Epidermix for Rifle Bedding Compound - Question

**414gates** · 03-10-2020, 10:10

It is generally recommended as a stock bedding compound, and I have used it before as well.

This week I did an experiment that involved a stock with liquid epoxy, and I realised that every epoxy is rated for heat.

I see from the spec sheet the maximum service temperature of Epidermix 372 is 60 degrees C.

Products like Devcon and Marine Tex rate much higher, 120 degrees C and up.

The liquid epoxy I used is rated for 120 C.

Why are we using this Epidermix to bed rifles if it can only handle temperature little more than the human body ?

I took the hardened remains of the mix, and immersed it in boiling water, and let it sit for a few minutes. I emptied it and filled it again with boiling water. After a couple of minutes, I emptied the water and the hardened material was still too hard to be scored by my fingernail.

**Pirate** · 03-10-2020, 14:54

Above the service temperature the chemical bonds may start to degenerate, and the epoxy will start losing its structural strength. This becomes a problem with structural bonds that have to support certain stresses.

For stock bedding the epoxy is not really used for structural purposes as much as for shape-forming purposes. In this case the higher temperatures from the rifle itself will only act on the outside surface of the epoxy, but I doubt it will cause any significant surface-dimensional changes, therefore it wouldn't make the product unfit for purpose.

I don't know the details of Epidermix but iirc it's supposed to be quite dimensionally stable with very little, if any, shrinkage on cure. This would make it specifically suitable for the shape-forming purpose, because the shape that is formed will not change due to internal contraction of the epoxy during the curing process.

For interest sake, what liquid epoxy did you use and for what purpose?

**414gates** · 03-10-2020, 15:14

I used a local product called ONYX, to fill a Howa stock ready for bedding.

https://ysterhout.net/docs/how-howa/index.html

Product info is here :

https://www.amtcomposites.co.za/prod...-slow-1-83kg-2

**Andrew Leigh** · 03-10-2020, 16:54

The limit of most people to hold something hot for but a second or two is around 50 to 55C. Your rifle barrel, at the chamber really should not be getting that hot so 60C is fine.

Having said which most polyesters and acrylics cope with double that with epoxy being more. These resins in small batches are formulated from large batches of stock resin from the primary suppliers. These resins in my opinion are horribly under specified, no need to claim anything higher in a domestic environment so why risk it.

The average test for a resin is that it should be able to cope, at full temperature, for 20 000hours after which it must retain 50% of it mechanical and electrical strength.

You are more than good to go.

**treeman** · 03-10-2020, 22:22

Been using Epidermix for years, and I believe that if you shooting your action hot enough to destroy the Epidermix integrity you should be more worried about what you doing to your lands and rifling than the epoxy.

I can not tell you how hot, but I have in other situations made Epidermix smoke and it was still stable and rigid afterwards(other than the part/surface area that smoked/burned).

If used on a hunting target rifle, the sudden hot - cool down again, not maintained heat will not harm it.
I can not comment on a SLR application of this product.

I have not in more than 30 years seen a rifle bedded with Epidermix fail at the Epidermix point of application. I had rifle where the epidermix was spider webbed with cracks and it was still solid and a **** job to clean it out.

**Fire-stick** · 04-10-2020, 10:38

When bedding with Epidermix, what is the most suitable stain to use to colour the mix as desired?
Solvent or water based?

**Pirate** · 04-10-2020, 10:55

Originally Posted by 414gates

I used a local product called ONYX, to fill a Howa stock ready for bedding.

https://ysterhout.net/docs/how-howa/index.html

Product info is here :

https://www.amtcomposites.co.za/prod...-slow-1-83kg-2

Thanks for the link to your site, I'll probably attempt something similar once the stars align and my 223 license eventually comes through. How much stiffness do the added liquid epoxy add? I looked at the Hogue stock's torsional flexing and I did get the impression that much of the flex happens just ahead of the action cutout where there's the least total material rather than just in the fore-end?

**Andrew Leigh** · 04-10-2020, 12:13

As long as at the stock at the recoil lug and the chamber portion is rigid then the bedding should work. I you have not done it before make sure to leave gaps around the recoil lug; to the left and right, below the lug as well as at the front. The only place the recoil lug should touch the bedding is at the rear of the lug, it is a recoil lug no a positioning lug. The depth and lateral movement is taken care of by the bedding around the chamber portion of the lug.

I use small quantities of paint dye to colour the white Epidermix mix in order to match the stock colour, approximately.

**Edwill** · 04-10-2020, 12:17

See this is available. Another option

https://247hunter.co.za/accessories/...flammable.html

Sent from my SM-G970F using Tapatalk

**Sean KZN** · 04-10-2020, 17:17

When bedding with Epidermix, what is the most suitable stain to use to colour the mix as desired?
Solvent or water based?

I use the standard Wooddoc stain, mix a little at a time to get the colour to match. Water based as Epideremix can be cleaned off with water, no need for solvents.