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Author Topic:   How much Gel Coat do I need?
Rastuscrab posted 11-16-2004 05:21 PM ET (US)   Profile for Rastuscrab   Send Email to Rastuscrab  
I have a 1982 11.5 sport and want to spray the inside of the vessel with new gel coat. I am in the process of scaping down the spider cracks and fixing all the holes. I have two Perval sprayers I bought at Boating World in San Jose. My question is will one quart of gel coat from spectrum color be enough? Also, will (2) sprayers also have enough juice to do (1-3) coats? Thanks in advance for your support!

Matt (Rastuscrab)

John O posted 11-16-2004 06:31 PM ET (US)     Profile for John O    
Spectrum would be the best place to ask about the amount needed.
jimh posted 11-16-2004 08:13 PM ET (US)     Profile for jimh  Send Email to jimh     
Gel coat is normally applied to a maximum thickness of 0.020-inches. To estimate the coverage, consider that 20-feet-square by 0.020-inches is a volume of

20 X 144 X 0.020 = 57.6 cubic inches

In one QUART there are 57.75 cubic inches.

Therefore, one quart of gel coat resin sprayed to a thickness of 0.020 will cover about 20-square-feet.

If someone gives you a different answer, ask to see their mathematics.

Tom W Clark posted 11-16-2004 09:06 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     

Jim's arithmetic is good. In the fiberglass boat manufacturing business, gel coat thickness is typically in the range of 15 to 22 mils. The surface area of the interior of a 13' hull is about 100 square feet. I would guess off the top of my head an 11 foot hull might be about 80 square feet.

It has been reported here that a gallon (four quarts) of gel coat is enough to cover the interior of a 13 foot hull (at perhaps a wee bit less than 20 mils thickness) I would say you will need every bit of three quarts to cover your hull with one coat and you might need four quarts.

You should not need to do more than one coat if you can apply it at the correct thickness.

There is no way on Earth that two little Preval sprayers are going to get you through your entire 11 foot hull's interior. I'm not even sure they would even get you through one quart.

keltonkrew posted 11-17-2004 05:33 PM ET (US)     Profile for keltonkrew  Send Email to keltonkrew     
Agreed with Tom W....That is not a job for a Preval sprayer. You need a gravity fed HVLP sprayer with a 2.2 - 2.3mm nozzle.
John O posted 11-17-2004 10:12 PM ET (US)     Profile for John O    
And the answer is... 20 square feet. I guess we all agree.
John O posted 11-17-2004 10:14 PM ET (US)     Profile for John O    
...that one quart will cover 20 square feet.
keltonkrew posted 11-18-2004 07:39 AM ET (US)     Profile for keltonkrew  Send Email to keltonkrew     
That's the number I used when I ordered gel for my boat.
WSTEFFENS posted 11-18-2004 01:36 PM ET (US)     Profile for WSTEFFENS  Send Email to WSTEFFENS     

I don't want to start a "fight". However from my experience with FRP fabrication, you wax the mold with PVA, spray the gell coat and then while still "green" you do the lay up construction with a "chopper" gun and mat. I don't think gel-coat is really foumlated for a repaint type application. However that said I have used it to repair nicks and gouges in relatively new fabrications (6 months old or less).

I would think (as I have seen) that a 2 part catalized paint such as Immron would be easier to apply and every bit as durible. They paint trucks (beer delivery) etc with the stuff and it wears like iron. I would think it will be easier to work with as its "kick" time is slower and will let it flow out (avoid "orange peel" and "pin holes" ) and not screw up the spray gun due to a "hot" mix. That said, it is a job for a "pro" as the paints are very toxic. I believe it is "cyanide" and requires a fresh air resporator not just one for "organic" vapors.

For what it is worth!


Taylor posted 11-18-2004 06:14 PM ET (US)     Profile for Taylor  Send Email to Taylor     
I can see Mr. Steffens' point - when I sprayed gelcoat, I ended up with a rough finish and a sand like texture that had to be wet sanded to get it smooth and shiny. The area we were working was small enough that we could labor over it carefully - I'm not sure I would want to do it over an entire interior. You can certainly recoat with gelcoat, but for me there is a practical upper end to how much area I'd want to mess with, especially on an interior. While I have no experience Awlgrip other than what I have read here, you might consider that, too.
13dave posted 11-18-2004 06:19 PM ET (US)     Profile for 13dave  Send Email to 13dave     
i took rougly a gallon to rhino coat a 11 of my frineds for what its worth i know its ovbviosuly thicker but if one gallon covers it with rhinocoat aht u cant go wrogn with a gallon of gellcoat
keltonkrew posted 11-18-2004 06:34 PM ET (US)     Profile for keltonkrew  Send Email to keltonkrew     
you CAN successfully re-spray gel on an entire boat. I know...I've done it! You have to add an additive to wax to the surface to keep it from the air so it cures.

Rastuscrab posted 11-18-2004 09:43 PM ET (US)     Profile for Rastuscrab  Send Email to Rastuscrab     
Kelton: So do you think (1) quart along with the additves and a 2.2 mm HVLP spray guy will be enough? The inside is not bad at all but does need to be re-gelcoated!Also, dumb question? What do you mean by a DA sander?

TX-Matt (Rastuscrab)

WSTEFFENS posted 11-18-2004 10:08 PM ET (US)     Profile for WSTEFFENS  Send Email to WSTEFFENS     

In the car body bussiness a "DA" sander is a randum pattern obrital sander. It is designed not to leave "Cat" faces in the sanded product. Only one's I have see are about 5" dia pad size and air powered. In the old days you would spray the pad with 3M adheasive and then stick the sanding disk to the pad. Sort of on the line of "trim" adheasive. Now it is peel and stick.

Hope this helps you.



WSTEFFENS posted 11-18-2004 11:07 PM ET (US)     Profile for WSTEFFENS  Send Email to WSTEFFENS     

A post thought, "DA" was "Detroit Air" the originator of the sander in question!



jimh posted 11-19-2004 09:27 AM ET (US)     Profile for jimh  Send Email to jimh     
As mentioned, in most boat fabrication the gelcoat layer is the first layer sprayed into the mold, and the rest of the boat laminated on top of it. I think this may be easier to do than spraying gelcoat as the final layer on a finished boat. Getting a good surface is probably easier in the mold than on a already finished hull.
John O posted 11-19-2004 09:40 AM ET (US)     Profile for John O    
I have had gel coat in the bottom of a plastic paint container cure and "popped" it out in the shape of the container. The gel coat is as smooth as glass. On the other hand it has taken alot of trial and erroron my part using a Preval Sprayer to get a smooth finish. I do add Duratec High Gloss Additive to my batches and have become pretty good using wet sanding methods.

I have had success gel coating over Marine Tex as well for deeper repairs.

WSTEFFENS posted 11-19-2004 04:01 PM ET (US)     Profile for WSTEFFENS  Send Email to WSTEFFENS     
Again you suprise me with your understanding of MFG. Not a hit, you are an electrical engineer. Normally they don't get down in the threnches. They have bigger fish to fry!

Now think of this, if you are building a "Bass" boat you spray "metal flake" gell coat into the mold, if the pressure and flow, is wrong and you are not using an "Eclips"(or similar) stiring cup gun and you have a "hot" mix (pot time about 15 min ) the "flake" will not stand up and look good it will just lay there and be flat! It is risky. And a pain in the prattt to clean up, (remember poly-esyter resin does not have a disolvent, it sets up on the line of a "rock" once "kicked".

Makes shooting "Desert Tan" look very tame! I still think that shooting "Gell coat" is not a good thing to do for refinish. Just my opinion.

As for the wax, all FRP fabs use the "wax" to make the system set "up" If they didn't they would stay "sticky" forever! That is why the repair "kits" send you a piece of plastic to cover the repair until it "cures"! It is a back up for the wax.



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