Antifoul, what to use if I don't know what the old stuff is?

Discussion in 'Materials' started by DennisRB, Sep 18, 2013.

  1. DennisRB
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    DennisRB Senior Member

    I need to antifoul my boat but I have no idea what the old antifoul is. Is sanding it all off the only option? What about barrier coats? What a good brand antifoul for use in Brisbane?
     
  2. PAR
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    PAR Yacht Designer/Builder

    You can take a pressure washer to it and get the bulk of it off. You can media blast it too.

    The choice of anti-foul is locally subjective. By this I mean, each area will have paint types that work better then others and according to use. Simply put, if you use the boat a lot, you'll want a different paint then a person that only occasionally takes her out. The locals will know what works best in your area, so ask around.

    I know this seems like a cop out reply, but it's the reality of bottom coatings. They're application specific.
     
  3. michael pierzga
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    michael pierzga Senior Member

    At the shipyard they take the solvent that is required for your proposed paint , saturate a rag with it , then wipe dont a test patch to see if the solvent is compatible with your proposed paint.
    As far as what paint. International makes good antifoul. Ive been using Trilux.

    The correct way to prep the bottom is wet sanding with a swivel head dry wall sanding stick fitted with 80 or 50 grit wet or dry. use plenty of water to lubricate the sand paper. Sand then surgically wash the bottom with soap and water with a soft yacht scrub brush. When you drag your hand on the bottom no antifoul colour shall appear on your hand.

    If you must remove the old coating sand blasting is the way to go. Again Ive hadvert good luck with International epoxy primers. the interprotect line has a long overcoat time...very useful when working on the bottom
     
  4. DennisRB
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    DennisRB Senior Member

    Thanks guys. Do I need a barrier coat? The is no blisters, well maybe one or 2 small ones, and any very minimal flaking, only on the keel

    So I use the solvent that goes with the proposed new antifoul. I then wet a rag with it and rub it on the antifoul. What happens if it is and compatible, and what happens if it is not?
     
  5. michael pierzga
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    michael pierzga Senior Member

    The solvent will desolve the old anti foul paint.
     
  6. michael pierzga
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    michael pierzga Senior Member

    There is a product called tie coat. Its a gray international primer that is used to separate old paint from new. I dont like the stuff.
     
  7. PAR
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    PAR Yacht Designer/Builder

    Barrier coats typically help prevent blisters from occurring or reappearing once you've experienced them. It's done over bare 'glass, not over any paint. Some primers are called tie coats, because they're designed to work over the various types of bottom paint. These are used if you can't identify what you have, but mostly they're a marketing tool to sell you one more product, that a pro wouldn't need. A tie coat is basically a primer and not entirely necessary if you old anti foul paint is in reasonable condition and not too thick. As a rule you don't want to remove all of the old bottom paint unless it's too thick or poorly adhered.

    A solvent may not remove all the old paint, especially if there are many layers. Sand blasting can damage the gel coat, so I'd recommend a softer media if going this route, maybe coke, soda ash or walnut shells, instead. You can use a chemical stripper, which works though it's important to use a stripper comparably with 'glass surfaces.

    The approach you use, depends a lot on the size of your boat too. Hand sanding after a solvent wash, on a 35' yacht is a career choice and decidedly not time effective, but just an afternoon on a 18' bow rider.

    Again, the type of paint you use is area/application specific.

    At this point it would be helpful to know what boat you're working on, how many layers of previous bottom paint there are, how well stuck these layers are, etc.

    It's common for ablative paints to oxidize once out of the water for a while, which may cause it to chip and flake. If the underlying paint is still well stuck, just sand off the last two coats of paint and apply more. The only reason to remove all of the paint is if you have too much bulk, damage, blisters or other reasons the paint can't be trusted any more.
     
  8. michael pierzga
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    michael pierzga Senior Member

    The solvent is to identify paint compatibilty. You cant remove antifoul with solvent...you will kill yourself.

    Anti foul can also be removed with a sharp paint scraper. Count on Plenty of blisters on your hands...keep the scraper razor sharp. A push stroke is most effective. Scrapers are automobile leaf springs....two. Handed...duct tape grip...90 degree sharpened edge for two sharp surfaces.

    After blasting a barrier coat is always used.

    A pro blaster with the correct gear can surgicaly sweep the bottom and cause no damage.
     
  9. DennisRB
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    DennisRB Senior Member

    Very helpful. Micheal I still do not understand the solvent thing! If the solvent DOES remove the old paint does this mean COMPATIBLE or INCOMPATIBLE? What do you think of this PAR?

    My boat is a 40 food production sail boat. Hunter Legend 40.5. I have never anti-fouled it. It was last done 3 years ago in California and I do not know the anti foul history (I have owned it for 2 years). I now have the boat in Brisbane AU.

    99% of the current anti foul is very good on areas of fiberglass and very well stuck on. Some small areas around the stern and rudder where large barnacles have been scraped off have ripped chunks of the anti foul off. No blisters, maybe on one the fiberglass part of the keel, but as usual the lead wingkeel bulb has a lot of bad anti foul on it and it may need some extra care. Particularly on the underside of the winged keel bulb, which I assume was very difficult for previous people to get to.
     
  10. DennisRB
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    DennisRB Senior Member

  11. rwatson
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    rwatson Senior Member

    Your pics arent working for me -


    Temporary Error (404)


    We’re sorry, but your Gmail account is temporarily unavailable


    maybe because you have them in your private email account
     
  12. DennisRB
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    DennisRB Senior Member

    Yeah, I will redo them when I get home. Cheers.

    Does anyone have an answer to my question regarding michael cryptic explanation of testing exiting antifoul with the solvent for the new antifoul?
     
  13. PAR
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    PAR Yacht Designer/Builder

    You don't need to test your anti fouling, just knock off the loose stuff, scruff up the surface sufficiently enough, to accept new coatings and start slathering on more paint. If truly worried about compatibility, between the two different anti foul coatings, do as described and apply new paint to a small area under the boat and let it cure. Incompatibility issues will quick show up as fish eyes, wrinkles, orange peel, lifting, cracking, etc. If these do appear, remove the new paint by sanding. It's a small area so not a big deal, then you'll need to prime first, followed with anti foul, but honesty, this is unlikely. These paints are designed to go over each other, knowing folks don't always know what was used on the previous bottom paint job.
     
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  14. DennisRB
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    DennisRB Senior Member

    Cheers Par. Thats what I was hoping to hear. Not sure what slip fees cost where you are from, but they will cost me $500 to haul in and out, and $460 a week on the stand. So I want to have my **** together to do the job fast when its out.
     

  15. PAR
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    PAR Yacht Designer/Builder

    Our slip, haul out and on the hard fees suck in this country too. You don't have a head lock on marinas screwing you out of cash. You can probably test the bottom paint compatibility, while still in the water, saving a day or so waiting for the stuff to dry. If it works, bingo, if not, you can sand it off once on the hard.

    On the hard fees are usually high, simply because they don't want you to make a career, out of what ever repairs or maintenance you might have. Nothing is more uninviting, to a prospective marina customer, then having a yard full of boats in various states of repair or decay, lounging around. No one wants their boat parked next to someone about to paint, or sand or use chemicals, etc., so they jack the price up, on the hard storage, especially in season, to get you back in the wet stuff quickly.
     
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