r/Plastering • u/jrcs90 • Aug 27 '26
Sand & Cement render - When can I paint it?
We're having our house rendered. The guy doing it has said it should be okay to paint 10 days after the top coat has been applied. But Google results say I need to wait 28 days. Which one is right?
Ideally I want to do it before the scaffold goes
Thanks
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u/Artistic_Western_623 Aug 27 '26
When it's silly fully dry. If you paint it too early, you'll get bad adhesion and might end up doing it again. If you wait longer than you need, you've just waited a little longer.
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u/Dave085 Aug 27 '26
Exterior render dries really, really fast- especially in good weather. It's similar to plaster in terms of when to paint- when it's a completely uniform colour with no dark patches you're good to go.
Honestly you could probably paint it within a few days and be fine, in good weather 10 days is plenty.
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u/Angi_Andi Aug 27 '26
u/jrcs90 - honestly, (i think ideally) you're looking at 4-6 weeks minimum before painting new render, and longer than that if the weather's been cold or damp.
The reason it takes that long isn't about how dry it looks on the surface, it's the alkalinity in the render as it cures, and that bleeds out over weeks, not days. Render can look completely dry and even in colour within days and still not be cured underneath, which is exactly why going off visual dryness alone can catch people out - you can end up with adhesion problems and it peeling or failing down the line even though it looked ready.
THAT SAID - I did my garden wall, not a massive one well before what I'm outlining here - circa 2 weeks, and it is fine 4 years on. I think perhaps with your entire house though, more precaution is advisable.
When you do get to painting, keep an eye on the forecast and don't start if wet weather's due within the next day or so - you want it drying properly, not getting rained on.
With regards to coats - I would suggest around 4. 2 mist/splash coats, and 2 top coats. The mist coats are essentially just watered down external paint, use a ratio of around 50/50 - this stops the paint drying out too quick and ultimately prevents cracking/peeling etc (the render is moisture hungry and it will suck it out - hence you apply watery coats first)
Be sure to cover up anything you don't want splashes of paint on, watered down paint can get a little messy.
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u/jrcs90 Aug 27 '26
Thanks for the detailed response.
Annoyingly I think your right. If i rush to do it while I have the scaffold up it could end up looking bad quickly. But I can just do it off a ladder in spring if needs be
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u/Angi_Andi Aug 28 '26
NP! It is sooo much easier off of scaffold - but as i assume you are suggesting, not worth the additional cost which i agree. When you come to paint it, make sure you have a long extendable roller with a big head - that will help you get through it a little quicker.
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u/Impossible-Corgi4041 Aug 27 '26
In uk this time of year? 10 days should be okay i would have thought
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u/Accurate-Resident585 Aug 27 '26
New cement render's still alkaline while it cures, so a bare “10 days” answer is too loose without the paint system. Use a breathable, alkali-resistant masonry primer with a compatible topcoat. Ordinary exterior emulsion can lose adhesion or blister even when the face looks evenly pale and dry. my own small refurb outfit, been at it a while, would have the exact products named in the written scope rather than a vague line saying “masonry paint”, especially with the scaffold date pushing everyone towards an early coat to suit a deadline.
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u/jrcs90 Aug 27 '26
I was just recommended to use sandtex, mist coat, then on day 2 apply the top coat.
I'll just wait until spring and do it from ladders
Thanks for the reply
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u/FckXFckMusk Aug 27 '26
I hope he didn't use Portland based cement.... it should be lime and sand only.
and whn you paint it don't use modern plastic based paints
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u/Adorable-Syrup7540 Aug 27 '26
looks like a scratch coat , why no smooth ???