How to Treat Exposed Gelgoat When Bottom Sanding??

[rardiH36]

Currently got my 1980 Hunter 36 out of the water for the second time since I bought it in 2007.

This time I have DIY power sanded the existing bottom coating more aggressively than last time. In more than a few locations, underneath the current blue bottom paint color, then past the previous black coating, then past the even earlier red ... I've encountered white. Which is either barrier coat ... or I've exposed some gelcoat. Total percentage of white compared to the previous bottom paint coverage = hardly nothing = say .1% of the total surface area

Assuming the white is gelcoat, can I just apply the new hard modified epoxy bottom paint. Or should I pre-prime with something first?

A picture is attached of me sanding/grinding away on the boat's bottom which also happens to be on the first day that I can claim SS benefits. (But I am still on the fence whether to wait a few more years before actually doing so.) Before I started sanding, the color of my boat's bottom was the same as the garbage bin and the boat hoist's frames also in the picture. Can't think or a better way to spend a birthday?! Except that evening, my wife and I enjoyed mango infused tequila tonics together ... albeit at a safe 15 miles away from the boat!

Thanks for your input.

 

[Picflight]

The better the surface is prepared the better the paint adhesion will be. I think priming should be considered.

 

[caguy]

The better the surface is prepared the better the paint adhesion will be. I think priming should be considered.

You mean priming with a sealer?

Rardi you are either more ambitious or cheaper than I am. I higher a day worker to do that, dress him up, and then sit back with a beer and watch.

 

[seadaddler]

Why

Why are you sanding down to white or gelcoat.
I think if you sand into the gel coat you need to barrier coat it.
Check and make sure what ever you have sanded to and most say to apply a barrier coat.
How old is the boat.
nick

 

[rardiH36]

Re: Why

seadaddler - Constructed in 1980. As to why I've sanded into the gelcoat (or barrier coat) hard not to along edges and high spots. Just a touch of the sander in those areas and I was through the bottom paint. I will look into obtaining the smallest quantity of barrier coat I can find.

 

[woodster]

seadaddler - Constructed in 1980. As to why I've sanded into the gelcoat (or barrier coat) hard not to along edges and high spots. Just a touch of the sander in those areas and I was through the bottom paint. I will look into obtaining the smallest quantity of barrier coat I can find.

i used 6 coats of west system epoxy with additive.....i had sanded all the gelcoat off.....it took 2 and 1/2 gallons to do this on my boat...i went 8 inches above the water line in order to have a overlap..i have a 25 ft waterline with a 5 ft draft ...it took me mixing and my 2 amigos 7 hrs to apply the coating......

 

[Scott T-Bird]

rardi, what is your ultimate goal? I'm curious because I need to tackle the same job at some point in time.

What kind of paint are you attempting to sand off ... are all 3 coats hard coats? Are you just sanding smooth and then coating or are you attempting to take all of it down to the gel coat? Then what are you going to use? I'd follow the preparation instructions that go with your intended coating.

I believe I have 2 coats of a hard coating, both burgundy. Much of the second coat has been scrubbed off by my constant scrubbing to knock the slime off (we're in relatively clean fresh water, so marine growth isn't an issue, just mild algae growth). The original hard coat has been particularly tenacious, as is the remainder of the second coat, since it can't be affected by scrubbing and doesn't appear to have worn any further in almost 10 years. I am pretty sure that the gel coat is directly under because I also have a few small patches of gel coat exposed. My intention when I am able to sand is to attempt to smooth it down to the point where the gel coat is just barely exposed and then start as if the boat where new.

 

[Barnacle Bill]

Just for the record, usually when applying a conventional antifouling paint (not VC17) you sand with an 80 grit sandpaper on the existing paint surface and clean the sanding dust off before applying new paint. If you are trying to smooth out the entire hull surface, then perhaps you wish to sand off all the paint. It really depends on the type of paint you are using, however. If a single season cuprous oxide type paint, then the paint is hard (like Fiberglass Bottomkote by Interlux) and the toxicants leach away from the paint leaving the paint behind. Once the toxicants are gone you have no antifouling protection left, but you have paint. Micron technology or any other ablative multi season paint leaches away with the toxicants. The paint and toxicants wear off your hull and in time you will see a bare hull again. This type of paint does not build up like the cuprous oxide paints do, but they can look blotchy because they are wearing off your hull in not so a regular pattern. As long as you see the ablative type paint on your hull, you can expect to get antifouling protection. Not so with single season paints. Since the toxicants leach away from the paint, seeing paint does not necessarily mean it will be still working for you. One other thing about the differences.......single season cuprous oxide paints when dry don't work so well when relaunched, but that is not a problem with ablative paints. They work no matter how many times the boat has been removed from the water, dried and relaunched. Ok, now with an understanding of the paint - back to the primer question. If you have bare hull that has been sanded, it is more vulnerable to water intrusion than gel coat that has not been sanded and it has been proven that water can penetrate that as well. So a water barrier coating is desired and epoxy is the material to use. Interlux has their Interprotect system and it works very well. It used to be that you put on at least 5 coats for prevention and 7 if you had blisters already (but only after proper preparation - i.e. sandblasting, stripping, etc.). Interlux now has a new product called Interprotect HS which eliminates all the multi coats of the 2000 or 3000 Interprotect products. You can get away with just 3 coats for protection purposes, which makes the job quicker. That's my 2 cents.

 

[bffatcat]

sanding the original gellcoat?

Thats a no no unless your planning on a new barrier coat system Ive got a vintage boat refurbished 2 years ago The area below the boot stripe was never \touched. How many layers of ablative paint are on there I dont know. If I do any sanding, when I see gelcoat I stop.

 

[Scott T-Bird]

Thats a no no unless your planning on a new barrier coat system Ive got a vintage boat refurbished 2 years ago The area below the boot stripe was never \touched. How many layers of ablative paint are on there I dont know. If I do any sanding, when I see gelcoat I stop.

What's a no no? Sanding to just expose the gel coat? I intend to start with a new barrier coat. I have no idea what has been painted on the boat. All I know is that I haven't put any coating on whatsoever ... nothing is needed where I currently have the boat.

Since there is a second coat of something that adhered to the first coat in some areas but flaked off in others, I have a rough uneven surface. I know that I want to start with a smooth surface and I don't want a substrate that will have poor adhesion quality with new coatings. I hope that sanding to the point where gel coat is just barely exposed will knock off anything that would otherwise flake off eventually.

 

[rardiH36]

rardi, what is your ultimate goal? I'm curious because I need to tackle the same job at some point in time.

What kind of paint are you attempting to sand off ... are all 3 coats hard coats? Are you just sanding smooth and then coating or are you attempting to take all of it down to the gel coat? Then what are you going to use? I'd follow the preparation instructions that go with your intended coating.

I believe I have 2 coats of a hard coating, both burgundy. Much of the second coat has been scrubbed off by my constant scrubbing to knock the slime off (we're in relatively clean fresh water, so marine growth isn't an issue, just mild algae growth). The original hard coat has been particularly tenacious, as is the remainder of the second coat, since it can't be affected by scrubbing and doesn't appear to have worn any further in almost 10 years. I am pretty sure that the gel coat is directly under because I also have a few small patches of gel coat exposed. My intention when I am able to sand is to attempt to smooth it down to the point where the gel coat is just barely exposed and then start as if the boat where new.

Scott:

My boat has alway been coated with modified epoxy (hard) bottom paints. And I am re-coating with hard paint again. My intention was to sand through the existing coat (blue), most of the next layer of paint (black ) and then stop when I saw lowest layer (red). Good in concept but hard to do. In some places, the blue and black disappeared quickly. In others, the blue was very stubborn and I just moved on.

So I did expose gelcoat (or barrier coat - I don't know) in places. And of course the surface of underlying small blisters exposed immediately. Also there were a few places where bottom paint had worn off to the gelcoat (bow and rudder areas mostly). And a very few instances where the paint had chipped off to the gelcoat. As I posted originally, these now exposed areas might have totaled 0.1% of the entire surface.

I also exposed some bare lead on the keel due to hard growth damage and me wanting to fair out decades of PO's repainting over chipped/peeled spots.

The yard I am at suggested Interlux Primacon to prime the lead. One part paint. And upon reading the label, another use is as below waterline primer before applying bottom paint. So this is what I used to "barrier" my exposed areas. Yesterday, I saw the yard workers sand the bottom an older 27' boat. I don't know what it's history was, but yellow fiberglass appeared quickly in many areas. Not much white under the bottom paint. After the sanding, the yard used Primacon. Then will apply the anti-fouling.

I recognize that Primacon is a shortcut compared to the Inter-Protect. And I am not sure that Inter-Protect can be applied over one-part paints which would happen due to overlap of my spot covering the exposed areas. So I am hoping that for the small spot coverage, Primacon will do the job. Further, I don't know if my hull even has a barrier coat already. If not, and I spot-use Inter-protect, then only 0.1% of the hull will be barrier protected!