Fiberglass Whitehall

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bobf13
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Joined: Tue Mar 12, 2019 9:22 am
Location: Campbell CA

Fiberglass Whitehall

Post by bobf13 »

I'm fiberglassing a 17' Whitehall. I've read articles and watched videos about fiberglass and I believe the process is, place the fiberglass on the boat, then apply the first coat of epoxy, then the fill coat before it's fully cured about 3 hours. Right so far? Then I'm not sure about the third and forth coats. I think they must be applied before the previous coat is cured, so can I apply coat 1 at 9:00 AM, the second at 12:00PM, then coat 3 at 3:00PM and forth at 7:00PM? With no sanding between coats? This has been a year and half project so far, so I really appreciate your advice.

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Ibrew2be
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Location: Cincinnati, OH

Re: Fiberglass Whitehall

Post by Ibrew2be »

Bob,

Fiberglassing is one of those tasks where there’s more than one “right” way to do it. Here are some thoughts based on what worked for me.

As a general point, you want to achieve a chemical bond (not just a physical bond) between each layer of epoxy that’s applied. This can be accomplished if you make a point of getting each subsequent layer of resin on within 48 hours of the previous layer. But you do have some time. If you can’t get to the next coat until the next day, you should be fine. Depending on the resin you’ve used, you may need to deal with amine blush, an oily coating that forms on the surface of the cured resin. If you do find that amine blush has developed before you get the next coat of resin applied, simply wash the cured resin with detergent and water to remove it, prior to applying the next resin coat.

Start by getting the glass cut to the size and shape that you need. Then apply a “seal” coat of epoxy onto my hull, without the glass. This ensures that you don’t have any dry spots between the wood and the glass cloth. If you go straight to trying to apply the glass to bare wood, there’s a risk that you end out with dry spots. Using a seal coat avoids this. Allow the seal coat to dry to the point where it’s tack free.

Next position the cloth on the hull, holding it in position with tape, staples etc. as needed. Apply resin to the cloth, spreading it with your tool of choice (squeegee, roller, brush). Don’t allow any white spots – that indicates an area where the glass is starved for resin. At this point, you aren’t trying to fill the weave of the cloth; that comes in subsequent coats. You simply want to get the glass wetted out. Trim any excess cloth when the resin is still green, i.e. after it has gelled so you don’t drag the cloth around, but before the resin sets up hard.

You can apply coat #3, the fill coat, when the previous coat is tack free. Same thing with coat #4.

Barry
Barry Shantz

Imp built and launched.

Build of Ken Bassett's Rascal currently on hiatus

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vupilot
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Re: Fiberglass Whitehall

Post by vupilot »

Yep, definitely multiple correct ways to do it. I also advocate for the seal coat prior to fiberglass. My main difference is I never liked applying more than one coat at a time, tried it once and didnt like the result which lead to lots and lots of sanding. Ever since, over 3 builds, I have always done one coat per day with a day to cure and then sand with 220/320 before the next coat. If you plan to finish the fiberglassed area bright and not paint it, use a high quality epoxy that doesnt blush like MAS, System Three or West. Any corners you want the fiberglass to overlap around need to be rounded to at least the radius of a pencil.

I found the plastic squeegee the best tool for the job of getting epoxy on the glass, just pour and spread. Pre-measuring multiple small batches of epoxy ready to mix and a dedicated person for mixing while you or two people apply is helpful.

Side note...Barry, I just noticed youre building a Rascal. I'd love to see some updates on that!

bobf13
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Joined: Tue Mar 12, 2019 9:22 am
Location: Campbell CA

Re: Fiberglass Whitehall

Post by bobf13 »

Thank you both so much for your responses. Just to be sure, I will apply the first coat without glass (as I've seen in videos), then wait until "tack free". Is tack free anytime within 48 hours to achieve a chemical bond? I plan on 24 hours, so that should be good?
Then apply the glass and wet out. Wait until the next day (24 hours) and apply the fill coat. I've read no sanding, but you mentioned sanding 220/320. Is this best? Then after another 24 hours apply the next coat. Is this the last coat or does it need one more for a total of four after the glass is applied?

One more issue I have, I tried to add a fillet where the planking meets the keel so I would have a nice radius for the glass, but it did not turn out smooth. Can I sand down and reapply to smooth out? Also, I used Silica instead of wood flour and it's white. Can I go over with wood flour to blend better with the wood?
The boat with be bright finished and I do want it to look great.
I know a lot of questions and I really appreciate your help. I've learned a lot building this boat and hope to use that on a second boat at some time. Thanks again. Bob

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vupilot
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Re: Fiberglass Whitehall

Post by vupilot »

I sand between everything. There has been a lot of talk about chemical vs mechanical bond on here and other forums but over 3 builds I havent had any experience that either would ever possibly fail. 24-48 hours to me seems way too long without sanding between but I'm no expert on applying multiple coats without sanding. By 48 hours Im usually already sanded and applied another coat so its usually quite solid by then.

The amount of coats is not set in stone. Apply as many coats as it takes to full fill the weave of the fabric. Heavier cloth (7oz) will take more coats than light cloth, (4 oz.)

You should be able to make the cloth fit against a good fillet on the keel. Yes, wood flour thickened epoxy will match better than silica. Masking tape on each side of the fillet and use the back of a plastic spoon usually makes for spreading the nicest fillets to save you on sanding.

bobf13
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Joined: Tue Mar 12, 2019 9:22 am
Location: Campbell CA

Re: Fiberglass Whitehall

Post by bobf13 »

Thanks again for your advise and sorry for a little more clarification, what is tack free at 80 degrees? Three to four hours sufficient?
So after cleaning up the fillet at the keel, I will
1) apply the initial coat of epoxy to the hull (both sides) Wait until tack free. (Is that 3 - 4 hours?)
2) pre-cut and lay the glass on one side
3) wet out the glass on one side
4) lay the glass on other side (this can be done immediately after first side?)
5) wet out other side
6) trim excess glass (after set up, again 3 - 4 hours?)
7) After 24 hours, sand to 320
8) apply fill coat
9) after 24 hours, sand and apply coat #3
10) after 24 hours, sand and apply coat #4
11) now ten cots of varnish, sanding between each coat
12) turn it over and start the interior.
Thanks again and I really appreciate your adivse. I'm excited about posting photos, one day.

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Ibrew2be
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Re: Fiberglass Whitehall

Post by Ibrew2be »

Bob, the time it takes to get to a "tack free" kind of surface will depend on the resin/hardener system you use, but 3 to 4 hours sounds like a reasonable estimate. Same thing with the time to trim. The key thing will be to keep a close eye on things as the cure of the resin proceeds.

One other thing I'd point out relates to varnishing over epoxy. You want to be sure that the epoxy is fully cured before varnishing. I waited in excess of two weeks, and I wouldn't think you want to get on the epoxy with varnish in less than a week. And choose your brand of varnish carefully. Some builders have had real problems with using Epifanes varnish over epoxy (for some reason, the varnish never hardens).

Barry
Barry Shantz

Imp built and launched.

Build of Ken Bassett's Rascal currently on hiatus

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