Gflex

S

Steve Beckwith

Joined
May 29, 2004
Messages
393
I am using some Sanbar stag for a handle. I removed the pith and had a fairly large void to fill. I mixed Gflex 50/50 by weight and filled it up. 24 hours later the gflex is tacky on the surface and is an amber opaque color. I expected it to be a transparent amber color. This is the first use of a new package of gflex. I've used gflex for 10 years and never seen this. Has anyone ever experienced this and does the gflex eventually set up?
 
Steve Beckwith said:
I am using some Sanbar stag for a handle. I removed the pith and had a fairly large void to fill. I mixed Gflex 50/50 by weight and filled it up. 24 hours later the gflex is tacky on the surface and is an amber opaque color. I expected it to be a transparent amber color. This is the first use of a new package of gflex. I've used gflex for 10 years and never seen this. Has anyone ever experienced this and does the gflex eventually set up?
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Sounds like it didn’t mix together properly for some reason. Was it clear before applying it, or did it develop the darker amber color afterwards?
In my experience, it’s usually fully hardened in less than 24 hours. I usually let it sit overnight and the handle is ready to work on the next day.
 
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Since Steve has been using Gflex for 10 years my guess is he does have an idea of how the glue sets up, he is seeing something different from his normal experience.

For weight the ratio is 1.2:1, resin to hardner. For years I did not realize this was the ratio and the glue still setup and I never noticed an issue but I use the correct ratio now.
 
J. Hoffman said:
G Flex gets mixed 50/50 by volume not weight. There is a weight difference between the epoxy and hardener. That is most likely your issue.
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well if this is the case then i have always had success even though i am mixing it wrong. The epoxy comes in a kit with 2-4oz containers. I think there is more to this. My shop is in east coast Florida, we are running at just about 100% humidity and 95 degrees. That might have something to do with it. A local friend suggested a call to Gflex and see what they have to say.
 
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So a phone call to West Systems gave me this info. Yes the correct ratio is 1.2/1. The tech I spoke with told me that the Gflex is very forgiving of the mixing ratio and my 1/1 mix should not have been a problem. The cloudiness is caused by moisture. I guess I will have to remove the Gflex, clean it up and bring it into the house in the AC. Humidity is certainly lower inside. Rats...this is a really nice piece of antler, I hope I don't screw it up...
 
I’m in the panhandle north of Tallahassee and the humidity has been high here. I’ve made quite a few Gflex mixes in the past week and it’s actually been curing faster, about five hours and clamps can be removed and scales can be drilled. Temperatures around 90-100. Is it possible your epoxy is out of date or went bad somehow?
 
With epoxy

- stir for one full minute
-transfer to new container after stirring

I hope this helps someone out!
 
This is a new kit from Amazon. According to West Systems there is no use by date on these epoxies. Interestingly, I had a 10 year old kit that I had used for years. I bought 1quart kit and I would refill the bottles just because the smaller bottles were easier to use. The hardener had gotten really dark brown. I mixed some of that up last week and it became cloudy and did not cure properly so I thought it had gone bad and I tossed it and bought new. So I had old epoxy and new epoxy both with the same issue. West System tech told me that the hardener darkening (or turning red) does not affect it's chemical properties.
 
If it's just being used as filler for the removed pith will the cloudiness affect anything? It might be a bit porous, but so is the antler anyway
 
Just an FYI, but the two 4oz. bottles are ounces volume, not ounces weight. (another reason the metric system works better)

Some tips and info:
Epoxy resin forms its hard and strong bond by creating polymer chains. The slower it cures and the longer the chains the stronger the resin. Shorter chains may cause a weak joint. Water in the chains may cause stickiness.

Measuring is important if you want/need maximum bonding and cure. The ratio is given on the bottles and is often 1:1 by volume. The weight ratio varies. It is often 1.2:1 R:H, but some brands state it as .8:1 H:R. Weighing is a better way to get small batches accurate. A cheap gram scale, a box of popsicle sticks, and a sleeve of the little plastic 2oz. condiment cups make for perfect measuring and mixing for years for most folks.

Mixing for one minute is very important. It assures all the catalyst gets distributed evenly and starts the chemical reaction. If not mixed fully, some places in the resin will cure too fast and others very slow. Eventually it should all cure, but stickiness on the surface or a softer hardness can result from incomplete mixing.

Transferring to a second container is what is done with larger batches of epoxy resins. This is not an issue for most knifemakers and usually only done by folks who are doing fiberglass work. I do it occasionally when gluing up a large batch of handles.
They are called the "mix pot" and "work pot". The reaction is exothermic. If left in the mix pot it may cure too fast. The mix pot works is taller and thinner to assure even mixing of the two parts. The work pot is wide and makes a shallow pool of resin. A wider bottom container is used to slow down the set time, by allowing a larger surface area to let the heat radiate out. It extends the "pot life" by delaying the "gel time". For knifemakers who want a work pot, a disposable plastic plate works well to create a thin pool of resin.

Humidity and ambient temperature are factors in cure time and surface tackiness.
Higher temperature speeds the set time and can make the surface sticky. It usually will get less sticky with time. Wiping off with alcohol, and if needed acetone, may help remove the sticky feeling.
Moisture affects the reaction between the catalyst and resin. It delays it. If enough moisture is in the air and resin, it can delay the cure a lot. The industry term is "blush". It is caused by the amines in the resin going to the surface and reacting with the humidity. A sticky surface is the main problem caused. It can also make the final product have a hazy or cloudy appearance. Again, this is more of an issue with doing fiberglass than for knifemakers. Wiping it off with denatured alcohol and letting it dry another day usually takes care of the problem, but I have had resin that took several days to get fully cured when the humidity is near 100%. A rainy day almost always causes some stickiness.
 
I use a palette knife to mix my epoxy, fwiw
 
I have a variety of old round nose table knives in the epoxy box. I use a popsicle stick sometimes, too.
 
I usually mix mine in the corner of a ziplock bag. Just massage it until I get a nice even color. I then cut the corner and squeeze it out where I need it. I think (hope) I am mixing it well enough. I am going to try mixing some from the same container inside of our central air conditioned home. Certainly has to be a much lower humidity.
 
Sorry to keep bringing this up but, in my own defense, I read the instructions that come with Gflex. In the second paragraph they say a 1:1 mix is required. Keep in mind that the Gflex tech reinforced the 1.2:1 ratio. Also, farther down the sheet they say that Gflex is good for joining damp wood. So there goes the idea that moisture is the problem IMHO. One possibility is that it is reacting with something in the antler itself. I guess for now I'll file this in the s**t happens category and move forward.
 
1:1 by volume. The bottles have 4oz. volume each.

I really doubt it is the antler.
Your use of the epoxy is a filler may also be the issue. Epoxies are best used to join things more than fill large voids. The amber color may not show much in a joint that is .010" thick, but would show in a 1/2" antler core. Cure time and heat from the reaction may work against an even cure, leaving a tacky surface.
Joints in damp wood are thin and don't have exposed surfaces, so you don't see or feel them. When epoxying damp wood, the cure takes longer, too.

I'm not sure what the issue is with the antler core being amber colored or sticky. You are going to put a tang in there later on.
 
I've found that the best material to fill voids in antler is the actual antler itself. If you've got any scrap pieces of antler laying around grind them to a powder and store it in a jar. When filling a void place the powdered antler in the void and douse it with CA. Don't dally with this as the CA reacts with the antler and it dries rock hard within a second or two producing a few wisps of smoke in the process. If you have a very deep void you might want to do it in a couple of layers (or more) as the reaction happens so quickly that it may harden before the glue reaches the lower portions.

Eric
 
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