Have you just had a wall rendered, a new plaster finish done or a concrete wall poured, and want to paint straight away? It pays to wait. New render holds water and is strongly alkaline, and paint put on too early can blister, peel or end up with white stains. This guide sets out how long manufacturers’ data sheets and paint brands say to wait, what alkalinity means, what a primer is for and how to tell whether the wall is ready.
Updated on 4 November 2026. General information, not a substitute for a technician’s assessment. Always follow the data sheet of the render and of the paint you will use.
The essentials
- There is no single waiting time. For cement render and concrete, the sources we read point to about a month (Neuce: about 1 month; Dulux Australia: 28 to 30 days). For gypsum plaster the time depends on the product, thickness, ventilation and weather.
- Cement render starts very alkaline (pH 13 to 14) and only falls to about 9 after roughly 30 days (Sherwin-Williams). Dulux Australia advises against painting surfaces with a pH of 10 or more.
- An anti-alkali primer protects the paint but does not replace the wait. The data sheets say it helps prevent efflorescence, not that it removes the problem.
- Paint on a wall that is still damp is the classic cause of blisters and peeling. See also peeling paint and stains.
- If the wall keeps pushing out salt or stays damp after the waiting period, the water is coming from somewhere else. Find the cause before painting.
Why paint fails on a new wall
Fresh cement render or concrete has two things paint does not tolerate well.
Excess water. Mortar is mixed with water, and that water takes a long time to leave. Dulux Australia explains that moisture inside the wall dissolves mineral salts from the cement or plaster and carries them to the surface. When the water evaporates, white crystalline deposits are left: efflorescence. If paint is already on top, the water and salt push the film off and form blisters.
Alkalinity. Cement is strongly alkaline. According to Sherwin-Williams, fresh cement, mortar and concrete have a pH of 13 to 14 and take about 30 days to fall to about 9. The same source says moisture can reactivate the alkalinity and cause efflorescence, blistering and peeling. That is why “anti-alkali” primers exist: the Robbialac Primário Isoclassic data sheet says it protects the topcoat from alkaline substances in the substrate and makes efflorescence less likely.
On salt, see salt on walls.
How long to wait, by type of wall
| Wall | What the sources we read say |
|---|---|
| New cement render | Neuce, Primário Silicatus (edition of 23-04-2010): wait for the cement to cure fully, “about 1 month”. Dulux Australia: at least 28 to 30 days. Cited through a web search, not read directly: Topeca (Rebetop) gives 4 weeks and Dacar 28 days. |
| Concrete | Dulux Australia: the same as cement render, 28 to 30 days. The Weber weberdecor betão sheet (03-04-2025) gives 3 days as the minimum before painting that coating itself, not the concrete underneath. |
| Thin finishing coat over render | Weber, weberev liso (11-08-2018): minimum wait before painting 3 days, “may be longer at low temperatures”. It only holds if the render underneath is already cured and dry. |
| Gypsum plaster and stucco | The Portuguese data sheets we read give no figure. Barbot (GS Slim, ref. 8868) asks for dry walls and usual relative humidity no higher than 70%. British Gypsum (Thistle BoardFinish) says gypsum plaster must be thoroughly dry before decorating, though a coat of permeable paint can go on in the meantime. Dulux (UK) says new plaster can take up to 4 weeks to dry fully. Dulux Australia gives 10 weeks for set plaster. |
The gap is wide, from 3 days to 10 weeks, and depends on the product, thickness, temperature and ventilation. Do not pick the shortest figure just because it suits the calendar.
How to tell whether the wall is ready to paint
No Portuguese data sheet we read defines a home test. What the sources say:
- Ask the render manufacturer for the waiting time. It is the most reliable figure. Ask for it in writing, with the thickness applied and the date of the work.
- Moisture and pH checks. Sherwin-Williams and Dulux Australia talk about pH, which a technician measures with indicator paper. A moisture meter helps compare areas, but readings mislead on walls with salts (see salt on walls).
- Time, temperature and ventilation. Dulux (UK) says a heater or an open window can speed up the drying of plaster. Weber warns that its times lengthen in the cold.
- Signs it is not ready. White marks appearing, dust coming off when you rub the wall, patches that are damp or cold.
A home test with paper stuck to the wall overnight circulates on popular pages, but we found it in no data sheet or official source.
Primer: what to do before the paint
After the waiting period, the usual sequence is: remove dust, apply a primer suited to the substrate, then the paint. The data sheets we read:
- Robbialac, Primário Isoclassic (technical sheet CC-VIP 134 16.1, no date visible): water-based, anti-alkali primer for new render or plaster. One undiluted coat, touch dry in 1 to 2 hours and topcoat after about 2 to 3 hours at about 20 °C. Coverage 10 to 12 m² per litre.
- Dyrup, Dyprolite (technical sheet no. 798, December 2015): anti-alkali primer for masonry, concrete and plaster, indoors and out. Temperature between 10 °C and 35 °C and relative humidity below 80%. About 4 hours between coats.
- Robbialac, Primário Anti-Salitre 1K (11-03-2024): two coats, topcoat after 1 to 2 days. The sheet itself says it is not suitable for walls with condensation dampness.
None of these sheets says a primer lets you paint render that is still green. Silicatus requires cured cement render, and the others ask for sound, dry substrates. A primer is the layer that protects the paint from the alkalinity that remains, not a shortcut around the waiting time.
Some English-language pages talk about a “mist coat”, paint thinned with water, on new plaster. We found no Portuguese data sheet that prescribes it: use the primer the paint brand specifies.
If you have already painted and blisters or white marks have appeared
- Do not paint over again. Let the wall dry.
- For light efflorescence, Dulux Australia says to dry-brush and wipe with a damp sponge and 5% white vinegar in water. For severe cases it mentions a strong acid that only a professional should apply.
- The same source says efflorescence from residual moisture “will cease naturally” as the wall dries. If it carries on, water is entering from elsewhere: a leak, rising damp or condensation. See the types of damp.
- Scrape off loose paint, let it dry, apply the right primer and repaint.
Related guides
- Skim and fill walls before painting
- Cracks and plaster before painting
- Plasterboard: damp and painting
- How much paint do I need and the calculator
What we could not confirm
- An official Portuguese waiting time for painting new render. We found no standard or public body that sets one; the figures come from manufacturers.
- Drying times for gypsum and stucco, which vary between sources (4 to 10 weeks) and which the Portuguese data sheets do not state.
- The Topeca and Dacar sheets, which we only saw cited by a search engine. The Topeca server would not open.
- CIN data sheets and other primers with a waiting time for new render. We did not find them.
- A reliable home test for moisture or pH.
- Prices for render, primer or labour.
Sources (read on 4 November 2026)
- Robbialac, Primário Isoclassic, technical sheet CC-VIP 134 16.1 (use, anti-alkali, drying times).
- Robbialac, Primário Anti-Salitre 1K, sheet of 11-03-2024 (coats, times, condensation limit).
- Dyrup, Dyprolite, technical sheet no. 798, December 2015 (application conditions, drying).
- Barbot, GS Slim, ref. 8868 (substrate preparation, relative humidity).
- Neuce, A7 Primário Silicatus, edition no. 1 of 23-04-2010 (new render, cure of about 1 month, precautions).
- Saint-Gobain Weber Portugal, weberev liso, MOD.FT.141/01 of 11-08-2018 and weberdecor betão, 03-04-2025 (times before painting).
- British Gypsum, Thistle BoardFinish, Product Data Sheet PDS-109-02 (Decoration section).
- Dulux Australia, Efflorescence (causes, waiting times, pH 10, removal).
- Sherwin-Williams, Alkali burn (pH 13 to 14, about 30 days).
- Dulux UK, Painting on new plaster (up to 4 weeks for plaster to dry).
- Topeca (Rebetop Primário) and Dacar (technical bulletins), cited through a web search, not read directly.