| Re: Gel coat problem
[Re: SoggyCheetoh]
#32067 04/05/04 12:27 PM 04/05/04 12:27 PM |
Joined: Jan 2004 Posts: 1,884 Detroit, MI mbounds
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Pooh-Bah
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Posts: 1,884 Detroit, MI | Gel coat doesn't cure completely when exposed to air. After sraying it on, you should spray a light coating of PVA (poly vinyl alcohol - mold release agent) over it to seal it up while it cures. After the cure, the PVA can be washed off with water. There are also additives that you can mix with the gel that form a protective film while the gel is curing to allow for a complete cure. For your particular problem, I'd spray another light coat of gel over the tacky section and use the PVA as described above to get it to cure completely. There's a good article on re-gelcoating here. | | | Re: Gel coat problem
[Re: SoggyCheetoh]
#32068 04/05/04 12:28 PM 04/05/04 12:28 PM |
Joined: Oct 2003 Posts: 248 Colorado SteveT
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Posts: 248 Colorado | I'm sure there are lots of experts out there, but I did a similar job to my Hobie 20. The gel coat won't cure unless protected from the air with a mold release (not the green fuzzy stuff, but what the boat came out of in the first place). The stuff I use is purple (I forget the name) and is available at West Marine. You spray it over the wet gel coat and that allows it to cure very quickly - 12 to 24 hours depending on the hardener mix. Without this buffer, you could be waiting weeks for it to cure. Once the gel coat is fully hardened, you just wash and buff off the mold release which has dried to a film coating.
H-20 #896
| | | Re: Gel coat problem
[Re: SoggyCheetoh]
#32071 04/05/04 02:19 PM 04/05/04 02:19 PM |
Joined: Apr 2002 Posts: 805 Gainesville, FL 32607 USA dacarls
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Posts: 805 Gainesville, FL 32607 USA | Poor stirring of your gelcoat and/or catalyst getting old? Think about scraping it off and redo. I once had to scrape and redo a whole sticky Hobie 16 Hull. @$%^&#$%^&@#$&*
Dacarls: A-class USA 196, USA 21, H18, H16 "Nothing that's any good works by itself. You got to make the damn thing work"- Thomas Edison
| | | Re: Gel coat problem
[Re: Seeker]
#32074 04/05/04 08:35 PM 04/05/04 08:35 PM |
Joined: Feb 2004 Posts: 1,012 South Australia Darryl_Barrett
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Posts: 1,012 South Australia | Like all jobs well done, 90% of the job is in the preparation, and the rest is usually getting the basics right. prepare the surface to be re gel coated by sanding it back to good clean original material, mask off the areas that you don't want to be covered with the new layer, wipe the area to be covered down with a rag wet with acetone ( this will clean the area of any dust, "oil", moisture, and actually "prepare" the old surface to best accept the new gel coat) It is often a good measure to apply a thin layer of "bog"over the area before you get to any gel coating, then fair it back with 240 grit dry paper this is to fill any pin holes, particularly if your back to actual exposed glass fibres. (always wipe with acetone before any layer is applied whether bog, resin, or gel coat) When it has been faired then masked and wiped down mix your gelcoat with a "small" amount of "wax in styrene" which it is best to purchase already mixed from a fibreglass supplier (or boat builder). It should be 5% wax in styrene, and a very small amount goes a long way. Better still, if you purchase, instead of just gel coat, "flo coat" which is already mixed for external (out of the mould) gel coating, this will leave your finished surface of the gel coat hard and non "sticky" when it has fully gel'd, and you can then fair it with sand paper and wet and dry with out the paper clogging up with every stroke. The MOST IMPOTANT THING ABOUT MIXING GEL COAT is that you NEVER NEVER add more than 2% catalyst to your gel coat/resin, as to increase the catalyst (incorectly called hardener) does several nasty things that you don't want. as a larger percentace of catalyst is added the chemical reaction becomes more violent, more heat is produced, the polymer chains formed are smaller and smaller to the extreme that the mix will smoke or the finished product is almost "chrystaline" but whatever the result the finish gel coat is appreciably weakened and at times, over catalysing will actually leave what appears to be "unset" areas of gel coat/resin. If you are working in cold temperatures, never increase the percentage of catalyst, but after applying the gel coat raise the temp[erature of the air around the job with heat lights,or blow heater etc. If you use the correct catalyst percentage mix, MIXED WELL with the gelcoat, ie stir for up to a minute or two, after aplying, when the temperature around the job is above about 20 degrees celcius, the gel coat will gel in 45 to 60 minutes, give it about another hour at that temperature and you can then fair it back and cut and polish it to finish. Don't try to put it on "thin" as that is not how gel coat is meant to be used, and it is very poor practice to "thin" it with acetone, (if you have to thin it, thin it with "styrene monomer") it is not like "painting" you cannot finish "off the gun" you have to be prepared to shape and fair back by hand. If really thin layers of gel coat are applied they become more succeptable to irregular settings. The volume of gel coat is so small that the required chemical reaction will slow down dramitically and in some instances not apparently go off at all, or if the ventilation is poor the whole thing can "tripe". If the application is done correctly polyester is a very easy material to work with, and will not need any thing applied "on top" of it to cure it, in fact by applying PVA over wet gel coat you suffer the great risk of breaking down the catalyst in the gel coat by the intrusion of the "wet" PVA | | | Re: Gel coat problem
[Re: SoggyCheetoh]
#32079 04/06/04 02:55 PM 04/06/04 02:55 PM |
Joined: Apr 2002 Posts: 805 Gainesville, FL 32607 USA dacarls
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Posts: 805 Gainesville, FL 32607 USA | Bog is OZ for filler mixed into polyester resin- Hopefully microballoons or (light) or silica gel (heavy) until it can be spread with a squeegee and won't run off. Note: When catalyzed will often go off FASTER than gelcoat.
Gelcoat is polyester resin with less silica gel in it, but with pigment too.
Dacarls: A-class USA 196, USA 21, H18, H16 "Nothing that's any good works by itself. You got to make the damn thing work"- Thomas Edison
| | | Re: Gel coat problem
[Re: Seeker]
#32083 04/07/04 03:43 AM 04/07/04 03:43 AM |
Joined: Feb 2004 Posts: 1,012 South Australia Darryl_Barrett
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Posts: 1,012 South Australia | Who's talking about epoxy?? what I understood was that we were discussing gel coating of a "polyester" FRP catamaran, nothing to do with epoxy, vynalester, or phenolic resins, acrylics, eurathanes, propolins, ethylines or any other of the vast array of so called "plastics" Mind you if you want to get really technical and "stuff up" some one who asked for simple advice for a non "professional" on the way to repair his cat by diverging, then yes. certain substances mixed with resin or gel coat DO have an effect on their gel times over straight resin and or gel cvoat, ie if aluminum tri hydrate is added, as a filler, or as a fire retardent then the effect on gel times is radically different, also if you add a product called "sealite" (a trade name) which is actually powdered "marble", (used for pour moulded vanity tops etc,) to have a finished effect undetectable by the general public from actual marble when done well, also changes the gel time ratios. But that is not relevent to any thing that was wanted on this original posting, simply why did his attempts at repair to the bottoms of his hulls fail and help in how to rectify the problem, Not a complete discourse on the FRP industry. | | | Re: Gel coat problem
[Re: Darryl_Barrett]
#32084 04/07/04 08:00 AM 04/07/04 08:00 AM |
Joined: Apr 2002 Posts: 695 Ft. Pierce, Fl. USA Seeker
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Posts: 695 Ft. Pierce, Fl. USA | My take on the matter is, yes…we want to answer the original question…basically… a batch of gel-coat is on the boat and it’s not setting up…where does one go from here…?
But just as important is how to avoid the problem again in the future…such as making sure there is wax additive in the resin, mixing the two parts thoroughly (not just a couple quick stokes around the bucked with the stir stick), mixing in one bucket and pouring it into/working out of another bucket, doing a small test batch if you are unsure of the correct resin/catalyst ratios for the temperature you are working in, avoid working in direct sunlight if at all possible, adding any fillers or thinners to the resin only after the resin and catalyst have been thoroughly mixed, and being aware of the fact that there are many types of fillers, if you put a filler in the mix which is easy to sand, it is also not going to stay on the bottom of your boat as long as one which is difficult to sand.
Bob | | | Re: Gel coat problem
[Re: SoggyCheetoh]
#32085 04/07/04 08:01 AM 04/07/04 08:01 AM |
Joined: Aug 2001 Posts: 190 Long Island, NY Steven Bellavia
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Posts: 190 Long Island, NY | Hi, I've only had 100% success when I started buying ALL the necessary stuff from MiniCraft in Florida. They sell gelcoat that can be sprayed with a normal sprayer and cures in air in 30 minutes. NEVER use acetone to thin. Minicraft sells a spray reducer that works perfectly. See: http://www.minicraft.com. Call them and they will set you up with everything. Unfortunately it sounds like your prior work will have to be removed. If it didn't kick by now, it's not going to. P.S. They also sell tints that can get you an exact color match. I did 9 large areas on a 31 foot boat and now I can't even find where they were.
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