Is this my OCD....again

[cvcman]

Ok floor is poured, and cut and sealed...looks nice,,,so far
Now question is this...if you knock on the floor with your knuckle it sounds solid,,,except next to the outside wall around the perimeter...it sounds like an echo or hollow under it...
Now the only thing I can figure is the concrete is poured right up against the 2x8 splash board and the metal siding is screwed to that so is it an echo ?
I cant imagine it can be hollow under the slab...I mean they compacted the pad...it was well settled and they added a inch or more of crusher and compacted that then poured over poly and wire mesh with fiber in the mix...
So am I a wack job ? HEY don't answer that...
Just seems weird...

 

[Old Man Roger]

Why were you knocking on the floor?

 

[ConCretin]

Why were you knocking on the floor?

I had the same thought until I realized it's probably something I'd do for no apparent reason.

Not sure how big your slab is or how it was cured. It's possible you have a little slab curling. If the top of a slab dries more than the bottom, it can create tension that lifts the slab, usually at the corners. If that's the case, it will probably settle back down as it dries out.

 

[cvcman]

Why were you knocking on the floor?

I thought I told you...im a wacko OCD

I dropped a pc of 2x4 on it,,,that started my quest...it just sounds hollow, I cant really see a way it could be so I ASSume its due to the concrete poured up against the splash board and the metal screwed to that..

Just want to be sure im not missing something,,,besides a few brain cells

 

[Old Man Roger]

l o l

 

[AA/FC]

If it sounds hollow, it's probably hollow..... and unless you saw-cut that section out to inspect it you'll probably never know for sure. I'm as OCD as anyone can be but if I was in your shoes, I'd forget about it until if/when it cracks. Nothing you can do about it now anyway, unless you cut that section out. But then again, your OCD will hate looking at the saw cut and patch job. Either way it *****.

Forget about it....

 

[cvcman]

I just don't understand how it could be hollow,the slab is 28 x40 and it's one day old... it was compacted the day before it was poured and many times before that

 

[alwaysFlOoReD]

The knocking sound traveled up your arm to your head.....? /jk

 

[Old Man Roger]

I had a concrete driveway, it had a hollow sound when you rolled a floor jack over it. I just assumed water washed out some sand, or red ants?

 

[mygarageone]

I had that same issue , what I had was an air space under the concrete . About a foot in dia.
Tapped with a hammer and it broke up , 1/4 “ deep. Mine was 4 ft from the wall and every time I roll something over it , I could hear the hollow sound.
Did a surface patch , took care of it.

 

[cvcman]

This is right next to the wall like an inch and I hear the same sound in many places around the perimeter so I just thought it may be because it's resonating off the wall ?? They went over this so many times both by hand screeed and power I don't see how it could be a pocket
I'll probably let the slab cure and see,, if something happens they should come back and fix it right ??

 

[cvcman]

The knocking sound traveled up your arm to your head.....? /jk

Highly possible

 

[cvcman]

I had a concrete driveway, it had a hollow sound when you rolled a floor jack over it. I just assumed water washed out some sand, or red ants?

And did it break up ??

 

[Old Man Roger]

And did it break up ??

34 years not a crack.

 

[stm317]

Is there foam insulation under the slab around the perimeter?

 

[cvcman]

Is there foam insulation under the slab around the perimeter?

Nope...the entire pad is bank run gravel,,,it was compacted in 10" lifts,,,sat for 5 months before building, rain snow etc...then the building went up, recompacted, 2" crusher put down to level, compacted, poly down, wire mesh, and ultra fibre in the mix...

It is now cut once up the middle and twice across the width...its 28 x 40

 

[66Caprice]

Maybe it's not fully cured?

 

[cvcman]

Maybe it's not fully cured?

Oh im sure it isn't but the rest of the floor doesn't do this ??
He called me this afternoon to get paid and met me over there, I showed him,,,he kinda shrugged and said " well it isn't hollow I can tell you that, but maybe because against the wall didn't get compacted as much because you cant get right up to it with the machine and the poles etc"

I said if it crack off and caves in will you fix it..he said "yup but it wont"

I gotta go to the Dr now becaue my knuckles are raw and bleeding

 

[tapered-pin]

 

[cvcman]

So,,, you are saying there is delamination ?? Even though the slab is one day old ?? And if so what will happen ?
There are a LOT of people on this forum that DO have real knowledge

 

[ConCretin]

I assume tapered-pin is suggesting with his illustration that you have some de-lamination and that it is the cause of the hollow sound you are hearing. De-lamination occurs during finishing so the age of the floor isn't a factor. So while it's possible, I think it is pretty unlikely.

Delaminated concrete is usually quite thin. It's more likely to break loose when you hit it than it is to create a hollow sound. You can detect de-laminated concrete by dragging a chain across it but all you'll hear is a change in tone not a hollow thunk.

I also tend to doubt your sub grade has settled since you placed concrete on it. You may just be hearing a different sound because it's near the edge or you may have some curling. In any case, try to rein in the OCD and stop worrying about it until something bad happens.

 

[cvcman]

Thank you, that sounds like good advise, the good thing is it's right next to the wall anyway so it won't see any traffic and probably not even foot traffic

 

[Augus7us]

I have OCD also. As others have said; take the lesser of two OCD evils. If you mess with it in any way and don't find or fix something, I think that would be worse than ignoring it.

I found tapered-pin's image on the net and the article associated with it is quite detailed. It may have solved your problem, if you want to pursue a non-intrusive method of diagnosing the issue.

Look at the ultrasonic inspection section. I quoted the easy part for you below.

http://www.theconcreteportal.com/nde.html

The wave velocities for the main waves are dependent on the stiffness and density of the material. The velocity of compressional waves, Vc α (E/ρ)0.5, while the velocity of the shear waves, Vs α (G/ρ)0.5, where E is Young’s modulus of elasticity, and G is shear modulus or modulus of rigidity. Vs is 0.5 – 0.6 times Vc, while the velocity of surface waves Vr is 90% of Vs.

When sound waves travel from one medium to another, a part of the energy gets reflected and the other part gets transmitted. The amount of reflection and transmittance depends on the acoustic impedance of the media.

Acoustic impedance, Z = ρV, where ρ is the density of the material, and V is the wave velocity. Z values for some typical materials are shown in Table 2. If the acoustic impedances of the media are known, then:

% transmitted energy Et = 4Z1Z2/(Z1+ Z2)2, and

% reflected energy Er = (Z1-Z2)2/(Z1+Z2)2.

I mean who doesn't know about Young's modulus of elasticity, looks like child's play to me.

-Clint

 

[lakeroadster]

Relax, put away the 2x4 and hammer (in their designated locations) and walk away from the slab.

Have a nice refreshing adult beverage and enjoy the fact that the slab is poured and soon you can use the building for it's intended purposes.

And watch this:

 

[cvcman]

Relax, put away the 2x4 and hammer (in their designated locations) and walk away from the slab.

Have a nice refreshing adult beverage and enjoy the fact that the slab is poured and soon you can use the building for it's intended purposes.

And watch this:

Agree...the guy that poured it has a great reputation and they seems VERY neat and fussy...my only fear was it caving in or falling apart...
Again its so close to the wall it wont see any traffic...
im sure IF something happens w/I a year he will make it right..
The whole job cost me 3600.00 with the mesh and fibre in the mix and poly and cut and sealed...
Not sure if its a good price but its done ...
Thx guys

 

[like2wheel]

Did you seal it? Cover it?
I think llwillysfan gave you the answer in post # 3
Especially since you used a vapor barrier

 

[NUTTSGT]

Your contractor wasn't working any late nights was he ? Like without the aid of lighting and in the dark so nobody would see him ? Does he run an under the table body disposal business ?

 

[JohnnyK81]

I think there is some great confusion about what OCD is in this forum.

 

[cvcman]

Your contractor wasn't working any late nights was he ? Like without the aid of lighting and in the dark so nobody would see him ? Does he run an under the table body disposal business ?

Hey ! I already told the police, my wife is overseas on a 5 year vacation...she will be back she is not missing !!!

 

[crankshaftdan II]

Hey ! I already told the police, my wife is overseas on a 5 year vacation...she will be back she is not missing !!!

Call the same cops back and see if they have radar/sonar equipment like they use for underwater submarine detection and tell them you forgot where the wife went-but check the floor in the garage with the "New concrete Job"-might be the clue they need to find her!!

"Don't Worry Be Happi Man"

 

[jd_1138]

I don't think it could be hollow. It's probably some acoustical **** going on with the building's walls.

I wouldn't worry about it.

 

[cvcman]

Yea that's what I thought too, that and it was hard to get that big compactor close to the wall so maybe that area wasn't compacted as well

 

[TerryH]

Yea that's what I thought too, that and it was hard to get that big compactor close to the wall so maybe that area wasn't compacted as well

And I thought I had it bad...

I'm sure you.it will be fine.