The original post: /r/diy by /u/brbeard on 2024-10-04 01:15:36.
It’s nearly go-time for my first big “new homeowner” project. We’re replacing a sill plate that’s below grade, and rotting out. I’ve got my general approach, but need help with a few fine details, that I hope someone here may have more knowledge about then me.
Located in Michigan. House is from 1968. Sill plate in question is in the garage.
What we’ve got: 4" thick concrete pad sitting halfway on 8" plain cinder blocks (so 4" of the cinder block’s depth still shows). That extra 4" is where the sill plate was. We’re going to add a 4x4x16 cinder block to this (bringing it level to the concrete pad) and then adding an 6x8x16 cinder block on that for another course. The studs will be cut short and the new sill plate will go on top of that.
My questions:
- Around the cement pad there’s a thing (3/8") thick piece of mdf (or something similar). My initial plan was to tear this off, and then fill the 3/8" gap between the new 4x4x16 block and the cement pad with mortar. I was also going to run some 3/8" rebar in this gap to tie the 8x8xa6 block below the pad to the 6x8x16 that’ll be above it. But…if the cement pad’s floating…this totally gets rid of any sort of expansion gap. Would I be better off leaving a gap there (or leaving a gap and filling it with backing rod and caulk)? I could still run rebar there if we think that’s a good move. I just don’t know if this thing is a form, or if it serves a purpose beyond that…
- When it comes to laying the 6" block, horizontally, it’ll be a little under 2" onto the cement pad. So there’s not really room to put an anchor into that. The top of the 4x4x16 is going to be level with the pad though, so the first thing to go down will be mortar. I’m gonna powerwash the heck out of these old blocks and the pad, but…is that all you’d do? Slap some mortar on the pad for the short space where the block will be? Or do I actually want it to NOT adhere to the pad at all (to allow for expansion)?
After that I’m just gonna fill some of the cells (run rebar from the 8x8x16 up through the 6x8x16), put on sill sealer and a 2x6 PT sill plate. My studs are 2x4s, so this is another complication, since the anchor bolt is supposed to be in the middle 1/3 of the plate (and 1 3/4" away from the outer edge of the cinder block). My original plan was to put a 2x4 on top of the 2x6 (to give something to frame drywall to), but the middle 1/3 of the 2x6 is the very edge of a 2x4. And, presumably, the anchor bolt should go through BOTH sill plates, if there are two stacked. So that would be impossible. So now I’m thinking two 2x6s as the sill (one PT one not), with the 2x4 studs aligned with the outer edge. I’ll toenail the studs into the sill from the top, once the sills are in place, and I’ll run titen anchor bolts down the center of the 2x6s into the the blocks. And then I’ll put some 2x4 blocking between the studs to give me something to drywall to.
I’ve already gotten a lot of helpful tips to get me where I am with this plan, for which I’m grateful! If anyone has any tips or suggestions based on what I’ve laid out, I’d be most appreciative. We’re looking to get this project started next week! It’s been a lot of planning.
Some pics:
This is the edge of the cement pad, with the thin piece of wood/mdf. Also making an appearance - half a sill plate:
And here’s a shot from further away:
