Morning Ivan - Your doing fine with your english and the tests. When you quote a ratio or % always state whether its by weight or by volume so others know what you mean. Also as a note you will need to dry your test sand before you use it!! In an oven is best. Fit it in with the sunday roast... If your achieving 70% volume fractions I think that's as good as you will get. Well done. I think this is the conclusion of the concrete companies as well. They used the high pack theories for years thinking they where getting 90%+ but in the end this is not achievable. 70% Vf which stands for Volume fraction vs Wr which stands for Weight ratio is a good number.

Infusion epoxy is very thin and yes it will stick even the smallest particles. It will take 1hr for the resin to gel (if you get 1hr plus hardener) and in that time capillary action will permeate everything as long as the sand is dry. I have glass tissue 0.2mm thick and epoxy will flow through this quite well under vacuum. So I expect if the sand is dry and you are not living somewhere where temp is below 15C then its fine.

Your resins density I estimate as 1095kg/m3, from the net quartz is 2650kg/m3 if you achieve 70%Vf then it goes like this if we work in litres:

700 litres quartz weighs 700*2.65= 1855kg
300 litres resin weighs 300*1.095= 328.5kg total = 2183.5 kg

sand is 1855/2185.5 = 0.85 by weight
resin is 328.5/2185.5= 0.15 by weight or 15% resin by weight. This is a weight fraction not a weight addition!!

The weight addition is 328.5/1855= 18% weight addition based on sand weight. Weight additions are usually used for pigments and modifiers, not the functional parts these are usually expressed as weight ratios. Check the maths and check your ratios on the day!

Not sure what you mean by air bubble inside? Can you see large air voids or lots of small bubbles? This sort of open process will always have small air bubbles unless you use a vacuum process. Air is 1.2kg/m3 so it takes a lot of air to change the numbers. As more info you can add a small drop of detergent to the water to improve its wetting of the sand and its bubble release. There are surface tension improvers for epoxy as well and I have played with these. They are expensive and I have not found them to be useful. If the air is in the epoxy resin (the hardener is very thin and it seems to self release) I have found heating it to 40-50 degs releases a lot of air as it thins out. But then allow it to return to ambient temp before use!! If you use a fast mixer its inevitable that air will be sucked in, that's how you whip cream and make pavlova.

When you use epoxy 1) make sure sand and mould is dry (water is your enemy, especially the stuff you can't see) 2) you could warm it slightly if air temp 20degsC or less but if 25C up then alls good. 3) when mixing do it slow with a paddle or spade vs fast with a mixer 4) use a long gel time hardener. This takes the pressure off getting it done, it reduces the exotherm peak and stresses the mould less.

If you have a scale you can weigh the test as well and this can then cross check your figures.

Onward to making some hard stuff.. Peter