cinder blocks as base rock?

[shelburn61]

I just want to be sure standard construction cement blocks are reefsafe?

In the interest of creating a very open reef structure, I was planning to use the cube blocks as a base. I realize they would have to be cured first.

[SCR]

Not knowing for sure what they are made of, I would say no.

[jcjstl]

much along the lines as diy rock as long as you cure it in fresh water till it stops leeching...(4-6 weeks changing the water every couple days youll be fine)

[shelburn61]

People use portland and hydraulic cement routinely. Are cinder blocks made of something different?

[Ewan]

Concrete contains 4 parts: water, portland cement, aggregate, and admixtures. Concrete and cement are not interchangeable terms, although I often see engineers refer to concrete as "cement". Drives me nuts.

You can track down where the concrete masonry units (cmu's) are being cast. In my case, there's a plant about 5 miles from my house. Aggregates contain a high amount of quartz and iron, as per an assay that was shared with me. This is because of the local aggregates that they are using. This can and will vary.

If you do plan to use them, at least find out where they were cast, and ask about any admixtures or aggregate information. In the ocean they would be fine, but in a closed system, they could leach and cause big problems. I wouldn't want too much iron in my system, for example.

Just something to consider. Good luck!

[Ewan]

Also, it is highly likely that they are not completely cured. I would expect them to release some heat, and raise the pH while they are curing.

[ksouers]

You also don't know what the aggregate they used is made of. They may contain metals. You may want to start with just one block soaking in a separate bucket for a few weeks/months then test the cr@p out of the water for anything that might even remotely affect your tank. If you soak it in salt water and there is even the slightest discoloration you can bet it has metals in it.

It would probably be cheaper, certainly safer, to make your own rock using some of the recipes from Travis Stevens DIY Live Rock thread.

[medic29]

Originally posted by Ewan
Also, it is highly likely that they are not completely cured. I would expect them to release some heat, and raise the pH while they are curing.

I'm quite sure cinder blocks, building blocks or whatever you want to call them are most definitely cured. During the process of making them they are baked in an oven at something like 1400 degrees...thus to speed up the process of the chemical reaction. We researched this when looking for a way to speed up the process when making MMLR.

[VaderWS6]

I've heard they need to be cured in a weak solution of some type of acid before being used in an aquarium?

[Ewan]

Originally posted by medic29
I'm quite sure cinder blocks, building blocks or whatever you want to call them are most definitely cured. During the process of making them they are baked in an oven at something like 1400 degrees...thus to speed up the process of the chemical reaction. We researched this when looking for a way to speed up the process when making MMLR.

They do continue to cure. It's not complete after the bake in the 2000F oven. Think of it as a half-life.
The result probably wouldn't be significant. I would be more concerned about the metals that could be present.

[NanoReefWanabe]

Originally posted by Ewan
They do continue to cure. It's not complete after the bake in the 2000F oven. Think of it as a half-life.
The result probably wouldn't be significant. I would be more concerned about the metals that could be present.

more on that...regardless of how cured you think a concrete mixture/product is it is still and will always be cuing...the older it is the harder it gets...continually...unless of course it is submerged...and then it just cures incredibly slower...

i would be more concerned with additives in the blocks (chemical) and any metals that may be present directly or by trace amounts...as ore found in the indigenous rock and aggregate used to make the blocks..

just my .o2 but it is easier to use PVC as an armature for your rock...or buy dry base fiji/ tonga rock or make your own rock to prop up your display rock..

[shelburn61]

Originally posted by shelburn61
I realize they would have to be cured first.

It always amuses me that people somehow find a way to argue an irrelevant point in these threads...

DIY rocks are considered "safe". Do we know any more about the contents of cement mixes used in DIY rocks than in preformed blocks?
I'm just worried about harmful impurities here: heavy metals, PO4, etc...

[angel2007]

This is what I used as my base. It cost around $10.00, and its working pretty well. I have to finish arranging my rock I will post pics soon of the finish product.

[hahnmeister]

I asked this a while ago (about cinder blocks) and was told that they are made with alot of fly ash... a no-no for our reefs.

[shyland83]

well, true "Cinder blocks" are made with fly ash. but what most of us consider to be a cinder block is actually a concrete block. people mistakenly refer to concrete blocks as cinder blocks. there is most likely no fly ash in the blocks he is considering.

[Gary Majchrzak]

Originally posted by shelburn61
I just want to be sure standard construction cement blocks are reefsafe?

In the interest of creating a very open reef structure, I was planning to use the cube blocks as a base. I realize they would have to be cured first.

Here's a TOTM that used cinder blocks as a reef structure to cement liverock onto:


http://reefkeeping.com/issues/2006-04/totm/index.php

FWIW I used uncured cinder blocks. I'm not recommending everyone do this as I feel good quality liverock is still one of the most important building blocks of any successful reef aquarium.