ᐅ Questions About Painting the Facade of an Older Building

Hello everyone,

I have a few questions about painting a façade. It’s an older building with an exterior plaster surface, and there is already an old layer of paint on it.

1. Should the surface be primed before painting? How long does the primer need to dry before you can start painting?
2. I read somewhere that you can mix the primer directly into the first coat of paint. Is that correct, and does it work? What would be the recommended ratio?
3. How many coats of paint are generally needed? I have seen some sources recommend three coats, but are one or two enough?
4. How long should a coat dry before it rains? Should painting be timed according to the weather? Or is it okay if it rains, for example, 1–2 hours after painting—does that damage the paint?

Thanks in advance,
Best regards

Does no one have a plan?

1. I was wondering why I applied primer... but I would probably do it again since it’s common practice, simply paint the next day.
2. I would skip that, it usually just causes trouble in the end.
3. One coat of primer, then it depends on the paint. We had a silicone-based one that covered very well, and one coat was enough for us.
4. Our paint dried to the touch quite quickly, in less than 30 minutes. But if I knew it would rain in 2 hours, I would do it another day. Although it might also work.

I would just prime on the first day and paint the next. It’s annoying to paint twice, but since you usually don’t do it that often, it’s manageable. I would also avoid mixing primer with paint or other time-saving tricks that a non-professional might not get right in the end. Sometimes you just have to accept that you won’t have much fun for two days.

Keytix schrieb:
1. Should this be primed before painting? How long does a primer need to dry before you can paint?

Yes, it should be. The drying time is usually indicated on the container.

Keytix schrieb:
2. I read somewhere that you can mix the primer directly into the first coat of paint—is that correct and does it work? What would be the ratio?

That would be a special type of paint.

Keytix schrieb:
3. How many coats should generally be applied? I’ve seen some sources recommending three coats—is 1 or 2 enough?

Our old house was repainted as needed, roughly every 8 years: primer plus one coat of white paint on top.

Keytix schrieb:
4. How long does a coat need to dry before it rains... should you time painting according to the weather? Or does it not harm the paint if it rains, say, 1-2 hours later?

Yes, it does harm the paint. You should definitely check the weather forecast beforehand, as rain can wash off the paint.

Basically, your questions depend on the specific paint you choose.

A primer is often necessary if the surface to be painted is porous or sandy, or for other reasons does not hold paint well. This can also apply if a different type of paint was used before—for example, if there was a costly lotus-effect paint before and now you want to switch to a conventional one.

I wouldn’t just buy paint at a general hardware store. It’s better to buy from a professional painter’s supply store, where tradespeople purchase their materials. They can give you advice on paint selection as well as how often to paint.

There are always new products on the market designed to save time, but these don’t necessarily perform as well as traditional methods.

Edit: It is important that the plaster is intact and there are no major cracks.
If needed, tap off and repair the plaster locally (don’t forget to apply primer afterward).
Small cracks can be filled with a special paint or primer.