MAS Epoxy recoat time

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ealger
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MAS Epoxy recoat time

Post by ealger »

My experience 2 days ago with the wet out coat on my Ranger was not too thrilling. I ended up with a lot of tiny air bubbles on the surface presumably from the brush action needed to get the epoxy layed on for the wet coat. Tipping off with a dry brush didn't help to reduce the bubles.

I let it setup for a day and then scrapped off the bubbles the best I could and then applyed the 2nd coat today along with bias strips over the outer stems. I was extra careful in applying epoxy to the bias strips to avoid surface air bubbles but to still got a lot. I tipped off with a dry brush reducing them somewhat.

At about the 3 hour point, I starting checking the cure using MAS's "cotton ball" test. At about the 3 1/2 hour point, the cotton ball would not leave fibers but the slightest finger touch would leave a finger print! Way too soft to scrape.

At the 7 hour point it was still too soft to scrape the bias tape but past the "chemical" recoat time as specified by MAS.

On the canoe I built 2 years ago, with the OLD MAS formula, I didn't experience the brushing problem and the extended recoat time was nice because I could let it cure to the scraping point and still recoat without sanding!

The shop temperature at 70 deg and the humidiy is low.
I'm thinking I'll look for another epoxy for my next canoe. On the other hand, maybe it's not the epoxy at all. :confused
Ed Alger
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Glen Smith
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Post by Glen Smith »

Hi Ed, you say this was a wetout coat but you don't mention using a squeegee to remove the excess epoxy. Do you not use a squeegee after applying epoxy with a brush?

Did you apply the epoxy as the shop temperature was falling? This helps prevent bubble formation. Also, did you just apply the epoxy and walk away or did you keep an eye on it for a few hours so you could eliminate bubbles as they formed?

I know you aren't on your first boat building project but sometimes we forget the basics.
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ealger
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MAS epoxy

Post by ealger »

Glen, I first applied a seal coat to the hull and let it cure for a day. Then cleaned it up with a light sanding and Scotch Brite pad.

I applied the epoxy pretty much like Ted Moores suggest using a brush to get the epoxy applied in sections. After a section had set about 20 minutes I then squeegeed the excess off. (I've not perfected this technique yet. It's going to take a couple more canoes to get this right!). I left more epoxy on the fabric than I should have.

I went back over the sections several times with a dry brush trying to soften the bubbles until the epoxy was too set to mess with. It seemed like "tipping" off didn't do much to rid the bubbles.

Today, when I applied the bias cloth, I was careful to watch how I layed on the epoxy and careful in using the squeegee not to leave too much epoxy but bubbles still formed on the bias tape. Tipping off removed some but not all.

I think the resin is more viscous than the epoxy I used on my last canoe and didn't flow on as well in the wetout step.
Ed Alger
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Glen Smith
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Post by Glen Smith »

Ed, I still don't see why you would have bubbles unless the temperature wasn't falling. I work in my basement and when I plan on glassing I turn up the thermostat a couple of degrees a few hours before starting the job. When I go into the shop to start glassing I turn the thermostat down a couple of degrees and I very rarely have bubbles caused by outgassing. If I precoated, I don't get any bubbles at all even using West 105/207 which is fairly thick. Maybe you are being too aggressive with the brush causing a buildup of air in the epoxy and it releases slowly and creates bubbles. :thinking
Rick
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Post by Rick »

Ed,
Today, when I applied the bias cloth, I was careful to watch how I layed on the epoxy and careful in using the squeegee not to leave too much epoxy but bubbles still formed on the bias tape. Tipping off removed some but not all.
Could it be the cloth that's holding onto the air? Is it any different from the previous cloth that you used?
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ealger
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MAS epoxy

Post by ealger »

Thanks all for the replies. The glass fabric is from the same source as my 1st canoe.
We stir the epoxy a full 2 minutes and there are a zillion tiny bubbles in the mix. I've been using "chip" brushes and trimming off 1/4" to make the brush stiffer. Perhaps in my zeal to do a good job, the combination of stirring and brushing results in a lot of tiny bubbles in the applied epoxy.
In applying the 2nd coat, I used a new 2" nylon paint brush. Stirring was the same but it seems that the surface was a lot smother with not nearly as many pimples. My wife does the stirring and she very conscientious about thorough mixing.
Tommorow I'll scrape the bias tape, sand some and go over the entire hull with a Scotch Brite pad and apply epoxy. Perhaps we'll stir a little slower and pour the mix from cup to cup once or twice and see what happens.
Ed..
Ed Alger
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Juneaudave
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Post by Juneaudave »

I really like the MAS epoxy...I assume you are using the slow hardener, given the cure time. The MAS slow has a lot longer open time than West. You might try to give it a bit more time between application and using the squeegie for the mixing bubbles to float out. As far as cure before the second coat, I've found that with MAS, you can apply a coat in the evening and come back in the morning and it's about right.

Just checking...but you don't have any halogen work lights shining directly on the hull do you?
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ealger
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MAS epoxy

Post by ealger »

Thanks Dave. No, don't have any hi-temp lamps on the hull. The instructions that we're getting now from MAS is that the recoat time has been reduced. Before they changed the formulation, waiting overnight for recoat was OK. Now they are suggesting that if cotton ball fibers stick to the last coat, then recoat is "chemically" OK. Otherwise, a scuff sand is required. In my case, at 70 degrees cotton ball fibers quit sticking in just over 3 hours which makes me duvious of the test. ( I use the MAS slow hardner)
You may be right about the length of time to start the squeegie application. Since I only build 1 canoe a year, I may have to makeup some test panels and fool around some (after I go fishing this summer) :big grin
Ed Alger
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ealger
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MAS epoxy

Post by ealger »

Well, we brushed on the second coat today. There is no way to stir the epoxy without creating bubbles in the mix. I flowed on the epoxy with soft flowing strokes and there are still a lot of bubbles that stay on the surface. Tipping off only moves the bubbles around. The surface tension keeps them trapped. I don't think I can lay on the next coat without waiting to scrape them off clean. I can't scrape without exceeding the recoat time which means I'll have to scuff up the whole hull again. Very frustrating.
Ed..
Ed Alger
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KARKAUAI
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Post by KARKAUAI »

Hi, Ed,
I used MAS slow on my two canoes and had very little problem with bubbles at 70 degrees. The canoes were built a year and two years ago. There were obvious bubbles as I spread the epoxy but they came to the surface and either burst spontaneously or were easy to tip out for at least two hours after applying the epoxy. The canoes were not ready to recoat for a good 10 to 12 hours, which reflected the long time before it set. When did MAS change the formula? If it sets too quickly I may have to rethink what I'm going to use on the next project.
A hui ho,
Kent
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John Michne
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Post by John Michne »

There has been some discussion here recently about the cure and recoat times of MAS epoxy, and also the perennial bubble questions.

I was using a Newfound kit, with the included MAS epoxy, for the canoe building course I was teaching. I got a surprise when I mixed some glue for laminating a stem using the epoxy from the kit. I had not bought any epoxy for some time, and proceeded to mix a batch using 75% slow hardener and 25% fast, as I have done for years. I spread a soak-in coat, and then thickened the batch with Cab-O-Sil. While spreading the glue, it started to set up. The mixing cup felt warm (it soon melted), and I had to scrape off the mess quickly before it went hard. I then mixed another batch using 100% slow hardener, and the job finished without incident.

As it turns out, MAS had changed the formulation of its slow hardener, reducing the cure time. The “new” slow hardener is roughly equivalent to the “old” slow hardener with 25% fast added. This would have made my surprise batch of glue equivalent to about 50% old slow plus 50% fast – a mix I have never used.

I was a bit concerned how the new hardener would work for the wet out and filling of the fiberglass. My previous normal schedule for application, as described on my web site, was to wet out with 100% slow on day 1, which would still be soft the next morning (day 2). Then a fill coat in the morning using 25% fast with the old slow, followed by another coat in the evening. On the morning of day 3, it was still within the recoat window, when two more fill coats were applied. This schedule obviously wouldn’t work with the new hardener.

I squeegeed on the wet out with the new stuff, and accepted the fact that I would have to sand. The next day, I tried scuffing with a Scotch Brite pad – too labor intensive. I then tried hand sanding with 80 grit paper – also too labor intensive. I then fired up the ROS and using a slow speed, lightly sanded. Note that I simply knocked off the epoxy on the tops of the tiny hills of the weave – never sanding into the glass as a whole. The first fill coat went on with a roller (see below for the bubbles and runs), followed later in the day by the second. I got back to it a few days later, by which time the epoxy was fully cured. Sanding at this point (80 grit) knocked down the few irregularities on the surface (dust nibs, a missed run or two, etc.) and prepped for the third coat. I noticed that the cloth was exposed only if I lingered on a spot with the sander – there was apparently plenty of epoxy on. Sanding was not intended to be varnish-ready, and some shiny spots remained that were of no consequence. The third coat was then applied.

In the past, when there was no need to sand between coats when using the “old” MAS slow hardener, I would routinely use four fill coats. With the new hardener, I only needed three coats. The initial sanding of the tips of the cloth weave left a slightly smoother surface for fill coats, and the sanding I had to do between the second and third fill coats further smoothed the surface before putting on the third coat. The overall effect was elimination of the need for a fourth coat. Incidentally, the new hardener is almost water white, being a very lightf straw color. This may change as it ages, but I am well satisfied with the new stuff. Once I readjusted my schedule and accepted the need for a bit of sanding, the results were gratifying. I will continue to use MAS epoxy.

Now for the bubbles and runs. There are three kinds of bubbles – those seen in the epoxy mixing cup, the relatively large ones seen under the fiberglass wet out, and the tiny ones in the uncured fill coats. Mixing epoxy thoroughly and completely is required for a good cure. Mixing it vigorously does so, but it also introduces air bubbles. So what? In MAS epoxy, they soon dissipate. Doing a wet out with a squeegee, followed by squeegeeing a few times during the cure, eliminates bubbles and smoothes out runs before they become problems.

The bubbles under a wet out coat, usually inside the boat, are not due to “out gassing” (can anyone define “out gassing”?) as mistakenly understood by many builders. Raising shop temperature, then fiberglassing as the temperature falls is extra work that has no effect on those bubbles. This can be shown mathematically with the classic gas equation. If cooling the shop atmosphere enough to contract the bubbles actually occurred, you would be in a vacuum. These bubbles are the result of voids between the strips during construction. The wet epoxy seeps into cracks and defects in the joint, forcing the internal air out under the cloth and forming a bubble.

The bubbles in the fill coats applied with a roller (I use Home Depot mohair rollers, specifically stated for use with epoxy and band sawn in half) are easy to get rid of. Epoxy is applied in batches, usually six ounces each. I pour it on, and then roll it out. Then the next batch is applied. After the second batch is applied, I brush the first batch with a dry chip brush, holding the brush at a high angle and softly brushing the surface. The sequence is repeated, followed by a quick brushing or three over the entire hull as the epoxy cures, eliminating runs.
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ealger
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Post by ealger »

John, thank you for taking the time to give us some of your expertise. It's appreciated.

My experience follows yours with regard to recoat time. I also used Home Depots epoxy mohair covers cut in half but my experiece with those covers was a disaster. When I cut the cover, I cleaned up the edge as best I could but tiny pieces of the cover shed out on to my epoxy.

On my last coat, we observed the mix closely as it was poured out onto the hull and then spread with the roller. It was difficult to tell if the bubbles were still there while/after rolling because of the stipple. The thing I did differently was to tip off immediatly after spreading instead of waiting until the next batch was mixed and spread. I'll try that tomorrow.

I only get to apply epoxy once a year, so my experiece level is low, low. Having to deal with changes in epoxy reaction makes it doubly hard. I read your site info over and over and I'm glad you posted here as it's makes me feel a lot better about why my experience was so different.
Thanks again.
Ed..
Ed Alger
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mas epoxy recoat time

Post by johnnycanoe »

i was thinking about using mas, now i probably will go to raka. i don,t want to sand, and i will probably need the time. Wiith raka, can i do 8am , 8pm and 8am again?
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Jim Dodd
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Post by Jim Dodd »

Out gassing that I've experienced is air that was trapped in the wood, between strips or in the staple holes.
Reducing room temperature as Glenn states, does solve this problem!!
Has anyone been concerned about sanding uncured epoxy? What I've read was it takes up to 7 days for a complete cure, at which time it's safe to sand. My concern is the health side here.
At what temperature was this epoxy stored pryor to use?
Old epoxy hardeners seem to cure much faster than fresh. Was the hardener darker than what you used previously?
Foam rollers have worked great for me over the years
I think I'd look for a different epoxy.
Jim
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ealger
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Post by ealger »

Jim, I stored the epoxy and hardner at 58 degrees for 4 months after purshase. I brought both up to 68 degrees about 2 weeks before my first application. The hardner is clear as is the epoxy. I let the epoxy cure 6 days before any serious sanding with ROS w/vacuum and resperator. Tomorrow I'll put on a coat with West 800 foam covers. I've cleaned up the hull as Glen suggested. We'll see if we can get the epoxy stirred without bubbles and see what happens.
Ed..
Ed Alger
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