gel coat repairs

hey guys,

got a two part question regarding gel coats. i have a coulple boats i take care of and they have had some gel coat patch work done. Before my eyes as the months go by the repairs have become more and more yellow, where as when they were patched it was a pretty close match.

Is there a restoration process, chemical or buffing that would bring them back closer to a match ?

second part same issue yellow gel coat original factory finish, some sections with same care and sun exposure are getting pretty yellow, while near by finish is a nice bright white. suggestions for correction / restoration

thanks, mark

 

First of all, let me say that the difficult thing is that repairs always seem to react different than the original thing, expeccially when a different type of gelcoat is used. To there is always some margin for error.

To correct this problem (short term) is to rebuff, and remove the yellow top layer. However, the process is very likely to start all over again.

Cause of the yellowing can probably be found in some factors:

-undercure of the gelcoat. Too little hardener added, or too little cobalt in the fist place. Tends to happen in hot areas, where people tend to reduce the amount of hardener, to get more open time. Please either ask your supplier for a slower gelcoat, or ask them for some retarder. Do not undercatalyse, for various reasons.
-type of gelcoat. For outdoor use, an orthophtalic gelcoat will not do the job. Use an ISO or an ISO-NPG gelcoat (the last one is better, and used throughout the marine industry). In the event a vinylester gelcoat is used (not likely), yes, these yellow. They are nice and scratch resistant however, so are used for moulds and in chemical resistant areas. (where yellowing is no factor)

Perhaps there are more factors, which I overlooked, but the above 2 are very common.

Of course I presume the gelcoat was colour matched to a cleaned and buffed area of the boat, not a dirty and dull area...

 

Frequently people use styrene to thin gel coat for spraying repairs, this results in premature yellowing. Most things used to thin gel coat for spraying will have negative effects, you don't always see it right away, but over time the repair will frequently age faster than the surrounding area. There's not much you can do to keep it from yellowing again after sanding and buffing, but it should look better for a while.

Part of the reason for some areas of the original surface yellowing and others not, can have to do with gel coat thickness. The thicker it is, the more it tends to yellow, so areas around a radius where gel coat can become thick will yellow sooner. Sanding these areas will help to remove the resin rich yellow layer at the surface, sometimes it will work very well and the gel coat will resist yellowing for a long time after sanding, but other times it will return sooner than you'd like it to.

 

yellowing

Thanks, Guys

I was wonder what was wrong with care the boats recieve which is excellent.

any tips on yellow flat deck sections (agressive) factory molded non skid to kill the yellowing (it makes a really nice boat look like crap) same effect bright white then a 2x3 ft yellow patch. Any checmical stain removers or restorer you like (tried soft scrub w/bleach ir did nothing same for west marine non skid cleaner)

thanks again
Mark

 

The Non skid areas are normally sprayed thick to fill the pattern on the mold, that's why they yellow faster. The yellowed surface needs to be removed, I've seen a solvent soaked rag placed on the non skid for a period of time break down the surface of the gel coat slightly and bring the color back. I can't say that I would recommend that method to someone though.

 

for the non skid use a scott brite pad say grey its fine and rub down the non skid this sould remove the stained gelcoat, after rebuff the area, a scott brite will sand with out losing the texture but go easy

 

thanks

thanks guys

can allways could on some solid answers

Mark