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One corner of my new slab-on-grade garage foundation is 1.375" lower than it should be. My garage door is level, but as a result of the low corner, there's a gap on one side:

garage door

The concrete guy has agreed to pay for whatever reasonable solution is necessary to address this. Here are the things I've ruled out:

  • Mudjacking the whole foundation. I don't want to tweak what is otherwise a level, square, plumb structure.
  • Adding more concrete to this corner. Getting enough in without messing up the drainage may not be possible.
  • Removing some concrete from the other side. This creates other drainage problems (after running downhill about 12", the driveway slopes up and away from the garage).

The door vendor has recommended getting a thicker rubber seal on the bottom of the door. I'm worried that this will be ugly, could skew the door over time (since one side will be compressed more than the other) and may not make up the gap.

What other/better solutions are there?

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    Taper the rubber seal. – Solar Mike Jun 5 '20 at 9:05
  • Wow, you found a good contractor! Sure he screwed up, but he's willing to acknowledge it and accept responsibility for it! Keep him around & give him good recommendations - sadly, that's a rare quality these days. – FreeMan Jun 5 '20 at 17:43
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    Another way to "patch" the door would be to rip a tapered piece of PT wood to match the gap. Paint it well, and sandwich between the bottom seal and the door. – DaveM Jun 5 '20 at 19:22
  • @DaveM I had thought of this, but the profile of the astragal makes it complicated. – LShaver Jun 5 '20 at 19:46
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Trough out the high side of the concrete where the door lands on it.

Get an angle grinder with a diamond blade. Mark the concrete on both sides of the closed door.

Cut 2 straight lines on high side and chisel/ grind away a trough equal in depth to the 1.375” gap.

I used a laser to determine how much material needed to be removed.

On my neighbors house it only required about 14 inches of trough to allow the gasket to make full contact.

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  • That sounds like an ugly, messy, nasty way to spend a hot summer afternoon, but it should do the trick. Just be sure to bevel the edge nicely so there isn't a sharp corner to the trough to drive over. Also, don't leave an actual trough...you don't want water & gunk collecting there, freezing in the winter, etc. – FreeMan Jun 8 '20 at 12:12
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That situation is undesirable not only because of the gap under the door, but also because of the way water will run. Garage floors get wet when they're washed down or when a car is brought in covered in rain, snow, ice, etc. A garage floor should be level side to side and sloped toward the overhead doorway so that water naturally drains to the outdoors.

Is this slab-on-grade construction, or do you truly have a foundation separate from the floor? In the latter case the floor often floats inside the foundation. If it's not doweled into the foundation then you may be able to mudjack the slab only and leave the foundation alone. Talk with a concrete lifting contractor to find out what they're comfortable doing and what outcome they expect.

Adding more concrete to bring up the surface is tricky. Ordinarily one wants aggregate (rocks, gravel, sand) mixed into the concrete to make it stronger -- but you can't get a coarse or even medium aggregate mix to taper down to nothing. You'd probably want some kind of polymer modified self-leveling overlay product for this.

As a last resort: you already have a saw-cut joint in the middle. Cut all the way through and fully replace the concrete on the low side of the room. Depending on the price of the other options this might not be such a bad choice.

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    I think the drawback to the mudjacking that the OP is trying to avoid, is that it will lift all the framing for the rest of the garage at the same time, thus tilting everything else while it squares up the floor. That would require a rebuild of the entire garage structure, not just the floor. (Unless I'm totally missing something - wouldn't be the first time...) – FreeMan Jun 5 '20 at 17:41
  • Yeah, you're missing something. In the foundation construction I'm familiar with we pour a footing and then a foundation. Then backfill. Finally, the floor slab is poured inside the foundation. It runs up against the inner face of the foundation but there's no strong connection between the two. One could, in theory, adjust the slab while leaving the footing and foundation as they are. It would depend on whether the slab edge is willing to slide up the face of the foundation wall -- if not, cut or break a little around the perimeter of the slab to ensure it's free to move independently! – Greg Hill Jun 5 '20 at 18:00
  • Ah, so you're saying jacking the slab would leave the foundation wall and not impact the wood construction. Got it. My garage was foundation & slab all in one pour. (And improperly sloped so that water collects at the far end, away from the roll-up door. :( didn't realize it until way too late) – FreeMan Jun 5 '20 at 18:05
  • Sounds like yours is "slab on grade" or "integral footing" type construction. You're right: there would be no way of adjusting the floor without also adjusting the wall in that scenario. In OP's photos we see the wood sitting on concrete several inches above floor level. It would be difficult to form the concrete that way with slab on grade, so this suggests that his construction might be the "T-shaped" footing/wall/floor style I described. Types of Concrete Foundations – Greg Hill Jun 5 '20 at 19:29
  • It is slab on grade, unfortunately. – LShaver Jun 5 '20 at 19:57

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