In short: it depends on the subfloor. Diluted 3 parts water to 1 part primer, one litre of Ultra Prime IT covers about 28 to 40m² of a porous floor. Used neat on a non-porous floor it covers 5 to 10m² per litre. Some screeds need a second coat at 1:1. Choose your subfloor below to get the dilution, coats and number of 5 litre bottles.
What you need
Parts list
Ultra Prime IT coverage and dilution
| Subfloor | Dilution (water to primer) | Per litre of primer | Per 5L bottle |
|---|---|---|---|
| Porous floors, first coat | 3:1 | 28 to 40m² | 140 to 200m² |
| Porous floors, second coat | 1:1 | 14 to 20m² | 70 to 100m² |
| Non-porous floors | Neat | 5 to 10m² | 25 to 50m² |
| Cementitious backer boards | 5:1 | One coat | |
Figures are from the Instarmac UltraFloor Prime IT technical data sheet for a smooth subfloor at the given dilution. Use clean water to dilute. Second coats at 1:1 are for tamped or pan floated concrete, sand and cement screeds, existing smoothing compounds and calcium sulphate screeds.
Why prime before underfloor heating?
Primer seals dusty, porous floors so adhesives and levelling compounds bond properly, and stops the floor drawing water out of them too quickly. Self-adhesive panels such as MaxHeatSolo need a primed subfloor to stick.
Frequently asked questions
How far does a 5 litre bottle of Ultra Prime IT go?
About 140 to 200m² as a first coat at 3:1 on a porous floor, 70 to 100m² at 1:1, or 25 to 50m² used neat on a non-porous floor.
Do I need two coats of primer?
On tamped or pan floated concrete, sand and cement screeds, existing smoothing compounds and calcium sulphate screeds, yes: a first coat at 3:1 and a second at 1:1.
How long does Ultra Prime IT take to dry?
Usually 1 to 2 hours at 20°C. The first coat on calcium sulphate screed should dry overnight.
Can I prime over old tiles?
Yes. Old tiles and other non-porous floors take the primer neat, at about 5 to 10m² per litre.