Where can I buy self-levelling compound for underfloor heating in Auckland?

Self Leveling compound

Heatwell sells self-levelling compound and fibreglass mesh from its Forrest Hill store in Auckland, which is open by appointment. Neither can be couriered, so both are collection only. Tiling wholesalers and the larger DIY stores also stock self-levelling compound, and any brand will do, with one exception explained below.

Does the brand matter?

Generally no. Any reputable self-levelling compound rated for the job will work over underfloor heating.

There is one exception worth knowing. If the floor was levelled before the underfloor heating went in, use the same brand again for the layer over the cable. Mixing brands between layers risks a bond failure between them, and a compound that delaminates from the layer beneath takes the floor covering with it.

How much do I need?

The screed over Heatwell's cable and mesh is thin — the finished system adds approximately 4mm to the floor height, and 5mm is the sensible budget. Usually one 20kg bag of screed will cover 4.5 square metres of floor. Work out the heated area, add the margin the manufacturer specifies for the depth, and buy a bag more than the calculation says. Running out partway through a pour is to be avoided.

What else do I need to buy with it?

Floor primer for concrete, tile and slate underlay, existing tiles and an type of wooden floor is not optional. The floor must be clean and free of dust, gib dust and paint, and it must be primed before the compound goes down. Without priming, the compound will not bond and can come away from the floor later. This is the most common DIY failure with self-levelling compound and it is entirely preventable.

Floor primer over waterproofing is not required. Primer is often not needed over noise proofing, insulation board, or anti-fracture mat either. Please check with the manufacturer before you install underfloor heating.

Heatwell uses fibreglass mesh, which goes over the cable before the compound is poured. Heatwell sells it by the metre in store. Do not fold or crease it — a creased mesh does not lie flat. A mesh that does not lie flat makes screeding more difficult.

How do I prepare the floor before pouring?

Clean it properly. Gib dust is the usual culprit on a building site and it is exactly the kind of fine dust that stops a primer working. Remove all paint. Paint overspray is as bad as gib dust. The floor must also be free of cracks, holes and sharp protrusions before the cable goes down, and if the floor is being renovated, every trace of old glue and adhesive has to come off first.

Then prime, following the primer manufacturer's instructions for coverage and drying time. Only use one coat of primer and make sure it is fully dry before you start installing cable.

How long does it take to dry?

For screed allow 24 hours. In cold conditions it takes longer, and a heater in the room helps. No floor covering goes down until the screed is completely dry — trapping moisture under any final flooring option causes problems that only show up weeks later.

Primer does not take too long. Usually primer takes around 10 minutes to be fully dry.

Can I use tile adhesive instead of self-levelling compound? 

No. The serrated trowel used for adhesive is a poor thing to drag over heating cable, and lifting a tile to relay it will very likely damage the cable beneath.

Where is Heatwell's store? 

258 Forrest Hill Road, Forrest Hill, Auckland, open by appointment. Call ahead on 0800 392 853.

Can I get it delivered?

Self-levelling compound and fibreglass mesh are collection only — Heatwell does not courier either. The self-levelling compound is too heavy. The fibreglass mesh should not be folded or creased.