Aragocrete

Works great as long as no pollutants/VOC's are dumped upstream as happened to me!

Well, I wasn't suggesting the Jordan River .

Ok, after a few trials I think I've stumbled upon a great mix that produces VERY pourous rocks with NO additional materials. I just cast some GARF style egg carton plugs with it yesterday and these things are light and holier (not blessed) than any live rock I've seen yet. Here's the rundown:

Mix (by volume):

1 part cement (portland type I/II will give the best strength)

3 parts aragonite sand

2 parts coarse crushed coral 1/8" - 1/4" nominal size (I used Caribsea Florida)

VERY little water (this is important)

The key to high strength, well made concrete has always been saturated aggregate (sand and gravel). It's important that your materials be saturated-surface dry, no excess moisture but no absorption either. To acheive this, wet your materials (minus cement) a while in advance making sure not to add too much water, stir to ensure even absorption and allow time to saturate. If after a few hours you have free water, pour it off and add some dry sand till it's not shiny at all.

Once you have this, go ahead and mix with cement first to coat and then add the very little water 1/3 part by volume should do it. you want it to be super dry, think oatmeal haystacks, the idea is to add only enough water to hydrate the cement. If your aggregate is dry when you do this it will suck the water out of the cement and weaken it too much.

Now go ahead and mold your pieces in whatever form you've chosen making sure that if the mold is absorbent that it is presatisfied as well. once cast it will seem to be less than solid and you will want to rod or pack it, don't. Simply vibrate the form slightly to ensure contact between the cement coated particles and cover to avoid dehydrating.

Sorry this has been so verbose, I hope somebody still finds it worthwhile and reads the whole thing. If anyone is interested and wants to try it let me know how it goes, or if you want to see some of the finished product contact me.

Got it, thanks Mark. Actually it turns out so pourous because rather than the hydrated cement filling the voids between the coarse aggregates it meerly coats them and bonds them together. Like Rice Crispy treats. So rather than enclosed air pockets there are actual tunnels all through it. I'll see if I can post a pic but I doubt that would really give you an idea of the nature of the pieces. I'll bring some to the next meeting and perhaps could throw in a quick demo when the DIY meet rolls around. Or if you or anyone for that matter would like to come by you're all always welcome.