-standing unit in a bathroom where the water and waste connections are already in the right place and the wall is flat. These things add time and effort:

• A plasterboard partition without reinforcement, where the studs have to be found or special cavity fixings used
• Aerated concrete blocks or hollow bricks, where standard wall plugs do not hold and fixings made for that material are needed
• Supply pipes or waste outside the trap space, which have to be rerouted
• Cutting or adjusting openings in the back panel or shelf of the unit
• Removing an old basin with seized joints or corroded valves
• Large ceramic basins that need two people to lift

In a new build with plasterboard walls, it pays to plan ahead. If a timber or metal support is built into the partition before tiling, a wall-hung unit will hold reliably.

If you have a drill, a spirit level and some patience, you can fit both floor-standing and wall-hung units yourself. With a heavy basin, ask someone to help you.

1. Close the isolation valves and check that no water comes from the tap.
2. Put a cloth and a bowl under the trap, then remove the old trap, hoses and unit.
3. Assemble the new unit according to the instructions and leave the doors and drawers aside for now.
4. Mark the height and drilling points, check them with a spirit level and make sure no pipes or cables run where you will drill.
5. Drill tiles without hammer action and masonry with hammer action, then insert fixings suited to the wall type.
6. Hang or stand the unit and level it in both directions.
7. Fit the tap to the basin and attach the hoses to it.
8. Place the basin, level it and screw it to the wall if the manufacturer requires this.
9. Connect the trap and the hoses to the isolation valves, tightening the joints gently rather than with force.
10. Open the valves slowly, let the water run and wipe every joint with a dry paper towel.
11. Run silicone between the basin and the wall, smooth it and let it cure as the manufacturer states, usually about a day.
12. Fit the doors and drawers and adjust the hinges.

If supply pipes or the waste in the wall need moving, leave that to a plumber. A badly sealed joint inside a wall often shows only after some time, when the damage is already bigger.

A unit that is not level. Even a slight tilt means the doors do not close straight and water collects in one corner of the basin. Keep the spirit level in your hand at every step.

Weak fixings. In practice, ordinary wall plugs are often used in aerated concrete or plasterboard. The unit holds at first, then slowly starts to lean away from the wall. Choose fixings for the wall type and the weight they have to carry.

Sealing tape in the wrong place. Flexible hoses with a flat rubber washer are sealed by the washer, and PTFE tape on the thread does more harm than good. Tape or hemp belongs on threads without a washer, for example when fitting an isolation valve.

Untreated cut-outs. When an opening for the trap or pipes is cut into a chipboard unit, the raw edge soaks up water like a sponge. Seal the cut edge with silicone or varnish.

Kinked or overstretched hoses. A hose pulled tight or bent sharply is more likely to burst. It should run loosely in a gentle curve.

A smell from the waste. This is usually a badly seated trap, a missing washer or a trap with no water in it. Tightening the joints or replacing the washer normally solves it.

• The unit is level and does not rock when you push it
• A wall-hung unit is firmly fixed and does not lean away from the wall
• The basin sits straight and water drains towards the plughole
• All joints stay dry after running hot and cold water for a while
• The isolation valves open and close and are easy to reach
• The hoses are neither kinked nor stretched
• The trap does not leak when the basin is filled and emptied
• The silicone joint is continuous, smooth and without gaps
• Doors and drawers move easily and are aligned
• Cut-outs in the unit are sealed and the area is cleaned up