[greybeard]

Forgive me that I have read only random posts from here but I'd like to ensure couple of points I have in mind:

1) Has anyone tried thoroughly cleaning stones/sand before mixing? Dust or dirt on surface of particles will reduce adhesion and weaken the composite.

2) Has anyone compared different brand epoxies? In my experience, some poor quality epoxies are gummy and better ones get seeimly hard as glass.

Also accurate mixing ratio is very important for epoxies. If I recall correctly a TUT university course called "Composites", less than 1% error is preferred.

Welcome Xerxes, and I can understand your reading method, even with it's drawbacks.

Washing has been suggested. I washed my stone/sand as a matter of course to remove all the clay which is present in commercial ballast - my starting point.
The use of both methanol and also isopropanol have been suggested as a way of "activating" the surface of the aggregate, a slightly different direction of thought, but I'm sure you will understand that most of these criteria have been taken on board by everyone.
I think those who are doing practical tests are already using solvent free epoxies, chosen for several reasons, ie zero VOC's and low to zero shrinkage. This choice should in itself avoid poor quality epoxies.

Regards
John