Blemish-free epoxy finish coat

[Konrad in Lincoln]

Hey all,

I'm doing some un-boat-related fiberglass work, and it requires final coats of epoxy after the layup is cured, to produce a very nice clear smooth finish. I'm having trouble keeping blemishes out of it.

I think what I'm getting is very small air bubbles near the surface of the finish coat. Perhaps these bubbles are forming during my mixing process and aren't all getting worked out during application. I used a cheap 1" paint brush (hair bristles, not synthetic bristles) to apply this final coat of epoxy. Does anyone have a suggestion for a better application method? I'm considering trying a throw-away foam brush, but not sure if that'll do the trick.

Any thoughts?

[Konrad in Lincoln]

During the drive home from work I was thinking about this a bit more. The layups are 5 layers of cloth. I have been applying epoxy to the previous layer, and placing the next layer (dry) on top and working it in.

Is it possible that by placing the dry cloth down, I am trapping small amounts of air in the layup, in spite of my efforts to work it in thoroughly? I think I will try saturating each successive layer of cloth, and then carefully applying it to try to keep any air from getting in between.

I'm talking about very small bubbles, the size of pin heads. Any thoughts are welcome.

[Craig]

The mixing process may be the source of the bubbles and your idea of dry onto dry is also possible. Are you making all five layups at the same time or curing the first and then applying the second? What are you making? A cold mix will also trap more air then a warm one. (90-100 degrees vs. 55)

[Frank Hagan]

I remember a couple of tips on this ... one was to try using your wife's blow dryer, moving it so it blows the warm air very lightly at the surface.

The other one involved a mist of something, but I can't for the life of me remember what it was. Alcohol? Acetone? Something like that. Maybe someone else here remembers that one (if he lived).

[Konrad in Lincoln]

Possibly acetone or MEK (Methylethylketone). Those are both epoxy thinners. I would never spray a mist of MEK, though. That is some bad krap, you can go blind if you get it in your eye. :shock: Acetone is more benign, but misting still doesn't sound ideal, what with the toddler around and all.

I did find the following text on the West System's web site. I know my equpment is clean, and there's no wax in the containers, but I may try the plastic spreader thing. Thus far I've been using my gloved hands. I'm using a plastic male mold, so it's not a question of the substrate (since the substrate is a plastic mold)

I'm making small motorcyle body parts. I'd include a photo if the pinholes would show up, but they're small enough that they don't show up in a digital image.

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PROBLEM: Fish-eyeing in coating.

POSSIBLE CAUSES & SOLUTIONS:

Contamination of the coating or surface or improper abrasion for the coating.

Be sure mixing equipment is clean. Avoid waxed mixing containers.

Be sure surface is properly prepared. Use proper grit sandpaper for the coating, e.g., 80-grit for epoxy. See paint or varnish manufacturer's instructions for proper surface preparation. After surface is prepared, avoid contamination--fingerprints, exhaust fumes, rags with fabric softener (silicone). Coat within hours of preparation. After wet sanding, rinse water should sheet without beading (beading indicates contamination). Wipe with appropriate solvent and re-rinse until rinse water no longer beads.

[Levi]

My heat gun (On low settings) has often made the difference for a nice bubble-free finish but there are obviously other answers. I will gratefully listen here for them. This is a problem we all face and maybe we can lick it together?

LEVI

[Guest]

You maybe getting some outgassing, too? You may also have a difference in temperatures, between the glue and surface, and also using natural light or artifical lights up close to the surface causing this, too? Also certain paper has a glue that leaves a film causing a fisheye affect to your surface? Any thing there that you may read that may fit one or more criteria? What resin and ratio are you using?

[Charlie Jones]

Konrad- you sure you aren't thinking of MEKP rather than MEK? MEKP is the catylst for Polyester resin and really IS bad stuff. I think MEK isn't much worse than Acetone.

I don't know what epoxy you are using but the Gougeon's make a different hardener especially for clear finish with epoxy. 207 special hardener if I remember correctly. Designed for finishing where you want maximum clearness. You might look into that. It does take a special hardener pump because it mixes 3 - 1 rather than 5 - 1.

[PAR]

You have to be careful about what you use as an epoxy thinner. All epoxies aren't the same and the different formulations use differing solvents. Acetone will clean up the uncured epoxy I use, but Xylene is the solvent I need to cut it for spraying or penetration.

Foreign particles in the goo, bugs and other little beasties that seem to love wet epoxy and varnish, gas out, too aggressive mixing or wet out and surface oils or contaminates are the things that come to mind when blemishes turn up in finish work.

I'm assuming your laying up in a female mold? Try to get the finish down and let it gel before you do you're build up. You'll still get a good bond and the bubbles can rise to the inside of the part. Bugs and other foreign matter can only be controlled as best as the conditions will permit. Ditto on surface contaminates. Florescent lamps can wreck any finish job. Some types of gloves have powders and/or oils on them for a number of reasons, insure yours are clean. Have you got dandruff? No kidding, it can also find it's way into a finish.

I wouldn't try to do the whole layup at once. I'd concentrate on getting a good finish applied to the inside of a mold and let it kick, so any additional layup can't really effect the finish surface.

Most of the time you can talk bubbles out of the finish coat of unthickened epoxy with a heat gun (keep it moving) Fish eyes are usually contaminates of some sort, either falling in or on the surface.

[Konrad in Lincoln]

Well here's a follow up. I'll try to remember all of the previous posts in my reply.

Charlie: I think I saw the MEK thinner comment on the West Systems Product Guide, but hell, I could be off one letter (the letter K).

It's a male mold, actually, with some gentle compound curves. I have essentially found a solution to the problem, although I'm still as-of-yet unsure of the source. It's in a controlled environment (my basement) so no bugs or airborne particles.

The small air pockets occurred when I was laying on the finishing coat in pretty thick applications. I had another go at it earlier this week with a very thin application, and no air bubbles. So that's the answer: Don't slather on an ultra-thick finish coat.

That sounds like common sense, in hindsight. Oh well, live and learn.

[Levi]

I used to think "thickerer" was better......now I'll re-think that.

Glad you found satisfaction and passed on the conclusion to us.

[tomstock]

I had a lot of luck using a squeegee rather than a roller... went on fast without lifiting cloth, and no bubbles. Actually it was just a piece of cardboard.

-tom

[kydocfrog]

I've had the most luck (of not much) using a squeege sort of approach rather than a roller too. At least on relatively horizontal surfaces. What happened on the cabin sides you don't want to know.

I'm wondering if a middle ground isn't available. We used to use a hard surface roller in rolling out ink for prints, silkscreens, etc. They were maybe a third the size of a paint roller; inch to inch and half in diameter out of very hard rubber. Kind of a rolling squeege. I may rummage around in an art supply house before I do hull seams.

sigh.

[Frank Hagan]

I have seen "blank" rollers that are a hard material ... like a resin impregnated paper (harder than the ink rollers used in graphic arts). They look almost like a regular roller cover that has all the "fuzz" taken off. They are for applying thin coats of resin, so you're not far off the mark with your thinking of the rubber roller things.

[Guest]

FWIW, this is some of the fine tools I use for glassing. They all have a nice handle, and sturdy grips, keeping all of the resins away from my hands and human body, also keeping my hands free for handling raw glass, and even mixing additional resins, without wearing it, especially while I work most of the times by myself. Notice, I also use a small putty knife, grinding the blade down to a nice round, allowing me to work in extreme corners, and in limited areas, keeping the fillets a nice uniform curve, refining it after applying my bulk of glue in the seams. I also use a nothced trowel where sanding fairing compounds in the initial coat, or where multiple coats of fairing will be required, as this saves time and work in fairing and sanding too.

The tops are easily cut off, and will show highs and lows with the lines of the notches. I use heavy shingle snips to cut biaxall cloths in lieu of razor knifes when the cloth needs to be cut during the lamination of the glass on the parts of the boat. Its much easier and also keeps your hands away from the wet cloth. Make sure you clean them and even keeping them open afterwards preventing any sticking of the two blades.

[Konrad in Lincoln]

Well I'm gonna try posting a photo here, and show you the carbon graphite parts that I'm laying up. What I'm making is not boat-related. I'm making rear shock mud flaps for dirt bikes, and selling them on eBay.

Assuming this photo attaches, what you're looking at is a 2005 Honda CRF450 (arguably the baddest motocross bike on planet earth right now). From left to right is: The rear tire, the carbon fiber mud flap, and the rear shock. The front of the bike is to off the right, out of the picture.

Every layup is a learning experience, and I get better (or at least learn something) with each one. The basic process (to date) has been

1. Lay up the part in the mold and let cure.

2. Sand each side with 80 grit.

3. Clean surfaces with acetone.

4. Apply very thin finishing coat using a foam brush to tip it.

Using a bristle paint brush leaves bristles in the resin, more often than not.

They're not perfect yet, but I'm getting closer with each one.

Hope someone can take something from this, it's been educational.

[Howard]

Mud flap vs. rubber accordian boot for the shock debate aside...what resin are you using?

Try as I might, i was never able to mix and lay down a bubble free coating with West System or System 3 resins. They are both thick enough they always trap some bubbles in the mix. Maybe not for anyone else, but they do for me.

I do get a nice bubble free finish with RAKA, and if you use the slow cure hardener, it's a nice slick finish, suitable for clear coat or painting. The lower viscosity (thinner) mix that lets the bubbles go free also lets the epoxy run though, so it helps to have your coated surface laying flat. Or if your mold is convex in shape, the excess epoxy may just drip off the side where it can be trimmed off when cured. Either way, I'd give RAKA a try.

Howard

[Konrad in Lincoln]

Now that's interesting, I didn't know RAKA flowed at a thinner viscosity. I may have to think about them for my next purchase. I'm using the big-dollar West Systems resin right now. It only takes 3 pumps to lay up a flap, so it may be a while before I would try RAKA. :?

But I've recovered my initial investment in the West. 8)

As for the rubber boots, only the trail/off road bikes (like Honda's line of XR's or Kaw KDX's) are using them. The motocross bikes jettisoned them in the early 90's. They do have their place, though. Especially if you ride dunes/sand.

.

[Ken_Potts]

Since this seems to be a thread for experimenters...

I think I'll admit now that I've been having good results with plastic sheet to keep a (relatively) smooth surface. I wet out the glass and then lay the plastic over it and roll out the bubbles (so many bubbles) with a very narrow roller (1 inch wide). It's somewhere between infuriating and hypnotic chasing the bubbles out but it can be done. My glassing skills are not very developed so the result I get with the plastic is better than the result I get without it.

The reason I mention it is that I've seen a few posts in this thread that mention the terrors of vertical surfaces. A layer of glass with plastic rolled on well seems to keep my runs to a minimum.

I've had success using thin 3-mil plastic drop "cloths" which creates little wrinkles which need to be faired and I've also had good results from 10-mil vinyl from Wal-Mart that leaves shallow waves that need to be sanded out. I hope you will notice that I don't get a perfect finish with either material - There is still fairing to be done. This technique is not my invention - Actually I read about it on this board a while back. I think the only reason I get what I consider to be good results from it is that when I don't use it the results range from bad to scary bad

It will not work well for a compound curve but any bend that plywood can make seems to be okay for the plastic.

It's worth trying on an experimental basis but don't go messing up your pet project just cause I said it worked for me (it might not work for you). Also, it didn't work well for me the first time - I had to do it over and over to get good results. Come to think of it if I had spent all that time working without the plastic I would probably be getting good results without plastic by now.

Forget I mentioned it

For anyone out there who works in hot weather: Does Raka stay workable longer than West Systems? I'm currently using West Systems (with the slow 5:1 not the tropical 3:1 hardener) and the application of epoxy always seems to be well planned panic trying to get things right before it kicks...

[Guest]

If you are going the Raka route, by all means purchase the 2 to 1 mixes for all around results, keeping in mind that the slower hardeners create less blush, in most cases and also you can adjust Raka with its variable cure harderners, all ordered and kept for the proper ambient temperatures and the appropiate size projects when its just plain nice to have a quick kick for small areas, where mixing large amounts kick off with the faster hardeners.

I will say that the plastic use has some drawback when using it for your first attempts in glassing your pet project without experiementing with using a coating for wetting out your glass.

Here is a read only :wink: thread that addresses this very issue. Be careful, please do not stay too long over there. :twisted:

http://www.woodenboat-ubb.com/ubb/ultimatebb.php?ubb=get_topic;f=1;t=011106