Undercoat- yay or nay?

[Kelpie]

Just finished sanding down the hull ready for repainting with Toplac. Previous finish was also one pack, several layers by the looks of it. In a very small number of places the sanding has gone as far as the gelcoat. I'm happy with how smooth the hull is now and everything is faired and there are no steps or bumps that you can feel by hand.

I've already bought some tins of Pre Kote but I am having second thoughts about whether I should use it. I've got limited time, and a weather window of a couple of days starting tomorrow (boat is not under cover). If I go straight to the Toplac I can get two coats on this week and that's me done. If I use undercoat first, then I will likely have to wait till the next weather window to finish it. And of course I can sell the unopened tins of Pre Kote.

The boat is going to be up for sale as soon as I've finished tidying her up, so whilst I don't want to cut corners there is a need to balance time and cost with the quality of the finished job.

I had assumed that you really needed to use undercoat, but a recent PBO article suggested that it can actually cause the final paint job to be less robust, as the undercoat is softer and will allow more dings to appear. Hadn't thought about that.

So... what would you do??

 

[TopBanana]

I'd give the International tech team a call. They're very helpful

 

[FlyingGoose]

The undercoat is a tie to the top coat , as some paints do not like each other , if the other paint was one pack then I would see no issues , but there might be with the Gelcoat as the top coat might not stick so well, can you get away with priming exposed areas (gelcoat) and rubbing these areas down rather than the whole boat.

 

[burgundyben]

I'm doing a similar job, I am using the pre-kote.

what grade of sand paper have you used in your final prep?

I have used 600 grit wet or dry, I suspect I could get away without a pre-kote from the perspective of how it will look, but not the tie coat ability.

 

[PhillM]

Prekote every time. Not to is to bodge. Sorry!

 

[greeny]

Could be an expensive mistake in both time and money if the paint reacts or doesn't bond. Will need top coat removing then pre - kote then new topcoat. Ouch! See what the paint suppliers say but I'd be surprised if they give you the nod to do it without. It would put any problems firmly into their court.

 

[FlyingGoose]

Just to add another though process if you know the make of the original paint then you can see if your topcoat is suitable
When I was a lad working in the Car restoration buisness , in a respray one would not under coat or tie coat the whole car it would be rubbed down and parts undercoated were necessary , the key was to make sure the paint had a good key to hold , i.e clean, rubbed down, and cleaned with thinners , then the paint would adhere , not all car paints are the same , although based on the same principals, I can only asume that top coat paint (enamel) is the same .

 

[Kelpie]

Thanks for the replies.
The previous owner of the boat told me that he used Blakes/Hempel one pot polyurethane so I don't forsee any compatibility issues with putting Toplac straight onto that.
However in quite a few places I have had to expose the underlying layers, and in a small number of spots this goes through to the gelcoat.
So I think I will need to prime those areas at a minimum... and tbh I'm not sure that it's going to add all that much time just to cover the whole area, and at least that way I know it's done properly.

What about skipping the straight Prekote stage, and going straight for the 50:50 Prekote/Toplac? This would save me one coat and therefore one of my precious good weather days.

 

[LittleSister]

What about skipping the straight Prekote stage, and going straight for the 50:50 Prekote/Toplac? This would save me one coat and therefore one of my precious good weather days.

How many good weather days would you need if you found you had to strip back and do whole job again.