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Potential cure for "gummy" fiberglass resin.

62K views 22 replies 13 participants last post by  matt167 
#1 ·
I heard this from a guy I trust who builds his own airplanes. He says when the plane guys make something out of fiberglass and the resin does not set up completely, leaving a gummy surface or resin that gums up sandpaper too quickly, that they wash down the resin with 20 Mule Team Borax and if firms up the surface. Any of you glass pros ever heard of doing this? I'm thinking of doing a quickie experiment just to see if it works.
 
#2 ·
There is a reason it's gummy.

Many resins are called "air inhibited", and do not cure on the surface so you can put another layer on later, and then it will mix with the uncured resin, becoming one piece after it sets up.

All you have to do to make it cure is to skim coat it with bodyfiller, which is also a resin based product. This will cause the fiberglass to finish curing. It will also give you a filler material you can sand to get a flat surface.
 
#3 ·
Some glass has wax in the resin..Some don't..The one that has the wax will not be tacky after it get's hard...And you will have to sand in between each coats..The one that don't have the wax added to the resin, Will be tacky..This is what jay is saying.. ;) All you have to do is add the wax into the resin on your last coat..Then it won't be tacky.. ;)
 
#4 ·
Jay is right, NI is right, your airplane guy might be right....anything that seals the resin from the oxygen will get polyester or vinyl ester laminating resin to surface cure...I have seen it surface cure under a light coat of water, dust, paint, bondo, tape, saran wrap or a light coat of greenwax, PVA or Slime...You do need to be careful of what you put on resin to get it to surface cure though, as you want ALL traces of it to be gone before you put anything over it.

If I'm making a one off part, and I just scuff the surface with 36 or 40 grit, then skim it with bondo, the bondo sticks to the uncured resin just fine, as it is also polyester resin...then you can sand it without your paper loading up.

I know that some epoxy resin is a little different, when it cures, it develops a coating called amine blush, that usually needs to be washed or ground off..Maybe that's what the airplane guy is using the boraxo for..

Later, mikey
 
#5 ·
Here is a fix that was shown to me by a old friend,after getting your glassing done,take a sheet of plain old wax paper (the cooking type) and stick it to the wet resin and smooth it with a bondo spreader to eliminate air bubbles and conform to the shape of what was being glassed.When it is cured pull the paper off at a 90* angle and you have a surface that needs less prep work,less bondo,less sanding other than scuffing for painting.If a second layer was going to be added we did nothing.
I used the paper when I repaired outlaw sprint driver shields and have had them cure so smooth that it only had to be scuffed for paint.
Hope this helps!

Kenny
 
#7 ·
Shelby1 said:
Here is a fix that was shown to me by a old friend,after getting your glassing done,take a sheet of plain old wax paper (the cooking type) and stick it to the wet resin and smooth it with a bondo spreader to eliminate air bubbles and conform to the shape of what was being glassed.When it is cured pull the paper off at a 90* angle and you have a surface that needs less prep work,less bondo,less sanding other than scuffing for painting.If a second layer was going to be added we did nothing.
I used the paper when I repaired outlaw sprint driver shields and have had them cure so smooth that it only had to be scuffed for paint.
Hope this helps!

Kenny
WAX paper.
As others have said there are 2 types of resin, sometimes called casting and laminating, casting has WAX in it, laminating doesn't.
 
#8 ·
Old Fool said:
WAX paper.
As others have said there are 2 types of resin, sometimes called casting and laminating, casting has WAX in it, laminating doesn't.
Down here, "casting" resin is the stuff you use on bar tops or to make a paperweight out of.
We call the resin with a surfacing agent, (usually liquid wax),"sanding resin".

The wax paper trick works really well, as long as the surface is close to flat. Resin surface cures when you vacuum bag it too.



HI cboy, :welcome: it's hard to stay away from here, although with my new job, it's been a little tough to find time for HR.com.

Later, mikey
 
#9 ·
The homebuilt aircraft crowd generally stays away from polyester resin and favors epoxy for the strength issue. I have vacuum bagged radio control glider wings using polyester resin but they also have two full span 1" carbon fiber tapes for added strength. You should see those wings flex when the glider is launched via Hi-Start or winch. They look like they are about to break off, but are surprisingly strong. They come out of the vacuum bag almost ready to finish and paint. Some guys are even using mylar film to apply a finish color to then laying the glass cloth and resin on that then vacuum bagging the wing. I have not gotten that sophisticated but have seen some and they look exceptional with minimal finishing required.

Here is an interesting article on vacuum bagging wings.

Sorry to stray from the original post :rolleyes:

Vince
 
#10 ·
Actually as long as it applies to technical interest in the use of materials it is not straying from the original topic..never know some of the guys may wish to vacuum bag some parts for a car and knowing about the process is valid.

Sam
 
#13 ·
This is just a shot as I am not a fiberglass guy but if you have an "A coat" resin that has no wax, you simply need to put a "B coat" resin over it to seal it off.

You never put just a hardener on anything, that isn't going to work.

Now, this is if you really do have an "A coat" resin and your problem isn't more about your resin not curing properly, that is two totally different things.

Even an "A coat" resin isn't really sticky once it cures. Just a tiny bit of dust or something gets on it and it's pretty smooth and not sticky at all.

Soooooo, the other reason your fiberglass could be tacky or sticky is that the hardener you used wasn't good, or you didn't mix it properly using enough hardener, or I imagine too much hardener would do the same thing? Anyway the date code is stamped in the bottom of the tube of hardener in most cases I believe. An old hardener will most certain cause curing problems. You need to find out from the manufacturer what your date code says.

Brian
 
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#21 ·
I recently fabricated a couple of airplane parts (non-structural) using off the shelf resin, from Oreilly.
I had one broken part from which to pull a negative mold. using tape, cardboard, and bondo. I managed to "repair" the broken part well enough to get a mold.
I had some old bondo on the shelf, that had gotten old, and is useless for anything except making a mold. I cast my mold, and laid in the glass using my usual method.
I cut my fabric, or mat, to size, and lay it on waxed paper, then "pre-preg" it with mixed resin. Then flip it over into the mold, and using a bondo spreader, squeegee it into the mold, removing excess resin as I go. pull off the paper, and repeat, with as many layers as needed. Then let it set.
Out came a decent part, and I still have the mold to make more.
No sticky glass, mabe has to do with the waxed paper, mabe has to do with the release agent, I don't know.

pic1 ready to cast mold, 2 the mold, 3 in the mold, 4 ready to be trimmed, and painted.
 

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