Fiberglass work

[DavesNotHereMan]

Guys:
I know this question does not belong in this sub-forum, but everyone here has been so helpful, I thought I would post and then get it moved to the right place.

This is actually on my Donzi, not on my Doo. I noticed last summer a number of tiny 1/2 inch cracks on the gunwale. They are not stress cracks or spiderweb. It is only on one side. You can catch them with your fingernail. This has been buffed and polished every year. This photo is from one month ago.



Three guys have told me these are heat caused fatigue cracks. This is the "sun side" as it sits on the lift at the dock and only in the blue colored area of the hull.

Guy #1 says he can wet sand them out and polish ($). Guy #2 says wet sand, fill (marine epoxy?), paint with Awlgrip ($$). Guy #3 says grind off everything down to the base layup, reglass, finish with Awlgrip ($$$).

What do you all think?


-Dave
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[Seadoodoc]

Wet sand on day with water and 600 grit. Move to 1000 grit.then polish withcompound. It really thick and would be shocked how much material you take off.

 

[DavesNotHereMan]

Doesn't taking off that much material just lead to a thinner gel coat, leading to more chalking and cracking?


-Dave
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[Seadoodoc]

Gelcoat is super thick . You have nothing to loose sanding and buffing. Nothing can " fill cracks". Either cut and buff or re gel coat. I pulled off miracles on my Wakesetter#

 

[Sportster-2001-951C-Stock]

I would probably choose to do nothing, however, I guess the gel coat layer is cracked and the substrate is exposed thus wet sanding will not remove this blemish?

Anyway, if it's not cracked through to the substrate you might be able to wet sand it out before getting into uglyville.

If it doesn't work out I would repaint with Awl Grip, or I suppose some say gel coat can be sprayed but I have yet to try that myself.

In the case of white, I often use an epoxy appliance paint for touchups, spray can from Home Depot. It's epoxy though, so gel coat won't adhere to it is you want to use gel coat later.

Corvettes are painted, one of my boats I repainted using automotive paint and it has held up well. I don't leave it sit in the water for more than a day or two though, automotive paint wasn't made for that purpose and water will soak through into the substrate, causing destructive blistering.

 

[Sportster-2001-951C-Stock]

Doesn't taking off that much material just lead to a thinner gel coat, leading to more chalking and cracking?


-Dave
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Cracking can be a result of too thick gel coat. As the substrate heats and cools the expansion rates of the substrate and gel coat layer are too great and the gel coat cracks. The gel coat doesn't have the same rate of expansion and contraction thus cannot stretch if too thick this can aggravate the possibility.

That's one reason I avoid power buffing, heat can damage these materials.

Looking at that photo more closely, it looks like the gel coat is delaminating actually, so I think it's a good idea to remove it down to the next layer, hopefully the base gel coat. I would stop if I came to the underlayment.

Might want to take that to an autobody shop and see what they say, they can refinish Corvettes and it's not that different, really. The thing about gel coat is it's rather brittle and heat/expansion/contraction can cause colors that absorb sunlight and convert it to heat can become too hot, then delaminate. Might want to go with something other than gel coat since obviously it sees a lot of heat from sunlight exposure.

They may not be familiar with gel coat, but a good paint guy might surprise (some of them know more than just spraying auto paint), I think I'd go awlgrip or if the autobody guy has some idea for something flexible and durable enough to take the heat like the stuff used on plastic automotive bumpers.

Still though, the root cause is the dark color absorbs too much heat for the circumstances.

All IMO.

 

[Seadoodoc]

Just my experience! I build them from scratch. Good luck on fix.

 

[Sportster-2001-951C-Stock]

Just my experience! I build them from scratch. Good luck on fix.

Not arguing that wet sanding might remove surface defects such as oxidation, this looks like partial delamination to me?

 

[DavesNotHereMan]

I pulled off miracles on my Wakesetter#

Nice!

All 3 guys I talked with are boat guys. Since they were one end to the other, couldn't help to wonder if guy #3 was adding a bit.


-Dave
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[SabrToothSqrl]

Red fades so fast! Looks good!

 

[DavesNotHereMan]

Not arguing that wet sanding might remove surface defects such as oxidation, this looks like partial delamination to me?

I thought delamination was literally beginning to peel off. Looks like more Google-ing for me there.



-Dave
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[Sportster-2001-951C-Stock]

Well yes, delamination is a parting of the ways between the film layers, like peeling, checking or cracking can all be caused by thermal coefficient of expansion being too great. Assuming the substrate layer coefficient of expansion is not equal to the top gel coat layer then the top layer can literally pop off after numerous thermal cycles, the thicker the top layer the more prone due to the film stresses.

If the issue is just surface oxidation, you can wet sand that away quite easily.

Whatever you do, DON'T PUT SILICONE ON THERE b/c it will permanently contaminate the materials and make applying any finish greatly difficult.

 

[eddie708]

i would also try wet sanding. a d/a air powered sander with a wet sponge can save you a lot of work, just be warned it will spray everywhere

 

[DavesNotHereMan]

The cracks are very tiny in depth, at least right now. They are more than cosmetic cuz I can catch a fingernail in them. I have never seen this before and it is only on the sun-side of the hull and only on the blue, not the white.


-Dave
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[Sportster-2001-951C-Stock]

Looks like thermal stress fracturing to me, but if the blemishes aren't completely through the gel coat they can be removed by wet sanding. This might not have happened if the gel coat layer was thinner to begin with.

Here are some goo ideas of how to accomplish various fiberglass layup repairs, beyond simple wet sanding.

http://www.michiganfiberglass.com/gelcoat.jb/must_read_repair_tips.htm

You can also google "fiberglass resin blisters" as well, but that's not related to this damage.

 

[Seadoodoc]

Lol.. sometimes you just gotta push aside the pencil and computer mouse and dig in.. " it aint rocket 8science" . Funny saying in production .. engineers spend 10 hrs designing it. Then Installers spend 10 mins making it re 9engineered to actually work. (;

 

[DavesNotHereMan]

Guys: thanks for all the input, especially that reference to Michigan Fiberglass, Sportster. I do not have the skills or the tools to tackle something this large or this visible. I have never done any glass work or gelcoat work and I don't think I can tackle the hull of my Donzi on the first attempt. There are a number of shops around Lake Lanier that specialize in repair work. Guy #2 estimated $1500 to sand it and repaint the blue with Awlgrip.

Does that seem like a good deal? What kind of pricing should I expect?


-Dave
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[Seadoodoc]

I tried surface gel cote and failed misserably. Local guy did repair on my Malibu for 200 bucks! Actually reglassed a cleat in place and gel coated it. Yes and yes that red is just a bitch for oxy. Not gonna lie ..my boat looks rough up close. 10 yrs old 700 hrs. Its just a floating stereo-cooler- seadoo refueling station. Lol

 

[Seadoodoc]

Maybe do a decal or wrap?

 

[Sportster-2001-951C-Stock]

Sounds like wet sanding is the way to go, regardless of whether or not the gel coat has failed.

Probably not something that has to be repaired right away, I don't see the urgency, but a job like that will likely cost $1500.

If you can swing having gel coat applied, that might be preferable over paint of course.

I can say that's at least where I'd value similar refinish projects. It takes time and materials, proper preparation, etc., it all adds up quickly.

 

[Sportster-2001-951C-Stock]

I tried surface gel cote and failed misserably. Local guy did repair on my Malibu for 200 bucks! Actually reglassed a cleat in place and gel coated it. Yes and yes that red is just a bitch for oxy. Not gonna lie ..my boat looks rough up close. 10 yrs old 700 hrs. Its just a floating stereo-cooler- seadoo refueling station. Lol

I'd be tempted to shoot that fast oxidizing gel coat by dewaxing, wet sanding with 400 grit and PPG2042 clear coat as a sealer.

 

[Sportster-2001-951C-Stock]

Notice in this article on repairing blisters, the author recommends using epoxy for repairing this water damage and provides his reason why. Keep in mind, gel coat will not adhere to epoxy but epoxy will adhere tenaciously to gel coat and other polyester resins, just about anything except for polyethylene.

So in the case of this water damage blister repair, I predict the author is probably using a paint for the refinish, such as Awlgrip. Repainting has been the normally accepted approach I'm accustom to.

Is this correct for your case (gel coat vs paint) well I don't know, I don't have experience with shooting gel coat but if it works it would be more like the factory finish.

http://www.boatus.com/boattech/casey/blister-repair.asp

 

[DavesNotHereMan]

Sportster: your stuff looks great! Do I understand that you applied gelcoat on top of the fiberglass? I thought it only went in the molds.

Yes, the discussion I have had so far was that the guy would wet sand the entire blue portion of the hull, fill anything left with epoxy and paint with Awlgrip. That is, no gelcoat over the blue portion, just Awlgrip. The rest of the hull would be left as-is.

The guy works at the local marina that does repair services and painting, and because for the past 12 yrs, all my service has been done by the Merc technician that works there and he hooked me up. Sounds like that is the way I need to go, huh?


-Dave
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[Sportster-2001-951C-Stock]

Dave, gelcoat is generally pretty thick, so sanding away imperfections might be possible. In the case of covering over gelcoat issues I've only worked with various types of paint with a similar approach as would be taken for refinishing a fiberglass Corvette, I haven't tried my hand at applying gelcoat. That said, it can be done but the adhesive bond will not be equivalent to the factory gelcoat b/c it will be a mechanical bond similar to paint. There are many good paints available, so I'm not sure of the benefit of gelcoat vs cost.

Polyester resin gelcoat which is sprayed into a mold is slightly different from the formulation of gelcoat that can be applied (sprayed or rolled) onto a surface, the formulation is application specific. Polyester resin gelcoat is anaerobically cured, which means it can only cure in the absence of air. Thus in a mold, the gelcoat layer has a primary bond with the layup and adhesion issues are practically eliminated b/c it cures as part of the layup, there is no boundary surface or mechanical bonding, it's one homogenous layer. No curing of polyester resin gel coat is possible until the layup is applied on the inside of the mold, on top of the gel coat thus it cures as one.

So you would need to use a top coat polyester resin with color pigment, as explained here:

http://www.cfsnet.co.uk/acatalog/methods_flowcoating.html

Whichever route you choose, any top coat will result in a secondary bond as opposed to the primary bond obtained in the factory layup, thus will not be of the same quality, however, could still perform quite satisfactorily depending on the compatibility of materials used and quality of preparation, etc..

AwlGrip is a great product commonly used in marine boatyards familiar with refinishing boats of all sizes, especially large($$$ cost of materials), maybe you can find a shop capable and familiar with applying a polyester resin top coat. Also, I would entertain the thought of having an autobody shop perform this repair using a high quality paint.

 

[DavesNotHereMan]

Great info, as always. Looks like I have some work to do.


-Dave
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