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Old 19-02-2020, 16:12   #1
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Epoxied Mat over Polyester Hull

I epoxied some mat over the inside of my hull in a small 1’ x 2’ area. When I was cleaning up the masking, I inadvertently caught the edge of my knife underneath the new mat (between mat and hull) and it started to delaminate from the hull. I used west with fast hardener, 1.5 oz mat, and peel ply over the top. The area is below the waterline and is probably a consistent 50 degrees. It’s been curing for about two days now. The hull surface was preped by removing paint with a wire brush on a drill, than cleaned with acetone, then brushed with a hand wire brush, then cleaned with acetone, then lightly hand sanded with 80 grid, then vacuumed. I have very little experience performing fiberglass work, but I would think that I wouldn’t be able to pull the newly epoxied mat off the hull by just wedging a knife in there. Boats are hard.
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Old 19-02-2020, 16:45   #2
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Re: Epoxied Mat over Polyester Hull

Sounds like you did a great prep. That's how I fix blisters and I fixed some big ones last year. Make sure and wet the surface you are adding the glass mat to with raw epoxy after the acetone cleaning. Then lay down a wet mat and roll it well.
Good luck.
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Old 19-02-2020, 16:47   #3
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Re: Epoxied Mat over Polyester Hull

Mat?
Like chopped strand mat?

Pretty sure it doesn't work with epoxy.
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Old 19-02-2020, 16:49   #4
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Re: Epoxied Mat over Polyester Hull

My first thought is that you didn’t get the correct ration of hardener to resin. How did you measure it?

I’ve seen people using the pumps give it five pumps of resin to one pump of hardener. This gives you way to much resin and not enough hardener. The pumps are calibrated to give the correct ratio with one pump resin to one pump hardener.

If I was doing the job my first step would be to degrease / dewax the surface with alcohol. The acetone should work as well. By first cleaning the surface, you don’t drive the wax / grease into the surface when you grind. Apply the solvent with a clean rag and quickly wipe it up with another clean rag.

Once the surface is clean, I would use a disc sander with 60 or 80 grit paper to grind the surface smooth while leaving a good “tooth” for the epoxy to bond to.

Brush or roll a thin layer of mixed resin on the surface, roll the mat down into contact with the surface, then work more resin into the mat until it’s saturated. Be sure you don’t add too much resin which can cause the mat to float above the surface.
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Old 19-02-2020, 16:58   #5
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Re: Epoxied Mat over Polyester Hull

The epoxy was measured with the pumps 1:1. I ensured the pumps dispensed the full amount. Both the risen and hardener were preheated in the sun before dispensing. The epoxy was mixed in a paper cup with a west plastic stir stick. It was mixed for at least two minutes. I brushed epoxy into the surface, then laid down the mat, then, wetted out the mat over the top, then laid down a layer of peel ply, then wetted out over the top of peel ply. I used a fin roller throughout the processes. I used a space heater to heat the work for several hours after completed.
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Old 19-02-2020, 17:30   #6
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Re: Epoxied Mat over Polyester Hull

Your prep sounds very good. Which epoxy?

I want to say that chopped strand mat has binders that are more suited for polyester than epoxy.
You would not need epoxy on the outside of the peel ply.
I would mix a test batch of epoxy and try to attach a small piece of woven cloth and a small piece of your mat to another surface prepped as before.
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Old 19-02-2020, 17:35   #7
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Re: Epoxied Mat over Polyester Hull

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Your prep sounds very good. Which epoxy?

I want to say that chopped strand mat has binders that are more suited for polyester than epoxy.
You would not need epoxy on the outside of the peel ply.
I would mix a test batch op epoxy and try to attach a small piece of woven cloth and a small piece of your mat to another surface prepped as before.
West epoxy.

I already tried the test with two layers of cloth. I was also able to pull the cloth off. I was also able to pull the two layers of cloth apart.
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Old 19-02-2020, 18:34   #8
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Re: Epoxied Mat over Polyester Hull

Just a thought, was the paper cup a waxed paper cup? You possibly could have contaminated the epoxy. I use yogurt cups or sour cream containers, well washed. A lot cheaper than buying mixing cups.
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Old 19-02-2020, 18:35   #9
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Re: Epoxied Mat over Polyester Hull

West also has a very good tech department, you could call and speak with them.
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Old 19-02-2020, 18:36   #10
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Re: Epoxied Mat over Polyester Hull

Wow. Sounds like maybe you got a bad batch of hooch.

The only time I had trouble with epoxy setting up was a small batch that for some reason had a lump in the hardener. I picked out the lump, not even thinking, and it messed with the ratio enough that it never set up hard and woven cloth peeled off like you described previously.
Another time I had a gallon of epoxy resin 'crystalize' on me. Procedure was to heat it up to 140 F in a water bath and stir it until the crystals were gone. That jug worked fine afterwards until it was gone.
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Old 19-02-2020, 18:41   #11
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Re: Epoxied Mat over Polyester Hull

No wipe down with acetone after 80 grit? Even vacuumed it will leave a layer of dry dust that could give you those results. Other possibility is hull condensation? If the ratio was wrong as mentioned above 5:1 you’d have a gooey mess not a hard sheet popping off. Could also be temperature indifference. Try throwing a heater directly at the location you’re fixing. Get the hull good a warm before applying the fix and keep it that way.
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Old 19-02-2020, 18:44   #12
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Re: Epoxied Mat over Polyester Hull

Just another stupid question but the west pumps are sold in 3’s did you mistake the 205 pump for the 207?
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Old 19-02-2020, 18:57   #13
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Re: Epoxied Mat over Polyester Hull

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West also has a very good tech department, you could call and speak with them.
That’s a good idea. I always feel hesitant to do that because I feel like it’s not the responsibility of a vendor to teach me how to fix my boat, especially whenever they have such a breadth of literature available to teach yourself. But I’m feeling pretty stumped on this one.
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Old 19-02-2020, 18:58   #14
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Re: Epoxied Mat over Polyester Hull

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Just another stupid question but the west pumps are sold in 3’s did you mistake the 205 pump for the 207?
You can’t. They are different sized openings in the container.
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Old 19-02-2020, 19:04   #15
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Re: Epoxied Mat over Polyester Hull

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No wipe down with acetone after 80 grit? Even vacuumed it will leave a layer of dry dust that could give you those results. Other possibility is hull condensation? If the ratio was wrong as mentioned above 5:1 you’d have a gooey mess not a hard sheet popping off. Could also be temperature indifference. Try throwing a heater directly at the location you’re fixing. Get the hull good a warm before applying the fix and keep it that way.
The West literature specifically says to not use acetone after sanding and to just vacuum. I used a space heater to pre heat the area to eliminate any condensation. The epoxy is hard. It just won’t stick. I used a space heater to heat the work after completed. Even without the heater 2 days at 50 degrees should be more than enough time with the fast hardener. I’m also not sure the heater does much to heat the completed work since it’s below the waterline. And I’m stating 50 degrees because that’s about that the water temp is. The air temp without the heater is about 60. With the heater is about 70.
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