agrocrete curing

[ekclark]

I just made my first batch of this stuff last night and I was wondering if anyone knows any tricks for the curing process? I am thinking I will just put it in a tub in the backyard and try to change the water every few days. I hear some thing about adding vinegar, but I have no idea what this will do. Is everyone's agrocrete so brittle? I guess I thought it would be a little stronger than it is. I used agro and type one portland, with some crushed coral mixed in that I used for the molds. Any advice would be great. Thanks.

 

[dakar]

Got my first batch curing right now as well, curing probably isn't the right term here. But from everything I've read so far, best bet is to just soak them in fresh water for at least 6 weeks, or until the ph of the water stabilzes at 7.0 and stays there. I change the water twice daily. I've not found anyone reporting any conclusive results (that were repeatable) of any method that will accelerate the process, just need to leech off all of the alkaline over time.
BTW I used crushed oyster shells and type I portland in a 4:1 ratio and they are not very brittle.
Dave

 

[jlem]

I have also read that after 4-6 weeks if the PH stay below 8.0 for a couple days the you can start to add the rock. As long as the PH isn't spiking to high levels. Sometimes the rock is so large that even after months it still leaches some which actually helps maintain a high PH and ALK.

 

[squidd]

Portland cement "cures", that is the correct term for it ...
It is a chemical reaction that takes place slowly as the grains bond/bind to themselvs...
You may find that ,especially with complex pieces, that if you let it sit/cure in the sand mold for a couple days before removing it will not be "brittle" and break up on you...
If you spend alot of time on a really complex piece...you will be very grateful if you follow this advice...
Vinegar is an acid and will neutralize some of the alkalinity as well as dissolve some of the surface Portland cement..
It won't speed up the process of leaching alk but it will help in cleaning up your pieces...
If you have the skills, you can also use a dilute solution of muriatic acid to wash your piece and bring out the surface shells/texture if you wash and scrub during the curing process...
Ask a mason about "exposed aggregate" concrete...
All said and done cleaned or soaked, it still takes 4-6 weeks to stabilize..

 

[dakar]

Just out of curiosity I tested the PH of the water after 12 hours of the 'new' (4-5 days old now) rocks soaking in it... off the chart of half a dozen FW test kits I'm trying to use up... my SW kit shows 8.2 (perfect for the SWA)... then for comparison i tested my tap water (50' well water that is)... 8.2 again, aright bout the same as the rocks' water. Not sure what effect if any this will have in the leeching process. May have to haul some 'city water' home from work to see if i can detect the alk leaching off.

 

[squidd]

Sounds like your SW pH kit is wacked...
What do the FW pH kits say your well water is...?
I'm guessing MUCH closer to 7
"Off the charts" sounds about right for a pH test on 5 day old agrocrete...

 

[ekclark]

Thanks guys...Squid, do you cure yours in saltwater after the fw curing? I read that an extra two weeks of this can be helpful, though I don't remember why-I guess to just make sure it doesn't do something unexpected when introduced to a marine system. I hope I can put this new cave in by august...nothing with this hobby is quick I used styrofoam packing to make my caves. I hope this isn't a problem, but does anyone know is really alk water will mess with the stuff before I dig it out?

 

[dakar]

Originally posted by Squidd
Sounds like your SW pH kit is wacked...
What do the FW pH kits say your well water is...?
I'm guessing MUCH closer to 7

after posting last night I got to thinking so i tested the well water again... 8.2 straight outta the pipe across all 5 FW kits.. I'm figuring across all of them it's got to be right, I've always have a hard time keeping the Ph down in the jacuzzi. Must be some goofy stuff in the ground here, then again I'm only a few hundred yards off the Wisconsin River too....
Tank water turned out to be 8.2 after adding salt to the water testing with the SW kit when I set it up two weeks ago and is still holding steady. I'll pick up another SW kit on the way home tonight and repeat them all again just to be sure something isn't whacked.
Dave

 

[squidd]

Might be that your Tap is 8.2 or so, lotta limestone around the Dells area...
Might be that, that high a pH will slow the leaching process...ie: a more acid water would neutralize alk faster..
I also reread and saw the "rock" was 5 days old, but had only been soaking for 12 hrs...
What's your readings after a few days of soaking..?
What I'm not following is that your SW kit says rock water 8.2 and tap 8.2, and the FW kits say rock water high but tap is 8.2...
One of those numbers or one of those test kits are off...

 

[dakar]

Originally posted by Squidd
Might be that your Tap is 8.2 or so, lotta limestone around the Dells area...
Might be that, that high a pH will slow the leaching process...ie: a more acid water would neutralize alk faster..
I also reread and saw the "rock" was 5 days old, but had only been soaking for 12 hrs...
What's your readings after a few days of soaking..?
What I'm not following is that your SW kit says rock water 8.2 and tap 8.2, and the FW kits say rock water high but tap is 8.2...
One of those numbers or one of those test kits are off...
I must have confused myself and you with me... what I meant was I was testing to see if I could measure the Ph increase from the rocks...and so far they have not raised te Ph at all (above the tap water), i was expecting to see 9+ from my readings... maybe in time, or maybe I'm just changing that water too often to see anything measureable. Think I'll let it all sit until the end of the week in the same water and re-test then.
In any event, I'm building a separate tank for this rock to cure in, after a couple months of soaking in FW.
Dave

 

[zap800]

you are changing the water alittle too often. i have read on another site that i cant rember for the life of me said that he changed his water about once every few days to a week. the person who used 4:1 ratio using prtland type I and oyster shells is the method that this website used. he placed his rock into a garbage can, filled it with tap water and a power head to circulate it around. also the styrofoam trick might not bet the best way to go. try useing a rubbermaid tub filled with damp sand to cure your cement for a few days next time and it will be stronger. the longer cement takes to dry (cure) the stronger the product. thats why most contractors put plastic on top of a newly poured cement side walk.

 

[ekclark]

I am noticing a lot of white "snow" appearing in my curing tub. Is this calcium carbonate? If I am losing calcium, how do I counter this? The agrocrete itself looks fine, I just hope I am not turning this stuff into nothing better for my tank than if I had I made it with mason sand.

 

[jlem]

Originally posted by ekclark
I am noticing a lot of white "snow" appearing in my curing tub. Is this calcium carbonate?
That is what you want. You want to percipitate all of that out of the rock so it will not leach into your tank and spike your levels. It's the same thing that happens when you mix Kalkwasser and get the film on the water and in your mixing tup.

 

[ekclark]

Cool, thanks jlem!