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digexpressions 12-10-2007 01:57 PM

Cracks in concrete slab
I will be installing new flooring in the first floor of my house and noticed that there are long cracks in the concrete slab foundation. What is recommended for treating this before the new floor is installed?


KUIPORNG 12-10-2007 02:38 PM

cracks are normal in concrete as long as the gap is not too thick and no leak.... I mean real thick.... to help psycologoically, you can apply those concrete filler... I doubt it really help anything physically besides your psycological comfort factor, this thing is at least better than those grout filler for tiling as at least you can visually see them filling up the gap... those grout filler, you can neither see them, feel them or taste them....

concretemasonry 12-10-2007 03:52 PM

Is this new or old concrete?

You should determine if the cracks are old (stable) or new (active and moving).

Probably not a big problem, but you should know before you cover them up.

so-elitecrete 12-10-2007 04:05 PM

cracks aren't 'normal',,, rather they're an indication someone didn't do the job properly,,, if inside, you're probably ok as there isn't much of a swing in temp which would change the dimensions of the conc,,, just be sure your flooring can 'bridge' the crk & not reflect it,,, h/dlowe'sacehdwe carries patching acrylic-modified mtls which work well for the avg. h/o

concretemasonry 12-10-2007 04:28 PM

Cracks are normal - it just depends on the size, pattern, displacement and activity. You can have some small shrinkage cracks that are of no consequence even if things were done right.

You may have a structural problem, so make sure you know what you have before you patch unless this is a "flip".

so-elitecrete 12-10-2007 04:36 PM

its not unusual to find
cracks in conc but, again, its not 'normal',,, if they were, i wouldn't have made a good living for 10 years repairing conc & cutting green conc so there wouldn't be ANY random cracking.

again, not unusual but not 'normal'

concretemasonry 12-10-2007 04:54 PM

I have looked at and been involved for over 40 years and concrete cracks are are normal, but not necessarily bad.

Anybody that can pour concrete and not have any cracks is better than 99.99% of the real contractors using normal materials and semi-exotic materials at reasonable prices and scheduling.

You can make a good living, but the concrete still cracks. The trick is for the owner to be satisfied enough, avoid structural problems and to not cause too big a dent in the reserves.

so-elitecrete 12-10-2007 05:16 PM

residential & commercial owners,,,
are much more forgiving than the feds &/or state dot's,,, our work involved std conc paving mix's which're more difficult to place & finish.

from my 6yrs exp here in ga (h-gwy, airport, residential, & commercial), nothing's changed,,, the primary reason conc cracks uncontrollably's poor joint patterns &/or not sawing control jnts at the proper time,,, granted, this may involve early cutting or staying thru the nite,,, we still place conc & guarantee it not to crk as a result of our methods/techniques.

i won't disagree w/your comments, either.

joasis 12-10-2007 05:51 PM

Just curious, but what do you suppose happens in the control joint you cut? I pour a lot of concrete, and we have several large floors that have never cracked, but that is the exception. The very nature of concrete, and this information can be found in every reference, will tell you that concrete will crack, not if, but when, and "controlling" the cracks will always be the issue, especially in flatwork.

If you have 6 years, and have great results, I applaud you. You must get a perfect mix every time. Between concretemasonry and myself, we probably have close to 65 years experience, and I haven't seen anyone get the results you are saying you get consistently.

so-elitecrete 12-10-2007 07:59 PM

isn't that why we call 'em 'control jnts ' ?,,, so the crk'll be where WE want it ?,,, even in 100k sf flatwork laser-screed plac'd, no random cracking,,, yes, conc's subject to great tensile & flexural force,,, that's why we have dedicated labor just for sawing,,, yes, it'll always be the issue 'cause that 1 random crack ruins everything.

we've dump'd 2k cy a day & its not always that 'perfect mix' every time, even j-mix or 1" slump from our own plant,,, so 'tween the 3 of us, make it something like 100 yrs,,, still learning, too, but its not uncommon in our field,,, & every pour's different,,, only 6yrs down south, btw,,, the rest was in the ne & middle atlantic states.

Bondo 12-10-2007 08:50 PM


Cracks in a Home Floor are pretty Normal..........

Or maybe it's Natural...............:whistling2:

so-elitecrete 12-11-2007 06:05 AM

this is getting,,,
tedious, i agree :thumbsup:

Zero Punch 12-11-2007 09:28 AM

OK, we have heard the experts on concrete but was the question answered?

As a flooring installer, not an expert just 39 years experience, fill all cracks, voids or depressions with a cementious floor patch like ARDEX feather or similar. Sand flush when dry.

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