sandy spots on new concrete


  #1  
Old 01-06-12, 02:18 PM
D
Member
Thread Starter
Join Date: Jan 2012
Location: usa
Posts: 27
Upvotes: 0
Received 0 Upvotes on 0 Posts
sandy spots on new concrete

This is probably nothing but my imagination but my newly poured concrete basement floor has a few dark patches maybe say 1 foot square that seem kinda sandy. so most of the floor is hard and dry a few patches are gritty so I sweep off the grit or sand and it seems to get more sand but just in a few spots maybe 5 x 1 foot areas.

could there be a problem with the concrete or is it just curing

Happy to try to give more details if it helps
 
  #2  
Old 01-06-12, 07:29 PM
B
Member
Join Date: Feb 2006
Location: Michigan
Posts: 353
Upvotes: 0
Received 0 Upvotes on 0 Posts
There is always a chance you got a bad load but not likely now days if you used a reputable redi mix company. Did you have any freezing weather or get water from a hose or rain directed at these sandy areas when it was still plastic? Any chance the aggregate was frozen when they batched out the load?

When you sweep it does sand actually come loose to the extent you could sweep the sand in a dust pan?

bs5
 
  #3  
Old 01-06-12, 07:48 PM
D
Member
Thread Starter
Join Date: Jan 2012
Location: usa
Posts: 27
Upvotes: 0
Received 0 Upvotes on 0 Posts
its inside a basement so no freezing. I assume it was a reputable dealer I dont deal in concrete much but everything else the concrete company provided was very professional

It is enough to sweep into a dust pan. its not exactly a beach but I was expecting a hard surface

and like I said its only spots not the entire floor maybe 6 spots that no matter how much I sweep are still sandy
 
  #4  
Old 01-07-12, 03:59 AM
P
Member
Join Date: Feb 2005
Location: USA
Posts: 1,306
Upvotes: 0
Received 0 Upvotes on 0 Posts
Did they use kerosene heaters to heat the space as they were finishing it? Sometimes the CO2 fumes from such heaters can cause the surface to "dust" and become sandy.
However, since it seems to be only in spots, my first guess would be that they either poured atop puddles of water, or that water was otherwise introduced to those spots during or just after finishing. This could even be from overhead drips. At any rate, the extra water would create a high water to cement ratio in those spots, leading to weak paste which might be sandy.
How old is the slab and why did you feel the need to sweep it already? How soon after finishing did you sweep it?

Steve VandeWater
 

Last edited by Gunguy45; 01-07-12 at 06:41 AM. Reason: Removed Possible Advertising
  #5  
Old 01-07-12, 05:50 AM
D
Member
Thread Starter
Join Date: Jan 2012
Location: usa
Posts: 27
Upvotes: 0
Received 0 Upvotes on 0 Posts
the slab is 3 weeks old now, it was dusty (not sandy just fine dust) and my cats feet were getting the dust everywhere so I swept and vacuumed it. The slab had gravel then a moisture barrier put down then more gravel so there should have been no water under it. We have spilled some water on it but only after 1 week. for 1 week we stayed off it 100%.

I will add a link with a picture today after I get some coffee the input has been very helpful this is a great site.
 
  #6  
Old 01-07-12, 11:40 AM
P
Member
Join Date: Feb 2005
Location: USA
Posts: 1,306
Upvotes: 0
Received 0 Upvotes on 0 Posts
It sure sounds like "dusting" to me. However, I'm trying to wrap my head around the idea of how your basement was only poured 3 weeks ago and you're already living there.
Were you living in the house with a dirt floor basement, which was then poured in concrete 3 weeks ago? If so, I doubt they would use kerosene or fuel oil heaters to heat it because the fumes would have gone upstairs to where you were living.
Please give more details.

Steve VandeWater
 
  #7  
Old 01-07-12, 02:36 PM
D
Member
Thread Starter
Join Date: Jan 2012
Location: usa
Posts: 27
Upvotes: 0
Received 0 Upvotes on 0 Posts
ahh sorry this is a house built in 1964 my basement was gutted and because of improper foundation prep durring original construction my concrete slab had settled uneven by about 3 inches. I could not refinish the basement with it that bad so I tore it up all 50 x30 feet of it and had it repoured and french drains installed. WE also live in a wet area so the chance to do it right even though it was a fortune was well worth it.

Its a split level house (raised ranch) so we had full facilities on the main level.
 
  #8  
Old 01-07-12, 03:34 PM
D
Member
Thread Starter
Join Date: Jan 2012
Location: usa
Posts: 27
Upvotes: 0
Received 0 Upvotes on 0 Posts
I think this link to a pic should work

https://picasaweb.google.com/1142926...36759813549570

Its tough to photo but thats the worst spot thats about 2 foot by 3 foot section out of 1000 + sq feet
 
  #9  
Old 01-07-12, 08:13 PM
B
Member
Join Date: Feb 2006
Location: Michigan
Posts: 353
Upvotes: 0
Received 0 Upvotes on 0 Posts
That is kind of hard to make out. You might not want to do this but I'm wondering what would happen if you were to attempt to scratch that patch with a nail. If the floor has the intergity at this point that it should have it should resist a light attempt to scratch.

bs5
 
  #10  
Old 01-08-12, 03:19 AM
D
Member
Thread Starter
Join Date: Jan 2012
Location: usa
Posts: 27
Upvotes: 0
Received 0 Upvotes on 0 Posts
so unfortunately it scratches easy. my next questions is could it be a surface issue that can be sealed or hardened or does it mean the entire load might have been bad? any way to tell without a core
 
  #11  
Old 01-08-12, 05:05 AM
M
Forum Topic Moderator
Join Date: Mar 2005
Location: USA - N.E.Tn
Posts: 45,783
Received 871 Upvotes on 762 Posts
Have you discussed any of this with your concrete contractor? or did you pour and finish it yourself?
 
  #12  
Old 01-08-12, 05:53 AM
B
Member
Join Date: Feb 2006
Location: Michigan
Posts: 353
Upvotes: 0
Received 0 Upvotes on 0 Posts
I hate to be the first one to arrive at the following concluion and certainly hope I'm wrong. I don't see any surface treatment available or in existence that is going to be capable of hardening or sealing those spots on your new floor. If the damage was not the result of cooking the surface, water erosion, over trowel at an early stage or even freezeing then you must be left with the posibility of a botched load. If it's a bad batch (insufficient portland amounts) it will not get any better but over the years will continue to chalk and even wear.

Don't take my word for it. I'm a long ways away and have nothing to look at but a picture. If if you have more than one sub par spot as you seem to telling us you do it is probably logical to assume the whole batch might be bad.

Start by asking your contractor for an explanation maybe it can be resurfaced with a thin layer or. Iif the contractor fails to be responsive I would ask the redimix company to send out somebody. You deserve some answers. I hope you can arrive at a substantive cause from somebody on the scene not just a naysayer like me.

Please keep us up to date on this dilemma.

bs5
 
  #13  
Old 01-08-12, 06:19 AM
P
Member
Join Date: Feb 2005
Location: USA
Posts: 1,306
Upvotes: 0
Received 0 Upvotes on 0 Posts
There are liquid densifiers that claim to correct dusting. It's usually just a surface issue and the integrity of the concrete is fine. Find out what ready-mix company delivered the load and have their QC guys (not just a salesman) come out to look at it, along with the finishing contractor. Ask the ready mix company for a copy of the batch ticket to see if excessive water was added. Ask the contractor if his guys used water as a finishing aid. Too much water in the mix or troweled on top of it can cause dusting as well. If the heaters aren't to blame, that would be my next guess.
 
  #14  
Old 01-08-12, 07:30 AM
B
Member
Join Date: Feb 2006
Location: Michigan
Posts: 353
Upvotes: 0
Received 0 Upvotes on 0 Posts
You could be right Pecos. The indicator that is most worrisome to me is the scratch test. Too bad we can't try that ourselves. if the inspector from the supplier is honest and objective that will help the OP and be a good source of information for him.
bs5
 
  #15  
Old 01-08-12, 08:32 AM
D
Member
Thread Starter
Join Date: Jan 2012
Location: usa
Posts: 27
Upvotes: 0
Received 0 Upvotes on 0 Posts
Sad news as this cost us allot of money I have to hope now the contractor is a stand up guy and fixes this problem for us. I still have some hope its surface dusting and can be be corrected without tearing it all back out. im not sure the ready mix company they used but the contractor to this point has been great hopefully that continunes through a potential issue.

in an attempt to stay positive are there degrees to a bad load. is it possible the surface cement is weak and can be cut and repaired similar to if we were going to have it polished. This is not load bearing in anyway but needs to be structurally sound
 
  #16  
Old 01-08-12, 10:23 AM
P
Member
Join Date: Feb 2005
Location: USA
Posts: 1,306
Upvotes: 0
Received 0 Upvotes on 0 Posts
If it's a bad load, it's bad all the way through. However, I think that's a long shot. Almost every problem I've seen has to do with contractor error. In my 20+ years of contracting/finishing, I've gotten exactly 1 bad load (too much flyash), and that one would have been okay over time. One of the most common errors with concrete is adding too much water. This can be done in several ways:
1) In the case of basements with limited access for pouring, the finishing contractor often tells the mixer driver to add water to the truck to wet it up. The concrete is often poured excessively wet to make it easier to rake around. Are there any cracks in your new concrete? If so, how wide are they? If they are wider than a hairline, it means that a lot of shrinkage has occurred and the concrete may have been poured too wet.
2) The finishers can get bored waiting for the concrete to set up enough to begin finishing operations. Often, they begin trowelling while there's still bleed water on the surface, which re-wets the paste on top. This creates a high water to cement ratio which weakens the surface, making it more prone to dusting. This is usually just a surface issue and the rest of the depth of the concrete is fine.
3) The concrete begins setting up faster than the contractor can finish it. He sprinkles water on the slab to make it easier to trowel. This does the same thing as trowelling bleed water back into the slab (creates high water to cement ratio).
None of these 3 scenarios constitutes a bad load of concrete. All 3 were caused by the contractor. If the truck showed up excessively wet before the finishers added water, then it could be considered a bad load.
That's where the batch ticket comes in. It contains all the info one would need to figure out the problem. At my company (I work for a ready mix company now), our drivers are instructed to document any water that was added to the load in transit or while on site. I'm sure other companies do the same thing.
I'm not saying that any of these things happened on your job. Just giving you some likely scenarios as I see them. Meet the contractor and ready mix company, get the batch ticket and let us know the results.
 
  #17  
Old 01-09-12, 03:56 AM
P
Member
Join Date: Feb 2005
Location: USA
Posts: 1,306
Upvotes: 0
Received 0 Upvotes on 0 Posts
I just thought of something else. If the contractor finished the slab with a power trowel, the carbon monoxide could have come from the exhaust. Particularly if the basement wasn't well-ventilated.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description: