slab cracks

[Jim Robinson]

There were some large cracks visible in the interior slab. The house is not finished, so the majority of the interior slabs are visible.

We were trying to figure out what might have caused this to crack this bad. Number one bet would be poor compaction. Out soil is pretty stable here, but they may have over dug and not compacted the back fill enough. A little is not unusual, but there were pretty big cracks.

One question we had was if the concrete froze after pouring, would that cause this? I haven't been able to tell when it was poured yet, but we're working on it. It was in most of the rooms, not just in one area.

This place was a doozy. Second question. The builder told my client that he treated the cracks with something to make sure that the tiles didn't crack later if the crack widened. I've never seen anything like this used, but it looks more like purple paint than anything else. I don't see how it would make any difference.

[Jerry Peck]

Looks like bonding agent, just the opposite of what you would want to do over a crack.

Those LARGE cracks, all over like that, make me this the footing soil, not the slab soil, was not fully compacted as you are thinking. Pour the slab, build the walls, put the roof on ... all that wall and roof load now go down to the footing all around perimeter, compacting the soil under the footing ... and with NO LOAD on the middle of the slab, the middle of the slab stays put, with the edges being forced downward, it all cracks just like you are looking at.

From the sizes of the cracks I'm guess that all of the cracks are 'V' shaped, wider at the floor surface and narrower deep down in the cracks. Like if you were to take a just baked square cake and set it down over an upside down cup saucer in the middle of the cake - the cake will break apart as the outer edges drop down and the center stays up on the saucer.

Now the other question is, did the builder use WWM in the slab or fiber reinforced concrete? If he used WWM there is at least some reinforcement in the slab to somewhat keep it together, if fiber reinforced concrete, you are simply SOL.

[John Arnold]

...The builder told my client that he treated the cracks with something to make sure that the tiles didn't crack later if the crack widened. I've never seen anything like this used, but it looks more like purple paint than anything else....

Did this builder happen to mention anything about the Concrete Fairy around this time?

[wayne soper]

Now think about all the slab construction homes you've inspected and wonder if all the slabs you never saw because they were under wall to wall carpet look just like that:eek:
3 out of 10 would be my quess.
Condition of slab undetermined due to floor coverings. Whew!

[Joseph C. Miller]

My guess would be that red stuff on the floor is Custom Building Products RedGard Waterproofing and Crack Prevention Membrane which is supposed to be used over minor surface cracks. Those cracks appear to be far beyond the capabilities of this product.

Custom Building Products :: Architects & Specification Writers :: RedGard(R) (http://www.custombuildingproducts.com/ProductCatalog/SurfacePrep/WaterproofingAntiFractureMembranes/RedGard.aspx)