Bubbles in epoxy fairing

[Captain Smollett]

Asking for tip here, not offering one.

I've been doing some fairing around odd shapes, which leads to some thicker-than-ideal fairing compound.  For fairing, I'm using WEST epoxy with 410 Light Fairing Filler.

The problem is bunches of bubbles/voids forming in the layer sometime during curing...they are not apparent when it's spread.

I have two theories, but welcome input/corrections:

(1) Spreading too thick, enough heat is building to cause bubbles.  When I say thick, I'm talking 1/8 - 1/4 inch spreads, in some cases around a square foot or so (not all of it is that thickness).

(2) Though no longer, I was at that time using FAST hardener, which may simply have been too aggressive for the application temperature, again generating too much heat too quickly.

I did some fairing yesterday with the SLOW hardener, but have not inspected for bubbles yet.  Also, they were smaller and thinner areas.

As of right now, I'm thinking the best bet is to just build up with cloth first to get a much thinner fairing necessary.  This cloth (or chopped strand mat) would not be needed for strength, just "filler."

Any thoughts?

[CharlieJ]

Working with  thick stuff (actually for everything outside) I like to work as the day is cooling, and the surface is also. Seems to stop the bubbling to a large extent.

If you glass/fill over aa cool surface, then put it out into the sun (or let it heat significantly) it'll bubble like crazy.

[jdsackett]

That's pretty thick for a finishing product. You shouldn't go over 1/8 and even that is pretty thick. I was in the auto body biz for a long time so some of this may not apply to boats, but a friend of mine is a boat painter and he uses a product called duraglass for filling. It's a polyester resin with chopped glass fiber mixed in with it. works very well, have used it for repair of corvettes. It's waterproof and tough, sands like concrete though. Then you could finish with anything of your choice. Bubbles, or pinholes we used to call them are the nature of the beast and are going to happen. Try pressing harder when you apply it, that will help, but you're still going to get them. Also make sure everthing is mixed well and completely. Speed of the activater has no bearing on the bubbles but if you mix it too hot it will weaken the product. Evercoat makes a nice polyester 2 part spot putty that works well ti fill the holes and is waterproof also. Tony uses it all the time on big, high horsepower fast boats all the time and hasn't had any problems and those things shake and vibrate to beat heck. I think mainly you're trying to put on too much material at a time. Good luck. regards, j.d.

[CharlieJ]

He's working with epoxy. Polyester wouldn't play well with it.

[Captain Smollett]

He's working with epoxy. Polyester wouldn't play well with it.

Right.  I was thinking the same thing.

One section of deck that I had to recore had at least three formulations of "goop" applied during the previous attempt at repair.  It's no wonder this section broke apart, leaked horribly and allowed much more damage than necessary to the core material.

Aside from the pin hole woes (which will be removed, even if I have to sand ALL the fairing away and do again...I'm taking no chances with voids in the glasswork), I am trying to be VERY particular, thorough and meticulous with this work.  Under no circumstances do I wish to come back next year and have to start all over.

I just needed good suggestions on how to apply THIS fairing without additional pin holes forming.

[SamHunter]

Unfortunately, not an uncommon problem.

A post above noted what is probably the best "cure" (no pun intended).  Apply / let cure during cooling (downward ambient temperature movement) conditions.

I used to have quite a bit of problems with "tiny bubbles".  Finally found a couple of articles that didn't exactly set out to address or answer that question, but did provide some answers.

The first concerned the first coat or two (whether glassed, thickened, or just plain unthickened epoxy), over wood or other porous substrates.

The issue there is "Outgassing". the tendancy of the substrate to actually emit small gas bubbles as they heat up, even only a few degrees.  These outgassed "bubbles" end up either as bubbles or worse, as pinholes (that was my most frequent problem).  Worse, with pinholes, subsequent coats get the same problem!

The other article was about the problem of bubbles or pinholes even on "hard" (supposedly non-outgassing") substrates (which would include good previous coats of epoxy.)  Note that failure to get "perfect" saturation of glass layers also acts as a source of gasses.

In both articles, the same solution was recommended... ensure your curing, and better, application and curing both, occur in declining-temperature conditions.

Easiest way to do that... warm things up first.  E.g., heat up the shop or shed a few degrees, THEN apply.  Ofg course, working in the late afternoon, when temps are declining, works great, too.

This has helped me a LOT!  Though, to be honest, I often just don't bother, especially when using slow-cure hardeners.

Finally, for reasons of which I have NO comprehension, sometimes, even in sharply warming conditions, bubbles are just not a problem.

Hope this contributes at least a bit.