repair garage slab

[mdhills]

What should we be looking for in a contractor to repair our garage slab?

Our 1950's house has some pretty big cracks in the garage slab, with some resulting unevenness and one section able to shift slightly.
I don't know the original cause of this -- whether settling from when it was first poured or maybe helped along with one of the earthquakes we get occasionally.
The garage walls are built directly on the slab.

Thanks,
Matt

[MT Woodworker]

If it where me, find a very good concrete worker, that is good in flat work, completely tear out the old stuff and lay a new slab.

[mdhills]

If it where me, find a very good concrete worker, that is good in flat work, completely tear out the old stuff and lay a new slab.

I'm thinking about something like that;  is it feasible to do with the wall sill plate resting on the outer edge of the slab?  (i.e., can  you cut out the majority and replace?)

[Roly]

I'm thinking about something like that;  is it feasible to do with the wall sill plate resting on the outer edge of the slab?  (i.e., can  you cut out the majority and replace?)

You may also look at mud jacking which will raise the sections level.  Not sure how either options work when the wall is on top of the floor.  Is there a footing under the slab around the outside ? If so maybe the wall could be supported from it.  Roly

[srv52761]

My last shop was a 24x24 slab on grade construction, near the bottom of a slope, on loam type soil.   Soil would just soak up water.
  Freeze / thaw cycle was a problem.  Slab cracked down the middle both length-wise and width-wise, forming four almost uniform  rectangles.  
  Tried patching it,  it cracked again next winter. As time went by the subtended rectangles moved independent of each other creating a ridge about an inch to an inch and a half difference in height. This made moving my tools problematic.

Knew I couldn't control the ground/soil problem, so I cut the crack out with a diamond blade, making about a 14" trough between the rectangles.  Found no rebar or mesh.
  Put in treated lumber sleepers in the trough, sand between the sleepers, then covered that with 3/4" treated ply to grade and even with the differing edges.  That gave me a 14" wide transition from rectangle to rectangle.  Made moving tools easy.

If your ground is not stable, any fix may be temporary.  My soil continued to move.  About ten year ago another ridge started to become apparent between one rectangle and the rest of the floor.  But, I was able to unscrew the ply, adjust the sleeper and all was good again.  It was still pretty good when I moved a few years ago.

[mdhills]

My last shop was a 24x24 slab on grade construction, near the bottom of a slope, on loam type soil.   Soil would just soak up water.
  Freeze / thaw cycle was a problem.  Slab cracked down the middle both length-wise and width-wise, forming four almost uniform  rectangles.  
  Tried patching it,  it cracked again next winter. As time went by the subtended rectangles moved independent of each other creating a ridge about an inch to an inch and a half difference in height. This made moving my tools problematic.

Knew I couldn't control the ground/soil problem, so I cut the crack out with a diamond blade, making about a 14" trough between the rectangles.  Found no rebar or mesh.
  Put in treated lumber sleepers in the trough, sand between the sleepers, then covered that with 3/4" treated ply to grade and even with the differing edges.  That gave me a 14" wide transition from rectangle to rectangle.  Made moving tools easy.

If your ground is not stable, any fix may be temporary.  My soil continued to move.  About ten year ago another ridge started to become apparent between one rectangle and the rest of the floor.  But, I was able to unscrew the ply, adjust the sleeper and all was good again.  It was still pretty good when I moved a few years ago.

Thanks for the suggestion; I may end up pursuing something like that.
We don't get much frost here in sf bay area, so I'd think any soil movement would have been early-on (or maybe the '89 earthquake);.
I'm pretty sure there is no rebar or other reinforcement in the slab, so I was wondering if it is viable to cut out a majority and replace with reinforcement and tie in to the original (?)

As you say, moving tools across the gaps/steps isn't great.

Matt

[carpenter wisdom]

What should we be looking for in a contractor to repair our garage slab?

Our 1950's house has some pretty big cracks in the garage slab, with some resulting unevenness and one section able to shift slightly.
I don't know the original cause of this -- whether settling from when it was first poured or maybe helped along with one of the earthquakes we get occasionally.
The garage walls are built directly on the slab.

Thanks,
Matt

You may be able to find a concrete floor contractor that specializes in crack repair. 
It all depends on how far you want to take it. If you want to break out the existing floor and start over it will require lifting the building and suspending it while the work is done.

[Willyou]

As Carpenter Wisdom said, a correct fix may require lifting the garage and pouring a new slab including under the walls. Could be quite expensive and doing less may not last and you will have wasted your money. If the slab cracks do not extend under the walls (can you see the cracks along the outside edge under the walls?) you may be able to have the interior of the slab removed by cutting it parallel to and as close as possible to the walls. If you do this, make sure the subsoil is dug out and replaced with a filter fabric and a thick layer (8" or more) of coarse gravel before pouring the new slab. An alternative might be to remove the slab and replace it with gravel only. If you are still use the structure as a garage, the gravel should work fine and future shifting shouldn't be a problem.

[mound]

What should we be looking for in a contractor to repair our garage slab?

Our 1950's house has some pretty big cracks in the garage slab, with some resulting unevenness and one section able to shift slightly.
I don't know the original cause of this -- whether settling from when it was first poured or maybe helped along with one of the earthquakes we get occasionally.
The garage walls are built directly on the slab.

Thanks,
Matt

I just moved into a house built in 1963, original garage slab was very beat up - cracks, depressions, rebar sticking through, water coming up during heavy rain.. not suitable for a shop! Before we moved in I had a concrete guy come in and bust out the entire thing, then pour a new 6" slab. (he crushed up much of the waste and incorporated that into the gravel bed below.)  He got the whole job done in about 4 days, 24' square (2 car) garage for $5k.

The walls though weren't on the slab, not sure how much harder that makes things.

[fixtureman]

2 years ago I had my garage floor replaced they crushed the old slab and used a lot of it for fill then new stone to level and then they poured it along with my side walk 2 days and $7000