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PostPosted: June 26th, 2007, 3:19 am 
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Location: Kitchener ON
I recently edged my paddle with fiberglass using a west system patch kit. After it was all done, I lightly sanded the rest of the blade and gave the whole thing another coat of varnish.

Two weeks later there is still a slight tack to the varnish where it contacted the glassed area. I figured that the epoxy would be pretty inert after it cured (I waited about a week before varnishing). Was I wrong?

Fred


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PostPosted: June 26th, 2007, 8:07 am 
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You may have experienced "amine blush". When topcoating epoxy, you need to let it cure two weeks, then remove the amine blush by wet-sanding, washing with soapy water, etc. before painting or varnishing.

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PostPosted: June 26th, 2007, 11:05 am 
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fredk wrote:
I figured that the epoxy would be pretty inert after it cured (I waited about a week before varnishing).


Hi Fred,
As Dan stated, it could have been an blush problem. I gather that the amine blush is a byproduct of the chemical reaction during curing which results in the waxy blush to be deposited at the surface. Aside from the amine blush, my understanding is that epoxy that is not sufficiently cured can cause the a very slow varnish cure and 1 week may not have been enough time before varnish. Epoxy can take months to fully & truly cure, but normally I think a couple of weeks is good for varnishing.

What temperature was the paddle stored at while the epoxy cured? What epoxy was used? What hardener? What temperature has it been kept at while the varnish cured?

The above questions all relate to the amount of amine blush that may have occurred, and the speed of curing. For more on epoxy & varnish, try posting over at the Bear Mountain Boats forum where those with a lot of experience (i.e. others who've already been down the same road as you) will be able to chime in with some resolutions.

Given the time of year, you are probably ready to use the paddle. One resolution may be to use a varsol-type solvent to wipe off the uncured varnish, just at the tip. Maybe you can just scrape it off. Don't use acetone as it will react with the epoxy. Then make sure you get rid of that amine blush by washing well with soapy water. I would then probably leave it at that and head out for the season of paddling. In the fall, sand the blade lightly and give it a coat or two of varnish and give it some time to cure before putting the paddle away. Spar varnish is slow to cure and if you do it now the varnish will be pretty soft and susceptible to damage for a couple of weeks, hence the reason I suggest waiting until you don't need the paddle for awhile before re-varnishing.

Cheers,
Bryan

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PostPosted: June 26th, 2007, 12:23 pm 
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What you have seen is strange, at least to me. The normal finish over epoxy is a spar varnish to provide UV protection. In other words you did the same thing I've done many times. I won't say that the reaction isn't related to an amine blush, but that is usually a consideration when applying more coats of *epoxy*, I've never worried about it when applying varnish over the epoxy.

On a side note - once the epoxy has cured, it is safe to wipe with acetone, the acetone doesn't react with the cured epoxy even though it is the solvent used to clean up when working with uncured epoxy.

Are you sure the epoxy was fully cured before you varnished?

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PostPosted: June 26th, 2007, 12:47 pm 
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Thanks for the replies. I don't know what type of epoxy it was other than west system. It was a fast curing epoxy, ~ 15 minute working time.

Because it was fast curing, I ended up with a rather thick coat of epoxy which I dry sanded a LOT (too much in places). I wiped down with a tack cloth between sanding. Would this have been enough to remove the blush?

Looks like I will have to remove the varnish from the epoxy for now.

I will probably sand off the epoxy fiberglass completely this fall and try again as the first go was not a very good job. This time around I want to use a less vicous epoxy with a longer cure time so that I add the minimum of material to the edge of the paddle.

Fred

P.S. I'm glad I am learning all this on a cheapy paddle rather than while building a stripper.


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 Post subject: blush
PostPosted: June 26th, 2007, 1:58 pm 
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You had blush. Sanding alone will not remove it. After epoxy cures you need to wash it off with a weak ammonia solution, a rough pad (like scothbrite) and water, let throughly dry and then sand.

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PostPosted: June 26th, 2007, 2:42 pm 
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Thanks for the correction regarding acetone & cured epoxy.

To make things easier for next time make sure the paddle, resin, hardener, and work area are all warm. Warm epoxy will go on much easier. If you are using glass cloth the lower viscosity of warm epoxy will wet out the cloth more readily. Warm it for a time under a light bulb, on a heating pad, in a warm sink, etc. and make sure the surface you are applying it to is also warm. Also, cool curing temperatures can cause amine blush, the degree of which depends also on the hardener used (I don't remember, are the fast curing hardeners more susceptible to this or less?).

For some reading on epoxy and temperature, go here.

Paddles & canoe repairs are where I practiced with epoxy before building my kayak. Still lots to learn of course.

Cheers,
Bryan

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PostPosted: June 27th, 2007, 3:09 am 
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Thanks again for the replies. The temperature would have been in the low to mid 70s so this should not have been an issue.

Something occured to me at work earlier. I applied another light coat of epoxy 3 days before coating with varnish and I only did a light sanding before applying the varnish. Live and learn.

Fred


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PostPosted: June 28th, 2007, 12:00 pm 
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It was that second light coat that got you.

Humidity and temperature affect the "degree" of blush caused during cure. As does the resin choice.

I'd say just use a scraper to clean off the excess material and use it for the season as it and redo it in the fall...

The epoxy will be plenty durable for a season without varnish. Even in full sun all day. It may go a bit chalky by season end but you'll remove that when you redo it.

As for cleaup of epoxy a safer and less toxic method of cleaning uncured epoxy is with ordinary white vinegar. Much less "unhealthy" not to mention cheaper. Just buy your own bottle so you don't contaminate the "kitchen" vinegar.

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PostPosted: June 28th, 2007, 2:04 pm 
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I've been cleaning my epoxy brushes with white vinegar. Jst a heavy dunking and rinse, then another washing with denatured alcohol. They dry clean and soft for the next application.

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PostPosted: June 28th, 2007, 3:17 pm 
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I use vinegar, then soap and water.... Then let dry....

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PostPosted: July 2nd, 2007, 7:05 pm 
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No need to scrape off the uncured varnish. four days in the water and its pretty much gone. I didn't have time to scrape it off before I left for the French river.

Good tip on cleaning. I used a couple of small foam brushes and tossed them because I didn't know if there was a solvent for cleaning brushes. I will use vinigar and alcohol next time.

Fred


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PostPosted: July 2nd, 2007, 7:09 pm 
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I had mixed results trying to clean foam brushes. I now use the bristle chip" brushes to apply epoxy and save the foam brushes for tipping off. I still throw those away.

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PostPosted: November 3rd, 2007, 5:08 pm 
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A bit late, but I just saw this post now.
Often, the cause of varnish not hardening over epoxy is an interaction between the epoxy and the particular hardeners or "driers" used in the varnish. Varnishes are primarily oils. Oils harden or "dry" very slowly. To make a more convenient product, chemicals often called "Japan driers" are added by the varnish maker. The particular ingredients vary from varnish maker to varnish maker. Epoxy makers don't like to recommend specific brands of varnish because they don't want static from other makers and because the maker they recommend may change their formula leaving them (the epoxy makers) with outstanding recommendations that are no longer valid. The poor user is left holding the bag.

On my first stripper I used WEST system epoxy and a varnish that I don't recall. After several days without drying I called Gougeon Bros. tech support. They told me to use Z-Spar Captains 1015. When I asked them why that critical advice wasn't in the epoxy instructions they explained, essentially, what I explained above.

The good news is that the varnish will eventually dry and perform just as well as it would have had it dried in a timely fashion--no need to scrape it all off. The bad news is that in the time it takes to dry it will likely pick up an awful lot of dust and other shop crud that will need to be sanded off before continuing.

I now test a varnish over epoxy before applying any to a project.

b

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