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Couple questions? Answered

Hi, Mike. Thanks very much for these lessons. It's tying together a lot of what Dad and I did when I was a kid (sidewalks mostly), and some of my engineering classes, but I never really looked into the details of the process.

One of my interests is making planters for growing food plants (tomatoes and so forth). Our yard is resting on the "bones of the world" (bedrock) and therefore we have super-shallow soil, especially where there's light for growing. I like the thought of concrete planters for durability versus wood. But, is concrete a suitable container for food crops, or only should be used for decorative planting?

A second question is related to coloring. I had researched concrete polishing once for our foundation slab, and came across one image where a penetrating dye had been used to highlight the cracks in the slab. For small applications like this, does fine cracking occur naturally as part of the curing process (I am guessing not if done properly), and if no, would there be a way to induce cracks without destroying the integrity? This would be for decorative projects, not the previously mentioned planters, I definitely don't intend to use dyes in a crop container.

Thank you again!

2 Replies

mikeasaurusBest Answer (author)2017-03-27

Concrete planters are fine for food, some examples you may notices are grain silos and water dams.

Almost all concrete will have fractures, some larger than others. Depending on the volume of the concrete pour cracks are more likely to occur. To mitigate this concrete is covered while curing to inhibit moisture loss from evaporation before hydration has completed, sometimes additional water is sprayed on the surface while it's curing to achieve the same results. For large slab areas you will often see a relief cut in the concrete, this an indentation line in the concrete that is a designed weakness to localize any cracking to this relief cut and not creep into the slab.

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danzo321 (author)mikeasaurus2017-10-16

Concrete planters are great but you need to wait until the concrete is truly cured and does not exude any gases, so leave them out for a season (a few months) before use.

Concrete casts often get very shallow fissures which do not affect structural strength. If you have cracks, something is very wrong, like demolding too soon.

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