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Old Feb 01, 2005, 09:47 AM
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Fiberglass For Mahogany Hulls -- How To

There was such a terrific response to the RCBM fiberglass article that I thought it wouldn't be a bad idea to work up a detailed thread on the fiberglass process. As luck would have it, the next step on the T-bolt is to get the finish started. It also appears that there are several mahogany boats under construction lately, too. It looks like the time is right, so here goes.

First, I'll start the process with the actual glass work. It's assumed at this point that all the prep work is done and the stain applied.

I learned a long time ago that the quality of different materials varies widely, and that "hobby quality" resins and cloth can create some problems that can add a lot of time and effort to the process. For that reason, I will only recomend "full scale quality" materials. I use West Systems epoxy and 2 weights of cloth for the process, both of which are available from Aircraft Spruce and Specialty, or better hobby shops can order it from Composite Specialty or Aerospace Composites.
With that being said, if you're using a system that works for you, by all means, stay with it. I just hate to see a guy make a mess of things with the "canvas" style cloth and sticky gooey resins from some of the hobby suppliers.
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Old Feb 01, 2005, 10:08 AM
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Getting Started

The cloth used on the bottom of the hull where it will be painted is 3.16 oz. crowfoot weave, This cloth is woven on the bias, lays down nicely, and conforms well around compound curves.
Mix the resin according to the manufactureres instructions, then add about 20% denatured alcohol (available from hardware stores), DON'T use isopropal alcohol! Then once you get started, you;ll taylor the mix for best handling.

Lay the cloth over the area to be glassed with a little extra around the edges. If you just can't make the cloth conform around the bow, cut a slit up the centerline as far as is necessary and trim the cloth so it lays flat.
Mix up a batch of resin and brush it into the cloth. The idea is to get a good soak, without puddling, but not so thin that the cloth floats up and causes ripples in the surface. If the brush draggs, or the mix has a "sticky" feel, the resin is too thick, if it wicks in very quickly, it's too thin. It will take a little practice to find just the right blend, but once you find it, it will be obviouse.
Wet the cloth evenly, taking care not to drag the cloth around with the brush. Again, your tequnique will develope quickly with practice.
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Old Feb 01, 2005, 10:15 AM
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The Top Side

The decks and hull sides will be done using a standard weave 1.5 - 2 oz cloth. It will also be cut slightly over sized, layed out over the area to be glassed, and smoothed onto the surface. I like to use a business card to smooth the cloth, and the static cling created bt the rubdown holds it in place nicely.
Wetting is done as described above, but the cloth is a bit more "delicate", so take care not to drag the cloth around causing it to pucker and wrinkle. When it's all been wetted, lightly brush the surface to insure a nice even application of resin.
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Old Feb 01, 2005, 10:23 AM
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Trimming the Edges

Now that the fiberglass has been applied and cured for at least 24 hours, the excess cloth can be trimmed from the edges. Two easy ways to do this are either by running a sharp hobby knife along the edge and then sanding the edge smooth, or, by simply sanding the edge to "cut" the cloth off.
At this point, I know it's tempting to keep going and finish the small parts now, but it's a good idea to glass up the whole thing first, then add subsequent coats of resin all at once so things stay nice and uniform. The end result will be worth the wait.
Stay tuned, the procces will continue soon, PAT
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Old Feb 05, 2005, 07:36 PM
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The Deck is Glassed

The cloth is on the deck now. As you can see in the photo, the cloth is cut slightly oversize. When the epoxy is brushed on, care should be taken to brush up to the edges, but not let the resin dribble down the side of the hull.
If you do get a dribble, be sure to wipe it up right away to avoid having to sand it away later. When wiping up those pesky dribbles, you can wet the rag with a bit of denatured alcohol, it makes cleanup a bit nicer.

Once the deck was completely wetted, the cloth was carefully trimmed away from the transom and the cloth added back there too.
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Old Feb 05, 2005, 07:42 PM
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Trimming the Edges

After the layup has cured for at least 24 hours the excess cloth can be trimmed from the edges and cut away from the cockpit and hatch openings. Trimming can be accomplished either by cutting the cloth with an X-Acto knife, or by sanding the edge. Personally, I like to cut the hatch openings with a knife, but prefere sanding the edge at the sheer. Whatever works best for you is the one to go with.
Next will be to put the cloth on the aft bottom, then do the sides.
PAT
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Old Feb 10, 2005, 09:25 PM
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Progressing Nicely

All of the cloth is in place now. The sides were done first, then the aft bottom last.
On the bottom, the strut location was marked and drilled. Then the cuts were made in the cloth where the stuffing box and rudder bearing tube exit. The cloth was then laid in place and wetted with resin. Notice the cloth was cut slightly oversized to make alignment easier for wetting..
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Old Feb 10, 2005, 09:34 PM
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Building Up the Resin

With all the cloth in place, the edges are sanded to remove the excess cloth. Then the entire hull was given a good rubdown with plain water to remove the wax residue from the surface. Once cleaned, the enire hull and deck was recoated with resin. The resin was thinned just enough to brush smoothly, but not enough to be "runny". At this point, you want the resin to build up smoothly and begin to fill the weave.
Once this coat has curred out completely, the entire boat will be wet sanded with 220 grit paper to smooth the surface in preperation for the next coat. That process will be repeated untill the surface is smooth and even, and the weave is completely filled.
PAT
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Old Feb 13, 2005, 04:07 PM
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It's Time Now for the "Finishing" Process to Begin

All the cloth is on, the surface has been brushed all over with 3 coats of resin, ans wet sanded between. The last coat of resin has been curring for 2 days now and is ready for wet sanding.
As of now, I think theres been enough resin built up with the first 3 coats to sand to a "polishable" surface. But if not, another coat of resin will be applied, but from here on, they'll be srayed, not brushed. By spraying, subsequent coats will go on more smooth and even, with less build up. The goal now id "shinyer", not "thicker".
PAT
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Old Feb 15, 2005, 08:07 PM
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Pat,

Do you apply a marine varnish over the epoxy finish? I have read that some epoxy may yellow if exposed to UV rays if not protected, is this true? And have you ever used the WEST System 207 hardener? I think the 207 is a type of clear coat hardener with some level of UV protection.

Thanks

Mike
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Old Feb 15, 2005, 09:23 PM
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Mike, I've been using the 206 hardner for years and haven't had a problem with "yellowing". The Cobra is the oldest at about 6 years, so far, so good.
I've never tried putting marine varnish over the resin, but guys who have tell me it works fine.
I plan to shoot 2 coats of catalized clear on the Thunderbolt. The Guys at Dumas are doing that and theirs always come out great. As it stands now, the bottom is masked and primed, ready for color. Once the mask is removed, I'll put the decals on and get it clearcoated. Photos will follow.
PAT
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Old Feb 16, 2005, 11:51 AM
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Cloth

Pat, very informative thread! In your first post, you mention that you will be using two different weights of cloth to cover- Why is that? You called out the weights in the thunderbolt thread, I think...
Thanks!

Aero
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Old Feb 16, 2005, 02:05 PM
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Aero, I used 3.16 oz. crowfoot cloth on the bottom for strength. Since it will be painted anyway, the weave is leveled up with resin, then cleaned up with putty and primed to get the finished surface. Much faster that way then using resin all the way up.
PAT
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Old Feb 16, 2005, 02:10 PM
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Got it! that way you spend less time/effort than is necessary on doing build coats on the painted bottom, great idea!
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Old Feb 16, 2005, 04:44 PM
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Pat,

Thanks for the help, I have learned quite a bit reading your threads.

Mike
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