Untinted vs White Gelcoat Anarchy

I am doing some minor gelcoat repairs, fixing a lot of scuffs on the white cockpit and other white areas on my J/35, fixing a few bigger marks on the medium gray non-skid, and fixing some small marks on the light gray topsides. Most of the work is in the cockpit and other white areas.

I will need to tint at least some of the gelcoat for the gray non-skid and topsides. I am curious if it is better to start with white gelcoat and add some darker tint; or if it is better to start with the untinted gelcoat and just mix up separate white and gray batches.

Thoughts?
 

CaptainAhab

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Matching gelcoat is a real pain. If you can remove a seat and take it to a fibreglass shop that will match it you will be miles ahead. My local guy can do it by eye in a few minutes and charges me $25 to tint a litre. You can spend hours yourself mixing little batches that never look good.
 

phill_nz

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im always for the DIY side
if you can colour match already no biggie
if you cannot then buy a cheap set of acrylic paints and learn .. the skill never goes away it just becomes progressively more useful

as a rule of thumb ( and because of the way computer colour matching works ) most gelcoat colours are made of a base colour ( almost always white ) and 3 other colours .. usually yellow ochre, red iron oxide and a darkish blue

that should also answer the question as to what coloured gelcoat to buy as your base start .. you will then need at least 3 gelcoat compatible tinters to do your matching ( the gelcoat may last 6 months the tinters will last years )

for a basic start you can play with these to get an idea of what to move and how much
 
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Will1073

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Matching gelcoat is a real pain. If you can remove a seat and take it to a fibreglass shop that will match it you will be miles ahead. My local guy can do it by eye in a few minutes and charges me $25 to tint a litre. You can spend hours yourself mixing little batches that never look good.
Tip this man handsomely. I charge much more. I charge the guys working for me a beer when they can’t get a colour and need my help
 
Matching gelcoat is a real pain. If you can remove a seat and take it to a fibreglass shop that will match it you will be miles ahead. My local guy can do it by eye in a few minutes and charges me $25 to tint a litre. You can spend hours yourself mixing little batches that never look good.

Hah, LOL. You are absolutely correct, but it's a 39 year old J/35 that is mainly a raceboat. It is in very solid condition but scuffed all over from hard use. If I match the gelcoat that well, it's going to raise questions in any future sale... ;-) The boat has had a lot of pro fixes over the years from racing damage and even those aren't perfect matches, they are very close but a fresh repair ages differently from a weathered bit of gelcoat.
What it really needs is all the hardware pulled, new non-skid shot with fresh gelcoat in the white smooth bits, and the topsides reshot. New winches, clutches and blocks all around wouldn't hurt. A deck refit worth more or less the present value of the boat. A friend of mine did that with his J/35 and it is now much more sound, and quite beautiful... he had the advantage of having a six or eight month break in between jobs and a bit of cash on hand. I'm not quite there yet, timewise or mental commitment-wise... One of my life goals is to own a keelboat whose appearance I can worry about and keep up...


im always for the DIY side
if you can colour match already no biggie
if you cannot then buy a cheap set of acrylic paints and learn .. the skill never goes away it just becomes progressively more useful

as a rule of thumb ( and because of the way computer colour matching works ) most gelcoat colours are made of a base colour ( almost always white ) and 3 other colours .. usually yellow ochre, red iron oxide and a darkish blue

that should also answer the question as to what coloured gelcoat to buy as your base start .. you will then need at least 3 gelcoat compatible tinters to do your matching ( the gelcoat may last 6 months the tinters will last years )

for a basic start you can play with these to get an idea of what to move and how much

Thanks! I checked that out. That's some PhD level color matching stuff right there.
I've done some repairs previously and basic white gelcoat is very close and it blends in completely within a month or two in the sun and rain. I think I can start with base white and put in some black and blue to get the color and tone that I need, which is actually a very light gray on the wheel. I'm going to study that a bit more. My head hurts now.
 

phill_nz

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thats close enough
almost no greys will be made with black in them ( mention again thats the way computer colour matching works )
and trying to counter the black ends up an almost impossible mission without more than doubling the original batch size
 
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Gouvernail

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After fifty six years doing color matching for boat gelcoats I am almost good enough to satisfy My own inspection.

It is frustrating while doing it and thrilling when I can’t see my repair.

Note: most brands of MEKP cause a slight to obnoxious yellow/ green color shift. Our favorite catalyst has been in short supply for about a year now.
30 years ago ALL catalysts caused color shifting and we had to tweak our color match by leaving out a bit of green.
As I am older, with less accurate vision, and way less patience, recent color matching hasn’t been much fun.
 

Major Tom

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Note: most brands of MEKP cause a slight to obnoxious yellow/ green color shift. Our favorite catalyst has been in short supply for about a year now.
30 years ago ALL catalysts caused color shifting and we had to tweak our color match by leaving out a bit of green.
As I am older, with less accurate vision, and way less patience, recent color matching hasn’t been much fun.

Hah, this might be what happened with the yard's last repair on my boat from two years ago. They took two or three attempts at getting it right then quit as they were going over my repair budget. The light gray does have a very slight yellow tinge to it, like diluted mustard. As a well-weathered race boat I don't sweat it, there's plenty of areas where it is scuffed, but this would be a big deal on one of the local dock queens or a much newer boat.

On the thrill... I do a little autobody work b/c there are very few guys doing small repairs around here any more for a couple reasons. I blended the paint mostly okay just feathering with sandpaper. Half the repair is wonderful but did not sand out far enough to feather it perfectly and get the match perfect on the other half. Didn't have a perfect color match either, had to use the Universal High Gloss Black rattle can touch up paint, but apparently the right sanding technique can make the repair disappear. The repair is invisible to the casual viewer despite my grave sins but knowing what it should look like, it bugs me to look at it closely.
 

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Start with white and add gray to get gray. Adding black to get tray will get dark really fast.

Gouvernail: Color shift with MEKP, is that why my color match attempts seem to darken slightly when fully cured?
 

Sail4beer

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Definitely white based gelcoat. A spot of black tint in white paint makes it pop, but with gelcoat, it just darkens it. Use styrene to thin it if spraying it with a disposable Preval sprayer. If you thin with acetone, white gelcoat can tend to turn yellow before the sun bleached it out in a couple of years.
 

Gouvernail

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Definitely white based gelcoat. A spot of black tint in white paint makes it pop, but with gelcoat, it just darkens it. Use styrene to thin it if spraying it with a disposable Preval sprayer. If you thin with acetone, white gelcoat can tend to turn yellow before the sun bleached it out in a couple of years.
Interesting. I would swap the location of the words “styrene” and “acetone” and otherwise agree 100% with your post.
Adding styrene permanent alters to composition of the gelcoat. Sprayed Acetone mostly evaporates Before the paint even hits the surface.
On a small patch I might spray ten thin coats with a minute or two between to be certain the acetone has a chance to fully escape.
 

Sail4beer

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Ahh, that’s interesting to hear. I sprayed white with acetone for years and only once did it appear
off color. I have a couple of Optis to repair this week. I think I’ll try the acetone again.
 
Interesting. I would swap the location of the words “styrene” and “acetone” and otherwise agree 100% with your post.
Adding styrene permanent alters to composition of the gelcoat. Sprayed Acetone mostly evaporates Before the paint even hits the surface.
On a small patch I might spray ten thin coats with a minute or two between to be certain the acetone has a chance to fully escape.

Gouv, does the source/quality of the acetone have any effect? I've been warned off using big box store acetone as a paint thinner for topside or bottom paint, as a lot of it is allegedly recycled from other industrial processes and contains some minor amounts of oils and other materials that are apparently no bueno in the finished product. I use the big box store acetone (same brands as West sells, mostly) for cleaning large areas prior to painting or minor gelcoat patching but stick to Petit brushing thinner (120) whenever I need to cut paint or to pre-clean where I need a perfect finish, and always get good results, but don't know enough about it to know whether this is true. Wouldn't mind more confirmation given the cost of brushing thinner... I guess Petit also makes a pre-surfacing hull cleaner (92?) that removes wax, oils and dirt, but I have the 120 handy and paid for, the can is practically winking at me, so that's what gets used...
 

phill_nz

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no lab i know of would recommend using acetone to thin gelcoat
porosity is another of its problems
yes styrene will change the basic formulation of the gelcoat .. but mostly in a good way( so long as you dont use to much )

the only reason i can see the styrene making it yellow faster is if its diluting the uv blockers and absorbers ( it stays as part of the gelcoat )..
good northern hemisphere surface coatings ( gelcoat included ) tend to use smaller percentages of uv blockers and absorbers than good southern hemisphere ones do ( or at least did when i was testing them )
 
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I am doing some minor gelcoat repairs, fixing a lot of scuffs on the white cockpit and other white areas on my J/35, fixing a few bigger marks on the medium gray non-skid, and fixing some small marks on the light gray topsides. Most of the work is in the cockpit and other white areas.

I will need to tint at least some of the gelcoat for the gray non-skid and topsides. I am curious if it is better to start with white gelcoat and add some darker tint; or if it is better to start with the untinted gelcoat and just mix up separate white and gray batches.

Thoughts?

I'm certainly no expert but just saw a youtube video on a channel called boatworks or something that shows you how to do this.. Definitely check that out before adding any tint to your gelcoat as he gives a great demonstration as how the experts colour match. Pretty easy to follow along and a few great tips that should stop your boat looking like a patchwork quilt.
 

Gouvernail

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The key to thinning is allowing the solvents to escape. When using thinners, I spray thin layers. In fact, I have never seen anybody spray thinner layers.
When repairing, my acetone thinned sprayed gelcoats ALWAYS remain shinier than the adjacent Older gelcoats . ( as in twenty years later the reiaurs are still barely weathering. )

Repairs I did in the seventies with styrene AC nd wax looked like shot in a year or two and ALWAYS looked powdery compared to the rest of the boat.

Other folks have opinions. Other folks do things differently. I am happy with my results
 




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