Devcon Set up Issue

I recently bought a couple of packages of Devcon Plastic Steel Bedding Compound, a two-part epoxy, which I have used successfully in the past.

My project this time was to FINALLY pillar bed a Savage 110 action/CBI barrel into a Savage laminated stock. Okay, my project was to have a friend to do this job for me. My friend mixed up a batch of this stuff and glopped it into the prepared stock. He turned his back for a few minutes and the next thing he knew the Devcon had set up almost solid. This occurred in less than five minutes. He had used this same material to bed an action into a fiberglass stock for me on a previous occasion and the work time was much closer to an hour.

I had given him both packages and the wording on each was identical. It took him a couple of hours to grind out the hardened bedding material in order to start over. After all that work, nothing could convince him to use the other package of Devcon. He did, however, open the second package, mix a small batch from each of the packages, and test the hardening time. He found the first package that he had opened turned solid in about five minutes, while the second package remained workable for over an hour.

He ended up using Accraglass instead and everything worked out.

I was left wondering if anyone else has ever experienced similar results from Devcon.

I only use Marine Tex its got a good working time and has 12,000 psi compression strength

Ed

Most epoxies go through an exothermic reaction as they set up. In other words, they generate heat. The larger the volume of the epoxy mixed at one time, the greater the heat is concentrated. The more heat is generated, the faster the epoxy wants to set up and the stronger the reaction, generating even more heat. So usually, if one needs to mix up a large amount of epoxy at one time, one uses a slow hardener and then immediately after mixing, one pours it into a flat shallow container so that the depth is low. This way the ratio of surface area to volume is high and the epoxy can shed heat that is being given off with getting excessively hot or setting up faster than normal.

I am guessing that he mixed it in a small cup and then let it sit in the cup until he was ready to use it. One needs to have then entire job ready to go, then mix the epoxy, then immediately pour it and spread it out into a thin layer. Leaving it in 1 spot in a large mass is encouraging thermal runaway. When one uses fillers like glass bubbles or microballoons, they are usually insulating and exacerbate this situation even further. As far as I know, the fillers in Devcon are dense so I think the properties compared to pure epoxy are similar.

Since it is summer, remember that the ambient temperature matters. "Pot life" as it is called can vary quite drastically between 50F and 90F. If he were to keep the compound in an air conditioned space, it will take longer to set up too. if the ambient temperature is high, it is entirely possible that one may not get a reasonable working life out of certain epoxy blends at all. Bad technique just makes it worse.

Westcliffe is exactly correct, or at least I conpletely agree with what he said. I deal with epoxies, sealants, glues and fillers daily working as an airframe mechanic (c130j sheet metal) and dependent on our humidity, temp, and batch size the working time varies greatly. Sometimes in my favor, many times not. If anybody has ever mixed Hysol in a cup before of about 50 grams or larger, they will know it gets hot enough to burn you while a small 5 or 10 gram batch is simply "warm."

Get everything completely set up, double checked and ready to go then pour in your choice of bedding material and fit the action immediately.

Thank you for your replies! I feel better informed about the dynamics and working characteristics of epoxies in general. In this particular instance my Devcon question was prompted by a specific set of circumstances. My friend and I have used this product successfully on several occasions so we weren't unfamiliar with its use.

In this case, however, we had two identical packages of Devcon Plastic Steel. In a side-by-side comparison, under the same environmental conditions the mixed contents of the first package hardened within five minutes while the mixed contents of the second package remained very workable for over one hour. An apples to apples comparison under the exact same circumstances.

While we enjoyed success with this product on another of my rifles; this situation caused hours of extra work work. That was a surprise & disappointment for both of us, and I wondered if anyone out there had experienced anything similar with Devcon Plastic Steel.

Just to be clear on what was done:

Looking here http://www.devcon.com/prodfiles/pdfs/fam_tds_101.pdf Suggests that the mix ratio for Devcon is 2.5:1 The 2.5 portion coming out of the bigger container and 1 portion coming out the smaller.

So was the Devcon mixed with the right ratio or a 1:1 ratio. A 1:1 ratio would have far too much hardener and would therefore have an extremely rapid cure ?

I have had similar experiences with other epoxies. I was told it was probably an old batch that had been stored in a very high heat situation. I'd mix a batch and have everything ready to go so if it set up in the mixing container all I'd be out is the epoxy and container. I personally use Acraglas and have had zero issues. I use the "Gel" and it has a peanut butter consistency and stays where you put it.

Quote:

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Originally Posted by OLEJOE

I have had similar experiences with other epoxies. I was told it was probably an old batch that had been stored in a very high heat situation. I'd mix a batch and have everything ready to go so if it set up in the mixing container all I'd be out is the epoxy and container. I personally use Acraglas and have had zero issues. I use the "Gel" and it has a peanut butter consistency and stays where you put it.

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I tend to think, in this case, old stuff versus new stuff might well be the culprit. My buddy has always gone with Acraglas with zero issues. He liked the way Devcon worked on our last project; but I don't think he's going to be able to shake the memory of digging out all that hardened Devcon on this round.

Westcliffe you bring excellent information to the table and for the collective knowledge bank, I'll lay this out. These were two completely separate blister packs of Devcon Plastic Steel. Each pack contained two small tubes, identical in size... 1 of hardener & 1 of resin. My friend used a scrap piece of lumber, which was divided into two working areas. He took the contents of each package and mixed equal parts (1:1) of hardener & resin, mixed well, and let stand in the open air on the piece of lumber. The mixed contents of the first package was solid as a rock at the five-minute mark, while the mixed contents of the second package remained almost runny for half an hour before thickening up to a workable consistency at the one-hour mark. This is what was done... no more... no less.

Thanks to all who took the time to reply.
Cheers

Sounds Odd. Sounds like someone is re-packaging the bulk product. Possibly even using a different hardener. Based on the data from the manufacturer, it should not be mixed in a 1:1 ratio. It is possible that if one buys the 1lb of product that one may get different results since it came packaged by the original manufacturer.

One can also use west system epoxy and add your own fillers. Short chopped fibers will flow well enough and will be tough as nails. Resin by itself is brittle. This is a great site for composite supplies http://www.fiberglasssupply.com/

Here they list milled fiber fillers. One is shooting for a 1:1 by weight glass to epoxy ratio.
http://www.fiberglasssupply.com/pdf/.../MilGlsFib.pdf

Many thanks for the additional resources.

http://i224.photobucket.com/albums/d...asticSteel.jpg

You used the wrong Devcon product. Devcon 10110 is the proper product for bedding rifles and IMO is better than Acraglass.

I've had great results with Devcon 2-Ton Epoxy.