Gel Coat Cure -

Hello all. I'm looking for some insight and/or suggestions on my re-gel coating project.

I'm currently restoring a classic fiberglass boat and have decided to re-gel coat the entire hull rather than paint it. This is my first time dealing with gel coat but, think I've done my homework in the product and the correct process to follow, but, I'm running into cure issues that I hope someone can help with.

What I've done:

* I'm working in my garage (created a dust-free tent environment) that I've managed to keep at a constant 70-72 degrees
* I'm using PolyGard wax-free neutral gel coat from Infinity Composites with blue/white pigments
* I've been mixing my batches for the gel coat cup gun one Pint at a time

Coat 1: Mixed colored gel coat and hardner and covered entire hull
Coat 2: After an hour, mixed colored gel coat and hardner and covered entire hull
Coat 3: After another hour, mixed colored gel coat, hardener, and Wax Surfacer and covered entire hull

I measured the amounts for the hardener and wax additive precisely to the manufacturer's specifications. I was hoping the boat would have reached full cure and be ready for sanding w/in 24-48 hours. I'm now entering day three and the surface still has a tack to it - not great, but it's too tacky to think about sanding.

Should it have reached full cure by now? What can I do, if anything, to help the curing process (increase the temp in the garage, cover with plastic sheeting)? Or, am I S.O.L. and will have to re-do the whole thing? If that's the case, where'd I go wrong in the process to not make the same mistake twice?

Thanks!

 

Has it not cured, or is the surface just tacky enough to want another coat? Do you know how long it took to reach its current state of cure?

I've seen surfacing agent get rebellious at lower temperatures and kind of glob up rather than mixing properly and doing its job. Is there a kind of waxy sheen on the surface when you look at it sideways and kind of squinch up your eyes?

You said you followed the hardener and surfacer ratios. What I would do is crank the temperature in your booth for several hours, just in case. Then to knock off the sticky, I'd either keep the surface wet (just regular water) for a couple hours, or wipe the surfaces down with acetone (I don't like doing this because of the explosion danger. MAJOR ventilation is required, and be careful not to build up static electricity.)

 

Tinhorn,

Thanks for the reply. That's a good question. With this being my first exposure to applying gel coat, I'm not sure what to expect. From what I've gathered, I expected a completely tack-free finish after mixing-in the Wax Additive.

I noticed a slight improvement after two days - it was a bit less tacky - which got me thinking that I may just be impatient and it would take an extra day or two. I'm anxious to check it when I get home tonight. However, I kept all the cups that I used with each of the batches I mixed and they all seem to be rock hard and the last few (with wax) were not tacky.

There doesn't appear to be a waxy sheen to it like you described, but, it's kinda tough to see with the orange peel and the rougher texture where sanding will be required. I'll give your suggestion a try this evening by bumping up the heat and wetting down the surface with water. For now, I'll try to avoid using acetone. Not only have I read this may impact the coloring but, I'm not looking forward to the fumes I endured to get me to this point - even with a mask and ventilation, it got pretty brutal.

Worst case, I can shoot it again, but, if I do that, would you recommend adding a different kind of surfacing agent or something? Should I be waiting more than an hour (initial lay-up time) between coats?

 

You're using polyester gelcoat, right? I've never heard of applying coats of gel in such quick succession. Come to think of it, I never heard of applying more than one layer of topcoat.

Your mix cups cured hard - that's good. I wouldn't apply another coat. If there IS some wax on the surface, the next coat probably wouldn't stick well anyway. Your surface should have been tacky-free when the resin cured.

See, normal gelcoat (and resin) have a magic chemical that reacts with the oxygen in the air and inhibits a complete cure at the surface. (This is because it's waiting for another layer to bond to.) The wax you added was supposed to find the surface and seal it off from the oxygen in the air. Your wax didn't do what it was supposed to, but I've seen water seal resin enough to effect the cure without tackiness. I expect it would work with gelcoat as well.

I sure hope your coats were thick enough to allow the gelcoat to build up the heat they needed. If the coats were too thin - like spray paint, for example - then it may not have cured adequately despite it hardening in the cup, where of course there was enough material to build up some heat.

No harm in "autoclaving" it overnight, then keeping it wet for a few hours if necessary. Your next option is to simply tackle the tacky surface with sandpaper. Yup, done that, and it ain't fun - the paper loads up right away, but the sanding process seems to knock off the "tacky".

It was a long time ago, but I vaguely recall a shopmate sprinkling a tacky surface with baby powder before sanding it. I wish I could remember how THAT turned out.

 

I would cook it, do whatever you find easiest, simple room heaters lefy overnight should do wonders.

As for the sanding off, wash the surface with detergent in water, and start to wet and dry the surface, do not rub out the dimples, just do whatever you feel liiks right. Once you have sanded down, using say 240 wet and dry, then wash off the soapy water and dry. Apply a dust coat of some sort of contrasting paint, you can just buy a can of acrylic lacquer from the car shop if you like in ....., spray a light cover coat over all the gelcoat, and allow to dry. Sand this off with 320 w& d again with the soap added, untill the marks have been removed. You will be left with a fairly fair boat.

Repeat the sanding / dust coat process one more time if required, then start using 800. Once sanded down, redust coat and this time go to 1200. do it again with 1800/2000 and you will have a perfect surface ready to simply polish up.

Have fun, and do not worry about a bit of tackiness, it will be gone after a few minutes of sanding.

 

Thank you, gentlemen, for your replies.

I hear what you're saying about not applying another coat because, with the wax I did add, I'd be concerned another coat wouldn't bond very well. I thought I got the coats to the proper thickness, but, now I'm concerned that if I didn't what harm will come of it? I can go forth and sand, but, am I still faced with the issue of an incomplete cure? Would I then have a perfectly sanded, yet uncured, boat?

Last night, I tried a couple of things. First, I hit the heaters and got my 'booth' up to 80 degrees - nice little steam box for me to work in. I then misted water over one area and let it sit. In another small area, I tried wet sanding w/320 - figure at this point, couldn't do much more harm. And, Tinhorn, you're right on - the paper gummed up almost immediately. I managed to knock down the surface to what you'd expect to get from 320 - smooth with some pores that will need to be addressed with subsequent sanding passes. The sanded area was far less tacky - only the slightest hint of tackiness was apparent after I left my hand sit in one place for a minute then pulled away. I was optimistic for the first time but a bit disappointed when I stopped to think of the daunting sanding task that possibly lies ahead. I'm no stranger to sanding, but, this one will be a true test of patience and stamina.

Tonight, I'll give the detergent/water and sanding approach. I guess worse case, after sanding, I'll have removed enough of the wax that floated to the surface to - gulp - do this all over again.

 

You said you followed the directions, what % did the directions say to catalyze at, or how many CCs per quart did they say to use?

The wax you used can also be a problem, it's a wax and styrene solution, the wax will separate from the styrene at temps below around 70*F and if it's not warmed and mixed back into solution then it just stays at the surface of the styrene. This can even happen before they sold it to you and when it get's poured off into the container you bought it in, the wax content can be very low, resulting in a poor surface cure.

Pigments do have an effect on gel coat, and some pigmnets have more of an effect than others, it can slow the the cure and increase the back side tack, this can be a real problem for some colors of blue.
When colored gel coats are made by the manufacterer, they're QC'd after the pigments are added to ensure the gel time and viscosity are correct.

Each layer of gel coat needs to be applied thick enough to get a good cure, this is even more important in a refinish type application where no laminate will be used over the gel coat to help drive the cure. A thin layer of gel coat, even with wax, can stay tacky and never really get hard. 18 to 20 mils is what's recommended and on a refinish you typically go thicker because much of it will be sanded off.

Another thing that may have helped would be to have used a patchaid type product, these products will speed the cure of a thin film, reduce the viscosity and they also have wax in them. This gives you less orange peel, and a better cured gel coat. Since they do speed the cure, you need to work faster, or mix less at one time though.

Gel coats aren't really formulated for refinishing purposes, although they do work most of the time. Only a very small percent of the gel coat made gets used this way, so all of the R&D is directed towards it's use as an in mold coating.

The newer low emission gel coats are more prone to being tacky than the older products, so this may be part of the problem.

 

Test a small area first, sand and buff it as you normally would have and see if you get the desired results. If it still seems softer than it should be it may be time to start over, but a tacky surface does not mean there's a problem with the underlying gel coat.

Acetone is a common way to to remove the tacky surface, but' it's not that safe, even a static spark can ignite it.

 

To test your cure, find something - a piece of threaded rod, for example - that you can lean against the gelcoat with a just a few pounds of pressure on it. If it leaves an indentation after resting there for half an hour or so, then the gelcoat is soft. If not, then THAT worry is behind you.

So how did the water-misting idea work in this application?

 

Ondarvr:

I'm still not 100% clear on the terminology as far as 'percent by volume' to mix (gel coat / hardener). Fortunately, the manufacturer (PolyGard) simplified it on the instructions: 1 fl oz of hardener / gallon of gel. Since I was mixing in Pints, I measure out 1/8 fl oz of hardener. When it came time for wax, they instructed 1 fl oz / Quart. Following suit, I measure out 1/2 fl oz / Pint.

Great insight into the potential downfalls of wax additive although, you've left me wondering how the consumer would ever be able to ensure they're getting a quality product from the retailer.

I'm going to proceed as suggested and work with a small test area and buff it down (or up) to 1000 grit and see where we are.

Tinhorn:

I'll give your test a shot this evening, but, I think I know how it'll turn out - it will not leave an indentation. Reason I can say that with relative confidence is because I've used my fingernail to test for hardness and I've chipped my nail and almost bent it back once, so, It was pretty hard (just a bit tacky). I also compared one section of one of my tent curtains where I test sprayed (getting the hang of the cup gun) and I can definitely tell that the wax did something beneficial on the hull. The difference b/w the two was night/day (unbelievably sticky vs mildly tacky).

I'll shoot you an update on how well the misting worked . . . sprayed last night and again this morning before I walked out the door, but, didn't really do a status check.

Final thought . . . anyone ever tried 'Goo-B-Gone' in a situation like this? Or would that be asinine?

 

I like Landlubber's idea of spraypainting the whole thing. I'd be looking for some mid-price primer myself, not Goo-B-Gone.

 

One thing I don't like about the directions they gave you is the 1oz to 1 gallon gel coat, this gives you less than a 1% catalyst ratio, we recommend at least 1.25 % and a max of about 3%, I like 1.5 to 2% though. When refinishing with gel coat the extra catalyst is needed to help cure the thin film and reduce the chance of a tacky backside. It is possible that this product is formulated for this low percent, but it can be much more difficult to mix it in correctly and if the measurement is off even a little there may not be enough catalyst for good results.

 

Your suspicion on the mix supports my latest test on a piece of plywood. I increased the catalyst to approximately 1.25% and also increased the wax additive slightly. The result was a more complete cure with a smoother orange peel and considerably less tack. After 48 hours, I thought I'd try my luck at wet sanding.

I first started sanding using only water and the paper (320) began to gum up (slightly) after a bit. Since it was a test piece, I thought I'd experiment. I mixed a batch of 50/50 (water and Simple Green) and went back to wet sanding. The result was the same as with water, but, there was little to no gumming of the paper whatsoever (granted, I wiped away the residue periodically), but, this mixture helped eliminate any tackiness and made the sanding process much much easier. I don't know if anyone else would benefit from this 'discovery', but, it managed to save my sanity and give me the hope I needed that I'd be able to complete this project. After finishing my test piece with 400, I could clearly see this was the product I was looking for - perfectly smooth and ready to move on to finer grits and polishing.

Thanks all for your time in analyzing my problem, insight, and suggestions. I've got some sanding ahead of me, but, have the optimism now that this boat is going to be sweet! Thanks again!

 

Man, I love happy endings.

 

Me too . . . you all were THISCLOSE to seeing "1979 Glastron Carlson - PROJECT Boat . . . NO RESERVE . . . TAKE THE DAMN THING!" on Ebay. : )