Clear coating wood gunwales

Discussion in 'Wooden Boat Building and Restoration' started by johnnythefish, Jan 8, 2023.

  1. johnnythefish
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    johnnythefish Junior Member

    I have a stitch and glue center console with mahogany gunwales that I built. I covered the mahogany with with Gurit SP115 epoxy resin which is supposed to have some UV protection in it.

    I then sprayed 3 coats of De Beers MS clear over it. This is an 2k automotive clear coat and from my understanding is the best UV protection in a clear coat that is locally available.

    It has lived in a covered shed for a year and a bit now, but the boat itself does not have a cover - so light can get do it - though not direct sunlight.

    We live in the tropics in East Africa. Marine paints/ varnishes are limited here.

    Boat has spent maybe 6 weeks actually on the water in direct sunlight.

    I have now noticed a whitening/ change of colour on the gunwales.

    A few thoughts/ questions:

    1) This seems like a pretty short time frame for this to start happening?

    2) Could I delay further damage with more coats of MS De Beer clear? This would be possible, but the coating is expensive and would need to me masked, taped and sprayed.

    3) Leave as is and when finish looks truly awful, sand it back to bare wood and do something different…

    Here I am open to suggestions? The same clear coat without epoxy underneath, or a brushed varnish of sorts?

    I am torn between trying for something that lasts much longer between repair and something that is easy to touch up/ maintain regularly but easily.

    We can get a product here called Woodoc 50.

    I had initially used the epoxy undercoat so that the wood would remain stable. But if a good brushed varnish / oil Fishinh will achieve this I would be happy with the option as well.

    Here are some images:

    [​IMG] [​IMG]
     
  2. Rod Tait
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    Rod Tait Junior Member

    Not familiar with those products, but my guess is the epoxy had blush. So question is about amount of blush that particular epoxy gives off and what prep was taken to make sure it is all clean before varnish went on.
     
  3. johnnythefish
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    johnnythefish Junior Member

    I wondered about that - can blush occur a long time after application? This is occurring nearly a year after the epoxy and clear coat were applied - and it seems most concentrated on areas more exposed to sunlight?

    The clear coat was applied at least a week after the final epoxy coat. Which was washed and fine sanded
     
  4. Rod Tait
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    Rod Tait Junior Member

    blush absorbs moisture and that is what turns it white over time, so still that is my guess. I know of a person who built a beautiful cedar strip kayak and put a thousand hours into inlays and then used a blushing epoxy and did not prep it well. 6 months in, it was almost all white everywhere.
     
  5. johnnythefish
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    johnnythefish Junior Member

    Please can you elaborate on the “not prepping well part”?

    I will note that the boat was sprayed in a fairly humid climate
     
  6. Rod Tait
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    Rod Tait Junior Member

    Normal procedure is to wash well with soap and water after fully cured, then sanded for varnish. Again not familiar with that brand of epoxy, but only use non/bushing epoxy for clear coating. The faster the cure, generally the more the blush as more amines help cure faster.
     
  7. fallguy
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    fallguy Senior Member

    So odd, on closer look, it almost looks like the clearcoat magnified all the surface problems. I think I see the sanding that was done.

    I'm less certain it is blush and more wondering if this is uv chalkout.

    I tried to see if the topcoat had any uv protectant and was unable to see that on quick reviews of the datasheets.
     
  8. Blueknarr
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    Blueknarr Senior Member

    I think the problem lies in the epoxy so additional clear coats will NOT help.
    A few questions
    Was every coat of epoxy de-blushed?
    Was the mahogany fully encapsulated including the underside?
    What was the moisture content of the wood when epoxied?
    How many coats and thickness of epoxy?
    What different procedure was used on the rod holder pads?

    I believe that heat from sunlight is vaporizing water from within the wood. The water vapor is starting to blister the epoxy away from the wood.
    The rod pads contain less moisture to vaporize, therefore are not affected.

    Only cure is to remove all the finish fully dehydrate the wood and start over ensuring that no vapor can enter from the backside.

    Traditional varnish is far easier to touch up than any catalyzed clear. It will seal those csp rails just fine without epoxy. The longer the contact with standing water - the greater the need for epoxy. Incidental momentarily splashing doesn't need epoxy.
     
  9. johnnythefish
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    johnnythefish Junior Member

    Thank you to everyone who has responded… I am most appreciative.
    In answer to some of the questions and some further thoughts…

    1) Gurit is a well know international brand of epoxy and I have written to their technical department for their thoughts.

    2) Epoxy coats were either washed and sanded between each coat - or applied whilst still within the “chemical cure” window.

    3) Washing and sanding was done prior to clear coating.

    4) @fallguy … well I guess boatbuilding ain’t for sissies!

    Would you recommend more than 7 days cure for an epoxy before a clear coat?

    5) @Blueknarr where I live is humid - so obviously Mc is hard to get right down - but we were as diligent as we could be. To the point where the boat and the mahogany lived under a plastic sheet with a dehumidifier on days before we coated the wood. The wood was heated with a heat gun before applying the resin to prevent out gassing. I cannot swear that the Mc was below 10 as I think most ambient wood (in the workshop) measured was about 12%. We certainly tried quite hard to only coat wood that was below 10% quickly after the tarp came off.

    6) I now recall that almost immediately after the console was coated and painted it had some of these “white blemishes” - I am beginning to think that these were definitely caused by some sort of outgassing. I remember the console was coated in the morning - and we did not heat the surface with a heat gun before coating (because there was paint on the underside) so it’s quite possible that rising temperature during the day caused more significant outgassing than on the gunwales.

    7) The vertical wood transom portions and a thin wood veneer on the side of the boat don’t seem to have this issue so far. These veneers were thinner and are vertical.

    8) Sunlight/ heat is somehow playing a part because the parts of the gunwale that are most hit by sun in the shed are worst affected.

    9) The covering to the locker at the back (where you see the black downrigger mount) is SP115 only - no clear coat. If this was UV damage I would expect this to look the worst - not the best of everything!

    10) The gunwales are fully sealed/ encapsulated all round.

    I am assuming in short the reality is that without stripping I will have to live with it for now as an overcoat won’t make the white go away - but the question is - do I re-clear coat the transom where it is as yet unaffected - on the assumption that this is some sort of UV damage.

    That is the big question - is this UV damage or just the heat of the sun causing gassing/ vapour that was trapped in there to show up!
     
  10. fallguy
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    fallguy Senior Member

    I think outgassing would result in surface deformation through the clearcoat. And blush would result in total failure or delam of the clearcoat.

    This looks more like UV chalkout of epoxy which means the clearcoat does not protect as well as you expected as applied.

    Consider I have brightfinished a boat with mahogany gunwhales!

    My decks and topsides got 15 plus coats of varnish brushed on, sanding after about each three. My hullsides got 8 coats of varnish.

    I am quite certain I got up to around 20 coats on the decks and gunwhales.

    The product I used was Epifanes Wood Finish Gloss.

    Just based on the mil variation between what I did for Minnesota which is not a high sun climate and what you did for Africa would suggests the mil thickness you applied was insufficient for conditions.

    I cannot tell you with precision my final mil thickness vs yours, but it is considerable. I cannot tell you with certainty the UV protection from my product versus yours, but since the product I used is not clear; I'm guessing it is better.

    The way the debeer is used is over a paint that is inherently more uv stable than epoxy.

    My final assessment is the debeer was applied too thin and is not an ideal coating versus say 20 coats of epifanes.

    In your conditions; you should expect annual maintenance on the finish which would be sanding the existing finish with maybe 220-400 and then a single or two coats of new finish. (Epifanes). You decide how many coats based on how much sanding, so if you banged it up or it was very sun faded and sand with 220 a lot; you may do more is all, but say 320 grit, a single coat would be okay..it all depends on grit progression and your final desire, so bad fade 220, three coats, sand 320 and a fourth or light fade, sand 320 one coat, etc

    When you are ready to repair, sand it all to wood, remove the epoxy, and get as many coats as you can of a spar varnish on. I like to apply 3 coats and then sand it back to dull and continue. Avoid seeking perfection, what you want is build. So, for example, if you get a fly or large dust nib, sand it, but do not attempt to make it perfect. After the next 3 coats; the flaw will start to get buried in the finish, and disappear. When you get to a good build for sun protection; you can sand a little nicer with 320 or 400 and do a single coat for the final instead of the 3 times and getting dust each time.
     
    Last edited: Jan 9, 2023
  11. fallguy
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    fallguy Senior Member

    I did check the debeer datasheet and debeer says 36.9% solids.

    So, if you sprayed a light coat to start at 2 mil, then a heavy at 3mil, then scuff sand, then a 3rd coat at 3 mil, you would end up at 8 mils @37% or 2.96 less a tad for scuff, call it a finished dry film of 2.5 mils.

    Compare that to Epifanes which has a dry film of 1 mil. If I applied 15 coats and sanded after each 3 or so, I would end up with a 15 mil thickness less sanding say 3-5 mils or a 10 mil thickness. So, my topsides were at a minimum 4 times thicker on the material alone.

    And the stuff has UV protection which may be higher..
     
  12. johnnythefish
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    johnnythefish Junior Member

    All this is very interesting.

    There certainly seems to be quite a difference of opinions over whether clear coating epoxy is a good idea or not!

    You may enjoy a post from a Service Manager at San Juan Yachts over at the wooden boat forum on this subject who describes how their clear coating of west epoxy would give their yachts “3-4 times the normal varnish schedule”…

    In any case I suspect I shall just use her till she looks very tatty and then decide how best to solve the problem next time… I would rather be fishing than sanding at this stage!
     
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  13. Blueknarr
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    Blueknarr Senior Member

    Automotive clearcoats are ment to be applied over automotive paints witch have little need for additional UV protection. Therefore automotive clearcoats have little UV inhibitors in their formulations. Certainly not enough to provide the UV protection that epoxy requires.

    On handrails there is little need for epoxy as a water barrier.
    BUT a base coat of epoxy could provide safety insurance against abrasion. In that anything could scrape away the varnish top coat but leave the epoxy base intact.
    However all clearcoats will eventually need to be replaced. Removing an all varnish system is easier than removing an epoxy/varnish system.
     
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  14. fallguy
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    fallguy Senior Member

    While I agree the epoxy gives some protection as a sealer, the thing I discovered is wood that gets wet turns dark. Not really rocket science, but easy to spot abraded varnishes or even damaged glass and epoxy. A dark spot tells the captain to get fixin..
     
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  15. johnnythefish
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    johnnythefish Junior Member

    [​IMG]
    Are you sure this is correct?

    I am not discounting the fact that maybe they aren’t designed to be applied to epoxy over wood; or that this is a pain to remove/ maintains - but from what little research I did automotive clear coats are meant to have quite good UV inhibitors and are designed to protect the paint beneath them.

    When I spoke to a technician at one of the paint companies here, he was adamant that a 2 part automotive clear coat had much better UV resistance than all of their best varnish systems.

    In my particular case, what leads me to wonder whether this is UV damage or something else is the fact that the rearmost piece of wood in the picture below (the paler wood) is only SP115 epoxy resin - no clear coat.

    I would have expected if it was UV damage the uncoated epoxy would have shown whitening as well?

    My other suspicion that this may not be UV damage is that there was whitening in small places on the console almost immediately after spraying.
     
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