Laminating gelcoat is hard in 16 hrs??

I bought a gallon of white laminating Seahawk gelcoat. Did some trials with none of the provided wax added and was surprised to find it was tacky/no transfer at 1:50 hours (OK), but was hard after the overnight. Fingernail made no impression. Sandpaper 80 grit sanded easily with no gumming on the paper. What gives?

Trial as in a 58 degree basement, low winter humidity. They recommend above 60.

Does this sound like defective product? If I do use it, I assume I should apply the second gelcoat and the first mat/resin layer at the gelcoat tacky stage and not let it go hard.

Thankls

 

For the best results the laminate should be applied as soon as the gel coat is hard enough to accept it, but waiting over night is common. Some gel coats cure to a greater degree on the surface than others, and some feel almost tack free without wax, but you can still get a good bond with the laminate.

I can't say what's in the can you bought, it may have wax in it, or it may just feel that way.

Try rubbing a little resin on the surface and see if it slightly dissolves the gel coat, if it does your fine.

 

Thanks ondarvr. Very helpful.

"Apply the laminate when the gelcoat is hard enough to accept it" means what, tacky but no transfer to your finger?

Same for applying the second gelcoat layer?

The gelcoat came waxfree, with a separate bottle of wax to use if needed- which I didn't.

Thanks

 

Yes, still sticky, leaves a print but nothing on your finger.

Each layer is the same.

Even though it says wax free doesn't mean they didn't miss label it, not that that's what happened in this case, just that it does. And even if it has wax in it as long as you laminate on while it's still sticky it will be fine.

 

After several brushed trials with no problems, I started doing the panel at 60 degrees and 2.7% cat. First gelcoat rolled on fine. Two hours later it was tacky, no transfer and did the second and final gelcoat. Within 6 minutes, it started to wrinkle, big time. Actually I think it was the first coat that wrinkled. Stirred in the cat for 2 minutes.

What happened? The only odd thing is after 3.5 hours, the gelcoat in the tray is still liquid. SOme of the sections on the form are not wrinkled at all. Maybe that is where I came back and rolled over it again and could have sucked the first layer off the mold?? But the wrinkles didn't appear until about 6 minutes.

It's been 1 1 /2 hours now. The wrinkles can be pressed down flat with waxed paper. Should I salvage this by rollering it flat with wax paper?? Before it cures.

Thanks

 

Sounds like the first layer was not cured enough. Your 60 degrees(F) looks to be down the low end of allowable temps(16-30C), also the ambient temp may have been highrt than the mold surface temp which is what you want to measure- it may lag behind as the day warms, also your gelcoat may be cooler too, the mold & tin of gel have a thermal mass which will lag behind the air temp.
That the gelcoat in the tray is still liquid is a concern- it should through it's thickness/mass rocket ahead of the gelcoat on the mold surface, maybe something not right with your process or product here.
I usually spray gelcoat with a simple cup gun, though brushing is nessesary on some detail. I apply the squeak test where you outstretch the rude finger/bird and lightly drag ..... to the surface, if it squeaks its coming ok, if its greasy its not ready, I will generally wait 4-6 hours before adding a surface tissue or light chop to the laminate- the main laminate will happen/start the next day.
I dont think you can salvage it, too many ifs on whats been applied already & will lead to reworking the surface at great effort, the whole point of contact molding with gelcoat is to incorperate the products finish at the lowest effort.

Jeff

 

Thanks. Basement job- mold, gelcoat, air all 60 degrees. I gambled at the 1 1/2 hr. point and put down waxed paper and squeegeed it down the wrinkles. Most flattened. Some didn't. There will be a lot of rework on the surface.

Jeff, read the first part of this post. In my trials, the LAMINATING gelcoat with NO wax was almost hard after the overnight. Could not embedded a finger nail. Odd. SO if the gelcoat in the tray is still not rubbery at 4 hrs, I'm thinking the solvent flashed off and the product on the form leaving a hard-ish surface- but not cured enough for a 2nd coat. 2.7% catalyst should have been enough. I did not add solvent, the Seahawk gelcoat was thinner than expected. Like fresh paint.

Thanks

 

There is really only one reason for the gel to alligator (wrinkle), it's from being under cured when more material is applied over it, but there can be many reasons for the under cured condition.

Too much catalyst, too little catalyst, cool ambient temps, cool mold temp, didn't wait long enough, applied too thin, bad product, etc.

If the gel coat in the tray didn't cure in 4 hours something is seriously wrong, and it's not salvageable. Your best bet is remove it from the mold and start over.

Make a test batch and reduce the catalyst a bit, 2.7% is at the very high end and some gel coats don't like that high of a ratio.

 

Thanks.

I did several multi-layer BRUSH trials on the mold. Same temps, same cat %, same approx. thickness (.008 DFT). The can says 3% max at 60F. No aligatoring. The only changes were; pigment was added to tint it to off-white and in several places I rolled over the same section 2-4 minutes after the initial application to smooth it out or thicken the layer. As some rectangular sections had no aligatoring at all, I think the re-roll caused it. Stupid. Comment?

 

The re-rolling had nothing to do with it, other than maybe picking up and removing some of the gel coat already applied. The roller can't remove catalyst, and you said the product in the tray didn't get hard in 4 hours.

To cure correctly the thickness needs to be around 18 to 20 mils, less than that can leave it under cured.

Adding what type of pigment, and how much?

Pigment is made with resin that doesn't react, that's why it has a very long shelf life, adding pigment can reduce the reactivity of the gel coat.

 

OK, not the re-rollering.

You don't mean 18 mils per coat do you? The 2 coats would have been about 16 mils together.

Used the classic Evercoat pigment "for poly or epoxy resin." Off-white so very little used. One tube was probably 20 yrs old.

 

18-20 total, but that should be applied at one time, coating over 8 mils that's been left to get hard will alligator about 80+% of the time.

Use a mil gauge to make sure the thickness is correct.

Still another issue if the tray didn't cure though.

 

Oh! OK.

But the first layer wasn't left to get hard, only tacky.

With a 1/4" "for resin" nap (not foam) roller cover, I could only get about 8 mil DFT. Per your suggestion, I'll remove the gelcoat off the form, re-wax and start over.

The mfr rep for Seahawk said it's common to add Cabosil for brushing or rolling. I thought he was nuts. But doing that, I could probably get a 18 mil single layer. Or I could find a suitable 3/8" nap roller.

Then I still have to worry about WHEN to add resin and mat to start the laminate to avoid alligatoring. To play it safe, maybe I should let it cure rock hard (including what is in the tray), maybe 2 days, and sand with 80 grit first.

 

You said the gel coat was thin, so yes, you could add some cabosil and thicken it up.

You either need to apply all 18 mils at once, or wait for it to get hard, there is a no-go zone when it's tacky, this is an under cured state and will wrinkle up. That doesn't mean it needs to be totally tack free, but it can't be gummy. But at 8 mils you're in the danger zone no matter what you do.

Do not wait two days, that would just be complicating things, plus you then are subject to pre-release of the gel coat.

A 3/8" nap roller will help a little.

Even at 60F the material in the tray shouldn't last more than 30 minutes before it starts getting hard.

 

Styrene in the gelcoat will sink in a mold and inhibit curing, a fan will help move it around and out so it cures evenly.

Fun Fact...My material supplier said most of their Cabosil sales were to McDonalds for thickening their shakes.