Interchanging different Epoxy Brands

[Jon Matcho]

I have been considering and on the look out to pick up various parts abandoned from other builder projects. Are there any issues with bond strengths if interchanging two different brands of Epoxy together, or even MGS 285 and 335? For example, will I have any issues if the fuselage bulkheads were made with MGS 335, the sides with Aeropoxy, and I do the assembly with MGS 285?

[Len Evansic]

That's a good question. I was contemplating the same myself. With the recent increase in price for MGS (I had assumed that the dollar/euro thing had already kicked in), I find myself searching for a less expensive alternative. I would like to build my plane using a consistent system throughout, but now I'm thinking of using several systems to save costs.

 

In my gut, I think this is a bad idea. I mean, it's hard to tell what the bond strength between different types will be. I know that some people use WEST for finishing, but others for structural. Not sure about multiple structural epoxies.

 

I really wish there was a domestic equivalent to MGS 285, or a less expensive re-branding. The smell of the current alternatives is a big issue for me and my wife. Unfortunately, nobody seems to know of one.

 

-- Len

[Jon Matcho]

With the recent increase in price for MGS (I had assumed that the dollar/euro thing had already kicked in), I find myself searching for a less expensive alternative.

I'm not sure that MGS is as expensive as you might think. EZ-poxy is comparable in price. AeroPoxy may be close as well, and keep in mind that AeroPoxy resin is sold in 3/4 gallons whereas MGS is sold by the gallon.

 

I would like to build my plane using a consistent system throughout, but now I'm thinking of using several systems to save costs. In my gut, I think this is a bad idea. I mean, it's hard to tell what the bond strength between different types will be. I know that some people use WEST for finishing, but others for structural. Not sure about multiple structural epoxies.

Since asking the question, I've been told by a couple builders that they have used quite a few different epoxies in structural areas in their planes. Apparently, the bonds between cured epoxy layers, even using the same system, are entirely mechanical. So as long as you peel ply or sand between layers, as specifically instructed in the plans, you could mix and match as many structural epoxies as you cared to. The strength of the bond is as strong as the strength of the weakest epoxy.

 

Also keep in mind that the strength really comes from the glass itself and that the epoxy is there keep the glass in place so that the glass can bear the brunt of the load. In other words, a Cozy with just foam and epoxy wouldn't fly (here's where I find out that NASA has an epoxy where you don't need glass).

 

The smell of the current alternatives is a big issue for me and my wife.

So go with the MGS and cut down on purchases at the local vending machine. I'm building in my garage, so the smell issue is a MAJOR criteria. Still, keep in mind that while MGS may not smell, you still want to ventilate, and most importantly... do NOT eat it.

[Jon Matcho]

...the bonds between cured epoxy layers, even using the same system, are entirely mechanical. So as long as you peel ply or sand between layers, as specifically instructed in the plans, you could mix and match as many structural epoxies as you cared to.

I managed to ask this question to the authority on epoxy, Gary Hunter. Without hesitation, he said that there are absolutely no issues with mixing different approved epoxy systems.