I have a bottom plate leaking water underneath it after a rain and need some
advice. For reasons I won't bother to go into one wall of a barn sits
directly across the middle of a concrete slab patio. The exterior is hardie
panel that comes down to 1/2 inch from the slab. A piece of aluminum L
flashing (4"x6") is sandwiched between the bottom plate 2"x4" and the
concrete. Before bolting the bottom plate down, several beads of calk were
laid down between the flashing and slab but the joint leaked water after a
rain. I then caulked the outside edge with a bead of black flashing caulk --
the 50 year kind and it still leaks. Any suggestions how I can make this
water proof? Thanks.
You are fighting a no-win battle. Any seal that you might manage
will be temporary at best. The only proper solution involves
cutting the concrete, creating a stem wall (with footing by code)
and reworking the wall.
(top posted for your convenience)
Keep the whole world singing . . . .
DanG (remove the sevens)
If you had not applied the black flashing, I would say pure silicone
caulk. You could still try it, but that other stuff might restrict
the silicone from forming a good seal. I actually had a similar
problem in my garage. I build a garage on an old slab. The old
garage had colapsed because the garage was built on a hill, and the
water washed out under the slab, and the edge of the slab broke off.
However tbe rest of tbe slab was good, and I did not need as large a
garage anyhow. I tried to cut off the bad edge of the slab as best as
I could by hand, then built up the hill with fill. Then I placed my
bottom plate (green 2x4's) on the slab and bolted it down with
expanding concrete bolt fastners (whatever they are called).
Because in a few spots, the cement sticks out a few inches on the
outside, I had water coming in. I got a few cans of that urathane
foam (Great Stuff), and shot it under the wall, forcing it is as best
I could. In fact, I loosened the nuts and drove a few wooden wedges
under to lift the wall 1/8" or so. I filled under there with that
foam as best I could, and immediately removed the wedges and tightened
After the foam was dry, I used an old knife to remove all the excess
on both sides of the wall. Then I applied a nice thick coating of
clear silicone over the foam on the outside, which makes a good seal
and protects the foam. I do not think I have any leaks now, but it's
a little hard to be sure because there is always a little water coming
in under the door. Not enough to be concerend about though.
Of course, I dont have a patio draining toward the building, just a
little splash off that small amount of extended concrete.
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