I did some fieldwork today,actually visited Home Depot and a huge concrete place.Builders sand is soaking wet.Not suitable for epoxy.The bags of playsand seem promising as they are very dry and clean.The home depot suggested sandblast sand as it is graded and dry,but were out of stock.I checked the bagged gravel but it is not suitable as it is very dirty.Anything we use must be washed,to remove dust and clay.Crushed stone is not a good choice as it is jagged.Particles tend to "snag"on each other,making the mix thicker than necessary.Simply put smooth aggregates will "roll over one another like ballbearings creating a smoother mix.
On what is too big for aggregates,"If the aggregate is too large,1inch or larger it results in poor stregnth as the aggregate has different stiffness and properties compared to the binder[epoxy].The concrete place said 3/4 is their max size.Picture this 2"rough aggregate poured with cement into a 4" wide form.the rocks can lock together and not drop in forming a bridge.
Also if large aggregates are used,when you vibrate for air release and compaction the matrix becomes very fluid at certain frequincy and the large aggregate will drop like a stone[pardon the expression]to the bottom.
Is there a solution?Yes if you have read the links I posted Quartz sand is a good fine filler and max aggregate size is.375in.+smooth is better.
I don't know about you guys,but I am getting"AGREGATED about aggrates.I know a fair bit about epoxy.
Here is a few pointers.
Raw epoxy is solvent free and ships non hazmat.
Cheap reactive dilutents are used to thin the epoxy and thin the price.They also thin the properties.Ask your supplier if their epoxy contains Nonyl Phenol.
If your supplyer cannot ship non hazmat the epoxy has dangerous additaves.
Raw, neet epoxy has low vapour pressure{smell is not bad]
Reactive dilutents have very strong odour,might i add unbearable.Again if it ships non hazmat it is probably OK epoxy.To confirm request MSDS from the supplier.
We need thin epoxy to maximize filler loading.This would be called Laminating epoxy.Thinnest ? Probably 600cps which would be the consistancy of #one Canadian maple syrup.Suddenly I feel like bacon& pancakes.
Epoxy glue is 10,000cps or better.No use to us granite guys.Similar to honey.
We want a long pot life to maximize mixing time and reduce heat build up.Many times we have mixed or de gassed for too long and the epoxy is really hot.Now we are sweating granite bricks trying to get it in the mold fast before gell.
Why is epoxy such a great glue?Just before gell it thins out penetrating almost anything.I have in the past taped off mold edges only to discouver the epoxy penetrated the tape.This is also why the German guys saw pooling.Any how its near 1Am here to tired to go on and on.Hope you are not bored to death.Stay tuned for more epoxy 101 to-morrow.
Larry