If you're just using up an old batch and plan on using the same brand then you have no problems.

 But if you plan to change brands you might want to check for compatibility. There are differing opinions out there about this too. I have tried 5-6 brands before finding one I really like and have not run into any compatibility issues. The only thing I have done out of the norm is not counting on a chemical bond, sanding between brands. I have called suppliers and asked if their product is compatible with another brand and gotten a lot of tap dancing.

 As far as I've found first hand there is no concern other than the chemical bond. BUT (big but) there are too many different opinions out there for me to feel secure in giving that as advice. I would say if you're going to spend the time for a hybrid then play it safe and stay with the brand or shelf the leftover epoxy and get enough of the brand you like for the build.

 Hope that helps...

How old is your leftover epoxy?  According to MAS, the resin lasts forever, but the catalyst is only good for about a year.  Thankfully, you can buy more catalyst separately.

hello again,  

actually it would have meant a change of brands. 

but I was not sure about that thing, so I asked.

I will take no risk (while) building a hybrid. That is to big a projekt to mess up because of chemical differences that dont fit. 

So I will order a large batch epoxi to do the hole job and save the spare can for something different, perhaps a greenland paddle.

thank you and best wishes...

There is no problem using different epoxy...if one has a blush after it sets (West) then it must be left to set & washed & sanded. If no blush like MAS, you can re-coat every few hours...once it has gone tacky. Brands of epoxy have different stretch/elongation modulus, but not enough to matter in a kayak of this size. MAS medium hardener gives off some blush, but not slow hardener. Google it and read up to get the best info. Any metal, plastic, or resin will change it's final crystal or bonds if you heat them. Epoxy will get very tough if you wrap your kayak loosely in black plastic & put in the sun for a bit, but not above 120 degrees. You should be able to put your hand on it without pain. The epoxy needs to be fully cured & not yet varnished. The final basic epoxy molecule of different brands is the same, it is the chemistry of the catalyst which is different. Specialized epoxy, like they use for an F-18, is different & some have cure temps of several hundred degrees.