<a href=showthread.php?s=&postid=10508608#post10508608 target=_blank>Originally posted</a> by Travis L. Stevens
Hmm.. See. I'm so far behind I think that I missed something. The Perlite is a silica based product that helps the rock Cure, correct? Isn't it either absorbed in to the rock or washed out and a void is left behind?
It is silica, and initial test pieces did all have suspiciously low pH's, though I doubt it is because of the perlite, which is glassy and inert - thus, to my knowledge, not something that would engender a chemical reaction such as micro-silica has been reputed to do. Michealalans preliminary experiments with micro-silica have been disappointing.
A perlite Recap for those who are just joining us...
Think of silica as being glass popcorn. The base rock is heated, and then at a certain point, pops, creating rips and pores and increasing the rocks' volume and giving it a structure much like Crushed Coral, at least in respect to them both being fairly open. The only reason CC doesn't float is that the base element of calcium is heavy - silica is fairly light-weight compared.
A TDS test read 0 (two different users tested), and placing it directly in undiluted Muriatic acid produced no reaction - the acid actually evaporated (shot glass) and the perlite is still there...
Perlite is simply something to use in place of crushed coral, or at least that is the idea. Everyone who sees the "Disco Dancing Rock" in person, says it looks the most like real rock, and in part that is because of the round shape of the perlite - round had been a hard aggregate shape to find, but is the more commonly seen texture shape in rock like Fiji.
It also weighs next to nothing - so people wanting to make large rocks without having a 75lbs rock, can do so, and have that same rock weigh maybe 50lbs.
It should be noted that if cast fairly dry and loose, like we try to do with the Ol' Skool type rock, this stuff becomes crazy porous. Crazy. As in "I can see how this would collect poop and cause problems", kind of crazy. I'm finding that by using a slight bit more cement, and making a slightly wetter slurry, as well as slightly compacting it, all make for a rock that is porous, without having as much potential to collect crap.
My best pieces, IMO, have been to a 1 ratio, sand, cement, perlite, oyster shell, and then add a little more cement, like a 1/4 part. You don't really need salt, but I suppose it could be added like it would be in Ol' Skool+ recipes.
For those going really cheap, 1sand, 2perlite, 1 cement makes a very interesting, almost weightless rock that does not float.
Care needs to be taken while curing this rock - perlite is fragile, and while the hydration completes, it can be more likely to break then traditional rock with traditional aggregates does. It seems to harden up just fine though.
That is all I can think of right now.
Does that catch you up some?
Anyone want to add anything?
I think I'll have my work cut out for me.
