less than 4" of porous fill under slab on grade

[jechols]

thanks for responding to last question. same job as unsupported wwf. I have now discovered that the porous fill under the slab is only 2" to 2 1/2" on average and as thin as 1" to 0" is a several locations as well 4" in a few isolated areas. My concern is that this could lead to more cracking. An easy solution is to just decrease control joint spacing or should I insist that the contractor remove the wwf, vapor barrier, gravel and adjust sub-grade to the correct elevation. The second option would delay the job and make everyone generally unhappy. I just don't want to cause this much if the increased risk of cracking is small.

 

[Barbicane]

If the thickness of the slab is changing dramatically, it is going to be hard to get the control joints to agree with where it actually cracks. I assume that this is in a building and it will not experience a lot of freezing conditions during the service life. I also assume that this is not a floor that will have heavy equipment operating on it. If you have vinyl tile floors, expect to see the cracks eventually. With carpet, no one will notice, except if you put in too many wide control joints. This could increase the cost of the carpet installation later. The contractor will probably want a change order for that.

 

[jechols]

it is receiving VCT flooring, but the slab will be of uniform thickness it is the subgrade that varies and the porous fill that fills in the differences

 

[jdonville]

jechols,

In an analagous vein as "the die is cast", the slab is poured. What to do depends on the servicability impacts of extra cracking. Somebody needs to sit down and figure out what the most cost-effective option is - whether it's a new flooring choice to hide the cracking, or whether somebody wants to direct the contractor to redo the work.

Secondarily, whomever was responsible for ensuring that the subgrade was correctly graded may be on the hook for any extra costs (either way) over the original contract cost.

I hope that the aggregate base course was not intended to provide significant underdrainage for the slab, as that function may be impaired.

Good Luck!

Jeff


Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com

 

[jechols]

Thanks for the responses. The solution was to bulkhead off the thin areas and pour some of the slab. The thin areas will then be re-excavated to the proper elevation and then lay down the gravel, vapor barrier and the useless WWF.

Thanks again

 

[jdonville]

jechols,

My apologies, I thought I read that the slab had already been poured. That'll teach me!

Jeff


Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com