Applying a self-levelling compound to a concrete floor


Summary: Learn how to apply a self-levelling compound to a concrete floor.



If you want to fit any form of floor covering to a concrete floor with a rough surface, the only practical subfloor is a self-levelling compound. This is a latex-based compound that provides a very smooth finish but, despite its name, it will need some degree of levelling with a plastering trowel. Laying this form of subfloor will raise the floor slightly, so the bottom of any doors opening into the room may need to be trimmed.


Preparation

  • Thoroughly clean the floor, removing any loose debris and as much dust as possible.
  • Remove any previous bitumen-based layer or old tile adhesive.
  • A dusty floor surface needs to be primed with a PVA solution: mix 4 parts water and 1 part PVA.
  • Using a wide paintbrush apply the PVA solution over the floor's surface.
  • To prevent the smoothing compound seeping into the adjoining room or rooms, fix a threshold strip across any doorways.
 

Applying the compound

  • When the floor is dry, mix the compound according to the manufacturer's instructions in a clean bucket to avoid contamination. A power stirrer is ideal for stirring as it prevents too much air getting into the mix.
  • Pour some of the compound onto the floor at your chosen starting point, usually one of the farthest corners of the room.
  • Use a plastering trowel to smooth the compound evenly over the floor. The compound should be about 5mm (1/5in) thick, although this will depend on how uneven the existing floor is. Ensure all indentations are filled and any high spots are levelled.
  • Continue to mix and spread the compound until the whole floor is covered, tying each new section into the damp edges of the sections you have already laid. Self-levelling compound only remains workable for about 30 minutes so you will need to work quickly.
  • Allow the compound to dry overnight. The following day use a medium grade sandpaper block to smooth away any ridges caused by the trowelling.

 Starting at a corner, smooth the plaster evenly over the floor.