Gel Vs. paint

[Reese]

S&F test article.

We've got so many members it would be easy to find one or two test beds...we paint and gel coat a couple of stripes on the bottom of the pad and let er' rip.

Maybe even Greg would be interested in doing want to do a little test article? Maybe manufacturers could provide product for the test and we'll published on the S&F site.

Test could run for a week, month, up to three months...

[stan]

Hello
I am painting a hull with white Imron, I would like to know what other paints can be applied on top of the Imron mostly above the water line. For example if I paint a stripe pattern what paint would work on the imron white basse and the what clear would work on top of that. Is there such a thing a thing as clear gel-coat would that work?

Stan

[Racemore]

It isn't that hard Bro.To wet sand gelcoat that is badly oxidized I will start with 600 grit. After i scuff it i'll go to 1000 untill the 600 scratches are gone.Then I do an area maybe a couple sq ft with heavy compound,medium and swirl free to see if it is all uniform in color.The old color will be darker or dirty looking and the clean will of course look clean and brighter.I also look to see if it looks like the color is thinning or a color that was applied after one is starting to bleed through meaning the top color is getting thin.If everything looks good I might go to 1500 to take a little time off the heavy compounding.

The point, use this process on paint.Put a DA with 4or600 on your paint job.I use 320 to remove orange peel on fresh sprayed gel and 1000 on paint and finish with 2000.

[Superdave]

Bertram31.com



Re-Gelcoating Your Boat




Re-gelcoating has a few differences to painting. Both require the same amount prep and fairing, but the application and finishing is quite different.

The principle difference between the two systems is in the final shoot.

For paint, the primer is sanded and double checked for porosity and other mars, (sags, runs, drips, dips, etc.), and then the topcoat is shot or rolled & tipped. This is usually done as one application. Once the paint has cured, you're done if using a LP topcoat such as Awlgrip or Sterling. For Imron and similar topcoats a final buffing and polishing may be required after about 1 month. The cured topcoat thickness of the painted surface will be around 10 mils.

Gelcoat will need to be heavier in thickness for a couple of reasons. Foremost is that gelcoat doesn't level out and cure the same way that paint does. Even with additives to thin the viscosity, a certain degree of texture, (orange peel), will be present after cure and has to be sanded, sealed, and polished.

Gelcoat also oxidizes at a much faster rate than topcoat paint systems and will require more compounding and polishing over the years. The key to the best longevity here is to maintain the surface frequently depending on the atmospheric conditions in your location and how the boat is protected from those conditions. A boat in the tropics with little or no protection from the direct sun will require a more frequent maintenance schedule than one in a more moderate climate kept in a covered boat shed.

Gelcoat is normally sprayed on in multiple coats to achieve the final cured thickness. You want enough thickness to allow for the initial sanding and polishing process, and still leave enough thickness to last a decade or more of maintenance compounding and polish before getting too thin.

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. Gelcoat continues to cure and shrink through out its life span. Standard maintenance will reduce your thickness by about 2 - 3 mils a year if you do a semi annual compounding & polish on top side surfaces & 1 - 2 mils for an annual hull maintenance.

You should be able to spray 10 mils per application & allowing for shrinkage in the initial cure, this would be 4 applications. The application schedule would be as follows:

1. 10 mils gelcoat - little or no additives* & no surfacing wax
2. 10 mils gelcoat - little or no additives* & no surfacing wax
3. 10 mils gelcoat - with additives* & surfacing wax


Allow the gelcoat to harden for several hours between coats. Coat 1 & 2 will be tacky after hardening to the point that you can't put much of an impression in it with your fingernail. Coat 3 should have no tack at all at the same point.

The surfacing wax will migrate to the surface as the curing cycle takes place and create a barrier to air. This is necessary for a tack free surface when cured so that you can sand.

An alternative to using surfacing wax in the gelcoat mix is to over spray the gelcoat with PVA, (polyvinyl alchol). The problem with this method is getting the right amount of material misted onto the un-cured gelcoat to block the air out and in gauging just when to apply the PVA. Too much will adversely affect the gelcoat finish & cure, applied too soon will do the same. Not enough will allow air, leaving a tacky cure, too late will not block the air soon enough still leaving a tacky gelcoat cure.

PVA is misted on with a fine tipped gun at around 90 - 100 PSI. It must be applied at a point when the gelcoat has started gelling but hasn't hardened. The right amount of PVA is an unbroken film of less than 1 mill. The amount of PVA needed will also be more costly than the amount of surfacing wax needed.

* Gelcoat is quite viscous and almost impossible to spray without thinning it. The less you can thin it the better the gelcoat will be, so the use of a larger spray tip is required. I use both 2mm & 2.2 mm HVLP gravity feed cup guns for most of my heavy shoots. At this size the thinning is kept to a minimum.

Do not thin your gelcoat with acetone, MEK or lacquer thinner. Thinning with these materials can lead to an un-curable application that will aligator on the next shoot, destroying all the time and materials for both shoots, (been there, done that, got several T-shirts to prove it...). The best product to use, (manufactured by several resin companies), is called "patch booster". Patch booster is a high quality, low viscosity polyester resin with additives to minimize a tacky surface when cured. Depending on the tip size of your gun, 10% - 15% patch booster is all you may need. Try not to exceed 20% in the first three coats.

On the third coat add about 10% surfacing wax so that after the gelcoat cures it will be sandable. Allow at least 24 hours for final cure & before sanding. Sanding with 180 grit on the 3 coat will allow you to remove most, if not all of the orange peel texture and check your fairing.

The final gelcoat application will be done with a 1 mm tip gun, adding between 30% - 40% patch booster, & 10% surfacing wax. This application will be more like what you'd get shooting paint. Because of the lowered viscosity, watch out for sags and runs... Allow 2 or 3 minutes between overcoats to get your 10 mils. ie: spray about 5 mils over a given area and re-coat that area in 2 - 3 minutes.

Let the final application fully cure before sanding. Minimum 24 hours, 48 hours would be best... There should be very little texture present in the cured 4th application and you could start sanding with as fine a grit as 320 wet. Start with a finer grit first and back up to a coarser grit if necessary.

If you don't add enough surfacing wax the air will get to the gelcoat and it'll cure tacky and almost un-sandable. If you add too much the surface will have a waxy scum that will make sanding difficult. But too much surfacing wax is the lesser of the two evils. Remove the wax from the surface with naphtha followed with a soap and water wash. In lieu of naphtha, use a concentrated liquid laundry soap such as Wisk. Actually apply the soap directly to the surface, allow to stand for a couple of minutes and rinse well.

For the finest finish, you'll want to wet sand through 1,000 grit before compounding. Make sure that each grit has removed the scratches from the previous grit. Don't move to the next grit without thoroughly rinsing. A wet surface won't allow you to see fine sanding marks, so dry the surface and inspect it before moving to the next grit...

Once you've reached the end of your sanding, the 1,000 grit will have brought your surface up to a dull luster. A course rubbing compound shouldn't be necessary and you may be able move to a fine compound like 3M Finesse-it. Follow the Finesse-it with an automotive finish sealant such as Meguire's Machine Glaze. This is followed with a swirl remover such as 3M Perfect-it & a foam pad.

The resulting finish and the nature of the gelcoat will far exceed a painted surface in terms of longevity and repair ability, but you'll see why painting is the less expensive alternative. Gelcoat is less expensive in terms of material costs, but that is outweighed in terms of labor costs... Over a 20 year period the gelcoat becomes more cost effective, especially when compared with Awlgrip on topside surfaces since there would be at least 1 if not more re-paint jobs needed.

Best regards,

Patrick


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Have fun! Feel free to download and print this article, but please don't use it on a website without linking it to Bertram31.com.

Capt Patrick McCrary
Bertram31.com

[Techno]

Racemore I don't know what you mean by a sealant but if you seal fresh paint you've ruined it, the reason it isn't waxed for at least a month. Since you can use glaze on fresh paint I don't see how it can be a sealant. The paint can still release any solvents so how can it seal gel?

[inspectorlance]

I noticed that in the artical that SuperDave posted it mentioned Gel Coat shrinking over its life.
I have noticed small dark brown/ black pin head size marks in my gel coat. Is this the shrinkage ? It looks just like I would vision if it was shrinking. You can only see them if your face is about 6" away from the Gel. The boat is a 1994 X-Stream. I am in the process of wet snding the boat, and the marks are Not on the suface.

Am I suffering from shrinkage ?

Lance

[Superdave]

stand a foot away and it'll be okay

[Racemore]

Techno,the machine glaze is for the gelcoat not paint.Gelcoat has more porosity than paint that is why it chalks up faster than paint.Keeping it waxed will extend the life off the finish greatly.If it is keeped covered also it could outlast it's owner,look at Gregs boat,like new.At this rate he'll have to will it to his grandson.The machine glaze statement came form the Bertram post anyway.I don't agree with a few things he said like not using acetone,mek solvent and laquer thinner.The first 2 are used and lacquer thinner is used with Duratec which I would use anyway so all he says about surfacing agent doesn't apply.As far as curing gel I can apply it to the floor of you boat with no surfacing agent and fill it with water after it kicks and the surface will harden.

Lance,that is why it needs to stay waxed.Try scrubing an area with acetone to see if it will clean out.

[Reese]

"look at Greg's boat...like new"...yea, that's a real torture test...

[Stretch]

If you paint...use Imron
Imron is badass, but don't breathe fumes or vapors..nasty stuff

[Kurt Gilbert]

Interesting discussion! Having worked extensively in the boat and spa production industry, (both products requiring a high degree of water and chemical resistance), and, having been directly involved in the creation of hybrid gelcoats for those industries with Duratec, AKA Revchem Plastics, (Doug Dennis)...and...having repaired and rebuilt dozens of fiberglass boats...and...having managed and owned fiberglass ski boat manufacturing plants...I feel qualified to add this:

Tooling gelcoat certainly is tougher in some respects to standard orthophthalic or even most isophthalic resin based gelcoat, but is not necessarily the choice for a boat. There are many hybrid gelcoats out there now that are based on many different platforms that certainly outperform any paints in certain areas of concern when used properly and in conjunction with the right preparation products and process. Duratec is one example. Vinyl-ester based products are another. There is no clear answer for all applications. As to cracks, crazing, etc., that is usually as much a product of the lamination and structural integrity as anything. Gelcoat used for high performance boats should not be put on thick, but rather, in a smooth consistent layer. Certainly nowhere near 100 mils! When properly applied, it should be more like 15 to 25 mils, not including any barrier coats.

Last...building a boat without any gelcoat or similar surface is just asking for print through. A good gelcoat acts as a barrier to the shrinkage issues of the subsequent laminations. If you plan on painting the boat out of the mold, a plain white, vinyl ester gelcoat no more than 15 mils should work great. Also, I understand both sides of the concern about re-surfacing an existing boat. I have used both imron and gelcoat, depending on the application and service. Imron works great above the water line, gelcoat below. Properly thinned, (and it should not be acetone above 5%, use styrene instead), with a little duratec, gelcoat can be a great refinish.

Happy boating!

[Techno]

The thickness thing about gelcoats is I haven't seen these thin coats. 1/32" is .031"-31 mils. Maybe my eyeball needs recalibration but the thickness I've seen you can hide things in.

[Racemore]

Thanks for the post Kurt.I started getting serious about fiberglass 30 years ago when I had to repair my own boat.I have learned by listening to people in the industry and hands on experience.I learned the advantage of vinylester when Hydrex was developed.It dosen't mean you have to use it to fix a boat though.I make filler with talc and resin or gelcoat.A friend turned me on to that when he tried to bond Corvette door panels with some marine putty I bought from Polygard.It didn't work.He had been restoring Vettes for 25 yrs and never had a problem but wanted to try something premixed so he and I both learned,the company using that putty to bond their innerliners were in trouble.Some people just don't go with experience untill they have a bad one.Duratec is another product that makes re-geling so much easier.Mixing it with finishing resin to re-clear or repair metalflake jobs is the way to go.I don't think I would ever use urathane by choice again.Thanx for your input and welcome to Scream and Fly.Lonnie

[Mini Max]

A funny story about toxicity.

An old employee of mine used to work for Velocity in the early "80s and both gell coated and painted. He used to shoot the cockroaches in the shop with the Emron color du jour while painting.the graphics.

This was Florida. Remember its palmetto bug heaven. By the end of the week the roaches looked like NASCAR competitors. One of every color he had shot that week. The Emron didn't bother them a bit.

Later he would shoot the gell coat the night before lamination and then close up the shop till morning. The next day little Dale, Richard and Rusty were legs up having done gone to Bug heaven having expired from the fumes.

Go figure.

[Racemore]

Yea."it kicked",their ass.