Slab on grade crack cause and repair
Slab on grade crack cause and repair
(OP)
Good day,
I recently purchased a house and after removing the carpet i realized there were cracks at every corner of every room.
Some of the cracks sound hollow.
The house is a flat house constructed in 1991 and is approx 1600 sq.ft covered area, sitting on flat (reclaimed) land approx 4100 sq.ft area.
I am wondering:
1. What is the cause of this?
2. What the crack patterns mean?
3. How serious these cracks are?
4. The best method of repair?
Thanks!
I recently purchased a house and after removing the carpet i realized there were cracks at every corner of every room.
Some of the cracks sound hollow.
The house is a flat house constructed in 1991 and is approx 1600 sq.ft covered area, sitting on flat (reclaimed) land approx 4100 sq.ft area.
I am wondering:
1. What is the cause of this?
2. What the crack patterns mean?
3. How serious these cracks are?
4. The best method of repair?
Thanks!





RE: Slab on grade crack cause and repair
RE: Slab on grade crack cause and repair
Reclaimed land... you may be experiencing differential movement with the foundations settling more than the slab...
Are there other homes in the area experiencing the same type of problem?
Dik
RE: Slab on grade crack cause and repair
Lay a straightedge across the cracks. If one side is higher than the other, then the crack is "faulting". This means there is possible movement or displacement of the supporting soils below the slab. There can be many reasons for this, but fill control on reclaimed land is often suspect.
Based on your photo, assuming this is at an outside corner of the slab, it is probably restrained in two directions (by the footing) and is shrinking in its mass of the remainder of the slab (toward the middle of the slab). As for the location of the crack, it could be a thickness anomaly in the slab (thinner at the crack), but not necessarily so.
Since the crack is relatively tight and has been there for 20+ years with no apparent adverse affect, I would either leave it alone or if you are concerned with insect intrusion (termites, ants, etc) then fill the crack with a flowable acrylic or epoxy adhesive. You can use a sealant, but the crack probably wouldn't accept much material.
RE: Slab on grade crack cause and repair
M.S. Structural Engineering
Licensed Structural Engineer and Licensed Professional Engineer (Illinois)
RE: Slab on grade crack cause and repair
Dik
RE: Slab on grade crack cause and repair
The hollow sounds (and the photo shows a relatively isolated single crack only), may indicate a delaminated topping. Chain-drag other non-cracked areas of the slab and determine if they have hollow sounds too.
You need to trim your toe nails too
And wear boots before doing any construction-type work!
RE: Slab on grade crack cause and repair
dik:
A few of the neighbours claimed that they do not have any cracking whatsoever.
Ron:
The crack shown in the picture is in one of the bedrooms. All the other bedrooms all have similar cracks at all four corners.
Ingenuity:
I am uncertain but i believe it was constructed with only BRC re-inforcement if any.
It does seem as though the center of the rooms have sunken a bit because the crack is higher on the corner side.
I have a feeling though, that the cracks have opened a bit recently because when i first inspected the house i did not hear any hollow sounds but only after starting construction and demolishing the entire roof (there was a lot of rainfall some of which could have seeped through) I noticed the hollow sound.
Does this mean there is more cause for concern??
RE: Slab on grade crack cause and repair
If possible where you are located, I think advice by a local structural or geotechnical engineer is warranted.
RE: Slab on grade crack cause and repair
With the hollow sound, that already indicates local settlement to me.
As Hokie said, call in a geotech or structural to ease your concerns (hopefully). :) Good luck.
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com