General Advice on Gel Coat Repair and Paint Preparation

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
Cberglund
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Joined: Mon Feb 24, 2020 10:43 pm

General Advice on Gel Coat Repair and Paint Preparation

Postby Cberglund » Mon Apr 06, 2020 11:48 pm

I am a junior in high school. I want to get my 1976 13-footer extra pretty for the 2020 boating season.

I bought my 13-footer last summer and used it as-is last season. I used the boat on the North River and occasionally the Atlantic Ocean (south of Boston). I had a blast.

In the fall, I brought the boat into my shop class to repair a hole in the deck. I repaired this under the guidance of my very knowledgeable shop teacher.

Now that I am own my own, I need advice on how much repair I should do.

I realize there are other cracks in the gelcoat that may be a problem to be hidden by a thin one-part polyurethane paint like Interlux Brightside.

I have cleaned up the dings with a Dremel tool.

I do not plan to redo a ton of gel coat. I am willing to do whatever necessary to do the job right. I do not plan to redo [all] gel coat. I am willing to do whatever necessary to do the job right. I don't need to achieve perfection, but I want to do the work so that at the end of the season I'm not in the same situation regarding unsightly cracks.

I may use TotalBoat THIXO, TotalBoat Fairing Compound, and EX-TEX products.

Q1: For refinishing cracks and other damage to the gel coat, what are the best methods?

Q2: What epoxy should I use?

Q3: once I have repaired these cracks and chips, what paint preparation should be done?

Q4: what is the best git for sanding?

Q5: will a one-part polyurethane paint like Interlux Brightside cover cracks?

All advice will be greatly appreciated. Thanks.

IMG_6797.jpg
Fig. 1. Chipped gel coat
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IMG_6801.jpg
Fig. 2.Chipped gel coat
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IMG_6795.jpg
Fig. 3. Spider cracks
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Last edited by Cberglund on Mon Apr 06, 2020 11:58 pm, edited 3 times in total.
(1st boat) 13’ 1976 Whaler Sport
Purchased myself (2 years of saving)

Cberglund
Posts: 5
Joined: Mon Feb 24, 2020 10:43 pm

Re: ISO advice on gel coat repair/paint prep

Postby Cberglund » Mon Apr 06, 2020 11:49 pm

IMG_6803.jpg
Fig. 4. Boat with large area of damage in center of deck
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IMG_6796.jpg
Fig. 5. Chips and spider cracks
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IMG_6799.jpg
Fig. 6. Abrasion
IMG_6799.jpg (28.95 KiB) Viewed 1195 times
(1st boat) 13’ 1976 Whaler Sport
Purchased myself (2 years of saving)

jimh
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Re: Gel Coat Repair and Paint Preparation

Postby jimh » Tue Apr 07, 2020 7:08 am

TotalBoat has a good demonstration of use of their products to refinish an older Boston Whaler boat with plenty of cosmetic defects in the gel coat. See

Boston Whaler Crazing Repair
https://www.youtube.com/watch?v=4tZDBOYqdfA

As long as all the cracks are just surface cracks and are just cosmetic not structural, filling them with a fairing compound should be sufficient to prevent the cracks from reoccurring. If the cracks are due to the hull flexing and are thus a structural problem, the underlying weakness in the structure will need to be fixed, otherwise filling the crack with fairing won't likely prevent the crack from opening again.

To approach a solution to this problem, first decide on the extend of the refinishing you want to do. I think there is a fundamental branching of the methods.

Do you have so many cracks that you need to fix them all, fair all of them, then re-paint the entire boat?

If so, watch the presentation linked above.

If the hull only has limited cracking, perhaps each crack can be repaired individually, and the original gel coat finish of the hull retained. In that approach, you can fill the cracks with a color-match gel coat paste that can cure in open air. For advice see

Using SPECTRUM COLOR Gel Coat Paste
http://continuouswave.com/forum/viewtopic.php?f=6&t=5327

dtmackey
Posts: 457
Joined: Thu Sep 28, 2017 9:29 pm

Re: Gel Coat Repair and Paint Preparation

Postby dtmackey » Tue Apr 07, 2020 8:40 am

All good questions. Here is what I was faced with, similar in nature to what you have, but I think mine was far more extensive with cracks.

Image
Image

Q1: For refinishing cracks and other damage to the gel coat, what are the best methods?
I found that a carbide rotary tool (On the idea of a dentist grinder, but bigger worked great and I beveled out the cracks. You can see the carbide bit in this pic.

Image
[Note metal debris embedded in laminate.]

Q2: What epoxy should I use?
I did not use epoxy and instead chose a waterproof filler that has chopped glass mixed in. It's easier to sand and also holds up great as I've used this in many boats over the past 25 years.

http://www.evercoat.com/reinforced-fillers/us/

Image

On mine, the cracking was so bad, I was forced to grind down all the non-skid and fix those cracks as well. I found many defects in the floor with gelcoat voids and also metal shards that were imbedded between the gelcoat and fiberglass when the boat was built. This was surprising and visible in the 3rd pic from the top.

Image

Q3: once I have repaired these cracks and chips, what paint preparation should be done?
Once you have made all the repairs, you have to make sure the boat is clean of oil/dirt and you may want to wipe down with a strong solvent and may rags.

Q4: what is the best git for sanding?
The finish will only look at good as the prep, so sanding is very important. If sanding the entire boat in prep for primer, then I'd recommend starting with whatever grit you need to resolve any gelcoat problems, but end with 180 grit. 180 grit will give you a great surface for a high build 2 part epoxy primer. Primer provides a great binder between the gelcoat and the topcoat. If you are just doing a patch job and not intending to use a primer and only paint the repaired area, then I'd end with 320 grit.

Q5: will a one-part polyurethane paint like Interlux Brightside cover cracks?
- If just painting the cracks, yes a one part will cover the cracks, but I've never been a fan of one part paints (moisture cure) and prefer the robustness of a 2 part (catalyzed) paint. If only painting the cracks, you will see the color variations as the off-the-shelf paints are close in color.

For my project, I had to redo the non-skid due to the extensive gelocoat cracks.

Image
Image

D-

On edit - check out the thread what JimH posted for gelcoat repair kits from Spectrum if not diving in too deep on the repairs for your boat.

http://continuouswave.com/forum/viewtopic.php?f=6&t=5327

biggiefl
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Re: Gel Coat Repair and Paint Preparation

Postby biggiefl » Tue Apr 07, 2020 11:02 am

What is the circular "repair" in the middle of the deck [seen in Figure 4 above]? Is that what you fixed in shop?

This is going to be a pretty good project if you want to do it correctly.

The cracks need to be "dremell-ed" [widened with a Dremel tool] out and then faired in with a filler or bondo-like substance.

The hull needs to be completely sanded, primed, and painted , which will cost a few bucks in supplies. It will be a fun project if you have a place to do it out of the elements. Usually people remove the rub rail to do this, and that alone is $250 roughly. The original will be brittle and break if you try and remove. If it has been replaced then the rub rail should not be too bad as most use screws to install, not rivets like the factory.

I would eagerly take this on at your age. At 50, nah!
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall(for sale cheap).

Cberglund
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Joined: Mon Feb 24, 2020 10:43 pm

Re: Gel Coat Repair and Paint Preparation

Postby Cberglund » Tue Apr 07, 2020 11:23 am

I think the repair work necessary on my boat is very similar to the TotalBoat repair [demonstrated in their youTube presentation].

I was afraid i would need to apply new gel coat, [however the results from using] fairing compound, then primer, then paint looked beautiful. [The presentation mentions] light sanding in between coats [of something unspecified].

Q6: What grit would be recommended [for light sanding between coasts of something unspecified]?

Q7: Is priming highly recommended?

Q8a: Can the fairing compound fill the voids that are down to fiberglass?

Q8b: [or should voids down to fiberglass be filled with] just gel coat?

Q9: Can the damage [seen above in Fig. 6] be repaired with fairing compound?

Q10: How do I preserve the non-skid on the deck?

I will have to look closely again for cracks in the non-skid section of deck when sanding in preparation of painting my topside, after doing necessary repairs. I didn't see any needing repair.
Last edited by Cberglund on Tue Apr 07, 2020 12:36 pm, edited 1 time in total.
(1st boat) 13’ 1976 Whaler Sport
Purchased myself (2 years of saving)

Cberglund
Posts: 5
Joined: Mon Feb 24, 2020 10:43 pm

Re: Gel Coat Repair and Paint Preparation

Postby Cberglund » Tue Apr 07, 2020 11:33 am

My repairs:
MONTAGE.jpg
Fig. 7. Repairs.
MONTAGE.jpg (5.24 KiB) Viewed 1098 times
(1st boat) 13’ 1976 Whaler Sport
Purchased myself (2 years of saving)

jimh
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Re: Gel Coat Repair and Paint Preparation

Postby jimh » Thu Apr 09, 2020 3:28 pm

Q6: What grit would be recommended [for light sanding between coasts of something unspecified]?
I can't speak for TotalBoat, but I would assume that a "light sanding" means to use a grit that does not abrade the most recent coat (of whatever it is you are sanding) so deeply that it reveals the previous coat underneath the coat you are sanding and does not cause deep scratches that cannot be filled by the next coat and would need more filler coats to repair.

Q7: Is priming highly recommended?
All thin top-coat finish layers will only be able to hide very minor imperfections. Top-coats are generally intended to adhere to very good surfaces, not to unprepared, dirty, oily, uneven surfaces. The purpose of primer is to prepare the surface for the top coat to adhere evenly and for the top coat to not have to be applied in thick layers to hide flaws. The top coat should be applied to a primer coat that has a uniform finish, that is, no variations in colors. The top coat will then present a very uniform finished appearance and all repair work will be hidden from view. Top coat finish paints are more expensive than primer paints, and you really do not want to have to apply multiple top coats in order to produce an even and uniform finish. A top coat won't look any better than the primer coat it is applied to in terms of hiding flaws or covering variations in colors. Top coat paint cannot be applied with much thickness, so any flaws or mars cannot be removed by rubbing with mild abrasion. The paint layer is not sufficiently thick to allow this method of removing flaws.

Any painting with a top coat should be in accordance with the specific instructions for that paint, including adhering to the required minimum time for a previous coat to dry before application of a second coat. Some paints require a minimum time to dry of SEVEN days before allowing a follow-on coat to be applied.

Q8a: Can the fairing compound fill the voids that are down to fiberglass?
Fairing compound should be used to fill shallow and cosmetic defects. If the damage penetrates so deeply there is no underlying fiberglass, then a structural repair is needed

Q8b: [should voids down to fiberglass be filled with] just gel coat?
Gel coat resin should only be applied to about 0.020-inch thick. To repair small scratches a gel coat paste must be used. A gel coat paste is a gel coat resin with thickeners, and often with additives to allow the gel coat paste to cure to a hard finish while exposed to the air. To repair deep damage, see the Boston Whaler repair instructions in the REFERENCE section.

Q9: Can the damage [seen above in Fig. 6] be repaired with fairing compound?
A high-impact convex surface bend area like the abrasion that has removed the gel coat shown in Fig. 6 will probably not last long if only made with a fairing compound. A fairing compound is used to fill LOW spots between undamaged areas of a surface. The fairing compound extends only BELOW the regular surface area, not ABOVE the regular surface area. In the external bend area seen in Figure 6, you would be trying to build up the surface area over a large external exposed area, and to do that with fairing compound will probably not be sufficiently strong. You need to build up that area with a resin, either epoxy or polyester, mixed with some filler, and with fiberglass cloth. Then sand and shape it to the desired surface. If there are minor voids or irregularities, fill those with fairing compound. An excellent demonstration can be seen at https://www.youtube.com/watch?v=sfnL6L73h48

Q10: How do I preserve the non-skid on the deck?
Non-skid is preserved by not sanding it off and by not filling the recesses in the non-skid pattern with multiple coats of primer paint and top coat paint.

jimh
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Re: Gel Coat Repair and Paint Preparation

Postby jimh » Thu Apr 09, 2020 3:35 pm

Cberglund wrote:I think the repair work necessary on my boat is very similar to the TotalBoat repair [demonstrated in their youTube presentation].
You can, therefore, use the TotalBoat presentation as a guide to how to perform the repairs. Their presentation is very well done and has very high information content--all unusual in most youTube recordings.