Varnish Troubles.

Builder's Forum
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Hi -- I'm having some varnish troubles, and looking for some advice.

Here's the story.  I mostly built a Shearwater Sport a couple years ago - got all the way to the varnish stage -- (hull has been sanded to 220+)  Life got busy and I was intimidated by the varnish and the project got put on the backburner.

Fast forward to recently and I decided to finish the project.  I decided to try my hand at varnishing the interior of the cockpit to gain some experience.

I began by sanding the cockpit with 220, then vacummed and wiped the interior with denatured aclohol.

I'm using Schooner Gold Varnish, but couldn't find any of the listed reducer (Brushing 33??) locally.  I read that people had success using mineral spirits, so I reduced the varnish with that.  At the time I didn't think about it, but I probably didn't totally understand the "recuce by 50%" -- I mixed up a 1:1 mixture or varnish and mineral spirits, and applied this coating to the cockpit.  At this point I thought things were going great, and didn't know why I had put the project off for so long.  I came back the next morning and things seemed fine.  The varnish was dry.  It had a satin look to it, even though the varnish finish is gloss, but I attributed that to the very thin mix.

I had some of that varnish mix left, so I did some math and added the correct amount of varnish to make this mix now 2:1.  I lighly sanded with marron scotch brite, vacuumed and wiped down again with denatured alcohol.  And I applied that mix.  Again, it went on great, no issue.

Here's where it starts to unravel.  Next day I go back for a third coat and notice that the second coat is ever so slightly tacky.  Not sticky - nor do finger prints leave permanent marks, just like a bit sticky -- like a cheap sticker, so to speak.  I probably should have stopped at this point.  But I didn't.  Same routine - light sand with marroon scotch brite, wipe down and application of mixture, although this time I used a 4:1 mix.  Again great application, no sags or runs... 

I return the next day -- same tackiness.  This time I decide to ask here on the forum prior to proceeding.

A few other facts - that I know are relevant.  The shop is approx 22C in the morning when I applied and max 24-26C in the afternoon.  Not massively humid, but its not desert dry either.  There has been 20-36hrs between coats.

Any suggestions -- help -- advice?  This isn't giving me the confidence I wanted for the exterior of the hull.

AHH!!!!

Thanks in advance -- Dave.

 

 

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   I'm not sure I have the answer, but do have some suspicions and suggestions. Your mineral spirits might be the culprit - either some contamination or a very "thick" blend - low volatility.  You might do a test piece somewhere with a different thinner and see how things go.  And BTW - unless coating raw wood where I try to get the first coats of varnish to sink in, I don't think I've ever thinned beyond 10-15% when varnishing over epoxy.  Sometimes no thinning, some times just a bit of thinner if things (temp/humidity) are causing things not to flow so well when brushing. I did look up the Schooner instructions just now and see that you've followed their guidelines, but for "previously unvarnished wood."  Varnishing over epoxy doesn't qualify for the previously unvarnished thinning down to the 50 and 25% recommendation.

Meanwhile, perhaps due to the low volatility or due to temperature/humidity (especially with your fist coat being overnight) I think you aren't getting a varnish coating that is dry/hard enough to support second (and third) coats.  And once you overlay a non-dry coat with another (and another) coat, drying time goes up significantly for all coats. 

Your options are to find a solvent (paint remover or similar) that will soften what you've put down and allow you to wipe it all off, then start again -

or, try to get the boat out in warmest, sunniest location (u/v helps) possible for long enough (could be a couple of days) to get what you've laid down really hard and dry, then proceed as per normal with subsequent coats.  I think this is the option I try first; some patience.

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So -- Thank you so much for the advice and likely analysis.

Some time has passed and I think there is some progress.  I wasn't comfortable leaving the boat outside as the weather around here can be quite unpredictable this time of year, with local thunderstorms.  Instead I turned the boat upside down on some sawhorses and place my halogen work lamp to shine into the cockpit.  My thought was this would add some heat, like a sunny day.  I left it like this for two days, then I shut off the light and left it for another 16hrs.  This morning, it was dry in most places.  The hip boards/braces, were just ever so slightly tacky -- but way less than before.   This leads me to believe that I just need to wait some more and I'll get a full cure.

In the meantime I mixed up some epoxy and made a few repairs to the deck of the boat.  I have purchased some new mineral spirits and I'm going to mix up some 10% reduced varnish and try that on the hatch lids to see if I get a complete cure in 12hrs.

Thanks again for the advice -- I do think it was likely old mineral spirits -- that the lid may have been off the bottle for some time allowing for the reduced volitility. (My fault this time..)

Dave.