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TOPIC: Trying to figure out what to do with my below the water line cracked gelcoat.

Trying to figure out what to do with my below the water line cracked gelcoat. 26 Aug 2017 22:43 #1

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My new to me boat was left sitting in the water unmaintained for many years..

As a result most of the gelcoat has cracked. Not really any blisters maybe one or 2 just lots of cracks in the gelcoat.

I'm looking for advice on a proper repair. I plan on doing a barrier coat and new bottom paint. The question is what to do with the gelcoat. My first thought is to strip the gelcoat then just barrier coat it ( not replacing the gelcoat) the bottom paint. I don't know if I should regelcoat or not. I just want it to be right.
The subject....




The cracks......


Most of the bottom has these cracks. I don't really want to leave them.

Any thoughts?

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1989 Avanti 3450 Sunbridge twin 454's

1979 Bayliner Conquest 3150 hull#23

1979 Bayliner Conquest 3150 hardtop hull#24
Twin chevy 350's

Trying to figure out what to do with my below the water line cracked gelcoat. 26 Aug 2017 22:47 #2

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I have already removed the gelcoat from the exhaust holes.
I will probably regelcoat that area.







What I found was that the gelcoat was really thick in the exhaust pockets. Like 1/4 inch thick. :(

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1989 Avanti 3450 Sunbridge twin 454's

1979 Bayliner Conquest 3150 hull#23

1979 Bayliner Conquest 3150 hardtop hull#24
Twin chevy 350's

Trying to figure out what to do with my below the water line cracked gelcoat. 27 Aug 2017 05:17 #3

  • makonnen
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I'd be happy to find 1/4" of gelcoat. Gelcoat is basically colored fiberglass resin. It strong... I'm not sure what you mean by "barrier coat", but whatever you do I'm sure you going to want to apply a new layer of gelcoat. I'm not sure how one would apply a whopping 1/4" of gelcoat though. If using a spray gun you would have to spray it many times and it would be a total waste of gelcoat due to the overspray.

Regardless, gelcoat is pretty easy to work with. As mentioned, its nothing more than tinted fiberglass resin. Get yourself a quart, and some catalyst and experiment with color matching and also get a feel of working with it using a spray gun, different sized nozzles (I use a 1.4mm nozzle in my HVLP touchup spray gun), rollers, brushes ... get a feel of how much catalyst to use. You're gonna want to stock up on some Lacquer thinner.

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1998 Bayliner Ciera 2655, 5.7 BIII

Trying to figure out what to do with my below the water line cracked gelcoat. 27 Aug 2017 07:37 #4

  • mr.bent
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The gelcoat is not so important if you plan to paint the boat with antifouling but what ever you choose to do it's important that you paint the bottom with epoxy to make the boat waterproof, for a trailerboat it's not so crucial but a boat laying in water more the 3 weeks should be painted with minimum 4 layers of epoxy primer before applying anti fouling. (the gelcoat and fibreglass tend to soak up water after some weeks).
Best way is to use 2 different colours so you are sure you cover everything perfect, use a good quality paint and a good roller and make each layers as smooth as possible, when the final layer is starting to dry up, (getting tacky) then it's time to apply the first layer of antifouling, this way you get a real good bonding so the bottom paint won't fall off in flakes after some years.
If you take your time it will look real nice, enjoy.

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Trying to figure out what to do with my below the water line cracked gelcoat. 27 Aug 2017 08:07 #5

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Please read this prior to gelcoating.
Gelcoat should never be 1/4" thick, that is why it cracked, use a-isophthalic polyester gel coat it has more water/moisture barrier than general purposed gelcoat.
A good marine filler such as a 3M product made for boats, this is one type of 3M filler I use.

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Pat says: DO-IT-RIGHT THE FIRST TIME!

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Trying to figure out what to do with my below the water line cracked gelcoat. 27 Aug 2017 13:50 #6

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Well I'm no stranger to gelcoat or fiberglass.

What has me asking the question is the large scope of the problem. I do think im going to strip it down on the bottom. The question might be how to go about striping it.

I believe the problem to be gelcoat too thick combined.with sitting in the water unprotected for many years. It was in an area the freezes in the winter. I believe the gelcoat absorbed water then froze then cracked.

I guess on question is do I have to replace the gelcoat or can I remove it for the most part then just apply epoxy barrier coat.? It only has this.problem below the waterline.

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1989 Avanti 3450 Sunbridge twin 454's

1979 Bayliner Conquest 3150 hull#23

1979 Bayliner Conquest 3150 hardtop hull#24
Twin chevy 350's

Trying to figure out what to do with my below the water line cracked gelcoat. 27 Aug 2017 14:32 #7

  • Pcpete
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In the bad old days of blister repair the gel coat was sanded off, everything dried out and an early on barrier coating like interprotect was laid on 8+ mils thick. The last time I did the big bottom paint removal to my former boat I used a seahawk product for the barrier. Really interesting stuff and worthy of calling them to get their advise about application. It goes on fast and if you worry it a bit much, like more tan a few passes with the roller, it starts acting like cotton candy. That action, of course, is how the barrier is formed, but its kind of an "oh sh%t" moment the first time I did it.

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Trying to figure out what to do with my below the water line cracked gelcoat. 27 Aug 2017 14:39 #8

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I'm no expert but if I had to attempt a repair like that I'd think applying an epoxy instead of gelcoat would be a superior water barrier and likely bond to the prepped surface better too. As far as a DIY removal of the old gelcoat a grinding or planing party comes to mind. Gonna be quite the job :pinch:

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Dave
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Trying to figure out what to do with my below the water line cracked gelcoat. 27 Aug 2017 19:24 #9

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I'm pretty sure most of the gelcoat has to go. With that said my plan is to 40 grit sand it. Not all of but most is cracked below the water line.

Looked into a peeler but I think with chines it will have limited use. After the 40 grit going to go over it with 80 grit. I don't have more than 2 or 3 defect areas so I don't suspect I will have a lot of fiberglass repair.

Then I think the plan is strip sand repair I have about 10 gallons of west systems epoxy so i think im going to 3 coat it with that. ( i still need to talk to a rep about over coating.) Ill use that as long as there is a no sanding opperation to use with interlux protect2000e. Then I'm going to coat it with interlux protect 2000e 6 coats. Then bottomkote bottom paint.

I want to use the interlux because it's more time and technique forgiving.
That's the plan any other ideas?

I have until about the end of October to finish sanding the bottom. The put it in my shop. I know what I'll be doing order labor day weekend.

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1989 Avanti 3450 Sunbridge twin 454's

1979 Bayliner Conquest 3150 hull#23

1979 Bayliner Conquest 3150 hardtop hull#24
Twin chevy 350's

Trying to figure out what to do with my below the water line cracked gelcoat. 27 Aug 2017 23:36 #10

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if you are going to barrier coat, why would you go thru the trouble of gelcoating?.. its a needless process. the ONLY reason gelcoat even exists is to make the boat look good. it does not add any weather resistance, water proofing or strength to the hull what so ever.... its only for a shiny finish coat.

smooth FRP can be painted with the same results, BUT gelcoat is more durable and thicker so it can be buffed more times than paint to keep it looking good.

if it was my boat in the photo, I would let it dry for a few months and then sand it well, and then give it several coats of thickened epoxy barrier. totally removing the gelcoat before barrier coating would be premium, but its expensive/time consuming and in my opinion its unnecessary as long as its sanded well before the barrier coat.

note that I said epoxy barrier coat rather than the vinylester barrier coat... vinylester is a good barrier coat for a hull with no issues or has been stripped of its gelcoat, but the epoxy adheres better, is stronger and more forgiving on a hull that has some blems in it...
both types are waterproof and will seal the moisture out, or IN, as the case may be, and that is the reason you need to keep it out of the water and let it dry for a couple of months. you dont want to barrier coat over a damp hull, because then you WILL be stripping the hull, so you can do it all over again.
gelcoat is NOT waterproof and absorbs water over time, which is why blisters and delamination occurs.... some gelcoat resins are of better quality than other brands, but if its polyester, it will absorb a certain amount of water.

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Trying to figure out what to do with my below the water line cracked gelcoat. 28 Aug 2017 01:09 #11

  • Solandri
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makonnen wrote: I'm not sure what you mean by "barrier coat", but whatever you do I'm sure you going to want to apply a new layer of gelcoat.

FRP is normally made by imbedding the glass fibers in polyester resin. Polyester because it's cheap. Unfortunately, polyester is somewhat water permeable, and will result in slow water ingress if you store your boat in the water. Same with gelcoat (usually pure polyester resin), which is why you get blisters. Consequently, the FRP in boats use vinylester or epoxy as the resin in fiberglass below the waterline, aka a barrier coat since it keeps the water out.

The smooth surface of the gel coat is actually useful for reducing drag when moving slowly (e.g. below hull speed). But at faster speeds it can be a detriment as the water "sticks" to it better. You want the water to detach (switch from laminar to turbulent flow) at higher speeds to reduce drag. That's what the dimples on a golf ball are for - to disrupt the laminar (smooth) flow and cause premature transition to turbulent flow, for reduced drag at high speed.

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Trying to figure out what to do with my below the water line cracked gelcoat. 29 Aug 2017 00:42 #12

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For future reference for who ever reads this thread.....

I spoke with West systems tech department today. The said west systems could be laid down minimum 2 coats work best. Then before West systems epoxy sets up solid but after it gels interlux interprotect 2000e can be applied directly over west systems without Sanding. Without any I'll affects.

So..... at that point once the epoxy is laid down and the firs5 cohlle of coats of interprotect is applied then you can set a little without sanding. Interprotect has a 2 week max reapplication window which is a lot better than laying down 2 coats epoxy 6 coats barrier coat all in one day.

On a side note. Interlux said the bare fiberglass doesn't really need a epoxy coat first but it works better if you do that first. That is because interprotect is a epoxy already.

Also if you read the texh sheet on interlux epi 9000 interlux epoxy. It says let it cure and dry then sand then clean again the apply bottom paint.

I think I prefer West systems no sand method. Especially on a 13 foot wide 34 foot boat.

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1989 Avanti 3450 Sunbridge twin 454's

1979 Bayliner Conquest 3150 hull#23

1979 Bayliner Conquest 3150 hardtop hull#24
Twin chevy 350's

Trying to figure out what to do with my below the water line cracked gelcoat. 29 Aug 2017 00:58 #13

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West also has their "no blush" hardener that supposedly can be coated over without any sanding. I used it a couple times, it does cure up but stays a bit "sticky" for the next lay up.
You probably knew that already :silly:

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Dave
Edmonds, WA
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'93 2556 5.7 Bravo II 2.0:1 18 1/4x19 P
.030 over-Vortec top end-part closed cooled
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www.baylinerownersclub.org/index.php/for...ansom-repair-my-2556

Trying to figure out what to do with my below the water line cracked gelcoat. 29 Aug 2017 01:02 #14

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Once you coat the bottom with epoxy forget applying gel coat, it may be hard to get epoxy smooth unless sanded.
Sand it until smooth, fill as necessary with a 3-m marine product, then spray on gel coat, first layer no wax, second no wax, third use wax, do not forget the catalyst on all 3 layers.
after cured sand smooth, and if bottom painting you will not need to use a fine grit.
If not gel coating a epoxy barrier is best, been there done that when I had my small boat yard.
If using gel coat use an iso based gel coat you can use a layer of vinyl ester resin prior to using gel coat.
Using a peeler is hard work, and the tool has increased in price considerably since I bought one in 1995.

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Pat says: DO-IT-RIGHT THE FIRST TIME!

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Trying to figure out what to do with my below the water line cracked gelcoat. 29 Aug 2017 03:42 #15

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Three years ago I sand blasted the bottom of my boat to expose any flaws and remove way to many layers of bottom paint, no cracks or anything like your pictures but a few scrapes and dings. The sand blaster was careful, he felt it would take the gel coat right off if your weren't paying attention. We didn't try but it might be worth asking somebody if it could be striped that way, It was such an easy process the job was done and cleaned up in a day for $600 bucks. Still lots of sanding involved but nothing like it would have been. After washing and drying I coated my hull with the west system epoxy (regular, not the low blush) washed again lightly sanded and applied six coats of 2000e. They do have a no sand application window and It was a bit tricky but totally manageable, I wouldn't look forward to trying to following around a rapidly gelling epoxy with the stuff on the first coat though, that sounds a little harder than a quick wash and sand. That being said I pretty well did just what you want to do and I can't say that there is anything I would do differently, worked great.
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