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Spinaccio t1_jaai8wc wrote

Install two temporary adjustable Lally columns near the middle of the beam to level it while you work. Drop a plumb bob from the center of the beam to the floor and mark it, then make that the center of a 12” square to cut out of the floor. Dig down to whatever the frost line is where you live (say, 4 feet). You can calculate how much concrete mix you should need, but I always buy more than I think the job will take, concrete mix has no expiration date. Pour about 12” into the hole, using the sides as a form (if you want to install steel reinforcement, bend it so it extends up 2 feet above this). Once that has set drop an 8” Sonotube onto it and fill it with concrete to the level of the floor. 72 hours later, level the joist with adjustable columns. Go slowly and check for cracks in the masonry above. Measure the distance from the beam to the new footing, taking base and top plates into consideration and cut a cement filled permenant Lally column to fit. I cut the pipe with a grinder and break it with a hammer. Raise the joist 1/4” or so to fit the new column, plumb it from 12 o’clock and 9 o’clock and lower the beam onto it. When you remove the temporary posts the beam should be level and solid. If the crack is bad, I would sister an LVL to it with 3/8” galvanized through bolts and washers. Next step, build a fire, crack a beer, and put on the game.

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Homebrewsailor t1_jabswpb wrote

Bags of concrete absolutely have an expiration date. If you live anywhere humid they will absorb moisture and will set up in the bag. Never plan on storing bags of concrete or mortar long term

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beazzy223 t1_jadiv9i wrote

Quickcrete is like $8 a bag. If your really worried about it going bad id just wrap it in a plastic bag.

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Audio_Track_01 t1_jachycm wrote

Sounds good to me. I'm also reminded of advise i received on my saggy old house - it took 100 years to get like that. Best to lift it slowly to level. And expect some cracking noises.

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Buffyoh t1_jacetsg wrote

Good advice. Did the same thing with sagging joists in my 1850 house. Still rock solid after forty years.

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Charliefromlost t1_jablyft wrote

Is it necessary to dig to the frost line if the building is heated? I ask because I have little floor jacks under my kitchen that I presume the renovators put in to help support the tile and granite that was installed. This is on a crawl so it gets cold below the house but it doesn't freeze or else my pipes wouldn't be very happy

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Homebrewsailor t1_jabt8uy wrote

You don’t need to dig below any frost line. Your basement already does that. You’d cut out the floor below your post because you can’t trust the concrete floor. Who knows how thick it is and how well it was done

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Charliefromlost t1_jadfk2u wrote

My crawl space is just a dirt floor and only the foundation wall footings are below frost line. The dirt in the middle isn't dug as deep.

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nsmith0723 t1_jaact74 wrote

The correct way would be to either put in enough joist to support that big of a live load or more likely you should probably just have a beam going crossways below the fireplace with some posts or even a 2x6 wall underneath the fireplace. Ofcourse this isn't ideal if it's a finished basement, that might be right in the middle of a living room, but me personally I would get some wood between that fireplace and the cement floor. Your right to be worried, it's going to be cheaper to fix it now

Edit: you'll probably need to cut out the cement floor and put in some real footings too honestly, god knows what they have for a floor and I bet it doesn't have rebar. Even spread across a long 2x6 wall would be pushing your luck with say a 2000lb+ fireplace. I highly doubt your going to get a joist to hold that with any span over say 10ft

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willxthexthrill OP t1_jaaqmo1 wrote

Here’s some pics. The first one shows under the fireplace from the side. The right hand is the front of the fireplace and you can see an area of concrete or mortar which is the fireplace floor. The red arrow is pointing at the crack.

https://imgur.com/a/Wa3akM8

The second is a close up of the crack.

https://i.imgur.com/5czNq1G.jpg

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nsmith0723 t1_jaay0sz wrote

Jesus, I would get some poll jacks under that asap. Dont try to lift it, just hold it in place. The floor probably won't handle the entire load. I think your going to need some professional help with this one I think. I mean if you really love that fire place I would be tempted to just anchor it in place where it is with 3 6x6s and some nice big wide fat footings. You may also want to consider just getting rid of the fireplace. They cause so many issues, next you'll be redoing the roof because its leaking. But that's not cheap either. Trying to lift those things sketchy, but it's also super sketchy now and it would be all around better if it was entirely vertical again. Hard to say what's best

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justcallmetarzan t1_jac4164 wrote

I second /u/Spinaccio's approach for putting a post in. Or posts - I'm having some trouble envisioning how exactly the fireplace is supported by that (where is the ash pit?)

Another option to explore with an engineer... In our house (1931), I've got full access to the exterior basement wall "top plate" (concrete) and the interior wall top plate. If I had this problem under my fireplace, I would just raise the floor a bit temporarily with a jack and slide in at least two brand new joists. I don't know that you would want to sister these to the old joists, though.

But as for your dip... really depends. I've noticed a lot of uneven spots in my floors, but no damage to the joists underneath. What I suspect is happening is 100 years of uneven wear and settling and compression in the softer wood subfloor. If it moves, you could also have the classic subfloor board that ends just shy of a joist.

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Spinaccio t1_jacco9l wrote

I’m guessing that it’s the hearth in front of the flue that’s the problem. The chimney itself would never sit on a wooden floor.

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justcallmetarzan t1_jadv1r9 wrote

Yeah, I was thinking maybe it was a large hearth that had wings to the side. I don't know that the hearthstone on the floor would cause that sag though.

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ezbake_fpv t1_jaadca3 wrote

I'de go with option #2 or #3.

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ElleRisalo t1_jacv8ou wrote

Steel telepost under the floor to crank it back to place.

Steel plate across the Crack.

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ezbake_fpv t1_jaadql3 wrote

I'de go with option #2 or #3.

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stealthxstar t1_jabryk1 wrote

Did your home inspector not catch it??

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Whatasonofabitch t1_jacjmxy wrote

A home inspector’s only responsibility is to cash your check. Never trust them to find anything.

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beau_loop t1_jadkmgk wrote

I'de go with option #2 or #3.

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