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Ran into a retired guy at the hardware store who had a killer trick for setting posts in clay
I was grabbing some concrete bags in Spokane last fall and this older guy saw my work shirt. He said, 'Son, you mixing that whole bag for a corner post in this gumbo?' I told him yeah, and he shook his head. He told me to dig the hole a foot wider than usual, line the bottom with 3 inches of gravel for drainage, and then use only half a bag of mix, but let it cure for a full 48 hours before putting any weight on it. Said the gravel stops the post from heaving as much when it freezes. Tried it on a job two weeks ago and those posts are rock solid. Anyone else use a gravel base in heavy clay soil?
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abby1896mo ago
Ever try using a bit of sand in the mix too? I mean, it helps the concrete grab better in that slick clay, at least in my experience. Makes a solid post even with less mix.
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paulm956mo ago
Used to skip the sand thinking it was just filler. Tried it last season on a gate post in pure gumbo clay, and the difference was crazy. That post hasn't budged a millimeter, even after all the spring rain.
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kareng275mo ago
Wait, hold up. You mean you actually tried his tip and it worked that fast? I gotta be honest, I thought that old timer advice was just old timer nonsense. I've been fighting clay soil for years and always just used the whole bag, thinking more concrete meant more hold. That heaving from the freeze really messes stuff up here too, especially after a wet spring like we just had.
You're telling me a layer of gravel under a half bag of mix does the same job as a full one? That is wild. I've got a gate post I've reset three times now because the frost keeps pushing it sideways. I'm actually tempted to rip it out and try this gravel trick next weekend. I bet the drainage part is key, keeping water from pooling right under the post in that thick clay.
I might have to eat my words and give that a shot. Thanks for sharing it, seriously. I never thought to go lighter on the concrete and heavier on the base.
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