Overshot Gel Coat...now what?

[JohnV8r]

Guys,

I overshot a layer of gel coat to the tune of 28 mils. I used 10% Patch Booster and apparently was admiring how well it was laying down.

The intent was three layers at 10 mils with surfacing wax on the last layer; then Patrick's recipe on the final application with a 1 mm tip gun, adding between 30% - 40% patch booster, & 10% surfacing wax.

What is my best course of action now to avoid spider cracks down the road?

[Bruce]

John,
I'm no expert on gel coating, but my experience with boats I've been involved with with gel coat instead of paint is that anything over 18 mils will have to come off.
Sanding it off is what I've seen done.

[Tony Meola]

John

Send Jimmy G a PM. He is a body man so he should have some input as to how safe you are.

[Corey Mason]

Guys,

I overshot a layer of gel coat to the tune of 28 mils. I used 10% Patch Booster and apparently was admiring how well it was laying down.

The intent was three layers at 10 mils with surfacing wax on the last layer; then Patrick's recipe on the final application with a 1 mm tip gun, adding between 30% - 40% patch booster, & 10% surfacing wax.

What is my best course of action now to avoid spider cracks down the road?

I feel completely lost by this. I have no idea what this is. I know I can't help, but could you explain your post? how are you guys measure how much you're spraying? Patch boosters? etc.

[JohnV8r]

Corey,

Read this from the "Building Tips" by Capt Patrick: http://www.bertram31.com/proj/tips/re-gelcoating.htm

That will give you the basics so you can understand the issue.

My objective was to shoot three 10 mil layers of gel coat per the instructions where the 3rd layer has surfacing wax that seals and allows the gel coat to cure. Then, I would sand, and shoot the fourth final layer. I have a 5 stage Apollo HVLP turbine that does a great job shooting gel coat with a 2.0 mm tip. I shoot other coatings like varnish and polyurethane with a 1.3 and 1.0 mm tip respectively. However, I had never used patch booster to thin gel coat before and was gawking at how nicely the gel coat was laying down out of the gun when I realized a lot more gel coat was coming out.

You measure how much gel coat you have shot with a tool like this: http://www.bottompaintstore.com/fibergl ... 22377.html You put that in the wet get coat at a 90 degree angle and the last tooth with gel coat on it shows you how many mils have been laid down.

I shot almost three times (28 mils) what I wanted to.

Per Capt Patrick's article and Bruce's comments, you want the final gel coat depth AFTER sanding to be 18 - 25 mils max. Otherwise, you get spider cracks in your gel coat a few years down the road. Spider cracks look like this: https://www.boatdesign.net/threads/need ... int.39381/ In my experience, they tend to occur where a screw or other fitting enters the gel coat surface, which makes them a pain in the ass to repair.

So my dilemma is what to do now that I overshot the gel coat. Can I seal it with a follow up coat that has surface wax in it and sand it down to 18-25 mils from there, or do I have a bigger issue because I shot it so thick right out of the gate? Do I follow the procedure outlined in Capt Patrick's article and then sand down from there? Do I need to seal and sand the entire gel coat surface off and start over?

There is undoubtedly someone here who knows whether I can seal and sand the overshot gel coat and avoid spider cracks. While I feel like an idiot for overshooting the gel coat, I'm sure I'm not the first person it has happened to.

Hope that helps.

[CamB25]

Is it curing without wax? You can spray PVA with a Prevail sprayer to seal the surface so it cures -

http://www.fibreglast.com/product/PVA_R ... d_Releases

Not sure how to uniformly sand the surface down unless you have access to a drum sander or are willing to long board by hand. I would probably leave it thick.

Cam

[JohnV8r]

The good news is it was 106 degrees here yesterday with the temp above 100 all afternoon. I shot it in the morning when the temp was in the low 70's. By 8 pm, it was virtually tack free and I could not put a fingernail edge into it. So, yes. It has cured as well as anything without surfacing wax will cure.

The other good news is it is a relatively small piece. It's the piece that attaches to the port side bulkhead. On Shambala, the port bulkhead was cut in half to essentially give you a combination of Sportfish openness with an FBC head on the starboard side. Looks like this:



The piece in question is exposed to a very limited degree. It's the white piece with teak trim on top where the motor box rests against in the bottom right of this picture:



Here is the actual replacement piece I fabricated out of Coosa and shot yesterday:



The bad news is this piece gets screwed into at several different locations where the motor box supports and the pieces that connect it to the bulkhead go. So it's susceptible to spider cracks to begin with. I'm fairly confident I can get it sanded down to the correct mil spec because I can hold the measuring tool against the side to measure the cured depth after sanding. It's an easy piece to sand the last few mils fair by hand with a large block because it's not that wide.

I guess I'm just going to shoot another light layer with surfacing wax and try not to exceed 35 mils. Per Patrick's article:

"The cured thickness you want prior to initial sanding is a minimum 30 mils & max 35 mils. This will allow for a 5 - 10 mil thickness reduction, leaving around 20 - 25 mils after polish. Any heavier than 25 mils and you'll run the risk of spider cracks in a few years."

I'm just not sure what the implications are given that I've shot one large layer and will now shoot a thin layer with surfacing wax to cure. I guess the only way to look at it is that layer with surfacing wax would have been completely sanded off if I had laid down three 10 mil layers anyway.

Time will tell I guess. What a dumbass mistake though...

[CamB25]

I think you are being too hard on yourself. It looks fine..better than fine. A mil or two can't make that much difference. Rub or spray some wax on it, let it cure up hard, and put it to work!

If you second guess yourself on these parts you'll spend 9 years working on the boat...oh, wait...that sounds very familiar...:)

[JohnV8r]

If you second guess yourself on these parts you'll spend 9 years working on the boat...oh, wait...that sounds very familiar...:)

LMAO!!! If I counted the number of times Uncle Vic's line "Better is the enemy of good" popped into my head while I was redoing something I didn't think I had gotten quite right, I'd be in an insane asylum. The problem for me always is that I only see the things I wish I had done better instead of the one's everyone else thinks look great... But I do appreciate you putting this into perspective!

[scot]

"Better is the enemy of good"

My white whale :-(
It's a mental problem, not a quality of workmanship problem. Predrill that bulkhead where the screws will go, install it and use the boat before you end up like me and Cam.

[MikeD@Lightningshack]

Fyi...
If you never sanded gelcoat after spraying, you are about to learn that more is better because the valleys are normally deeper than you expect. On your quest for a mirror like factory finish, you have the luxury of not quitting until you get perfection. Hardest part of gelcoating a surface right is not burning through when sanding. You did yourself a favor, and there is no downside of having a thick layer that is unwaxed as long as you seal it at the end, and then sand until it is no longer too thick.

Gelcoat comes off quick even with 400 grit. Use flat sanding boards be careful on corners and don't sweat the buildup.

Mike

[JohnV8r]

Mike,

Thanks for that. I sanded the piece down essentially to start over. It's a small piece, so it wasn't that big of a deal. It was interesting to see how much gel coat was coming off with 400 grit on the sanding board. I tend to fawn over every inch when sanding, so I think it is better for me to start a little thicker...at least in the beginning.

Thanks!

[CamB25]

My white whale :-(
It's a mental problem, not a quality of workmanship problem. Predrill that bulkhead where the screws will go, install it and use the boat before you end up like me and Cam.

Hey! It's not a boat project, it's a lifestyle!