Fiberglass/Resin recommendations?

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CharlieO.

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Sep 21, 2020
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1,558
Location
Lake Champlain Vermont, USA
Vessel Name
Luna C.
Vessel Make
1977 Marine Trader 34DC
I am repairing an area in the bilge, is standard epoxy resin and glass cloth
compatible with the factory type layup?

Just working up an order list and want to be sure I order the proper stuff.

Thanks.
 
Most likely.... but I have seen lots of pro glasser repairs fail because they didn't grind deep or far enough around the repair area to get to/ensure virgin layup.

Most likely some sort of contamination of the failures...but when I redid the repairs, got to clean glass they worked.
 
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I'm a fan of polyester resin and 1 1/2 ounce mat. Then gelcoat when it's finished.
Prep is key. I use a disk grinder and 36 grit sanding pads. Then an acetone wipe after the dust is vacuumed.
 
I personally prefer working with epoxy. And for a repair where it needs to adhere to already cured resin (polyester, vinylester, or epoxy) it'll generally have the best adhesion. On a polyester boat, vinylester would work fine for a repair as well, but polyester doesn't stick as well to already cured resin, so I'd consider it a last choice.
 
I am a fan of proper prep, I will add a small grinder and discs to my tool kit.

I was planning on using epoxy resin because it seems to have a lot of universal uses too. Just wanted to be sure I didn't get something that wouldn't work.

Also open to any tips and tricks. I plan on cleaning/ grinding the area to clean fiberglass,brush on a thin layer of resin over the area, let cure then more resin/cloth layer? Then paint.
The area is the forward part of the bilge but above the keel, my first layer of resin would be on top of the cement in the keel.
 
That method sounds fine to me. Let the first coat of resin gel, but don't let it cure completely before you go for the next layer. If it's still wet, the next layer will bond better (and there's no concern for amine blush). You could also just do a slightly resin rich first layer with fiberglass, there's likely no need for a first coat of epoxy.



Once any layer of epoxy cures to hard, you need to wait for it to cure completely, then scrub with water to remove any amine blush before applying more epoxy (or you may have poor adhesion).
 
Agree on epoxy for bonding to old fiberglass.

Clean, grind and clean again before applying resin.

System Three Silvertip Epoxy does not blush and can be recoated without sanding up to 72 hours.

1708 fabric is glass and matt stitched together which being bulkier, speeds up building thickness
 
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Also open to any tips and tricks. I plan on cleaning/ grinding the area to clean fiberglass,brush on a thin layer of resin over the area, let cure then more resin/cloth layer? Then paint.
The area is the forward part of the bilge but above the keel, my first layer of resin would be on top of the cement in the keel.

That is not the accepted method. Cured resin must be cleaned and sanded or the new resin will not adhere well. Even so, it will not cross link with the cured resin.

Normal technique would be:

*Grind until you get to solid substrate (glass or whatever)
*Wipe thoroughly with acetone
*Coat area with neat resin (this is too make sure the bond line is not starved)
*Immediately lay up cloth and resin in as many layers as needed
*Cover with peel ply -optional but will make a much neater job
*Let cure
*sand and paint.

If the layup is too thick (say more than 1/2") then you may have trouble keeping up and in hot weather it may exotherm. If you have to stop the layup, cover with peel ply, allow to cure until "green", pull the peel ply and continue.

If working in an area with limited access, you can cut the cloth to the size needed, wet it out on a sheet of plastic, lift it and place it on your layup. The really experienced guys will lay plastic on the repair and draw an outline with a Sharpie on the plastic. Then cut a piece of cloth larger than the outline, lay it on the plastic and wet it with a second sheet on top. You can squeege the cloth to the perfect resin ratio between the sheets with no mess at all. Cut the sandwich (plastic, fiberglass, plastic) along the line originally drawn, carry it to the repair, peel the second sheet of plastic, lay on the repair, peel the marked sheet. You can do multiple layers at once this way, up to about 4 or 5 layers of 18 oz.
 
Always use epoxy resin for repairs, polyester resin will not bond as well to existing glass. Agree on using 1708 biaxial. Do not change the mixture of the epoxy from what the manufacturer says, no extra resin. I use a right angle drill with Roloc sanding discs. It works great for grinding the glass and is easy to control. And I have a right angle drill for other projects.
 
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Pros often use the same resin as the original structure due to flexing and expansion factors as well as costs. The larger the repair the more critical it becomes.

If bonding to the concrete is necessary, definitely use epoxy....if just sealing an area back up and you can get 12:1 scarfing on the original structure and the span doesn't have to support anything and isn't too wide....vinyester with high adhesive properties would be probably better than polyester...but in reality...the rest of the bilge is probably polyester resin anyhow.

The "resin rich" doesn't mean more resin vs hardener.... it usually means more fiber saturation than necessary and when you are laying the fabric on a surface dry...it just ensure better adhesion. Not recommended when strength is necessary..but makes it easier and ensure that the bottom of the fabric doesn't have dry spots.
 
What would be a good recommendation for a grinder tool? I prefer small and cordless to get into the tight areas. Right angle die grinder with pads? Or just go for a standard regular grinder? I have one of those.

Thanks for all the tips!
 
Right angle die for small jobs, 5 inch for all but huge jobs. The 7s get real heavy real fast.
 
Do you grind through all the gel coat to get to the underlying fiberglass? Is that what the epoxy resin and fiberglass mat adheres to?

Chris
 
Do you grind through all the gel coat to get to the underlying fiberglass? Is that what the epoxy resin and fiberglass mat adheres to?

Chris

Yes. Sticking it to gel coat doesn’t work very well.
 
Do you grind through all the gel coat to get to the underlying fiberglass? Is that what the epoxy resin and fiberglass mat adheres to?

Chris

Yes, that is my plan. Clean the whole area, aggressively sand down to clean fiberglass to get a thorough overlap of new resin and fiberglass mat. I'll be going over top of an area refreshed keel concrete.

Please don't quote me as an expert though, I figured this was a good spot for me to start my fiberglass education.

~Charlie~
 
Yes, that is my plan. Clean the whole area, aggressively sand down to clean fiberglass to get a thorough overlap of new resin and fiberglass mat. I'll be going over top of an area refreshed keel concrete.

Please don't quote me as an expert though, I figured this was a good spot for me to start my fiberglass education.

~Charlie~

Thanks Charlie.

Yet another question: what do I fill the hole with between the outer and inner transom?
 
Depending on the size of the hole I would use thickened epoxy so it doesn't sag or run. Is the hole through the transom solid glass?
 
Thanks Charlie.

Yet another question: what do I fill the hole with between the outer and inner transom?

It depends on the size of the hole. If it is small you can use thickened epoxy. If it is large the thickened epoxy may run out of the hole. You can try tape over the hole to hold it in. However if there is a large plug of thickened epoxy it can get really hot. It is called thermal runaway. As it cures it creates heat and the hotter it gets the faster it goes off which creates more heat and so on. So if the hole is large you might be better plugging it with a dowel first to fill the hole. Leave the dowel short of the surface so you can fill a little bit with thickened epoxy to seal the dowel up. Then use the glass over the whole area. With epoxy mat doesn’t wet out due to the binders in the mat. So you should use glass instead of mat. Some mat doesn’t use binders when it is sewn to glass like in 1708. 1708 is a biaxial glass, it has 2 layers of glass and one layer of mat. But it is sewn together so the mat will wet out because it doesn’t have a binder to hold the mat together.
 
Depending on the size of the hole I would use thickened epoxy so it doesn't sag or run. Is the hole through the transom solid glass?

Yes it is through the transom. It was where the original swim platform was attached. The through bolt was a 3/8 inch diameter.

I was thinking about glassing up one side fill with thickened epoxy then glass the other side.
 
I would get a 3/8” dowel and fill the hole with it and then thickened epoxy and glass. It will be difficult to fill a 3/8” hole all the way through the transom. Put the dowel in with unthickened epoxy.
 

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