OK to leave days between sanding and painting?

[Richard10002]

I've got 2 coats of undercoat on my roof and it needs sanding before the next coat, (havent decided whether to give it another coat of undercoat, or go straight for the topcoat, (International Interdeck).

 

If I sand it this afternoon, there is a chance the weather wont be right for painting over tomorrow or Saturday, in which case I would have to leave it to next Thursday earliest.

 

Is it OK to leave it sanded for a week before painting.... or should it be painted only a short time after sanding?

[kevinl]

I tried it and it didn't work, you need to sand then paint straight after a weeks worth of rain, dust and dirt means you'll have to re-sand if you do it now.

K

[bottle]

I think there is also a problem with moisture and undercoat absorbing it.

 

Then you seal that moisture in when you top coat and later it erupts with rust.

[Bloomsberry]

I didn't sand until conditions were ready to accept another coat as this removes any grime that has built up on the surface. If you sand then leave it a few days then wouldn't grime just build up on the surface again afterwards and you're faced with resanding it again ?

 

There is an opinion that this is not a good idea as the sanded surface stretches then gradually moves back to it's original shape, moving the new coat on top. I didn't experiance this although this is what the experts tend to recommend.

[Richard10002]

I suspected that a couple of days would be OK. As suggested, John Barnard in his videos recommends leaving a machine sanded surface a couple of days to "relax". But he is working in a temperature controlled environment, under cover, so I'm not expecting to achieve perfection.

 

I'm more wondering whether a week, or more, is too long, or whether, once sanded, its ready whenever you are.

 

More than a couple of days doesn't seem right.

[DHutch]

I think it depends on the surface you are leaving post sanding, and the conditions you are leaving it in.

 

- If your not going through the topcoat(s) and just giving it a light key then as long as you get it clean I cannot see an issue.

- If you are exposing bear metal, then it all depends on the paint system and primers etc you are using what they require.

- If your exposing undercoat then it somewhat depends on undercoat and the conditions between, etc.

 

Obviously it has to be clean, and taking the top off means it will be fairly clean bar the sanding dust, if you leaving it a week or two you would certainly then have to wash it throughly. if exposing bear metal unless deliberately waiting for a bloom of rust for your paint/conversion system to key to I would try and get something on it.

 

If the paint is spirit based or two pack (not water based) and its not the final coat, as long as the conditions are ok at the time of putting it on, if not much after, you should be fine if it is not dead hard when it rains.

 

Etc

 

Outdoor painting is never perfect, certainly not in the UK, but its done us perfectly find for the last 24 years of boating.

 

Having done two days of prep and priming on the areas needing it, I then put a key on the sound paint of the roof and top coated in all in one day, finishing in failing light. Three hours later it came on to hammer it down all night. The vents where off which got the inside (inc my bed) a bit wetter than ideal, but the paint looks great....!

 

 

 

Daniel