Epoxy Barrier Coat application question

[Matteo268]

Currently I'm striping bottom of boat. Before I apply the bottom paint I am wondering when applying the 2 part epoxy barrier coat do you cover the lifting strakes that are below the waterline with the barrier coat or do they only get the coats of bottom ablative paint. It appears that the lifting strakes are make of some form of composite plastic and want to insure that I get the best adhesion. Any help is greatly appreciated.

 

[Genius]

the epoxy barrier coat IMO does two things; it provides a great means of adhesion to the substrate and provides protection for osmotic water transfer. I'd coat everything underwater you are putting bottom paint on.

 

[[email protected]]

I feel differently about it. Fiberglass boats have been around without barrier coat for 50 years. The gelcoat is thought to be the protection against water intrusion except gelcoat is just resin that is so full of pigment that it's porous. The first layer that's impervious to water is the first layup of glass behind the gelcoat. If it's laid up well and made with a good resin, Isophalic polyester or vinlyester it won't accept water and blister. If it's made using cheap ortho GP resin and laid up poorly (true of many boats made in the Orient) it will blister no matter what you do. My old JC has never had a barrier coat and the first 6 inches of the bottom near the stem has had the gelcoat worn off for years from repeated beaching's and not a blister.
The one that get's me the most is "hot coating" where the bottom paint is mixed in with the epoxy barrier coat. I wonder what West or Gudgeon Brothers would say if you told them you were mixing copper based paint into their product.
I'm trying to set up my 36 year old boat for soda blasting and then I'm just going to have it primed and painted.

 

[novivin]

I feel differently about it. Fiberglass boats have been around without barrier coat for 50 years. The gelcoat is thought to be the protection against water intrusion except gelcoat is just resin that is so full of pigment that it's porous. The first layer that's impervious to water is the first layup of glass behind the gelcoat. If it's laid up well and made with a good resin, Isophalic polyester or vinlyester it won't accept water and blister. If it's made using cheap ortho GP resin and laid up poorly (true of many boats made in the Orient) it will blister no matter what you do. My old JC has never had a barrier coat and the first 6 inches of the bottom near the stem has had the gelcoat worn off for years from repeated beaching's and not a blister.
The one that get's me the most is "hot coating" where the bottom paint is mixed in with the epoxy barrier coat. I wonder what West or Gudgeon Brothers would say if you told them you were mixing copper based paint into their product.
I'm trying to set up my 36 year old boat for soda blasting and then I'm just going to have it primed and painted.

What would you prime with? There are not many paints I know of that are recommended below the waterline for boats that are kept in the water. I own a wooden DE, that I primed and painted with Kirby Red Lead before I put ablative on. For fiberglass, it is hard to beat epoxy barrier paint systems for longevity and toughness (scratch resistance). I own a trailered novi ob that I barrier coated after removing some pretty sad ablative antifouling. I like the look of a bottom color and bootstripe, so used epoxy barrier in 2010. It is still as good as it was after I did it, and besides accidentally bumping a rock it is entirely intact, except that scratch.

 

[Genius]

I feel differently about it. Fiberglass boats have been around without barrier coat for 50 years. The gelcoat is thought to be the protection against water intrusion except gelcoat is just resin that is so full of pigment that it's porous. The first layer that's impervious to water is the first layup of glass behind the gelcoat. If it's laid up well and made with a good resin, Isophalic polyester or vinlyester it won't accept water and blister. If it's made using cheap ortho GP resin and laid up poorly (true of many boats made in the Orient) it will blister no matter what you do. My old JC has never had a barrier coat and the first 6 inches of the bottom near the stem has had the gelcoat worn off for years from repeated beaching's and not a blister.
The one that get's me the most is "hot coating" where the bottom paint is mixed in with the epoxy barrier coat. I wonder what West or Gudgeon Brothers would say if you told them you were mixing copper based paint into their product.
I'm trying to set up my 36 year old boat for soda blasting and then I'm just going to have it primed and painted.

The barrier coat is a primer.

 

[traditions]

I wouldnt worry about coating pvc rails with a barrier coat, but I dont see it would do any harm. When new, paint doesnt stick very well to pvc, unless it had been sanded. As for soda blasting , I would imagine it will open up a lot of porosities in the gel coat. Unless the boat was vacuumed bagged, you will have porosities.Although there are hundred of boats that havnt been barrier coated, and most likely have water intrusions, I have never hard of a failure. Just look at how many 50+ year old 2 piece Bruno’s that are still in use.Blisters are under the gelcoat, not into the laminate. Also, most all older boats never gelled the inside of the hull, so wouldn't intrusion take place there, even though it isn't under pressure. Just a thought.

 

[[email protected]]

I get that, but I just need good adhesion for bottom paint to the hull not a two part epoxy system to protect against water working it's way into the laminate. I would use something like Interlux Primocon to keep the antifoulant on the hull, just like we use 1 part primer to keep the bottom paint on our steel boats. I don't think I need a whole two part epoxy process to "save" my hull from water intrusion like Total Protect say's. Now if I owned an old Island Gypsy Taiwan trawler than maybe I'd worry. Course, if I owned 1 of those I'd worry about me.

 

[novivin]

I get that, but I just need good adhesion for bottom paint to the hull not a two part epoxy system to protect against water working it's way into the laminate. I would use something like Interlux Primocon to keep the antifoulant on the hull, just like we use 1 part primer to keep the bottom paint on our steel boats. I don't think I need a whole two part epoxy process to "save" my hull from water intrusion like Total Protect say's. Now if I owned an old Island Gypsy Taiwan trawler than maybe I'd worry. Course, if I owned 1 of those I'd worry about me.

Thanks for including that detail about the product. I did not know Interlux Primocon was good on FRP below waterline as a primer.

 

[Genius]

I get that, but I just need good adhesion for bottom paint to the hull not a two part epoxy system to protect against water working it's way into the laminate. I would use something like Interlux Primocon to keep the antifoulant on the hull, just like we use 1 part primer to keep the bottom paint on our steel boats. I don't think I need a whole two part epoxy process to "save" my hull from water intrusion like Total Protect say's. Now if I owned an old Island Gypsy Taiwan trawler than maybe I'd worry. Course, if I owned 1 of those I'd worry about me.

No, epoxy is the product you’re looking for. That’s what it was designed to do before the osmotic issue even was marketed.

Our paint schedule on the rigs was three coats epoxy for underwater hull.

 

[[email protected]]

I wouldnt worry about coating pvc rails with a barrier coat, but I dont see it would do any harm. When new, paint doesnt stick very well to pvc, unless it had been sanded. As for soda blasting , I would imagine it will open up a lot of porosities in the gel coat. Unless the boat was vacuumed bagged, you will have porosities.Although there are hundred of boats that havnt been barrier coated, and most likely have water intrusions, I have never hard of a failure. Just look at how many 50+ year old 2 piece Bruno’s that are still in use.Blisters are under the gelcoat, not into the laminate. Also, most all older boats never gelled the inside of the hull, so wouldn't intrusion take place there, even though it isn't under pressure. Just a thought.

It's the first structural layer of GP resin acting as corrosive without oxygen under the gelcoat that causes the blisters. The only layer vacuum bagging wouldn't help is the gelcoat because that is put into the mold first, no trouble seeing what's covered and what's not.

 

[c1steve]

I would apply a quality barrier coat, and go wet on wet if spraying. Two coats of epoxy, ideally sprayed with a heated gun system, wait a few days between coats for any solvents to evaporate. Then one last coat of epoxy, clean the spray gun, and immediately spray on the first coat of bottom paint.

The only problem with epoxy is that if it is thick, it is hard to apply it in a thin, smooth coat. If it has solvents in it, then you have to wait as long as long as possible for the solvents to evaporate. Chemical bonding between epoxy coats is usually excellent as long as the paint has not completely hardened, which may be a week or two, or longer.

 

[[email protected]]

I'm not sure what solvents are in epoxy that have to evaporate, to me it's either cured or it's not, and yes, a chemical bond, "wet on wet" is the best bond, so why wait a week and add just a mechanical bond for the third coat?
Heated gun system? Yeah, sure, I'm on it, think I have two of those in the back of my service truck.
What boat owner is spraying bottom paint and what yard is allowing this? Could you imagine the overspray complaints?
Is it me or does this process seem a little complex for someone trying to bottom paint their boat"?
The original question though was about bonding to the lifting strakes as they may not be fiberglass.
If it was mine, I'd epoxy them too if I was coating the bottom but I'm not.
I did add pvc Fast Rails to my boat and they held paint fine with no prep.

 

[Bert1962]

I feel differently about it. Fiberglass boats have been around without barrier coat for 50 years. The gelcoat is thought to be the protection against water intrusion except gelcoat is just resin that is so full of pigment that it's porous. The first layer that's impervious to water is the first layup of glass behind the gelcoat. If it's laid up well and made with a good resin, Isophalic polyester or vinlyester it won't accept water and blister. If it's made using cheap ortho GP resin and laid up poorly (true of many boats made in the Orient) it will blister no matter what you do. My old JC has never had a barrier coat and the first 6 inches of the bottom near the stem has had the gelcoat worn off for years from repeated beaching's and not a blister.
The one that get's me the most is "hot coating" where the bottom paint is mixed in with the epoxy barrier coat. I wonder what West or Gudgeon Brothers would say if you told them you were mixing copper based paint into their product.
I'm trying to set up my 36 year old boat for soda blasting and then I'm just going to have it primed and painted.

I totally agree !
On an older boat just epoxy prime on everything that’s in good shape & use whatever bottom paint you prefer !!
Barrier coat will do nothing as only gel coat will blister.

 

[LuSea]

Are we missing the boat as to the real reason for a barrier coat? Most early fiberglass boats did not have a vinylester layup in the outer portion, then switching over to polyester. Water will eventually begin to degrade a polyester resin layup once the gelcoat surface has been removed. The same thing happens with gelcoat blisters.

After going thru the effort and expense to strip a fiberglass hull of its old dinosaur skin why not do a thorough job on the surface . You apply barrier coat usually only once. Yes, applying an epoxy barrier coat system is expensive and timing is everything during the installation until you have applied the first coat of ablative. BUT …. The effort is worth the reward.
- Media blast of chemical strip
- let the hull dry and sand to #80
- apply a tight epoxy skim coat over blisters
- sand
- apply a second tight skim if necessary
- sand
- apply the barrier system within the time window
- apply any color ablative first coat
- apply the color of your choice as the final coat
- the following season simply abrade and touch up the running surfaces that have exposed the base color ablative.

I too would like to know if it’s ok to barrier coat over my lifting rails. I have a new set in the garage floor that will be installed with Plexus very soon………

 

[novivin]

Sanded pvc lift rails should take the epoxy barrier coat. It will not adhere as well as it will to the prepped hull, but should adhere well enough I imagine. Will the plexus adhere to cured barrier coat? I bet it would, and I bet the best way would be to apply the rails to a barrier coated hull then finish coat and ablative over that. Thinking out loud, but knowing what I have experienced with adhesion of chemicals on plastic- and the proper application of coatings to ensure intended performance this seems to make sense.

 

[John Allin]

Are we missing the boat as to the real reason for a barrier coat? Most early fiberglass boats did not have a vinylester layup in the outer portion, then switching over to polyester. Water will eventually begin to degrade a polyester resin layup once the gelcoat surface has been removed. The same thing happens with gelcoat blisters.

After going thru the effort and expense to strip a fiberglass hull of its old dinosaur skin why not do a thorough job on the surface . You apply barrier coat usually only once. Yes, applying an epoxy barrier coat system is expensive and timing is everything during the installation until you have applied the first coat of ablative. BUT …. The effort is worth the reward.
- Media blast of chemical strip
- let the hull dry and sand to #80
- apply a tight epoxy skim coat over blisters
- sand
- apply a second tight skim if necessary
- sand
- apply the barrier system within the time window
- apply any color ablative first coat
- apply the color of your choice as the final coat
- the following season simply abrade and touch up the running surfaces that have exposed the base color ablative.

I too would like to know if it’s ok to barrier coat over my lifting rails. I have a new set in the garage floor that will be installed with Plexus very soon………
gen
View attachment 155516

You are 100% correct.
As far as lifting rails go..are they FRP or something else?
Blisters may not be an issue in this case.

 

[LuSea]

You are 100% correct.
As far as lifting rails go..are they FRP or something else?
Blisters may not be an issue in this case.

My lifting rails are PVC from Barbour Plastics

 

[John Allin]

My lifting rails are PVC from Barbour Plastics

I'm not sure you will get a good bond between epoxy and PVC. Couldn't hurt to try a small section first, but I wouldn't be concerned with blistering on those lifting rails.

 

[Good to Go]

I redid my bottom last year and went over pvc lifting rails with barrier coat and then bottom paint. No issues after a season. I also glassed in my pvc spray rails with epoxy. No issues there either. Only one season but looks like the day it was applied.

 

[Jjammer]

GoodtoGo your NB looks awesome.

LuSea scuff up your rails real good, and either barrier coat them if you want, or just go over them with your bottom paint...

I plexused some rails on, then scuffed and bottom painted, paint held fine.