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Thread: primer

  1. #1
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    Default primer

    hello boat builders; i have a general question about primers. i seem to get two conflicting opinions about priming the boat. one camp seems the suggest that the primer gets almost completely sanded off, and it's essentially for filling the wood for adhesion to the paint as well as a better finish. The other opinion is that primer is to be applied, slightly sanded smooth, and then a second coat goes on ; and then the painting begins. Sort of applying the color coat over a smooth white canvas. Sanding is minimal.

    Teach me,

    David

  2. #2
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    Default Re: primer

    I'm sure there are those more experienced than I who will chime in, but my 2c worth is that the primer is what guarantees adhesion between the surface of whatever is being painted and the finish coats on top, so your second example is what works for me.
    There are high build primers which are sort of the last step in a fine fairing process. I am more familiar with using this kind of primer on vehicles to remove any slight scratches from coarser earlier sanding. These are sanded down with very fine papers to a virtually perfectly smooth finish. In the automotive context any actual finishing and smoothing has to be done first, as high build primers dont fill blemishes, they just fill already fine sanding marks.

    Painting is a system, the correct ingredients and processes should be used as defined by the paint manufacturer.
    There is nothing quite as permanent as a good temporary repair.

  3. #3
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    Default Re: primer

    I may be wrong, but it's both and it depends on the type of finish you are going for. Primer does both of those things you mentioned. It adheres well and can fill. Certain colors dont cover very well and can appear splotchy over a mottled surface so by giving the boat a smooth single color surface, you get a prettier topcoat.

  4. #4
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    Default Re: primer

    Question is too general to be answered. What is the surface / material being primed and painted? Is "the boat" covered in epoxy? Solid wood of what species and grain orientation? Ply of what type? Stored and used how? What sort of paint??
    "The enemies of reason have a certain blind look."
    Doctor Jacquin to Lieutenant D'Hubert, in Ridley Scott's first major film _The Duellists_.

  5. #5
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    Default Re: primer

    marine ply, sealed with total boat penetrating epoxy, then primer ( kirby) and then top coat ( kirby as well) thanks!!

  6. #6
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    Default Re: primer

    If youre going to use Kirbys, call them and tell them your plan. They are very helpful and will not steer you wrong.

  7. #7
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    Default Re: primer

    Quote Originally Posted by dposner View Post
    marine ply, sealed with total boat penetrating epoxy, then primer ( kirby) and then top coat ( kirby as well) thanks!!
    As above Kirby's will give you excellent advice. From what I know, if the epoxy is fully cured and well-cleaned of any possible blush (waxy coating), there is no need to use primer as good paint will bond very well to the epoxy surface. If you're using a high-build primer to level & smooth the surface then just follow the instructions on the can. Best of luck with your build!
    "The enemies of reason have a certain blind look."
    Doctor Jacquin to Lieutenant D'Hubert, in Ridley Scott's first major film _The Duellists_.

  8. #8
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    Default Re: primer

    I use lots of Kirby's. You can't go wrong calling them. Over epoxy sealed ply, I'd make sure the epoxy is well scratched and leveled, no raw wood, and use the primer. I have not personally had a problem with Kirby's, no primer, over epoxy so long as the sanding was 80# but I believe you can get a nicer finish with somewhat finer sanding and then primer.

    Questions I'd have for Kirby's with what I happen to believe based on experience but not based on talking to Kirby's:

    Are there epoxy formulations that are not compatible with Kirby's? --- No idea.
    Does one need to give time for the epoxy to be very well cured? --- Yes. I give about a week in good weather.
    Should the amine blush be washed away before sanding? --- Absolutely. There are non-blush epoxies but I'd wash anyway.
    What's the best weight of sandpaper to use as last scratch before priming? --- For paint I rarely sand finer than 80# but perhaps the use of primer will allow finer.

    Just to add though not the OP's issue, on dimensional wood, I just thin the Kirby's for first coat. That has worked very well for me on both new and old boats. On old boats, if the sanding has not gone to bare wood, I just paint. If I've sanded to bare wood in spots, I spot prime with thinned Kirby's and then paint the whole.

    G'luck

  9. #9
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    Oct 2010
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    Default Re: primer

    According to Geoff Kerr in his Caledonia Yawl build video series for Off Center Harbor, modern paints do not need primers for adhesion. So his position was that a primer is primarily to fill pin holes and little low spots, and it is fine if you sand most of it off.

    On the other hand, the Epifanes tech guy taught me that, unless the sub-surface is one consistent color, some paints and some colors, including the deep red I used, won't cover very well. After my 1st coat failed to cover my many-colored sub-surface, I had to re-prime the whole boat and start again. And it made a huge difference. So there's that as well.

  10. #10
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    Default Re: primer

    Just a guess: What does the can say to do?
    Last edited by pcford; 05-08-2019 at 03:03 PM.

  11. #11
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    Default Re: primer

    Point of order: He said "penetrating epoxy". Their brand is up to about 60% diluted with alcohol and solvents, so it's basically a CPES clone, not real epoxy resin. If the surface is smooth and you aren't looking for filing capabilities, that stuff may be a better primer than paint primer in terms of paint adhesion. If it is fir ply, it may retard the eventual checking to some extent, but it isn't likely to stop it forever.

  12. #12
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    Default Re: primer

    thanks so much for responding

  13. #13
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    Default Re: primer

    thanks your comments are always superb!

  14. #14
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    Default Re: primer

    i did and george kirby was very helpful. turns out you have to thin the primer a great deal and also use penetrol; and then get a good coat smooth coat on.

  15. #15
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    Default Re: primer

    If you are using oil based paints such as those sold by Kirby, primer is nothing more than a quick method of filling the grain of the wooden planking, if you are doing bare wood topsides. The time tested method of application is to apply as many thin coats of primer as it takes to fill the grain.
    This is normally done by applying paint that is put on with no sanding between coats. Adhesion is created by the fact that the primer is not fully dry before re-coating is done. This will give a smoother job than two coats of primer out of the can which it will also take a long time to dry before sanding can be done. Only enough sanding is needed to produce a smooth surface, with a tooth, to be then painted with two gloss coats. Normally glazing compound, if needed is applied after the first gloss coat is applied.

    An alternative is to use no primer at all on bare wood. This wil allow the gloss enamel to penetrate deep into the wood and create a better bond than the primer produces. However, this method requires multiple coats of enamel until the grain is filled. Primer just makes the job go faster but it is often prone to blistering on hot days if it is not allowed to dry enough before sanding and top coating with the gloss enamel.
    Jay

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