Bedding epoxy cure time

[romad97]

I just did some touch up on a bedding job I did a couple of weeks ago. I basically just wanted to fill the front of the barrel nut region a little further up. I used the same epoxy I purchased from stockys. I did everything the same as I have before, removed the barreled action after 12 hours, everything seems good and looks good. When I went to start cleaning it up a little, removing the release agent and such, I noticed that the epoxy is a tad bit spongy. I checked the stuff that I had leftover in my mixing cup and its hard as a rock. Could it just need a bit more time? Its not tacky, its just a little spongy. Can epoxy sometimes take several days to cure or is it basically just a botched job that will need to be redone?

[olddav]

it's been my experience that larger quantities cure faster than smaller quantities. If the epoxy is not cured after twelve hours I would supect some contamination of some sort, possibly some oil on the surface of the stock. You may want to wait 24 hours just to be sure.

[MikeS]

Heat will help speed the cure , putting the stock in the sun for a few hours will help, or heat from a hair dryer or work light.

[romad97]

Thanks for the tip. It did appear to harden a tad overnight so I have hope for it to fully cure. I probably got my mix ratio a little off. I am putting it outside in direct sunlight for the day in hopes that that will fully cure it, plus its already in the low 90's here so maybe the heat will help it along.

[Texas10]

There could be a couple of things going on, first ( as you suspect) that your mix was not proportioned correctly or was not done thoroughly, or you scraped the sides of the container when removing it from your mix cup and got some raw material in your batch. This is a common mistake and can be avoided by thoroughly scraping the sides and bottom of the mix cup (I use a tongue depressor and cut the bottom off square with wire cutters) while mixing at least 3 minutes.

Second possibility is called cold cure inhibit. If your stock was allowed to get very cold during the cure, the epoxy may have stopped reacting…permanently. You may get lucky by heating the stock to 140 to 150 degrees for several hours in a hot box made of a cardboard box and hair drier. Use a thermometer to monitor temps and don't go any higher in temps.

If still soft, remove it and start over again, it'll never do the job as intended.

Good luck, and let us know how it turns out.

[romad97]

Well when I say its soft its not to the point of being easy to remove. It has appeared that over the last 24 hours it has gotten firmer, just not rock hard. I can't see how the stock was overly cold, I did this in my house which is typically at or around 76 degrees. What is funny to me is that the leftover that was in the mixing cup was as hard as a rock within the first 12 hours. I guess all I can do is wait it out another 24 hours and hope for the best. If not, then i guess its back to square 1. What sucks is that out of my 3 bedding job attempts to date, this one actually turned out the best, besides the fact that it may not completely cure.

[bloodhawke83]

You could try to add stainless steel powder next time, 1 to 1 mix.

[FW Conch]

Not "busting on you", my Brother of the Barrel Nut :-)

But your mistake came in "removing the barreled action from the stock in 12 hours". I don't care if it is labeled "5 Minute Epoxy", it ain't "fully cured" in 12 hrs, no matter what it says on the label. Patience in all things is a virtue, and it also helps in stock bedding :-)! Did you really need to use the rifle that quick?

I have learned, the hard way, to let the rig set for 4 days, then decide I wasn't going to shoot the rifle this weekend anyway, and take it apart next week.

Yes, it will finish curing with time, and you can speed it up with heat, but it will never be right, because without the pressure of the action against the stock, there is nothing to prevent the "less than fully cured" epoxy from expanding or contracting.

I have made your mistake, and others, and when I recognize it, I just get the Dremel out, hog out the mistake, do it right, then again I can say "it was the best bedding job I ever did"! :-)

Good Luck...Good Bedding! :-) Jim

[romad97]

Conch I fully believe everything you are saying. In the future I will absolutely do it this way. I am not in a rush to use this rifle. In fact, I don't even have the head-space gauge I need to finish putting it together. Like I said, this is only the 3rd rifle that I have tried to bed. The first was a disaster, the second was so so, and I thought that this one was was actually pretty good until I noticed the epoxy wasn't quite cured. As far as the 12 hours, its actually several hours longer than what stockys instructions recommended, that is why I thought it was good. Their instruction claim 3-5 hours before disassemble. I guess this is what this community and this hobby is all about though, meeting people with good info and learning how to do things. I am going to wait this one out and if it cures I am going to shoot it. If it shoots well then I will leave it. If it doesn't then i will dremel it out and start from scratch. I will heed your advice next time I try this though and I will let it set for 4 days.

[FW Conch]

Ain't it fun! :-)

[limige]

when I used the last bit of my acraglass it did the same thing. I don't know why but I had to grind all the bedding out and redo it. now I've tried the shoe polish and devcon and I must say, its very nice to work with and does a fantastic job. my win70 action released far easier than any savage I've bedded. not sure if it was the polish or the shape of the action.


I always wait for full cure as well. you don't want to have that bedding change at all when you remove it.

[scpaul]

Mr. Texas10, The cold cure inhibit that you mention, is it possible to cause this problem by the action/barrel assy. being cold? Say that the stockwork was done in the house and the action was in the shop. You bring the warm stock from inside and bed it with the bedding material and action that had been in the shop (40 - 50*) the previous night? I ask because I had a very similar problem, and redid it with the same materials and it worked as good as I'm capable of doing. I since then go as far as weighing the two parts of the epoxy because I had always thought that I must have gotten the portions wrong. Mr.97 congrats. on getting it right and purdy, I bet. Thanks and Later Y'all, Paul

[Texas10]

Scpaul,

Yes, quite possibly a cold barrel will stop the curing process before it can even get started. Epoxies are thermoplastics that respond well to SOME heat, but can be destroyed by too much heat, or too much cold. Most have a recommended minimum temperature that the MIXED ingredients AND material to be bonded must be maintained to insure a complete cure.

The best way to look at how epoxy cures was described to me as this; Picture a long chain epoxy molecule as a line of girls and boys lined up in girl-boy fashion with girls only holding boys hands and vice versa. Now imagine what would happen if there are 20% more girls than boys. Since they can't hold the boys hands they are standing around by themselves with their hands in their pockets. And when it gets too cold, they all stop holding hands and put their hands in their pockets instead of forming a long-chain (molecule).

This is why epoxy components (part A and part B) must be accurately weighed before mix, and kept warm during cure. Most epoxies are tolerant of 5% mix error, but more than that and the hardness and structural properties go out the window. Without that hardness, what is the point of the bedding job?

Additionally, most ambient temperature cure epoxies respond well to post cure tempering by heating the project to an elevated temperature after the initial cure has taken place. I use 160 degrees F as a starting point for most room temperature cured epoxy and will hold it at that temp for 12 hours or more.

Sometimes a partially cured epoxy can be heated after 24 hours to an elevated temp to help it cure more fully if cold cure inhibit is suspected. However if mix error is the reason for incomplete cure, remove it and replace as it will never work as designed. This includes properly proportioned batches that are improperly mixed by, for instance, failing to scrape the sides and bottom of the mix container completely during mixing or not mixing long enough (3 minutes is standard).

Epoxies generally remain good in original containers for one year when sealed tightly and stored between 50 and 75 degrees. Loose lids, and freezing temperatures will ruin them quickly.

OK, this is quite possibly more than you wanted to know, or you already knew…... I guess I'm just naturally blabby.

Did I just say "guess"?? LOL.

[1.618]

This probably has nothing to do with your issue, but one thing you should pay attention to, when adding another layer of epoxy over cured epoxy, is amine blush.

Most epoxies leave a layer of "amines" (or chemicals leftover from the hardener) on the surface of the cured epoxy. You need to remove these amines before adding another layer of epoxy (or even painting). A good way to de-blush is by scrubbing with a Scotchbrite pad wetted with water -- the amines are water-soluble.

If you add another layer of epoxy before the layer underneath has completely cured (in other words, if you can still dig your fingernail into the partially-cured epoxy substrate), there is no need to remove the amine blush. In fact, if you add another layer of epoxy over "green" epoxy (while it is still soft), the second layer will bond to the underlying layer at a molecular level, with cross-linking of the molecules, whereas new epoxy bonded to fully-cured epoxy bonds only on a mechanical level.

Not all epoxies blush amines, but most of them do – and if they don't, you won't harm anything by attempting to de-blush existing cured epoxy (with the Scotchbrite pad and water).

Edited to Add: I never had any problems with marine epoxy resins and hardeners freezing here (and it went down to 1°F this winter) and I have gallons of resins out in the barn, and they have gone through a decade or more of freezing winters with no degradation.

[scpaul]

I appreciate the info. I usually mix on a flat plastic lid for a good while and mixing the epoxy from the outer edge toward the center. I generally drill small holes in the underlying layer of epoxy for a mechanical bond and scuff with fine to med. wet/dry sandpaper then clean the dust etc. with acetone,MEK, or pure denatured alcohol. I've been doing the right thing by accident, for once. When it was cold 50* or less I direct a flex neck lamp toward the work. The directions actually say to use the same amount (volume), so I guess that the weights of the 2 compounds must be similar. MR.10 and Mr. 1.618, thank you both very much again. If you think that there's a way that I can help you just let me know. My e-mail is in my profile and is the best way to get me. I try to check it daily. Later Y'all, Paul