I am building a deck and keep getting some conflicting messages when it comes to backfilling the holes. Already dug down 24”, added gravel for drainage and 4-6” of concrete (hole día approx 12-15”). I am well below the frost line. Is it ok to just backfill with concrete for additional strength or is gravel/material removed the best way to go?
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As this is an opinion I will leave a comment. I find the soil conditions / hill or not. It sounds like you have a hole that will support either method. Remember many decks just have a pier block(s) as a support, next would be the spacing of supports and weight of the deck. Concrete will provide a better support but with gravel packed in the bottom it may not be necessary remember concrete also binds to the sides so that additional area with a wider area at the top the post will be very solid. Filling with crushed rock will support but may sink over time if in clay so if in Rocky soil use rock – Ed Beal Aug 5 '18 at 16:12
I would be on the safe side and use concrete.
