MAS Outdoor Epoxy - Woodworking Talk - Woodworkers Forum
 
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post #1 of 9 Old 05-12-2020, 11:22 PM Thread Starter
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Question MAS Outdoor Epoxy

Hello. I may have applied a MAS Outdoor Epoxy coating too soon on a boiled linseed oil finish. I waited over a week, but still have a couple of spots that cratered after applying the epoxy. Is the solution to wait 24 for the epoxy to cure, scuff sand and try again?

I don't know the science behind it, but think some of the maple grain cured quicker than others and there's still some oils or solvents not completely dried out that the epoxy was trying to get away from. The cratering only occurred on a few parts, but seemed to apply fine on the majority.
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Last edited by Thorn495; 05-12-2020 at 11:24 PM.
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post #2 of 9 Old 05-13-2020, 10:03 AM
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Thorn - the forum has been very busy lately and some posts
sink quickly to the bottom of the list without being addressed.
this is just a "bump" to bring it back to the top.
as for me, I would sand off the offending parts, lightly sand the
whole thing and apply a light coat of epoxy all over.
paying close attention to the directions on all of the products that you use.
let us know how it goes.

.

I am a painter: that's what I do, I like to paint things.
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post #3 of 9 Old 05-13-2020, 11:13 AM Thread Starter
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Quote:
Originally Posted by John Smith_inFL View Post
Thorn - the forum has been very busy lately and some posts
sink quickly to the bottom of the list without being addressed.
this is just a "bump" to bring it back to the top.
as for me, I would sand off the offending parts, lightly sand the
whole thing and apply a light coat of epoxy all over.
paying close attention to the directions on all of the products that you use.
let us know how it goes.

.
What grit would you recommend to scuff sand? I think I've gotten away with lower grits when this happened before. The epoxy was very good at cohering to itself and no scratches could be seen. 220 or 320'ish?
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post #4 of 9 Old 05-13-2020, 11:49 AM
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honestly, I don't have a clue about sanding epoxy.
I use epoxy for structural bonding 99.9% of the time.
others may chime in with some accurate infor.
there are just way too many brands and types to keep track of.
if your epoxy good at cohering to itself any amount
of roughing is only going to be to your benefit.
since you are doing this project on a regular basis, it would probably
be in your best interest to have a few practice boards set up so you
will know how to address certain issues that may pop up.


.

I am a painter: that's what I do, I like to paint things.
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post #5 of 9 Old 05-22-2020, 07:52 AM Thread Starter
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Thanks for the suggestions. I ended up scuffing the finish with 220 grit and cleaning all the craters in it with denatured alcohol. Then I applied another thin coat. Seemed to work fairly well. Customer was happy with it, but I felt the finish could've been smoother.
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post #6 of 9 Old 05-22-2020, 07:52 PM
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Many epoxies produce a coating when they cure called Amine Blush. It needs to be removed to ensure adhesion of a second coat.

Luckily, MAS epoxy doesn’t have this problem, but sanding can only help.

Did you topcoat it with a UV inhibiting varnish? Epoxy doesn’t do well in the sun.
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post #7 of 9 Old 05-23-2020, 07:34 AM
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Originally Posted by Quickstep View Post
.............................Did you topcoat it with a UV inhibiting varnish? Epoxy doesn’t do well in the sun.
Agree 100% and I have used a lot of epoxy in my day, both indoors and out.

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Retired woodworker, amongst other things, Sold full time cruising boat and now full time cruising in RV. Currently in Somerville, Tx
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post #8 of 9 Old 05-23-2020, 11:21 AM
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I’ve recently gone through my own unhappy epoxy results and can offer some general rules of thumb:

• ALWAYS check with the manufacturer RE compatibilities and these sorts of unexpected results.
• Scuff sanding between coats is intended to provide mechanical “keying” for the following coat, so the “key ways” (scratches) need to be substantial, and 120 - 150 grit is the right grade for that. Scuffing is NOT removing the coating, it is intended to simply roughen and remove the gloss from the surface — go over it quickly and lightly by hand.
• As already noted, epoxy requires UV protection, and a few coats of marine grade spar varnish are the best choice. The varnish is a sacrificial coating — it will have to be sanded back a bit and reapplied every few years as it ages and gets cracked, cloudy, or peels.

On an item like your birdhouse that doesn’t get too physically abused, you might want to save yourself the expense of the epoxy and just go with the spar varnish.
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post #9 of 9 Old 05-23-2020, 09:22 PM
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Often cratering happens when you apply epoxy on rising temperatures. I used to build stripper canoes. I would heat the shop to at least 80° when I started applying epoxy. The heat was turned off as soon as it hit 80°. Epoxy does not bubble or crater on falling temperatures. Some times I might see a couple of bubbles, then apply a heat gun to the bubble and it disappears.
The post about Amine blush and varnish coating was dead on. I use Raka epoxy and amine blush could be a problem.
I washed the canoes down with water and Dawn dishwashing soap after the epoxy was set. This removes the blush. I then apply another coat without sanding.
Why did you epoxy over a finish? I epoxy over bare wood and fiberglass cloth . When completely done I use a boat varnish.
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