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Epoxy below the waterline?

#1
I have a small Boston Whaler tender that's been in the family since '75. It's in rough shape, the interior green is crazed and cracked and has many small places where the gelcoat has popped off the glass, the outside is 40yr old Imron. The Imron is hard as a rock, to the point that 40g on a DA mostly just polishes it and makes a mess. Damn I don't want to start with chemical stripper for several reasons, but after talking with a commercial sandblaster friend of mine I plan to let him sandblast the whole thing.
The idea is to remove the Imron on the outside of the hull, trying not to remove all the factory gelcoat, and mostly mechanically etch and clean up the factory gelcoat on the inside.

At this point would SPI epoxy be the right thing to apply to get a base to start on? The inside has textured panels in the floor that would be hard to sand without flattening out the pattern, and at that, some of the pattern is gone and I may try to cast a plug from the other areas to duplicate it, or may sand the hell out of all of it and go a different route. But I need to get a game plan for the first step after sandblasting. I can use West Systems products etc... and have before, but I have enough SPI epoxy to do the boat and the Vette I think. Also, I'm trying to think ahead how I'm going to sand the epoxy in the textured portions of the floor. I have used low pressure sandblasting for this type of thing, but man that will make a mess.

So would the SPI epoxy be ok to use on the outside of the hull ie: below the waterline? It would prob be left in the water over a long weekend at most. No antifouling paint needed.
 
#2
yes the epoxy is the only thing that should be used. when you blast the hull, below the waterline you will probably end up with a ton of popped blisters. the gelcoat will pop off the glass in small spots. you'll need a can of 3m blister repair. its a specialty polyester filler for this. after that you will need to block sand the gelcoat flat over the whole hull because to gonna be tore the hell up from blasting and super uneven. once you get everything flat again then do 3 coats of epoxy, sand and paint the hull with awlgrip.
 

Dub

Von Dub... The Total Gearhead
Staff member
#3
Hull of my boat is just white epoxy. Been that way for 7 years now. Still looks great. If I remember I only put 2 coats on as I wasn't sure if I was going to keep it or not. It's on freshwater only. But I'd recommend it to anyone
 
#4
yes the epoxy is the only thing that should be used. when you blast the hull, below the waterline you will probably end up with a ton of popped blisters. the gelcoat will pop off the glass in small spots. you'll need a can of 3m blister repair. its a specialty polyester filler for this. after that you will need to block sand the gelcoat flat over the whole hull because to gonna be tore the hell up from blasting and super uneven. once you get everything flat again then do 3 coats of epoxy, sand and paint the hull with awlgrip.
Hey Jim, I heard that the marine blister repair/filler is not for use over epoxy, so that normal putties must be used for defect repair after epoxy primer, have you had any experience with this?
 
#5
Hull of my boat is just white epoxy. Been that way for 7 years now. Still looks great. If I remember I only put 2 coats on as I wasn't sure if I was going to keep it or not. It's on freshwater only. But I'd recommend it to anyone
Dub, do you keep the boat covered? I thought bare epoxy didn't play well with UV rays.
 
#6
Jim, I'm sure I'll have to spread the whole boat with fairing compound or "bondo" as it's prob 45yrs old and pretty wavy. If I put epoxy on first after sandblasting, wait three days and sand with 220 and keep it covered I should have a base to apply filler like a month later? Level everything and and re-epoxy and paint (or leave white epoxy?). I'm trying to spray the epoxy before I spray the Vette so as to get some practice.

The interior surfaces are rough, can't spend a mountain of time but it's family to me so I need it to be decent. I thought about colored Rhino Liner inside?
 
#7
Hey Jim, I heard that the marine blister repair/filler is not for use over epoxy, so that normal putties must be used for defect repair after epoxy primer, have you had any experience with this?
crash, the blisters are fixed before the epoxy. generally you want to get the glass issues straightened out first then once you have everything smooth then move to epoxy and paint.

slofut, kind of answered your question with crash's. its different when we work on our cars and we like to put epoxy down on bare metal to seal it then bodywork over. with glass, get all your repairs done first. you dont want to intermix a paint product or layer in the mix. glass should be repaired with glass. nothing between. dont use bondo on a boat. atleast down low. you can use the blister repair stuff but that is rock hard and doesnt sand easy at all. if you need a filler then use adtech p17. its a solid plastic filler. it spreads and sands like a filler but when its cured its solid plastic like kicked off epoxy or polyester resin. it doesnt absorb moisture.
 
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#9
crash, the blisters are fixed before the epoxy. generally you want to get the glass issues straightened out first then once you have everything smooth then move to epoxy and paint.
Yeah, I did not mean to say that epoxy should be applied first over the major repairs, that's never been procedure afaik. I'd been told not to even use a little swipe of blister repair material to fix a small spot after epoxy, was just wondering if that was your experience. Sorry if it's off-topic, but I would think some guys would do that if the stuff was on-hand, but you're not supposed to apparently.
 
#10
im not really sure, its been quite a few years since i have used it but as a general rule of thumb polyesters can be repaired with epoxy but epoxy cannot be repaired with polyesters. they just dont bond well to epoxy resin. it is kind of strange though that we do it on the automotive side but i would assume epoxy primers are designed a bit different than an epoxy laminating resin.
 
#11
Crash and Jim, that's what I needed to know. I've always done repairs first on bare glass but after finding this forum and everyone saying epoxy first on cars, I was thinking I've been doing it wrong. I'll get some p17. I need a fairing compound I can use over the entire hull. I wish I could use Feather Fill but I have a feeling that may not be a good idea.
 
#13
p17 is some bad ass filler for glass. i turned my buddy on to it who does nothing but vettes. he doesnt touch regular body filler anymore. unlike body filler that doesnt have any strength without being adhered to a surface, the p17 is a structural plastic when its done.
 
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