Painting a facade doesn't go as far as painting a living-room wall, and calculating it with the same coverage as interior is one of the most frequent mistakes when quoting exterior work for the first time.
Coverage drops on a facade
Facade paint, formulated to withstand weather, UV rays and temperature changes, covers 9 m² per litre per coat — less than interior because of the usual porosity and texture of exterior render. It is sold in 15-litre tins.
Worked example: to paint 90 m² of facade with 2 coats: (90 × 2) ÷ 9 = 20 litres, rounded up to 2 tins of 15 litres. This is the same calculation the PresupuestoYa calculator applies automatically for the Painter trade.
Never work with rain or frost forecast
Always work in favourable weather conditions: never with rain forecast within 24h or with frost. A freshly painted facade that gets wet before it cures can lose adhesion and leave stains that force the job to be repeated.
Waterproofing for terraces and roofs
Waterproofing paint for terraces and flat roofs is an elastic liquid membrane that prevents leaks, with a coverage of 3 m² per litre applying 2 crossed coats. Always check the state of the substrate and the drainage falls before waterproofing — applying over active cracks or ponding areas only delays the problem, it doesn't solve it.
Silicone coating: more expensive, but repels water better
Acrylic/silicone coating for facades repels rainwater better and gets less dirty over time than conventional plastic paint, although it has a higher material cost (coverage 5 m²/litre, 15-litre tins). Highly recommended on facades facing prevailing wind and rain.
Frequently asked questions
Why does facade paint go less far than interior paint? Because of the porosity and texture of exterior render, which absorbs more paint than a smooth interior wall.
Can I paint a facade if it's going to rain the next day? It isn't recommended: you should never paint with rain forecast within 24 hours, because freshly applied paint can lose adhesion and stain before it has fully cured.
When is silicone coating worth it over standard plastic paint? On facades very exposed to wind and rain, where repelling water better offsets the higher material cost in the medium term.
Conclusion
Calculating the facade with the real exterior coverage (9 m²/litre, not the 12 of interior) and respecting the weather window before painting is what avoids buying too little or having to repeat the job because of unexpected rain. Quoting the waterproofing of terraces as a separate item completes the exterior work of a renovation.
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