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Old 03-09-2015, 18:03   #1
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A few questions before our first fiberglass job

We are going to glass over four unused thruhulls (below the waterline) this weekend. Given that this will be our first time working with epoxy and fiberglass, and especially since it's below the waterline, we've been reading the West System books and "This Old Boat" very carefully. Nevertheless, I still have a few questions:

Backing the hole: I've seen various methods described for backing the hole: styrofoam, a plug, a laminate "sheet". Making a plug seems the most difficult as far as getting the depth and diameter exactly right. I assume the point of backing the hole is merely to keep the cloth from poking through, so won't the laminate or styrofoam method work just as well? I've read that whatever is used, it needs to cure thoroughly before continuing. Is "cure thoroughly" the cure to solid time as opposed to merely the end of the working time?

Thickness: 2 of the holes are 1/2" and the other 2 are 1/4" thick. With 9 oz cloth it appears that it will take 15 layers for the 1/4" and 30 layers for the 1/2". That sounds like a lot. Am I missing something? Also, I've read that you shouldn't cast layers over 1/2" because the curing epoxy generates heat. Since the thickest hole is 1/2", I assume it's o.k. to cast them all without waiting for a lesser amount to kick first?

Fairing compound: Should this be applied after the patch is fully cured, or when it's still tacky? I think I've read it both ways.

After fairing, am I supposed to apply yet another layer of woven cloth or can I move on to doing a final epoxy barrier coating and then applying bottom paint? The West System book refers to applying woven cloth after fairing and shaping are complete and before the final coating operation, but I wasn't sure if that was for a different type of project.

Sorry for the long post, but I want to make sure that we get this right. Thanks.
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Old 03-09-2015, 18:46   #2
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Re: A few questions before our first fiberglass job

Why not simply close the seacocks, wire them shut and put end caps on them? I just did that on a boat as it was quite simple and cost one seacock and one plug and took less than an hour to buy and install. Fiberglass repairs are not so simple and you are talking about four underwater holes, probably of an inch or more. For something this potentially critical, why would you seek advice online and read books rather than hire a professional glass technician who has all the tools and materials and probably knows a lot more about it than many of us ever will--and who will likely have liability insurance? You say you "want to make sure that we get this right." Of course you do, but I'd be interested to know why there are four unused through hulls on a 30' boat?
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Old 03-09-2015, 20:30   #3
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Re: A few questions before our first fiberglass job

We bought the boat last month and pulled out the marine head to put in our Nature's Head - there's three. There was also a salt water anchor wash that we removed - that's the fourth. The seacocks and thruhulls are already out.

Never mind. I'll just call the West number and ask them.
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Old 03-09-2015, 21:00   #4
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Re: A few questions before our first fiberglass job

Quote:
Originally Posted by Cthoops View Post
We bought the boat last month and pulled out the marine head to put in our Nature's Head - there's three. There was also a salt water anchor wash that we removed - that's the fourth. The seacocks and thruhulls are already out.

Never mind. I'll just call the West number and ask them.
whatever you do make sure to grind out properly on both sides before laminating
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Old 03-09-2015, 21:05   #5
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Re: A few questions before our first fiberglass job

Epoxy does get warm if multiple laminates are placed at the same time. Play it by ear but I've found much more than 4 laminates can generate smoke. The backing is just to keep the cloth from bulging. Duct tape will work or hot glue a piece of thin plywood over wax paper to keep the epoxy from bonding to the wood. If you have access, you can laminate from both sides which may make the job go faster though will make a mess inside the head with the grinding to feather the hull.

Might want to leave everything in place till you have a chance to be sure the composting head is the way to go. The true believers all rave about them but have heard that they don't always work as advertised.
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Old 03-09-2015, 21:21   #6
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Re: A few questions before our first fiberglass job

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Epoxy does get warm if multiple laminates are placed at the same time. Play it by ear but I've found much more than 4 laminates can generate smoke. The backing is just to keep the cloth from bulging. Duct tape will work or hot glue a piece of thin plywood over wax paper to keep the epoxy from bonding to the wood. If you have access, you can laminate from both sides which may make the job go faster though will make a mess inside the head with the grinding to feather the hull.

Might want to leave everything in place till you have a chance to be sure the composting head is the way to go. The true believers all rave about them but have heard that they don't always work as advertised.
Thanks! We'll definitely play it by ear re: the multiple laminates, and that's what I suspected re: the purpose of the backing. We had a Nature's Head on our Bristol 24, so we're already one of the true believers. Thanks again.

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whatever you do make sure to grind out properly on both sides before laminating
Thanks - we're planning on doing that.
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Old 03-09-2015, 22:45   #7
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Re: A few questions before our first fiberglass job

There was another thread about this recently, called "filling a hole in a thick hull" or something like that. I think the consensus was either to grind down the the area around the thru-hull but don't remove any layers and layer up up on the inside with a plug epoxied in the hole, or just epoxy in a plug. The West System (I haven't read it) apparently referred to some really serious grinding down of hull which some respondents (including me) did not seem to agree with. I did this years ago on my Columbia 24 which had a pretty substantial hull. I roughed up an area about a foot or so in diameter and put in 5 or six layers (can't remember) pretty dry, that is with a minimum of resin. The layers sagged into the hole a bit, which I wanted and then I filled the holes with Marine-Tex and put two layers on the outside and fared it in with putty too. I had no idea what the right way to do it was at the time, but it was fine and seemed very strong to the point of overkill. You'll likely need a few more layers I'd think. I'd say your patch should match or exceed the strength of the surrounding hull so that if you banged on it with a hammer (not too hard), from the outside or inside, that the patch remains as strong as the rest of the hull. BUT that is me, others recommended just epoxying in a plug and call it a day.
check: Fiberglassing in hole in thick hull.
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Old 04-09-2015, 00:53   #8
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Re: A few questions before our first fiberglass job

perhaps if you work from the inside out any mess will be inside and your hull will still look nice and fair. Eg, Put a heavy/temporary tape over the hole. Then use a light fill from the inside. Once cured, add a few more layers with glass to the desired thickness. Remove the tape on the outside and fair up with a little epoxy filler.
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Old 04-09-2015, 09:03   #9
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Re: A few questions before our first fiberglass job

Here was my attempt at following West Systems Example 8, on page 89 from http://www.westsystem.com/ss/assets/...aintenance.pdf
Filling a hole below the water line on both sides of the hull, to minimize the repair area.

I never did any fiberglass work before I purchased this boat, but I didn't start with filling in underwater holes. As a novice, it is more about perseverance than skill. When the results are disappointing to the point where it interferes with your sleep, then grind it out and try again. Since this is your first experience with epoxy fiber-glassing, I would recommend doing them one at a time. This will give you an opportunity to reflect on your work and make adjustments.

Some thoughts:
  • Use a filter and eye protection.
  • On an inside surface, wipe the area first with a fiberglass solvent wash.
  • Grind with a 4 1/2 inch angle grinder and course (~60 grit) flap disc. Work slowly and check often.
  • Rough up the surface by hand with very course paper and wash with acetone or the solvent wash.
  • You don't have to use West System products. I used a product without amine blush, a 50/50 mix ratio and bit more flex.
  • I used 1708 Biaxial cloth, contains double bias(17oz) stitched at 45 degrees along with one layer of 3/4oz mat.
  • Lay large cloth circles first then the smaller cloth on top.
  • Try to get any trapped air out. A fiberglass roller is useful for this.
  • I never had any issue with doing it all at once, but don't work in direct sunlight. Better to start early when the epoxy chemicals and air temperature are cooler.
  • You can apply thickened epoxy for fairing while it is still tacky for a chemical bond. If you do it after (a mechanical bond), then just clean off any amine blush, rough up the surface and wash it down with acetone or solvent wash first.
  • Covering it up with peal ply will yield a smooth surface.
  • If it ends up standing a bit proud, you can sand it down. This is why you started with the large circles.

Gluing an epoxy puck in the center of the hole:


Grinding back the laminate:


Fiberglass patches on outside of the hull:


And the inside:


After fairing and 4 layers of epoxy primer:
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Old 04-09-2015, 11:20   #10
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Re: A few questions before our first fiberglass job

You do NOT plug the hole and glass over it (except for repairing any existing coring). You must taper grind the edges such that the hole is filled by successive layers of the same material used to layup the hull, not 9 oz cloth, you can be certain of that.
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Old 04-09-2015, 12:40   #11
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Re: A few questions before our first fiberglass job

Quote:
Originally Posted by Cthoops View Post
We are going to glass over four unused thruhulls (below the waterline) this weekend. Given that this will be our first time working with epoxy and fiberglass, and especially since it's below the waterline, we've been reading the West System books and "This Old Boat" very carefully. Nevertheless, I still have a few questions:

Backing the hole: I've seen various methods described for backing the hole: styrofoam, a plug, a laminate "sheet". Making a plug seems the most difficult as far as getting the depth and diameter exactly right. I assume the point of backing the hole is merely to keep the cloth from poking through, so won't the laminate or styrofoam method work just as well? I've read that whatever is used, it needs to cure thoroughly before continuing. Is "cure thoroughly" the cure to solid time as opposed to merely the end of the working time?

Thickness: 2 of the holes are 1/2" and the other 2 are 1/4" thick. With 9 oz cloth it appears that it will take 15 layers for the 1/4" and 30 layers for the 1/2". That sounds like a lot. Am I missing something? Also, I've read that you shouldn't cast layers over 1/2" because the curing epoxy generates heat. Since the thickest hole is 1/2", I assume it's o.k. to cast them all without waiting for a lesser amount to kick first?

Fairing compound: Should this be applied after the patch is fully cured, or when it's still tacky? I think I've read it both ways.

After fairing, am I supposed to apply yet another layer of woven cloth or can I move on to doing a final epoxy barrier coating and then applying bottom paint? The West System book refers to applying woven cloth after fairing and shaping are complete and before the final coating operation, but I wasn't sure if that was for a different type of project.

Sorry for the long post, but I want to make sure that we get this right. Thanks.
I would go with Paul, wire them shut and cap the sea cocks. To patch and feather in inboard and outboard layers of glass. Not me.
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Old 04-09-2015, 13:38   #12
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Re: A few questions before our first fiberglass job

I just glassed over 5 thru hulls, four forward and one aft. I removed all of the head plumbing to replace with a composting head (3 thru hulls). Also, the sink and sink drain in the head--gone...imo, no need for two sinks on a 30' boat. The aft TH was the engine intake; I'm replacing the diesel with electric.

WS says that you can fill a machined hole below the waterline with a plug and use much less that a 12:1 taper. It's in the back of one of their manuals.

I plugged with thickened epoxy and used 1708 with resin for the bevel. Faired with epox and the fairing filler. Repairs look great and are strong.

Two remaining THs fitted with Groco flanged seacocks mounted on G-10 backing plates. The boat is much better than before, I think.
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Old 04-09-2015, 13:55   #13
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Re: A few questions before our first fiberglass job

My repair was much like Hilbert's, btw. Cleaned pervasively, sanded in those instances where a mechanical rather than chemical bond was used (i.e., for cured surfaces), cleaned again.
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Old 04-09-2015, 17:35   #14
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Re: A few questions before our first fiberglass job

I usually don't do more than 5 layers at a time with epoxy. Hot days will generate hot patches and cool days you can do more. I don't use just 10 oz cloth. I alternate mat, roving, mat, cloth. Let that cure until it's hard and cool then do the next layer after sanding or grinding a bit to provide a rough surface. I cut all my pieces to fit before mixing up the resin/hardener and make certain they are in a stack so I can pick them up one at a time. Each will be a bit larger than the last. My last piece will be cloth because it's easier to sand and grind. For backing, Roverhi's idea of a hot glued piece of ply is ok but you can use anything. All it is there for is to prevent the patch from sliding inside the hull and bulging. Styrofoam will be ok with epoxy but not with polyester. You can even use cardboard from your twelve pack. If you can't reach from inside the hull then poke something that will get through the hole and when twisted will stay in place. Use a piece of fishing line on a little stick as a spanish windlass to tighten into place. Once you have a hard patch on it then cut the fishing line and start layering more on your patch.

Good luck. Epoxy is easy to work with and once you do one or two patches you'll be doing it in your sleep. Just need the confidence. It's one of those things like concrete. You have to be finished before it hardens! Yikes!
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Old 04-09-2015, 18:45   #15
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Re: A few questions before our first fiberglass job

I did my below water thru hulls like Hilbert. I did taper it more though on both inside and out. My hull was about 1 3/4 thick in the spots I removed mine. I drilled out the thru hulls with a 3/4 inch hole saw. Made a plug from epoxy and some fiber glass matt. More epoxy then matt. Filed the plug down to fit really snug inside the hole and then epoxied that in the hole. The plug was only about 1/4 inch thick. After the plug dried in I started adding fiberglass patches and fiber matt in alternate layers. I only had time to add about 5 or 8 layers at a time before the epoxy would start to get to thick hot and sticky. I alternated fiber matt and fiberglass to improve strength. The matt does well to fill while the glass holds the strenght. I did this on both sides. Smoothed it out real nice on the outside and painted. Inside I knocked all the sharp edges and ridges off and just painted but didn't feather as much because of the mess of sanding inside the boat.

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