Basement Floor Repair

I spend a lot of time in the basement. It's where I have the wood shop set up, it's where I do laundry, and it's where I clean about once a year when the sewer lateral gets clogged with roots and the system backs up. 

​I gutted the basement in 2020, tearing out 2 layers of "finish": a lot of remnants from the original construction in 1878, and then a more modern (1980s?) iteration.

One of the byproducts of this effort was a LOT of holes left in the floor. Some of the holes were where the floor had been busted up to run plumbing for a basement bathroom (again, 1980s?).

Some of the holes were the remnants of old-timey construction. The basement has 2 layers of concrete floor, the original and then an early 20th century addition (the granitoid stuff); the bottom plates of the wood-framed walls, of which there are only a couple, were buried in at least 1 of those layers. 

Wood buried in concrete, especially below grade, isn't going to last forever and the door jamb shown above - with 2x4 wood framing between it and the limestone and plaster - is no exception. Removing that door jamb 4 years ago left me with a couple of these guys:

I've got these voids scattered all over the basement and while there are more critical holes to fill - I routinely step in a big hole over by my table saw, they make it tough to use certain spaces of the basement efficiently, and on more than 1 occasion I've seen mice scampering through them like it's their own little tunnel system - because I have almost no experience finishing concrete, I figured I'd start in a small, discreet place. 

Also, after sizing up the void I'd originally planned to fill, I realized I probably hadn't bought enough concrete. 

So...I cleaned all the dust and loose rock and mortar out of this cavity.

In the process, I realized that the void wrapped around the corner of the limestone wall and traveled some distance under the concrete floor. Due to limited reach and zero visibility I couldn't tell just how far the void went, so I pulled out as much debris as I could reach and called it good.

Those little bits of wood, those are remnants of wall framing from 1878.

I managed to remove a softball size chunk of the original concrete floor. I have no idea what went into the old concrete or what the mix was, but it seems real aggregate-y and sort of brittle, like the cement used wasn't real good (by today's standards) or maybe it just wasn't mixed real well. 

Once I got everything free of loose material, I wadded up some builder's paper (the big rolls of brown paper you can get at the big box stores) and stuffed it into the tunnel. I didn't want to start placing concrete and, in the event that the tunnel stretched further than I thought it did, have it all leak out into who knows where. 

The void, particularly the tunnel, was close to 8 inches deep, which worked out in my favor because it allowed me to add some rock as a base. For a space this small it's probably inconsequential, but a compacted - as much as I could compact it, anyhow - rock base is better for the concrete to sit on than dirt. 

I mixed up a bag of concrete, which was WAY more than I needed but concrete is cheap and mixing up a half bag is rolling the dice a little bit because you may wind up getting weird proportions of aggregate and cement. I dumped the fresh concrete in the hole and admired my work. 

I pushed as much back into the tunnel as I could, but concrete isn't a super flowable material and agitating it is necessary to get it in all the nooks and crannies, especially those that can't be reached with any type of tool. To accomplish the required vibration I duct taped a thin scrap of wood to the end of a junk oscillating saw blade, stuck it into the concrete, and ran it at low speeds - only a second or two at a time - in a number of locations.  

I'd share a vid of the DIY concrete vibrator making the concrete level drop - that's how you can tell it's working - but the vid I shot, with my phone in my hand, looks like I'm having a medical emergency. You'll just have to use your imagination. 

Once I was convinced that the concrete had traveled to all the below grade places I needed it to get to, I screeded everything as flat as I could get it (the floor is a little wavy right here) and then came the hardest part...waiting. 

This part of the process is the toughest, I think, for people that don't finish concrete every day: wait too long and it's tough to finish the concrete surface, don't wait long enough and you're gonna be dealing with a soupy mess.  

I'll preface the rest of this by saying that after finishing up some repointing work the day before, I left my small trowel in the bucket of mortar and forget to empty the bucket or clean the trowel. I did my best to scrape and sand off as much as I could but I ultimately wound up grabbing my big trowel, which is wider than the void, and going for it. 

For a guy that doesn't do this very often, the end result is perfectly acceptable. There are a few spots I wish I could have gotten a little better, but the only trowel at my disposal was literally too big to fit into some of the corners and between that and the unevenness of the floor right there...it is what it is.  

I probably worked the concrete a couple minutes more than I should have, but it was a good learning experience and now I know that I need to 1, have the right sized trowel(s) for the job and 2, do a better job of cleaning up the edges of the existing floor to give myself a decent shot at a good transition from new concrete to existing. 

Oh, and 3, unless I want a bunch of dog hair in the concrete (there's horse hair in the plaster, so maybe it's fitting?), I need to clean myself off better after running around the yard with the dogs. 

Up next is the corresponding void on the other side of the doorway:

Act like you don't see that mousetrap. 😏