My kid asked me why concrete is gray and I had no good answer

We were finishing a driveway in Tempe last Thursday and my 7 year old was watching from the truck. He came over and just asked, 'Dad, why is it always gray?' I started talking about cement and aggregate, but he looked so disappointed. It hit me that after 15 years, I'd never really thought about it beyond the mix. What do you guys tell people when they ask something simple like that?

3 comments

3 Comments

eric_price2mo ago

Actually concrete can be lots of colors with different mixes or dyes. The gray is just the cheapest and most common way to do it. Your kid probably wanted a more fun answer than the practical one.

blair_davis503h ago

Dyes actually don't work all that great with concrete. Most of the color you see in stamped or colored concrete comes from integral pigments mixed into the dry cement before water gets added. Those pigments are basically iron oxides and other mineral powders. They can scratch off or fade over time if the surface gets worn down though. The pink concrete in Arizona is probably from red sandstone aggregate or maybe even some natural clay in the local mix, not a dye at all. So yeah, your kid was onto something real.

mason4172mo ago

Ever seen that pink concrete in Arizona? Kid had a point.