# cracks in newly poured slab



## [email protected] (Jul 11, 2012)

i recently poured a 8'' thick slab of my new home....the ratio was 1:2:2 designed by my engineer....the temperature was around 33 degree...it was a hot day though. the concrete started at 8 am and ended 5 pm. 

however, i noticed cracks in different areas of the slab...people told me that this is no issue...but i still feel afraid of the cracks......is this really a non issue thing?....help would be appreciated


----------



## mae-ling (Dec 9, 2011)

What size of cracks?
Hairline cracks are probably no big issue


----------



## GBrackins (Apr 26, 2012)

all concrete cracks ..... the extend and size of the cracks is what is important.

According to the Section 2-2-4 of the 4th edition of the "Residential Construction Performance Guidelines for Professional Builders and Remodelers" as published by the National Association of Home Builders (NAHB), "Minor cracks in concrete floor slabs are normal. Cracks exceeding 3/16" in width or 3/16" in vertical displacement are a concern and should be repaired if the slab is in conditioned space or the crack interferes within the installation of finish flooring."

Hope this helps. Good Luck!


----------



## Canarywood1 (May 5, 2012)

[email protected] said:


> i recently poured a 8'' thick slab of my new home....the ratio was 1:2:2 designed by my engineer....the temperature was around 33 degree...it was a hot day though. the concrete started at 8 am and ended 5 pm.
> 
> however, i noticed cracks in different areas of the slab...people told me that this is no issue...but i still feel afraid of the cracks......is this really a non issue thing?....help would be appreciated


 
Don't know where your located,but those temps are pretty cold for this time of year,what was the condition of your grade when the pour was started,how many yards were poured,how was the concrete protected after the pour was completed,and why did it take so long to complete the pour?


----------



## Mort (Nov 26, 2008)

Canarywood1 said:


> Don't know where your located,but those temps are pretty cold for this time of year


I'm guessing he's Canadian, so that would be Celsius, which is pretty warm.

If it took that long, I would say there's probably a cold joint in there somewhere. How big is the slab, and are there control joints in it? Concrete is going to crack, it is a fact of life. The control joints just tell it where to crack.


----------



## [email protected] (Jul 11, 2012)

the weather was pretty warm. the concrete took that long because we poured it with mixture machine...the total area was 400 square yards.

those cracks are like boxes in shape..looke like as they are on steel....i mean...not long and straight cracks..but not that much wide...a matchstick cannot enter in it. 

however,my engineer told me that i used lots of water in it in hot weather...thats why those cracks shown up...but that is not an issue.


----------



## concretemasonry (Oct 10, 2006)

Since there was little information supplied, I assume the location referred to degrees C since 33 F would not exist for recent periods.

A slab of unknown size and 8" thick that took than long to place and finish was probably a locally site mixed concrete (instead of ready-mix) based on individual batch proportions of variable quality/properties and subjected to unknown curing conditions, it is not surprising there are some cracks showing in a short period of time after finishing/placement.

Based on the information, I assume the cracks seen are due to curing problems dues to temperatures and unknown curing are superficial and hopefully, there will not be other more severe to the structure. hopefully, it will not develop into more severe problems for the entire foundation of a costly home.

The excess of water will ultimately result in lower strengths and more cracks in the future.

Dick


----------



## Canarywood1 (May 5, 2012)

[email protected] said:


> the weather was pretty warm. the concrete took that long because we poured it with mixture machine...the total area was 400 square yards.
> 
> those cracks are like boxes in shape..looke like as they are on steel....i mean...not long and straight cracks..but not that much wide...a matchstick cannot enter in it.
> 
> however,my engineer told me that i used lots of water in it in hot weather...thats why those cracks shown up...but that is not an issue.


"those cracks are like boxes in shape..looke like as they are on steel."

Sounds like bleed water dried on the surface,not a problem because it will br covered.

Just curious as to why you mixed that large an amount of concrete,rather than use redi-mix,had to be around 88-90 yards,and did you use bag cement??


----------



## Mort (Nov 26, 2008)

I got 44.4 yards, and that is entirely too much to mix by hand and expect a good result. That's readymix trucks, I can't imagine loading all those bags into a mixer.


----------



## [email protected] (Jul 11, 2012)

i have had an bad experience with ready mix....i poured my retaining wall and got lots of honey comb .

however, i m posting pictures of the cracks ..they would not tell you the exact size and idea ..but it will be a big help though.....have a look at them please.


----------



## [email protected] (Jul 11, 2012)

Shot at 2012-07-13









Shot at 2012-07-13









Shot at 2012-07-13









Shot at 2012-07-13


----------



## [email protected] (Jul 11, 2012)

note. these pictures are from different area of slab. and only from surface level. its been three days now since we poured the slab.


----------



## GBrackins (Apr 26, 2012)

did you use a mechanical vibrator on the retaining wall pour?


----------



## Canarywood1 (May 5, 2012)

[email protected] said:


> i have had an bad experience with ready mix....i poured my retaining wall and got lots of honey comb .
> 
> however, i m posting pictures of the cracks ..they would not tell you the exact size and idea ..but it will be a big help though.....have a look at them please.




No that's not what I thought it was,but those pics are pretty close up,any chance you can post pics so we can see the slab from a normal distance??


----------



## jomama45 (Nov 13, 2008)

Looks like plastic shrinkage cracking to me........

http://nrmca.org/aboutconcrete/cips/05p.pdf


----------



## concretemasonry (Oct 10, 2006)

The problem is with a slab and not a retaining wall.

Too much water in the mix (high slump ordered) or water added to make placement easier will reduce the concrete strength and make placement easier with the result of excess water on the surface and the lower concrete to settle and pull away from the bars and cause cracks, shrinkage and and lower durability. Big slabs have a problem of overcoming the labor and experience available, especially with higher air temperatures.

Dick


----------



## [email protected] (Jul 11, 2012)

GBrackins said:


> did you use a mechanical vibrator on the retaining wall pour?


i used the vibrator in slab yes....those pics are of my ground floor slab...not retaining wall.


----------



## [email protected] (Jul 11, 2012)

Canarywood1 said:


> No that's not what I thought it was,but those pics are pretty close up,any chance you can post pics so we can see the slab from a normal distance??


okay,its difficult but i will try.

but as you guys have got the idea now....other guy says its look like plastic shrinkage...and he has given the link for this...i saw the picture on that link and it was almost the same crack which i have developed in my slab....so i think its plastic shrinkage.

what you guys suggest?...continue my construction or should take care of these cracks if they are realy a problem?


----------



## [email protected] (Jul 11, 2012)

tell me how long should i cure (with water) this slab?


----------



## GBrackins (Apr 26, 2012)

[email protected] said:


> i used the vibrator in slab yes....those pics are of my ground floor slab...not retaining wall.


No I was asking because you mentioned honeycomb in the retaining wall. It has been my experience that honeycomb is caused by air pockets/voids in the concrete.


----------



## Mort (Nov 26, 2008)

NRMCA says they aren't a problem, and shouldn't impair the structure, so unless you hate the look, I'd leave them. Usually you wet cure for 7 days. But if this is plastic shrinkage, it sounds like we were right in that it was too hot and the placement took too long.


----------

