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Finishing and Sealing Hulls  Bottom

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  • So my first catamaran project with a 1993 Mystere 6.0 is quickly coming to a close. I'm so excited! First off thank you to everyone for all your insight and help getting me this far. I have reinforced the bulkheads, removed and resealed the hull lids, Patched multiple small cracks and holes, and reinforced some areas with extra layers of fiberglass. I believe now is the time to begin repainting and finishing the hulls. Is that correct? Is it time to start thinking paint? I still need a rigger to do new shrouds and evaluate the mast but I am trying to control and accomplish what I can before sending the boat elsewhere.

    I have read mixed ideas about whether you can layer gel coat on top of other gel coat. Where I am currently is this; there are three surfaces at the moment in the hulls
    1) Factory Surface (old original gell coat
    2) Repaired areas m. Theses are a combination of new epoxy/ fiberglass, small hole patch like Bondo-Fiber, or squeezed out epoxy from the hull lids.
    3) gelcoat covered Fiberglass where the original owner did a repair and gel coats over it. The catch here is when I unpacked Rubbermaid tubs of spare parts there was a spray can of white primer. The surface is smooth and"thick" like gel coat but I'm not sure if there is primer underneath or if he just used it where else.

    My game plan was to

    1) take 80grit sandpaper to the twosome or patched areas to smooth the transitions between new fiberglass and old gel coat as well as knockdown high spots from the PO's or Jon trendiest the bottom of the hulls
    2) move to 120GRIT Ion an orbital sander to flatten and smooth the other repairs and scuff the factory surface
    3) Wipe down the entire surface with acetone or mineral spirits and then brush on the new gel coat, Sand with 300+ to remove the brush marks and then while down and apply a wax


    I'm sure I have made some nasty assumptions ( like in not sure how this will work on the kids that have some texture. Someone also suggested a thin bead of silicone where the lid meets the hull just to full small gaps and ensure there aren't any gaps - bad idea? ) but I am really excited that the structural repairs are done and this and the rigging are the final steps before getting out on the water.



    Edited by jgregs on Feb 26, 2022 - 08:46 AM.
  • If you have some patches, it is likely you will need to fair the repairs to be smooth enough for final finish. My favorite material for this is West System Epoxy mixed with 410 Microlite filler / microballons. This material lets you form a thickened epoxy that shapes easily and has no air pockets, pits or similar problems. I use a 12-inch long sanding block to have good control over the fairing of curved and straight repairs. It's much easier using a long narrow sanding block. You can spend a lot of money, or get a cheap one from Harbor Freight that works great. This one works great for me. https://www.harborfreight…dy-hand-sander-1727.html

    For final finishing, I used Interlux Primekote epoxy primer and Perfection top coat. https://www.wholesalemari…high-gloss-marine-paint/ It's expensive, but provides great results that are very durable. Other members have use AlexSeal 2-part paints. One advantage of paint is that repairs can be matched. For example, last summer my boat got holed during a storm. You can see the repairs in the following images resulted in a perfect invisible match. The filler shown is West 407 fumed silica over 7-layers of epoxy saturated woven glass. This was finished with 410 Microlite, faired and painted with Primekote and Perfection Arctic White.

    https://i.imgur.com/IhCDUiel.jpg

    https://i.imgur.com/dzCxn28l.jpg

    https://i.imgur.com/bPLzKaUl.jpg

    --
    Tom
    NACRA 5.7 (1984 Sail 181)
    Pennsylvania
    --
  • alright, so fair the hulls with a large sanding block, apply epoxy primer, then use a hih quality top coat?
  • The biggest part of the work will go into preparation. My boat was fully disassembled, and I painted the hulls while suspended from hangers. Others have used saw-horses. The boat needs to be carefully masked to protect surfaces and hardware that won't be painted, then cleaned and dewaxed BEFORE sanding. The hull parts t be painted are sanded with 180-220 grit paper and all defects fixed or removed. The hull gets wiped down again with a slow-flash solvent to ensure that the surfaces is dust and wax-free. The primer has to be totally smooth, and any orange-peel or defects will be seen in the top-coat. The primers are sandable, but to get the smoothest finish possible I thin and spray. The primer in the can can be very thick, and it can be hard to get a smooth result that does not take lot of sanding. The epoxy Primekote will work for 2-part or single part top side paint, and it is tougher and more waterproof than the original gel coat.

    Single-part top paint is easier and less expensive to use, and if you have no prior painting experience may be a better choice. Lots of information on this on JamestownDistributors and videos on using the Roll and Tip method of painting. 2-part epoxy and polyurethane finishes are more difficult due to need for special thinners and the fact it just eats foam rollers. 2-part poly emits isocyanurates which are toxic, so roll and tip is the way to go if you are not a pro.

    Research this on the internet and watch some videos of surface preparation and painting, and read the application guide of the paint you plan to use, then read it again. Several of us on the forum have done this and gotten very good results, and the boat can look like new, however there are no shortcuts and it takes time and the right weather conditions during painting. We can answer questions here as they come up, but you need to really equip yourself with more information and not just take my non-expert suggestions alone.

    --
    Tom
    NACRA 5.7 (1984 Sail 181)
    Pennsylvania
    --
  • On weather conditions - typical marine paints are WAY worse about blushing for some reason. It's not about temperature so much as ensuring you're nowhere near dewpoint before cure. Like don't paint with dropping Temps in the afternoon. Prep the day before and paint in the morning. I ended up having to throw another coat on, but after sanding and re-spraying, the results were fantabulous...

    --
    Chuck C.
    H21SE 408
    --
  • So I've been reading a lot and watching videos. Here is what I'm thinking through

    1) The hull lids. They have a texture build into them. Do I just need to hit this with a stiff brush while prepping the surface?

    2) In the hull lids, despite being glued down, there is a slight gap in places where the adhesive didn't squeeze out and/or the fit wasn't perfect. Someone elsewhere said a marine grade silicone could be used to fill these tiny gaps. In my head it makes sense that you would address this prior to finishing but then silicone doesn't seem like the right solution. Fairing compound maybe?

    3) I've read that gelcoat or paint can be used to add waterproofing. Do I need one or the other or both? I'm covering fiberglass+epoxy in some areas and Bondo Glass in others for small gap filling. I have a compressor and can buy a Wagner sprayer from Home Depot for ~$100, from the videos I've watched so far, looks like similar application

    4) If I'm going to be doing large areas, it makes sense to me to do the whole thing that way I know it is done right. Agree or disagree?
  • 2) Use thickened epoxy, do NOT use silicone!

    --
    Brgds
    Lars

    Present multihulls:
    Frankencat 5.8/F20
    Frankentri 5.5/Tornado/F18
    Aerow trimaran foiler

    https://www.facebook.com/groups/1192604934176635
    --
  • jgregs2) In the hull lids, despite being glued down, there is a slight gap in places where the adhesive didn't squeeze out and/or the fit wasn't perfect. Someone elsewhere said a marine grade silicone could be used to fill these tiny gaps. In my head it makes sense that you would address this prior to finishing but then silicone doesn't seem like the right solution. Fairing compound maybe?


    To confirm, you are talking about the deck on the hulls, not the lids of the round ports on top of the hulls?
    Silicone is a poor choice as is will break down and leak as the hull and deck flex differently under stress. Enlarge the space a bit with a scraper and fill with thickened epoxy.

    --
    Sheet In!
    Bob
    _/)_____/)_/)____/)____/)_____/)/)__________/)__
    Prindle 18-2 #244 "Wakizashi"
    Prindle 16 #3690 "Pegasus" Sold (sigh)
    AZ Multihull Fleet 42 member
    (Way) Past Commodore of Prindle Fleet 14
    Arizona, USA
    --
  • So I was talking to the guy at West Marine and he said polyester resin and fiberglass will fall apart for any applications in or around the water- even when painted. Do I need to undo my work and redo it with epoxy resin?
  • All hull repairs I have ever done are with epoxy. The mechanical bond of polyester resin is just much weaker, but if you were using a thickened polyester to bond the deck lid to the hull, it is not something left submersed, and is an adequate adhesive that you might be able to separate in the future if you need to access inside the hulls again. Epoxy is mostly permanent. If I had some minor gaps to seal, I would use 3M 4200 not silicone. It would help to know exactly what was repaired or bonded with polyester.

    --
    Tom
    NACRA 5.7 (1984 Sail 181)
    Pennsylvania
    --
  • tominpaAll hull repairs I have ever done are with epoxy. The mechanical bond of polyester resin is just much weaker, but if you were using a thickened polyester to bond the deck lid to the hull, it is not something left submersed, and is an adequate adhesive that you might be able to separate in the future if you need to access inside the hulls again. Epoxy is mostly permanent. If I had some minor gaps to seal, I would use 3M 4200 not silicone. It would help to know exactly what was repaired or bonded with polyester.


    I used polyester resin along with fiberglass cloth to fill and strengthen a crack along the front of the hull. Now I'm wondering if I need to get the angle grinder and redo it all
  • Well, the hull is all sealed and it looks good today. Go sailing when the weather and inclination aligns. I would let it go and see what happens rather than take any "expert" opinion here or at West Systems. Epoxy is better, but I bet you won't have a problem if the patch was well-prepared and finished. It's not like we leave these hulls in the water for months at a time.

    --
    Tom
    NACRA 5.7 (1984 Sail 181)
    Pennsylvania
    --
  • tominpaWell, the hull is all sealed and it looks good today. Go sailing when the weather and inclination aligns. I would let it go and see what happens rather than take any "expert" opinion here or at West Systems. Epoxy is better, but I bet you won't have a problem if the patch was well-prepared and finished. It's not like we leave these hulls in the water for months at a time.


    Remember the decks do more than keep water out. They provide a a good amount of structural support as well. When I removed and resealed the decks on my P-19, I used a thickened West System to rebond and never had an issue. There are a lot of different ways to rebond the decks, but keep in mind these boats are slapped together as quickly as possible and the best practices are not always used during initial production.

    Good job and get out on the water, because What's the worst that can happen?

    --
    Scott

    Prindle 18-2 Mod "FrankenKitty"
    Tornado Classic "Fast Furniture"
    Prindle 19 "Mr. Wiggly" - gone
    Nacra 5.8 "De ja vu"
    Nacra 5.0
    Nacra 5.8
    Tornadoes (Reg White)
    --
  • So I'm almost finished. I am currently fairing the hulls but a last minute cold snap kept the West System expoy (105+206 slow cure + fairing compound) from curing properly so it is a little gummy in spots. I'm probably going to hit it with a heat gun and try to scrape it off and redo it.

    Once that is done there will be lots of sanding and then priming then more sanding and then painting. Did I miss anything?
  • You are guys are the best. I've spent the last two weekends fairing the hulls and trying to be as meticulous as possible with sanding. I probably have another round of sanding to do before I can start finishing but we are almost there!!!!
  • If you're painting, be sure to use a prime coat/primer sealer for the paint to stick to. Need to go from final sand, to acetone wipe-down, evaporate and paint primer on. That has a huge impact on how well the topcoat comes out and how well it'll last. And, lastly - we need pictures!

    --
    Chuck C.
    H21SE 408
    --
  • charlescarlis . . . And, lastly - we need pictures!


    After fairing several spots and sanding smooth with 240grit
    https://www.thebeachcats.com/gallery2/main.php?g2_view=core.DownloadItem&g2_itemId=136558&g2_serialNumber=4

    A different angle. you can also see all the ropes have been replaced
    https://www.thebeachcats.com/gallery2/main.php?g2_view=core.DownloadItem&g2_itemId=136562&g2_serialNumber=4

    Gotta do some additional sanding on the bottoms were the original owner did some lousy repairs and then sand down the fairing efforts on the opposite side. from there it is just barrier coat, prime, and paint. Last thing is to get the diamond wires replaced and back on the mast and then get the boat and trailer registered and she will be good to go!
  • virtual phone
    he then shot a very last-spherical 76 on the carmel, ind., path on wednesday to finish in a tie for 2nd with a 4-over 220, 4returned of winner john marshall butler.i played super,” daly ii advised the indianapolis megastar. “itd had been cool to win, however i still have time. just a couple horrific 3-putts each days, however apart from that i played incredible.
  • virtual phone
    he then shot a very last-spherical 76 on the carmel, ind., path on wednesday to finish in a tie for 2nd with a 4-over 220, 4returned of winner john marshall butler.i played super,” daly ii advised the indianapolis megastar. “itd had been cool to win, however i still have time. just a couple horrific 3-putts each days, however apart from that i played incredible.
  • blogsandarticlesedvirtual phone
    he then shot a very last-spherical 76 on the carmel, ind., path on wednesday to finish in a tie for 2nd with a 4-over 220, 4returned of winner john marshall butler.i played super,” daly ii advised the indianapolis megastar. “itd had been cool to win, however i still have time. just a couple horrific 3-putts each days, however apart from that i played incredible.


    did we just get a transcription play-by-play of someone's golf game? Congrads I guess?

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