Another paint query, how long between coats?

[bluey]

Hi,
I'm painting a boat hull with 2 pack polyurethane paint. The boat is under cover, in my workshop out of the weather. I have prepped the hull, applied two coats of 2 pack undercoat and have sanded and washed it all down with acetone so I'm now all set to apply the first layer of topcoat. Problem is the weather has turned against me, a low pressure system has moved in and this has raised the humidity in the air. The temperature today is ideal but the topcoat MDS says don't paint if humidity is too high so I am thinking of waiting a few days for the weather to clear. My question is - how long can I wait? Is there a window of time in which you have to paint over the undercoat to achieve proper adhesion? The undercoat MDS says it fully cures in 7 days.

Thanks,
bluey.

 

[GT1000000]

Re: Another paint query, how long between coats?

Hey bluey,
You have to go by whatever the paint system you are using says is OK...if the undercoat/primer says it fully cures in 7 days and you need to wait longer, you will probably have to lightly sand it to open up the pores again so you get good adhesion with the top coat...
Give us the details on the paint, manufacturer, type, etc...and maybe we can look up all the pertinent info and see what the manufacturer says...

 

[bluey]

Re: Another paint query, how long between coats?

Hi Captain,

Paint is -
Forminex Supergloss Polyurethane

The recommended undercoat is -

Forminex Universal Undercoat

I think this brand is only available here in Australia. I have read all the data sheets for the product but they only mention recoat times (8 to 12 hours). No mention of how long you can leave the undercoat exposed for.

Cheers,
bluey.

 

[zool]

Re: Another paint query, how long between coats?

If youre out of the recoat window, it means you lost a chemical bond, so you need to scuff the surface, to get a mechanical bond to the primer...probably better to wait for proper conditions and sand...if the humidity fouls the topcoat, youll be sanding anyway...and cursing

 

[Scott Danforth]

Re: Another paint query, how long between coats?

you have already sanded. so your good. the recoat time is for chemical bond not relying on sanding.

 

[Tail_Gunner]

Re: Another paint query, how long between coats?

I am assuming its a good quality two part poly..if so the humidty bar is generally 70%. I use a interlux product and actually wet sand the product 24 hours after application using 600 grit...Done it twice now with no ill result's.

http://www.shipways.com.au/documents/ForminexSupergloss_000.pdf

Looks like 80% humidty

 

[bluey]

Re: Another paint query, how long between coats?

I rang the dealer today for advice on this matter and he said pretty much the same thing. Don't paint if humidity is high and there's no maximum limits on the length of time between u/coating and topcoating, but it will need a light sand and solvent wipe before proceeding.

Thanks to everyone for replying to my thread.