How much enamel or varnish do I need for doors, radiators and wooden floors?

Doors, radiators and wooden floors aren't painted with the same emulsion as walls: they need enamel or varnish, with their own prior preparation and their own coverage, which often surprises by how little it goes in small tins.

Enamel: synthetic or water-based

Enamel, for doors, windows, radiators and metal surfaces, covers 10–12 m² per litre and is sold in 0.75-litre tins — much smaller than wall paint tins, so more units are needed than it seems at first sight.

• Synthetic enamel: a harder finish more resistant to wear, with more smell and slower drying.
• Water-based enamel: much less smell and faster drying, recommended in occupied homes or with children/pets, although somewhat less hard to the touch than synthetic on high-wear surfaces.

Worked example: to paint 4 m² of joinery with enamel, 2 coats: (4 × 2) ÷ 10 = 0.8 litres, rounded up to 2 tins of 0.75 litres. This is the same calculation the PresupuestoYa calculator applies automatically for the Painter trade.

Prior preparation by material

• Wood: always sand with 120-grit paper between coats.
• Metal: apply an anti-rust primer or wash primer first to guarantee adhesion — never paint enamel straight onto rusty or untreated metal, because the paint flakes off in a short time. Remove loose rust first with a brush or sandpaper.

Varnish for wooden floors and furniture

Varnish for decking, parquet and furniture covers 9 m² per litre, normally applying 2–3 coats with sanding between (fine-grit paper, 180–220). The first coat acts as a sealer and raises the wood grain; the second and third give the finish and the definitive protection.

Frequently asked questions

Which enamel do I choose if I'm painting in an occupied home? Water-based enamel: it hardly smells and lets you ventilate and use the room again within a few hours, compared with traditional synthetic.

Can I put enamel directly onto a rusty grille? No: first remove the loose rust and apply an anti-rust primer before the finish enamel, or the paint flakes in a short time.

How many coats of varnish does a wooden floor take? Normally 2–3 coats, with sanding between each for a uniform finish.

Conclusion

Calculating enamel and varnish by their real coverage —much lower than wall paint— and not skipping the preparation (sanding on wood, anti-rust on metal) is what avoids buying too little in small tins or a finish that flakes after a few months. Quoting it as an item distinct from wall painting reflects the extra work it really takes.