laminating resin is a little sticky

[jraice]

After putting some laminating resin on my CF tube it has been curing for well over a week. It is dry but has a sticky feel to it, and there is some uncured epoxy. My dad says it didnt have enough hardner. I am using a pump system for the 3-1 ratio. Any tips? I have noticed it doesnt mix as well as thick epoxy but I have been mixing it for up to 5 minutes. The tubing is fine, but the reason I ask is I need a very runny thin epoxy to inject into the fin can of a small rocket to strength the fin joint. The laminating epoxy would be the thinnest I know of but I would like to make sure it will cure fully. any ideas?

 

[KermieD]

It does sound like your ratio is off, although it would be tough to say whether it was the resin or the hardener...maybe there was some air in one of the pumps?

 

[SwingWing]

My guess is it wasn't mixed well enough. Most epoxys should be mixed for 2 minutes, scraping the edges regularly. the scraping is really imporntant
Extra hardner will make things brittle, not cure faster or better

 

[jraice]

My ratio was correct, pumps had a pretty smooth flow so I doubt it was air. Mixing is problem the problem, it is super thin so it doesnt mix like a pasty epoxy would, thanks for the help. I have been using a paper plate, I will try a paper bowl or dixie cup so it is easier to get it REALLY mixed up.

 

[SwingWing]

What temperature has the tube been at? has it been in a cold area?
You might get some help by raising the temperature of the tube. Create a makeshift "oven" (heat lamps, plastic sheeting, hairdryer) to raise the temp to around 150 degrees for an hour or so, maybe it will cure.

 

[jraice]

I plan on "heat" curing the tube after cutting it to smaller lengths. My worry is that for the injection reinforcment it may all go in and then ruin the inside and not add any strength. I guess I will just use it for external fillets with fibers and I will design it so I can do internal fillets and then slide the motor tube into the slotted airframe. Actually, I have this design I made that I have been wanting to try out, you have a coupler that is pretty much like the airframe (rings get glued into it and fins go through slots) so you are basically building a rocket out of a coupler, then you slide that assembly onto the main tube with some epoxy, the main tube is 3-4"s shorter then the coupler and the coupler sticking out allows connection to the upper tubing.

 

[hoverhans]

Sounds like a problem I had with R/C planes. The trouble may be that you are using the wrong resin.
Laminating resin will remain sticky for a very long time as it is designed to have layer after layer of glass cloth laminated to it. What you need is finishing resin. This gets very hard in a short time. Having said that, even finishing epoxy will have a rubbery trait for a very long time. I stopped using epoxy resins years ago and went back to polyester resins. It may smell a bit but it works better than epoxy and the finish is stronger and lighter.
Hans

 

[agrippo]

I use a digital scale that has a tare feature to measure all my epoxies. I never have to wonder if I have the ratio correct because it is by weight instead of volumn and I've never had a mix come out bad like I did on occasion when using the small plastic mixing cups with gradients on them.

Andrew

 

[jraice]

The flow out of the pump was good (so there was no air inbetween the epoxy in the pump). I will try shaking the bottles but I probably wont use this till I do another layup job. Using weight it the most accurate way but be VERY careful. Most epoxies ratio, I will use 3-1 for example, are based on volume, if you do 1 ounce hardner and 3 ounces resin the volume may be off. I remember seeing one brand that showed the ratio to use for weight and a seperate ratio for volume. I think it may have something to do with the runniness of the resin and somewhat of the hardner. It just doesnt mix as well. I may try it for the fillets so I can add milled fiber and see how that turns out, I will probably mix it a tall skinny dixie cup for that, the flat plate just doesnt work. While it is somewhat sticky, the CF tube is the strongest 2.5" tube I have ever felt, no flex whatsoever...

 

[KermieD]

I'm not quite so intense as to use a scale to measure by weight, but measured mixing cups are SO cheap that I just don't count on the pumps for construction mixes. Most epoxies will give you a touch of "fudge factor" that is more than covered by the mixing cups. For large fiberglass layups, I'll use the pumps, but will waste a bit just to clear the air out of the pump lines.

Don't shake the cans/bottles. That won't do anything at all to help and may actually add more small air pockets to the mix. If you had a problem due to the pumps, it was air in the line, not something that will be solved by shaking. In fact, if you shook the containers last time, that may be part of your problem.

 

[jraice]

Well, for simplicity (and for a faster cure) I will stick to using this for layups and using 2 hour hobby grade mixed with the milled fibers I ordered for construction. Thanks!