chemical removal of yellowing white gel ?

[pescaloco]

Hey guys,

I was wondering if anyone has has sucess with solvents or acids to bring out yellowing caused by entraped styrene that has reacted with uv light in white gelcoat.

There is a company in Australia that someone mentioned to me (Top Gear)
they claim to have a chemical and buffing restoration "system"

They will sell only a complete system with a first step chemical / then compounds and buffing equipment. (very expensive)

Any clue what solvent would be efective to raise the styrene to the surface where it could be wet sanded out without excessive removal of the gelcoat.

Thanks so much,

[Fanie]

Try Amway's silicone glaze

[ondarvr]

Styrene can be from 30 to 50% of the gel coat and is chemically part of it, so I'm not sure how they would "raise styrene to the surface". There are products (chemicals) that can break down gel coat (cured base resin), but I can't see how this would work. Frequently there is a resin and styrene rich layer next to the mold surface that can yellow sooner than normal, this is typical with thick gel coat. When this surface layer turns yellow it can normally be sanded off and the yellowing may be slow(er) to return.

[Fanie]

On my gell coat I have found that only the surface layer looks dead. If you polish it with a high quality polish then the surface comes off and you get some gloss back. If the gell coat is stained you may not get it out, the stain will remain.

Acid. Oxalic is good. Be smart about application. Then take care of the surface.

[ondarvr]

Oxalic acid works very well on stains, but not yellowed styrene. If something was to work, it would need to penetrate into the gel coat and bleach it.

How does one know that it is Styrene that is yellowing?
I'd like to see a picture.

[pescaloco]

Thanks guys,

Just a little more info, there seems to be maybee several different patterens to the yellowing, some areas are striated and others are motteled looking almost like how fabric print through looks except yellow or brownish spots.

It seems in the areas that are porous and have the striated looking yellow, the yellow actually will raise to the surface after keeping the surface wet with a rag soaked with blackstreak remover on it. The yellow color becomes more intense and actually does come somewhat to the surface. Then it can be scrubed out fairly well with a cleanser and a hand pad, finally sanded and buffed back to like new.

I detail boats and do gelcoat repairs so this is something I need to deal with and really alot on a particular brand of boats.

Since I need to get results with out sanding all the mil thickness off the boat I would really like to find a solution. I am open
to all suggestions

EDIT: Just a little more info, I usually can start wet sanding with 800 or 1200 grit wetdry and remove surface yellowing, yesterday in an attempt to see just how bad the side of the superstructure was I went all the way down to 400 paper and if I kept sanding to the point where I knew things were going to go wrong very soon then the gel would turn white again.
So you can put in perspective this is a expensive 2 1/2 or 3 year old in the water boat that was not well maintained, but the condition of the gelcoat seems almost hopeless to correct.

[pescaloco]

Hey Fanie,

Can you tell me a little more about the silicone glaze.

Are you suggesting it as a way to mask the yellowing (put a shine on it) or a way to remove or lighten it ??

In spite of the yellow the gelcoat can be polished to high gloss it just looks ugly and the coloration of different parts of the boat are very uneven

Thanks

It is not mineral stains as I thought. I have no idea - good luck.

[pescaloco]

Hey guys here is a picture I had on file of a different boat same condtion with the gelcoat

Thanks Mark 775

[Fanie]

That does not look like yellowing to me. That looks like the gell coat wasn't applied correctly inside the mold prior to glassing or if it was the gell coat wasn't allowed to cure enough before the glassing was done. The fiberglass/resin is pressing through.

I may be mistaken though. If that is just dirt you should be able to scrub it clean. Silicon glaze is used to put on windows so water doesn't cling to it. It washes off after a while.

Or that corner of the boat was washed so much the gell coat is washed off

You can also try something with amonia in it, it works well to remove ie algea when you clean the boat as well.

You could match an epoxy paint with the colour and spray paint that part over if it is the gell coat that is showing the inner glass. I don't know of another method to finish it.

Maybe Par or some of the other guys can offer another opinion on it.

[pescaloco]

Thanks Fanie,

did you click on the photo to enlage it ?

The top of the shot shows a somewhat striated patteren of yellow spots, and it will come out or lighten with some pretty extreme wetsanding and polishing. Other places it almost looks like when you add a tinting agent to paint or gelcoat and it was not mixed well (how it would look in a mix cup)

I think you are probable right about the production process, because all this brand of boats seems to have the same issues in the same areas.

But the ones that are well taken care (waxed every 3 months) of do not get like this, it seems to take about 6 months from new but is subtle and really (NOT) noticible.

[Fanie]

I zoomed it, rotated it, fade in, fade out, with and without glasses, with the microscope, one eye, the quick look, the stare... but it is different on a picture than looking at the real thing.

Have you tried cleaning it with something ? Even laquer thinners will work to remove tough dirt. Soap and water does not always clean properly if the gell coat surface is course or pitted.

[ondarvr]

Originally Posted by pescaloco

Hey guys here is a picture I had on file of a different boat same condtion with the gelcoat

Thanks Mark 775

That's from the gel coat being sprayed at a sharp angle and too thick. The pigment, fillers and resin will separate and the resin rich areas turn yellow.

Sometimes you can easily see it as soon as it comes out of the mold because the resin base is typically an amber color. Other times it can take a little while and the more sun it see's the sooner it will change color.

Its possible that its too thin, but it doesn't look like typical alligation.

Looking at it in person should make the cause easy to identify.