Concerned about cement blocks

I'm seeing more and more use of cement blocks. Everything from raised gardens to smokehouses. My concern is the many chemicals used in cement blocks. Any thoughts on exposure to these chemicals when growing food in them, smoking food in them, baking food in ovens made from them?

Bonnie

Concrete is the new 2 most used resource on the planet (after water), so it gets studied...a lot. Most studies have found that the chemicals do not leach from concrete, they are tied up in the cement matrix. This includes fly ash (which has mercury and other heavy metals). Concrete, even with fly ash or blast furnace slag, has been deemed safe enough to use in the pipes for drinking water.

Well, this sounds like great news Stephen. Do you have any sources of this information? I sure would love to use cement blocks for a few things if I can be sure of their safety.

Bonnie

Unfortunately, I don't have anything readily available. I went through an engineering school that, at the time, won an award for concrete research. This question did come up because the fly ash contains mercury.

There is a lot of research on this because of how often concrete is used for everything. There is some leaching but it is extremely slow and extremely low levels. This is why it is allowed to be used for drinking water tanks and pipes.

Keep in mind this is also only with fly ash concrete (and maybe blast furnace slag concrete). The fly ash is usually only like 5% of the total mix and most of it is also non-toxic. Normal concrete is non-toxic.

Fly ash is not an inert filler in concrete. It chemically reacts with cement and water to form minerals (just like cement does) and this helps lock up many of the metals in it.

If you google it you can find a lot of articles. If you go to google scholar, you will also find a lot but most of it they will want you to pay for. Here is one that I found while searching.

http://infohouse.p2ric.org/ref/45/44766.pdf

The concern is with CINDER blocks, which do leach undesirable chemicals into the ground and your plants. Cinder blocks and concrete blocks are not the same thing. Unfortunately, many people use the terms interchangeably.

Concrete blocks are perfectly safe for anything you want to do with them.

And, if you have to use concrete, blocks are one of the most efficient and DIY friendly ways to do it. There really isn't that much concrete in a block, way less than a poured wall.

Ferne, I believe you're right and I've been using the term concrete when I meant cinder blocks. So, do cinder blocks leach are poor choice for gardens, smoke houses, outdoor ovens?

Bonnie

Correct. Cinder blocks are poor choices for anything that will contain something you're gonna eat.

The difference is that cinder is a mixture, but concrete is a compound.

What I have commonly seen for sale (in the Northeast) in recent years is only concrete blocks, not cinder blocks, so if you are buying new material you may not have to worry about it. Other regions may have a different mix of available materials.

Thanks for the replies. This has been very helpful.

Bonnie

Just sharing info - we use concrete blocks and pavers in our garden, I like them best after they have been aged a bit.  We lay them in a grassy area and let them sit until the 'new' color has faded, sometimes we spray the blocks with a liquid fertilizer to speed up the process. When the blocks show moss growing, I am satisfied they are finished leaching whatever they are going to.

Brie Robb wrote:Just sharing info - we use concrete blocks and pavers in our garden, I like them best after they have been aged a bit.  We lay them in a grassy area and let them sit until the 'new' color has faded, sometimes we spray the blocks with a liquid fertilizer to speed up the process. When the blocks show moss growing, I am satisfied they are finished leaching whatever they are going to.

I like this idea.  Thanks for sharing.

Bonnie