Re-painting my vessel

[trainingaid]

I own a marine ply boat (poxy painted outside, normal pain inside). I found that the inside normal paint (on the deck and hull) is coming away now and I want to re-paint with a sealant and gel coat to stop any wood rot.

I am about to start sanding back the old paint, I just don't know how much has to be sanded back before I can apply the sealant and gel coat.

Can anyone advise?

[PAR]

I'm not sure what you intend to use as a sealant, but only epoxy really works and if using epoxy, total encapsulation is the only way to truly seal wood.

To seal wood, you need to coat every square inch with epoxy, including screw holes, cut outs, notches, everything. If any portion of the surface is left without epoxy, then the wood isn't sealed and moisture content will rise and fall as required.

In other words, unless you can completely "encapsulate" the wood, then applying a "sealing" coat is a futile attempt. Naturally, you need to apply any coatings that will seal the wood directly to raw wood. Previously painted surfaces need to be sanded back to raw wood or you're not sealing anything but paint.

Paint usually peels for only a few reasons, most commonly because it's applied to a contaminated surface or is so old it's shrunk up considerably. In both cases the treatment is the same, remove the bad paint (scrape, sand, chemical stripper, etc.) smooth out the surface and then prep for a new paint job.

Painting is 90% surface prep and 10% actual brush in hand time, so get the prep right and most paint jobs look great, assuming you've don't use a whisk broom to brush it on.

To me, it sounds like you used good paint on the out side of the boat and not so good paint on the inside. Well, you've seen how this works out and this is typical of paint. Paint is one of those things you actually do get what you pay for. I have some paint just delivered here that's over $300 a gallon, but it's rock hard, dries very fast, leaves a very smooth finish, has very high gloss retention, is extremely durable, etc. At this price it better damn well apply itself, though it's just short of this, it's preformance as a coating is exceptional. On the other hand I could use paint that's $25 a gallon. Take a guess at how well the two might compare if used side by side.

In the end, scrape the interior of your boat clean of loose paint, sand and smooth out what remains, with proper surface prep for a new paint job. Use a few (at least 3) coats of good primer, blocking it down as you go, then a good topcoat blocking it down as you go if desired (at least 3 coats again). If you use a cheap paint, then don't expect it to hold up all that well, but if the prep is good, dry and clean, then it'll last a lot longer.