Poured concrete footings for 3 days straight and finally figured out my mix ratio

I was on a job last week outside of Columbus setting posts for a 200 foot privacy fence. The ground was pure clay and kept shifting after we dug. After the third day of redoing two sections, I dropped the water just a hair and added an extra shovel of Portland per batch. That last section held solid even after a rainstorm hit overnight. Anyone else struggle with clay soil screwing up your concrete set?

3 comments

3 Comments

hayden14416d ago

Idk, extra Portland just makes it crack worse when clay dries out and shrinks later on. @the_wren is probably right you'll see movement next month. That rain swell is a temporary bandaid not a fix. Ask me how I know lol.

graydavis16d ago

And how much time did you have between that rain swell and when you poured? Because I'm wondering if the timing on that matters more than people think. Like if you wait a few days after a good rain, does the clay start drying and shrinking again before the concrete even sets? Cause I've seen some guys rush it after a storm and still get cracks a month later, makes me think the moisture level when you pour is actually the bigger factor than what you mix in.

the_wren16d ago

Hang on though. Extra Portland isn't really fixing clay soil issues. That's just making a harder but more brittle mix. Clay expands and contracts way more than concrete does. If your soil moves, the slab or footing will crack no matter how strong the mix is. You need proper base prep, like 6 inches of compacted gravel underneath the footings. That gives the water a place to drain and stops soil from shifting under the pour. Clay is a whole different animal than sand or loam. Your last section probably held because the rain soaked the clay around it and made it swell up tight against the concrete. I'd bet a buck that same footing starts moving again when it dries out next month.