<a href=showthread.php?s=&postid=10520221#post10520221 target=_blank>Originally posted</a> by mr.wilson
Micro-silica may be the active ingredient in the fast-setting concrete additive they sell at Home Depot. It says on the label that it isn't calcium-based, but it could still be polymer-based.
Fast-setting cement only takes a few hours to stabilize PH, and standard portland seems to only take a week or two for many, so I don't see an advantage to using any other products or procedures.
It very well could be Mr. Wilson. I've noticed it being in one type of bonding cement Lowes carries that also happens to be white (don't remember off hand what it was). The problem is that it's in low proportion to what I'd use. Many of the applications that could use silica in the mix aren't designed for marine environments so the amount of it won't be the same as the silica isn't added for pH control per say which is our objective.
How much you use of it depends really on the total recipe you are using and it changes a little depending on the amount of different additives in your rock mix.
I've gotten some different PMs so I'll answer some of them generically here:
Is there a perfect recipe (IE sand, CC, CS, cement, salt)? No, not really. This is more of a texture thing and is in the eye of the maker. I personally try and keep the cement to 25%-33% of the total mixture depending on the type of cement and what's in the mixture. This is no different that has been discussed here.
Is salt OK to use? As already discussed, salt is an enemy of cement. HOWEVER, we're not building bridges/building so the "strength" can be compromised some with salt. Using a fast set cement mix takes some of the worry of salt away. As already mentioned add salt as the last step of the mix. I'd try and keep salt to 1/5 or under of the total recipe. You really don't need to use salt in the mix however. This does create "pockets" in the rock but it's really not needed for bacteria/fauna that live in the rock. Cement is very porous by itself if you ever look at it under a microscope or big magnifying glass. Salt & sand can be quite useful at casting time to create tunnels and holes, etc. This is more of a personal preference and I'd agree with most of the use of salt from the thread.
How much water to use? Tough call and really depends on ingredients used and type of cement. It's helpful to understand what water does from a hydration standpoint. As your fresh rock hardens it doesn't "move" to fill in voids. Where ever there was water there will be a void as the rock hydrates and this is one of the main reasons why cement is so porous. Some types of cement seem to work better with less water while others can be more moist and still be workable. There's a limit of course with any type of cement. In general for type I/II the "cottage cheese" description is pretty good but I'd go on the "squishy" side of cottage cheese. In otherwords a tad (small amount) more then maybe you presently use (try it). The downside is the pH stays higher longer in I/II cement but the rock ends up more porous. Other downside is you might need to leave the cast alone a little longer before moving/touching it.
Do I use CC or CS in my mix. Normally NO. Haven't found it to be needed or that useful in the mix. Again it's a personal thing and more of a texture you are going for. I do occasionally sprinkle a little CC in the mix at the end if my mix is a tad to wet or for a little variety but it's not a staple in my mix. Plus it adds to the cost and when you are selling it the objective is to keep costs down.
Do I add coloring to my rock. YES, same as Walt Smith does, only I don't make "red" rocks. I go for more of a tan color with maybe a touch of pink look. I'm not fond of white, gray or red rock (neither are those who buy my rock). I've also found off white or tannish color rocks look better down the road. White rocks gets more of a "black" look to it in time. Pretty much same comment from Walt Smith way back in the thread. I actually do intentionally add a little more or less coloring to different batches for variety.
Do I mix by hand or machine. Both, although I like to do it by hand as much as possible since it's the only exercise I seem to get lately. Mixing 50lbs of ingredients at a time really gets the heart going.
If I have a large order in the wings I'll step up production with a mixing machine. It mixes while I'm casting.
What do I use for casting? Not much really, I have hardened sand beds (from use) with interesting formations on them. I just pour over this. Depending on shapes I'm trying to make I'll flip the rocks over the next day and build on top of them. This is an easy way to avoid "flat-bottom" rocks unless you need that "feature".
How can I make a really big slab rock for an overhang without waiting 6 months for it to kure? How can I make boulder size pieces with the pH problem? With type I/II cement do it in stages. For example maybe you could make a bunch of golfball/baseball size pieces. After casting let them sit for a week (or two) in a moist environment (spray with hose and keep covered with plastic). This will reduce the pH a lot from the rock. Then take all your balls/pieces with more mix and cast them together for a large rock. You will definitely cut down on kure time doing this as much of the "internal" part of the rock is pre-cured.
Is it better to use fine or course sand? Yes
I use a combination.
Should I use white or brown sand? I don't know. I use white fine sand and brown course sand since that is what I get easily.
Should I use aragonite or silica based sand? What ever you can get easily. I don't buy into the silica based sand problems. I have a large silica based DSB and no problems. Silica is actually good in limited amounts to our tanks and it's a "trace element" in salt mixes. I believe Randy wrote up a good article on this and came to the conclusion that silicate based sands can be a good thing for many people. If you're making rock for yourself pickup a silica test kit and test your tank. If you're high then use aragonite based sand to be "safe" if this mentally helps. I don't think it makes a difference in rock.
I think that covers the individual questions I've received.
Keep in mind. I'm not a Rock God and neither is Walt Smith. We probably have tried a lot more things then most people but that doesn't mean we couldn't do things differently or better for the average person. We're making more rock then most people (especially WS) so you have to keep in mind "production schedules". Making more rock doesn't mean making better rock by any means. It just probably indicates you've tried more things and make "consistent" rock that sells.
Carlo
