Gel Coat

[Singedfur]

Hello,

How toxic is gel coat to spray? Does it have isocyanates in it? Can it SAFELY be sprayed using only an organic vapor/3M-style mask and not a fresh air supply?

My local paint supply house said you need a "pressue pot" in order to spray gel coat. Is this common knowledge? Why won't a large tip on a primer gun work? I have a source (Eckler's Corvette Supply) that sells "sprayable gel coat". Would sprayable gel coat still require a pressure pot?

Thanks!
Patricia

[doug]

An MSDS sheet for a 3M gelcoat says:
8.2.3 Respiratory Protection
Avoid breathing of vapors, mists or spray.
Select one of the following NIOSH approved respirators based on airborne concentration of contaminants and in accordance with
OSHA regulations: Half facepiece or fullface air-purifying respirator with organic vapor cartridges and P100 particulate prefilters.

It did not mention ISO's, but I guess that might be product-specific. Here's a link to the MSDS PDF, not sure if the link will work.

[Singedfur]

Thank you, Doug. Very handy. No, it doesn't appear to have iso's. Hopefully that is the same story with the brand I am considering. I will have to see if I can find an MSDS for that.

Anyone know if a primer gun will work, or must I use a pressure pot?

Patricia

[68-chevyman]

I bought a SATA LM for gell coat. Its a 3.0 tip
yeh, it'll put it on and on just has to be a G feed.

[Len]

Thank you, Doug. Very handy. No, it doesn't appear to have iso's. Hopefully that is the same story with the brand I am considering. I will have to see if I can find an MSDS for that.

Anyone know if a primer gun will work, or must I use a pressure pot?

Patricia

If I were spraying a strange product (I've haven't shot much gel coat) I'd look to the gel manufacturer to see what tip size they recommend for their product. Once the tip size and type of gun are known you can go shopping. I would think that different products are probably different viscosities and you may need to buy equipment specific for the material you're spraying. The only gel coat I've sprayed I used a 1.6 tip on a gravity feed gun and it did a nice job however that was on a sail plane and that was a long time ago plus the customer supplied the materials so I don't know what brand it was.

[68-chevyman]

?DID YOU KNOW?

Gel coat must have wax added to it when used as a top coat or PVA (poly vinyl alcohol) sprayed over it when used as a under coat. It can be a difficult product to use and costly.

Why not use polyester primer or epoxy

[Singedfur]

Thank you all for the advice. Good point to ask manufacturer directly about what type of gun/size tip they recommend. I'm beginning to realize some gel coats are harder to spray than others.

The reason I am going with gel coat is because, while I have heard conflicting opinions, I have read that nothing seals the errant fiberglass strands better than gel coat-not even a primer/sealer product. Whether this is actually true I am not sure, as I have heard that a good primer/sealer should do the same, but I would like to be certain. Also, the manufacturer of my aftermarket fiberglass panels recommended spraying the backside of the panel with either gel coat or a catalyzed urethane to prevent moisture from working into the panel. I am leaning toward using the gel coat because it sounds like it could be sprayed safely without a fresh air supply (such as the Hobbyair), as I do not yet have the $ for the fresh air supply.

[X711]

You might consider trying this as an alternate to spraying gel-coat

http://www.autobodybrands.com/primers/2k_poly.html

PRODUCT DESCRIPTION:
#5420 is a two-component polyester primer-surfacer which can be used on properly prepared fibreglass, aluminum, steel and SMC. #5420 has excellent adhesion, high fill and superior solvent resistance when properly cured. On fibreglass, it replaces damaged gel coat. The cured primer film is non-shrinking. #5420 is compatible with all automotive products and meets all current LOW V.O.C. regulations for primers. Isocyanate-Free.

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[Phil V]

No one has mentioned so far exactly what gel coat is. To understand how to spray it and how to protect your lungs while spraying it you need to know the chemical make-up of gel coat. MOST gel coats are simply a polyester resin (same resin used in fiberglass repairs) with color pigment added. Bondo (generic term for polyester autobody filler) is the same polyester resin with talc or micro-sphere glass beads added. Polyester primer like Feather-Fil etc are also fiberglass resin with a filler like talk added (spray bondo).

So the bottom line is that gel coat is just polyester resin with color pigments added and is catalyzed with regular liquid hardener that is also used for fiberglass repairs. Any dual cartridge painters mask is quite sufficient for spraying gel coat (in reasonable conditions of vapor concentration). The spray gun tip and air cap size will be dictated by how thick you mix the fiberglass resin. Or if you're spraying a large metal flake basecoat then a larger air cap/tip will be needed. You can reduce the fiberglass resin/gel coat with a reducer recommended for polyester resins.

[Phil V]

I guess a follow up would be in order. I personally avoid using gel coats in just about all cases because a gel coat is very brittle (we've all seen spider-web cracking in gel coat). Gel coat is durable but will scratch like any other surface. Most gel coats have poor UV protection so after a while the suns UV rays begin to degrade, chalk up and finally destroy that gel coat.

You would be much better served applying an epoxy primer to the back side of any glass panels as a moisture barrier. You would in almost all cases also be better served by substituting the newer urethane primers and paints in place of polyester based primers and get coats.

[Singedfur]

Phil-

Your description of gel coat is very interesting. I have never heard or read what it really was, and I'm surprised it's basically fiberglass resin.

I've never been around it, so I am surprised to hear gel coat can have spider web cracking issues. Does this mainly happen only when exposed to UV? Is it safe when under paint? I ask because I have high-quality, aftermarket, press-moulded panels on their way (Corvette Image brand), and they come with the *paint-side* surface gel coated!

I will certainly reconsider gel coating the back side of the panels, as I did not realize UV would destroy it.

Do you know if a good urethane or epoxy primer will actually hold down errant fiberglass strands, such as over a repair? I have read that NOTHING will do that but gel coat. I am actually not seeing loose strands after a repair, but I've read they can work their way up and lift paint. I'm nervous about that happening down the road. As far as toughness and moisture barrier characteristics, I am satisfied that a good urethane primer would be fine; it's more those supposed errant fiberglass strands that have me concerned.

Patricia

[Len]

Patricia
I don't know where you're getting your information but I've been doing Vettes for a long time and we never use gel coat and we have a lot of show cars on the road with no fiberglass strands showing.

If you use a fiberglass cloth rather than fiberglass mat you may see the texture of the cloth when the temperature changes but you won't get strands of material coming through the surface.

The pictures below show sanding Polyester Spray Filler (no gel coat) on a 54.



Here is the end result....


We also did the black 57 Vette next to the red one. We did it several years ago and it still looks like the day we finished it. No gel coat on either car.

[Phil V]

Patricia, I did a cut-n-paste of your last message so that I can address your concerns one by one. Anything in parenthisis are your words and no parenthisis are from me.

"Your description of gel coat is very interesting". "I have never heard or read what it really was, and I'm surprised it's basically fiberglass resin".

Patricia all the pre-1984 Corvette complete bodies were made of the same fiberglass resin and fiberglass matt. In 1984 GM changed over to SMC (molded compound) bodies to replace the older style fiberglass/polyester bodies.

"I've never been around it, so I am surprised to hear gel coat can have spider web cracking issues". "Does this mainly happen only when exposed to UV?"

The spider web cracking has absolutely nothing to do with UV damage from the sun, the cracking occurs because gel coat is very brittle. The spider web cracking can be cause by the body flexing a little more than the getl can can handle or it can be cause by some type of external or internal impact.

"Is it safe when under paint"? "I ask because I have high-quality, aftermarket, press-moulded panels on their way (Corvette Image brand), and they come with the *paint-side* surface gel coated"!

Gel coat under paint is just as safe as gel coat with no paint in reference to stress cracking/spider web cracking. If its going to crack then it won't matter if there is paint on top of it or not. The rest of your last paragraph has me a little confused. You say your new high quality aftermarket panels coming are "press molded panels". Whats confusing is the just about all press molder panels are SMC and not fiberglass gel coat. You can't use polyester resin on SMC panels because of a delamination problem (two dissimilar materials that aren't very compatible). If your new panels are in reality SMC panels then you would just need to scuff the surface and apply an epoxy primer followed by your color topcoats.


"I will certainly reconsider gel coating the back side of the panels, as I did not realize UV would destroy it".

Gelcoating the back side of a panel in my opinion gains you nothing that epoxy primer couldn't do better. (I recommend epoxy primer as a barrier coat and NOT use polyester resin/gelcoat). But again the UV prospective damage would have no effect on the back side of any SMC or fiberglass panel because the suns rays don't shine on the back side of panels, just the front/outside of the panels.

"Do you know if a good urethane or epoxy primer will actually hold down errant fiberglass strands, such as over a repair"?

Again I'm a little confused why a few errant fiberglass strands would be an issue you at all (assuming we're talking about the backside of these panels. I have never seen a need to seal the backside of a fiberglass panel with the exception of some type of undercoating material whose main function is for sound deadening and nothing to do with moisture sealing. What I'm saying is if there are a few "errant fiberglass strands) on the backside of a panel just leave them as is if they are out of sight. That is not a potential problem lurking there, basically is a non-issue.

"I have read that NOTHING will do that but gel coat. I am actually not seeing loose strands after a repair, but I've read they can work their way up and lift paint. I'm nervous about that happening down the road. As far as toughness and moisture barrier characteristics, I am satisfied that a good urethane primer would be fine; it's more those supposed errant fiberglass strands that have me concerned".

Patricia, I don't know who has been telling you this stuff about loose strands on the backsides of panels with or without repairs but my experience is they are telling you about potential problems that don't exist. Moisture is not going wick through fiberglass a cause paint to bubble, it just don't happen.
20 years ago I worked as a bodyman/paint man in a shop that specialized in Corvette repairs and repaints so I have a reasonable amount of working experience from back then up to this point in time.

Patricia

[Singedfur]

Phil V,

Thanks for your point-by-point help. Sorry I was a bit unclear about my new panels. Yes, the factory used the press-molding technique with standard mat and resin (no gel coat), later switching to SMC, which is also a press-molding technique but uses higher heat and sheets of 'glass fed into the mold, etc., which produces a bit more "plastic-like" fiberglass. The panels I have purchased are from an aftermarket source are attempting to replicate as closely as possible the earlier non-SMC fiberglass panels. However, from some reports I have read on the NCRS forum, some people have had some issues with paint blistering on those panels alone, while not over factory panels on the same car. Sometime in the past the company began gel coating the exteriors of those panels. So from all I gather, for some reason, the aftermarket panels, though they are the closest replicas you can buy, are a bit more sensitive to moisture/contaminants than the original panels. This is why I am considering some sort of coating on the BACK side of the panel.

My bad: the errant strands of fiberglass I was referring to is with regard to the front side of the panel. I have had to do some repairs on various spots of the body on the original 'glass (bare, no gel coat), and have read (Eckler's fiberglass repair book) that any repair should always be covered by gel coat. I guess that's why I was considering gel coat so strongly. I'm glad you alerted me to the fact that gel coat is brittle.

Thank you,
Patricia

[Phil V]

Patricia


"the factory used the press-molding technique with standard mat and resin (no gel coat)",

All molded fiberglass auto body outer parts have a gel-coat, without the gel coat the fiberglass matt/strands would be part of the outer surface, (not a good thing) so an outer layer of gel coat is necessary.

"The panels I have purchased are from an aftermarket source are attempting to replicate as closely as possible the earlier non-SMC fiberglass panels. However, from some reports I have read on the NCRS forum, some people have had some issues with paint blistering on those panels alone, while not over factory panels on the same car. Sometime in the past the company began gel coating the exteriors of those panels. So from all I gather, for some reason, the aftermarket panels, though they are the closest replicas you can buy, are a bit more sensitive to moisture/contaminants than the original panels. This is why I am considering some sort of coating on the BACK side of the panel."

I really doubt that the problem is from moisture penetrating though the fiberglass panels starting from the backside causing the outer surface paint to bubble and lift. I've never seen that in 35 years as a professional autobody man and painter. I would be more inclined to think that perhaps the real problem is that the outer surface of the new panels may have some minute pinholes/air pockets that may contain residual mold release agent which is causing the paint to bubble and/or lift. Fiberglass is for all practical purposes water proof, I just don't think that water will penetrate through a fiberglass panel and cause paint to lift (unless those fiberglass panels are paper thin).

My bad: the errant strands of fiberglass I was referring to is with regard to the front side of the panel. I have had to do some repairs on various spots of the body on the original 'glass (bare, no gel coat), and have read (Eckler's fiberglass repair book) that any repair should always be covered by gel coat. I guess that's why I was considering gel coat so strongly. I'm glad you alerted me to the fact that gel coat is brittle.