Prime fiberglass repairs before VC 17?

Aug 7, 2018
179
Catalina 350 Great Sodus Bay, Lake Ontario
I finished epoxy and glass repairs for a rudder blister and the remove of an old transducer. Thanks for all the great help here with that. I sanded and ground a lot of paint to get the work done. Should I be priming the affected areas before VC 17? If so recommendations of what product to use? VC 17 has been used by the PO for years, will the primer stick to the old VC17 or does that all need to go?
 
Sep 24, 2018
2,549
O'Day 25 Chicago
I'm under the impression that a barrier coat is what should be applied. If this is true then why does West Systems state that resin can be used as a sealer? Why is barrier needed on the outside of the boat but not the bilge?

Not trying to hijack your thread but hopefully this will clear up potential confusion in the future.
 
Jan 11, 2014
11,323
Sabre 362 113 Fair Haven, NY
Barrier coats are typically epoxy with additional fillers. The goal is to make the hull waterproof, so water can't infiltrate the gelcoat and eventually cause blisters. On newer boats, this is not an issue but older boats like the O'Days you both own it might be. I don't know the history of O'Days well enough to offer an informed opinion.

Gelcoat is slightly porous, epoxy isn't. West System will work as a barrier coat, I'm not sure if they recommend adding a filler. Interlux Interprotect has a filler that makes for a very hard and water proof finish. It can also be sanded and polished to a very smooth surface.

@daviddp If this was my boat, I get a quart of Interlux Interprotect 2000e and apply several coats. Prepare the surface as recommended by Interlux. They won't tell you this, however, if the new 2000e over laps some of the VC17 it won't really matter. I wouldn't do a whole hull going over the VC 17, but a little bit doesn't seem to matter. The VC 17 dissolves in the solvent used for the IP 2K and floats to the surface. I've done several small repairs and it hasn't been an issue.

Why is barrier needed on the outside of the boat but not the bilge?
Two words: Hydrostatic pressure. The pressure of the water pushing against the boat forces the water into the gelcoat. Some areas of your boat will be under 2 feet of water. If you have that much water in your bilge, you have bigger problems than water getting into the hull laminate. It is always good to have the bilge painted to keep water away from the raw fiberglass, but it is not as critical in the bilge as it is outside.
 

Gunni

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Mar 16, 2010
5,937
Beneteau 411 Oceanis Annapolis
Yes you need to prime the rudder/hull with an epoxy primer. Yes you need to remove the old bottom paint first. short cuts = wasted time and having to do it again. Soon.
 
Aug 7, 2018
179
Catalina 350 Great Sodus Bay, Lake Ontario
Thanks all. II 2000e it is ...... This weekend if the temperature breaks 60.
 
Last edited:
May 17, 2004
5,032
Beneteau Oceanis 37 Havre de Grace
Thanks all. II 2000e it is ...... This weekend if the temperature breaks 60.
2000e will work down to 40F. It takes longer to cure so you might not be able to apply as many coats as quickly, but it will still cure and adhere just fine. If it's a small area you can help it along with a heat lamp or space heater too.
 
Jan 11, 2014
11,323
Sabre 362 113 Fair Haven, NY
Thanks all. II 2000e it is ...... This weekend if the temperature breaks 60.
2000e will work down to 40F. It takes longer to cure so you might not be able to apply as many coats as quickly, but it will still cure and adhere just fine. If it's a small area you can help it along with a heat lamp or space heater too.
It is not the air temp that is an issue. If the hull temp is low it affects curing. The forecast for this weekend is for temps in the 60s, but if the hull is in the 30's or low 40's there will be curing issues. Warming the hull is one option.
 
Jan 11, 2014
11,323
Sabre 362 113 Fair Haven, NY
So blisters occur in the gelcoat layer?
No, blisters occur in the polyester resin. The water permeates the gelcoat and then enters the hull lay up. From there it forms an acid (?) and that causes the blister. The barrier coat seals the gelcoat.
 
Jan 11, 2014
11,323
Sabre 362 113 Fair Haven, NY
Got it. Do most manufacturers use epoxy based resin for hull layup these days?
No, epoxy is too expensive and too much exposure can lead to a skin sensitivity. I believe most builders are now using vinyl ester. Less expensive than epoxy and less susceptible to blisters.
 
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Sep 24, 2018
2,549
O'Day 25 Chicago
Can vinyl ester be used as a cheaper alternative to resin for repairs? At $70/qt for West Resin, this stuff adds up quick!
On another note you can find it for half that if you buy it by the gallon
 
Jan 11, 2014
11,323
Sabre 362 113 Fair Haven, NY
Can vinyl ester be used as a cheaper alternative to resin for repairs? At $70/qt for West Resin, this stuff adds up quick!
On another note you can find it for half that if you buy it by the gallon
Yes. Epoxy tends to have better adhesive properties than the esters, so for some jobs it is a better choice for those jobs. If you are working in an enclosed space, the fumes from the esters can be overwhelming, fumes from epoxy are pretty mild.

Total Boat epoxy from Jamestown Distributors is less expensive than West. At Jamestown the price difference between the epoxy and polyester is not as big.
 
Aug 28, 2015
190
Oday 28 St Joseph, MI
Let me start by saying I haven’t done any fiberglass work in about 8 years so it’s possible the chemical properties of the various resins have changes since the following was true. When repairing fiberglass layups the bond between the layup and the repair is purely mechanical rather than the chemical bond one would find with layers added to the partly cured previous layer. Epoxy resin has a stronger mechanical bond to existing fiberglass than either polyester or vinyl ester. Of course this mechanical bond depends on the coarseness sanded into the area to which the repair is made.
 
Jan 11, 2014
11,323
Sabre 362 113 Fair Haven, NY
Let me start by saying I haven’t done any fiberglass work in about 8 years so it’s possible the chemical properties of the various resins have changes since the following was true. When repairing fiberglass layups the bond between the layup and the repair is purely mechanical rather than the chemical bond one would find with layers added to the partly cured previous layer. Epoxy resin has a stronger mechanical bond to existing fiberglass than either polyester or vinyl ester. Of course this mechanical bond depends on the coarseness sanded into the area to which the repair is made.
Yep, that's pretty much still the same story.