my deck post are heaving. any suggestions on stopping and/or reversing this problem? a little background. i reside in the
north eastern us. the post are down 42″. and heres where i think was my downfall, i mushroom capped the concrete at
ground level.
Replies
Heaving
Yep, the mushroom cap would do it, and is 42" below frost line in your area?
Fix, Rent a Concrete saw and saw off the mushroom perimeter. Neatly.
Or go at it with a chisel, wear your safety goggles.
Good luck,
Dale
we put our
post footings top at 40" below finish grade
then we set our posts and backfill with compacted gravel
the gravel allows teh water to drain away from the posts
the concrete caps you used not only encourage frost heaves, they also tend to keep the posts wet
As others have indicated, using concrete around the posts increases the likelihood of heaving. By "mushroom cap" I presume you mean that the concrete spreads out on top, a doubly bad idea.
At the very least, attempt to chip away the cap to several inches below grade, then fill the resulting hole with gravel.
If this is a high deck such that you can readily work under it, you could attempt to remove the concrete entirely. Probably the easiest way to do this would be to cut off the posts (one at a time, with bracing) and dig/wiggle out the post stub and concrete. (An A-frame set above the post with some sort of hoist would help significantly.) Then fill the hole for about 6" with sharp gravel (or a SMALL amount of concrete will do), compact well, set a new post on top, and (after splicing) backfill with gravel. Splice new post to old with pieces of treated 1x, but make sure the two cutoff ends are pressing against each other so that the splice boards don't carry any of the load.
Presumably 42" is the frost line where you are (that's what it is here), and there's probably little advantage to going deeper. The heaving occurs not because of a shallow footing but because the frost near the surface "grabs" the concrete and pulls it up. (Where you feel you "must" use concrete around posts, use Sonotube around the upper 2 feet or so, to create a smooth surface that the frost can't grab as easily.)
The other thing that helps (too late now - sorry) is to drive rebar through the sonotube into the earth so that it is sticking out below grade to tie the (otherwise pretty smooth) concrete down.