Hi TZE Paul,
No worries about your English. I cannot speak a word of Russian. I did manage to find a web page on Russian Epoxy standards however and ran it through google translate. http://www.gosthelp.ru/text/GOST1058...epoksidno.html
The epoxy is not the most important part, it is the aggregate mixture. EG should work okay with most epoxies but will obtain better performance with good ones.
Based on what I currently know, I'd think ED-20 would be fine. PEPA appears to be equivalent to DOW DEH 29 hardener. The dow data sheet suggests that this is a hardener that is very flexible which may not be so good for E/G. I would also think that the dibuthylftalate will make the mixture even more flexible leading to the lack of strength mentioned.
In general, it is a sign that the epoxy is well bonded if the stone rather than the epoxy broke. The epoxy should have a higher tensile strength than the stone.
I found this Russian supplier's product list: http://www.chimexltd.com/eng/content...647&idt=static
Based on this, I would suggest ED-20 epoxy and isophorone diamine which I have used in some epoxy measurements.
80 MPa tensile for E/G is optimistic, 25 MPa is probably more realistic. For compressive strength American manufacturer Accures castings obtains only about 125MPa compressive strength. Modulus can be expected around 30GPa for a good mixture.
Flatness is probably achieved most easily by a precision ground mold. We think it may be possible to cast an accurate surface with a very low viscosity epoxy like tabletop epoxy but nobody I know of has actually tried it here.
The larger the stone, the weaker the material but the easer it is to achieve good modulus numbers.
A mixture of silica something like Greybeard and AFAIK are discussing is what I would recommend although it is important to get the 3-4 mm size range in addition to the other AFAIK has already found. The precise percentages of each silica size in the mixture are dependent on which sizes you have available.
I hope this helps.
Regards All,
Cameron