Does old gelcoat need to be fully removed?

Discussion in 'Fiberglass and Composite Boat Building' started by souljour2000, Dec 9, 2009.

  1. souljour2000
    Joined: Aug 2009
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    Location: SW Florida

    souljour2000 Senior Member

    I am doing some remodeling and closing up gaps between the shell/liner under the cockpit floor. It is a tough place to get under and use a grinder so I am wondering if I have to remove gelcoat in the quarter berth area to make a good bond with polyester resin or can I get away with roughing/scoring it but not total removal.

    I'm wondering if gelcoat is waxiest on the top layers and if just removing those will be sufficient.

    I suspect it all has to go...especially with a polyester resin bond but just need my wrist slapped right now....
     
  2. marshmat
    Joined: Apr 2005
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    marshmat Senior Member

    Gelcoat has terrible structural properties. Epoxy will stick to it, but you're left with the gelcoat itself as a weak link in the joint.

    For something lightly loaded, this is not much of an issue. If substantial loads will be transmitted, it's better to bond to well-prepared structural laminate.
     
  3. souljour2000
    Joined: Aug 2009
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    souljour2000 Senior Member

    Thanks Marshmat...it's a joint that will incur flexing to a fair degree at least in a shock load I have no doubt...might as well do the job right...I just need a hood for my disposable hazmat suit thingy...and some real eye protection glasses..and I'll be fine...
     
  4. Fanie
    Joined: Oct 2007
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    Fanie Fanie

    Oh my soul ! :D

    Souljour, it could be easy to do that job. What I would suggest is to do most of the layup. If you're layzy and not worry about the extra weight then don't worry about removing the old part floor. You have to course sand it for a bond between the old and the new.

    When the layups cured, but within a few hours and without the new bond breaking loose, drill holes around the edge in a zig zag pattern and pop rivit the new glass to the old, all the way around. Then do a 2 layer strip layout over the rivits. Use peel ply every time. You can paint or paint a non skid over that. The rivits will prevent delaminating which is a probability even if you grind the surface course.

    Large areas can also be glued in place if you use a sealant type glue like Dow Corning - it's used between car body parts and sticks like you know what.

    Don't sniff the polyester. You will get addicted and start building boats... :D

    All that said, replacing old parts is never easy. You have to check that the support structure under the floor is sound, otherwise you may have to replace that, especially if it is structural, don't take that lightly.
     
  5. souljour2000
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    souljour2000 Senior Member

    Your suggestion of pop-rivets is interesting Fanny...had not thought of going that route but it seems like a method that would certainly hinder delamination...I am refurbishing and modifying an old 20-foot '83 Hunter as you may have gathered from some of my other posts...
    I have taken a sawzall to the rear cabin wall and the seat area of the cockpit. I decided that I like the boat enough to put some real effort and time into her..and maybe learn a bit about boatbuilding/contruction in the process...The boat is very similar to a catalina 22 and many other sailboats from that era.The Hunter 20 always had a large main berth that shifts into a dinette area and then 2 quarter berths that slide up under each cockpit seat. These berths are impractical ...going to use them as storage areas and seal/bulkhead them off semi-watertight but still have them able to open from inside the cabin and be sealed up when not in use. There are gaps between the underside of the cockpit floor sole and the quarterberths to each side that are unsightly and encourage compartment flooding. Just tabbing those off at the moment and re-doing some of the bulkhead further astern by the battery compartment before I emplace the new cabin wall and it becomes nearly impossible to reach those areas...I'll try to post some pics..but the computer that has them is being uncooperative...infernal machines...take sailboats now: they're a much older and proven invention....
     
  6. Fanie
    Joined: Oct 2007
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    Fanie Fanie

    Hi Souljour,

    Yes well it's a pity nothing lasts forever. I have these very nice socks I was hoping would last the next 50 or so years :D The rivits is the only way I found that prevents delamination on GRP, and they are amazingly strong. The aluminum ones I used before was to get the deck to stay in the boat. First time round the deck delaminated when we landed in a storm, after the rivits there was not even a hint of delamination.

    If you like the boat then it's something you can spend a bit of time on. Something I haven't done before but I'm going to do it in the future is to put foam on the floor. We have a product here that is a PE flotation foam and it is durable enough for one to walk on. It is pleasant on bare feet also and since one get it in a few colours... At least that area of the boat won't sink ;)

    Good luck, it's always nice if guys put up a few pictures of what they're doing. It also gives the been there done that's a chance to comment of what they did on their's and possible problems. All help helps.
     
  7. Fanie
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    Fanie Fanie

    Maybe who ever deducted points for my suggestion on the pop rivits can come up with something that works better.
     
  8. troy2000
    Joined: Nov 2009
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    troy2000 Senior Member

    Seems to be a few self-righteous people passing judgment around here.

    Personally, I don't think anyone should deduct points just because they don't agree with what someone wrote. If they insist on deducting, they should save it for things like personal attacks.
     
  9. Frosty

    Frosty Previous Member

    Could'nt agree more,-- some new comers think it a tool for disagreement. Its something we all have to tolerate for some reason.
     
  10. marshmat
    Joined: Apr 2005
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    marshmat Senior Member

    There's been a lot of debate regarding the "reputation" thing.

    Most of us (myself included) seem to have agreed that we should only deduct points for personal attacks or for repeated, blatant attempts to hijack or derail threads with spam, flaming, etc. I have only had to do this on rare occasions, and while I don't have the actual numbers, I suspect I've only deducted a total of a few dozen points versus several hundred (if not a thousand plus) that I have given.

    Jeff has set it up so that newcomers can only leave comments in the reputation, they can't actually add or deduct points until they've been here for a while. If you see a large drop in your rep and a negative comment, it must be from someone who has been here a while and has earned a high rep themselves- few of these people attack just for the hell of it, and perhaps a sober second look at the post in question will clarify matters.

    I'll suggest that further comments about the point system be directed to the http://www.boatdesign.net/forums/forum-questions-suggestions/forum-reputation-11086.html thread.
     
  11. Fanie
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    Fanie Fanie

    Hey look, if I was penalised for a bad idea or suggestion then it would be fair. I know of no better and stronger way to join old and new glass with polyester, I've done it before.

    Whoever disagreed should at least have come up with a better idea, maybe I can learn something here.
     
  12. souljour2000
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    souljour2000 Senior Member

    I am no structural engineer and have no hard science to back this up and no diploma from Stanford school of engineering. wait...we all knew that...anyways...what I AM able to extrapolate from real-life experience is that de-lamination is progressive...whether the fibers are glass or carbon or whether the resin is polyester or epoxy. Anything that helps prevent the initial start and advance of de-lamination should be given a fair evaluation...I plan to experiment with Fanie's pop-rivets which may well prove to be a wonderful and low-cost low-profile fastener that gives alot of coverage and adhesion to your glasswork with merely a smattering of drill holes spread across the surfaces to be easily joined without brads tacks or staples or heavier high profile bolt-heads (we all have done that c'mon) and since I assume aluminum rivets are up to the job...epoxy should adhere to it when covering the rivets. to whoever deducted points from Fanie...to be honest it sounded a bit of an amateur approach to me too at first...but now that I thought about it and had a more open mind to it.seems like a damn good process really...certainly lightweight and fast..and good coverage quickly..Thanks Fanie...
     
  13. Frosty

    Frosty Previous Member

    I raised my eybrows at this at first but as Soul has said anything that can hold back the start of de lamination has to be helpfull.

    Pehaps not quite to the crux of the matter , what do you call old, I mean how old is old?

    If the hull is still under 1 year old, is it not still curing, and therefore a bond can be made? with preparation of course.
     
  14. Herman
    Joined: Oct 2004
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    Herman Senior Member

    A couple of things I do not like:

    -the reputation system. For obvious reasons.
    -the possibility to anonymously deduct points. For obvious reasons.

    -leaving poprivets in a laminate.

    Perhaps I am wrong, but although poprivets can probably hold layers together (as used in airplanes, combined with glue), they can also be the source of microcracking, causing larger cracks (as in airplanes...)
    While airplanes are under continuous inspection, boats usualy are not. (and a good story about airplanes: I was once sitting next to the wing, and I followed a line of rivets. At some point the rivets were dancing in their holes, and some already were gone. I told the stewardess, but she did not feel it neccesary to warn anyone. I was glad when I got out of the plane... I love epoxy glue...)

    I would still try to grind away the gelcoat or topcoat, then apply further laminate with epoxy.
     

  15. Frosty

    Frosty Previous Member

    Perhaps the "deductor" could step forward, Putting aside any animosity, I for one would like to know a better way if there is one.

    I would really like to know why the rivet idea needed a deduction.

    Please if you have any testosterone at all,--we cant hurt you , own up and explain why you don't like rivets.
     
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