Cracks in concrete deck, Opinions please!

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B

Bart

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Jan 24, 2010
309
Northern Virginia
We had an inground pool put in last summer, but because of permitting delays it wasn't finished until October. Anyhow, last week the snow finally melted and as I walked around the deck I noticed a long crack in the concrete deck that extend over several "pannels". It's about 50 feet long and is pretty much in one direction but there are some other "side cracks" in some of the pannels.

Here's a close up of the crack:
P10105811280x768.jpg


Here's a shot of the crack crossing two concrete "pannels":
P10105701280x7682.jpg


These next two show the length of the crack across the deck:
P10105741280x768.jpg


P10105731280x7682.jpg


I called the builder (and sent photos) and he's sending his concrete subcontractor out there today to look at it. When we spoke on the phone he said it looked like it was a bad batch of concrete. Does that make sense? To my untrained eye it looks like the ground/gravel under the deck settled and caused the crack.

What do you pros think?

Thanks!
Bart
 
Have you looked at your coping. Is the concrete higher than the coping? I had similar and different problems, but nothing as close to the amount of cracks that you have. Fortunately, the deck is coming down, but I still have significant damage at the skimmer as shown. What frustration for you!!! I've got my issues documented here at this website: http://www.golfmd.com/baurphotoalbum/po ... haseVI.htm
 
I don't see how it could be anything other than poor compaction of the sub-base under the concrete.

Concrete has very poor tensile strength and, if the base settles away from the concrete underneath, the concrete cannot "flex" to accommodate that void and it simply cracks.
 
If you think of it in terms of a cake rising its easier to understand those cracks developing from upward pressure. If it were from settling you would see more spalling around the edges of the cracks. You could put a screed on it to see if its moving down in the middle. It could be contraction from a weak mix but you would have probably noticed some cracking shortly after the pour. My money would be on the uplift from a frost heave.
 
Did they put coping in? Or just pour to the bond-beam (which is kind of what it looks like - but should not have done)? Can't really tell with the cover on. I've seen a few pools that have cracked decks like this when they poured onto the bond-beam instead of installing coping.

Oh, and to others points - An old concrete contractor's quoted guarantee, "I'll guarantee that concrete will do two things: Get hard, and crack." (albeit your crack looks abnormal).
 
I am an old concrete contractor and will agree that the vast majority of concrete placed for residential and light commercial work is 'pour'ly done. However its comforting to know that the concrete contractors that build our bridges, dams and nuclear plants don't subscribe to the notion that all concrete cracks.
 
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Thanks for all the input folks! To try to answer some of the questions:

The builder put the coping in, but there was a big lag (~2 months) from the time they did the gunite and coping from when they poured the deck. The deck is not "attached" to the coping, there's a spacer between the two.

The pluming trench is not in this area (if I understand your question). The main pluming run from the pool to the pump does go under this area, but it's only under one concrete pannel and it's perpendictular, not parallel to the crack. But let me add to that......I just check the photos in my "construction" thread and the pluming run does go in the direction of the crack. See the third picture in this thread:
va-blue-ridge-pool-pics-t24552.html
 
renovxpt said:
I am an old concrete contractor and will agree that the vast majority of concrete placed for residential and light commercial work is 'pour'ly done. However its comforting to know that the concrete contractors that build our bridges, dams and nuclear plants don't subscribe to the notion that all concrete cracks.
Click to expand...

I second that!
I'm pretty certain that the concrete job I have undertaken to build our pool won't crack. It takes a little time and money to get it right but when it's done it's pretty much done and will lay still for long time.
It's not only mixing cement with sand and water and belive that will be good enough.
 
I'm pretty certain that the concrete job I have undertaken to build our pool won't crack.
Click to expand...
Of course not! Mats (aka King of Rebar)did very little concrete work. It was actually 3.5" of rebar with a little concrete on the top to smooth out the ridges!!! :mrgreen: :mrgreen:

Just kidding, Mats, and actually posting to agree with you. My large deck has yet to crack after 7 years, but I went to great pains to make sure my sub-base was as compacted as I could get. A commercial builder simply could not take the time (almost a year, in my case) to compact and re-compact to make sure I had a solid subsurface.
 
If I am seeing the pictures correctly, that is exactly where the plumbing trench is :shock: Looks to me like there is a wall and steps leading from your home to the pool. If I look at the construction pics, it appears that you took the photos from the house, and shows the plumbing trench closest to you. It also looks like it snakes around the pool in the same fashion as the crack.

Hard to tell if I am looking at it correctly with the cover on, but I think I am.
 
Not that this helps;

When we moved into this house there was a long crack all the way across the rear patio. When the septic guy came to locate the tanks the septic line followed the crack all the way to the tanks (which were UNDER the concrete). Everyone seems to think the original concrete guy didn't properly compact the dirt after they installed the septic line.

I had my guys double compact the decking area where they ran the trenches.

Good Luck
 
Compacting the soil is just one part of subsurface prep before laying concrete. You can actually overcompact clay if its too dry and its important to add water back to it to "lift" it before placing concrete on top of it. This is commonly done in highway construction or any place a lightly loaded structure (as a concrete slab) is constructed. If you liken a clay particle to a kitchen sponge its easier to understand the properties and how it can affect a concrete slab. When the sponge is dried out its mass is less, when you add water the mass increases and then if you freeze that water it increases even more. The force from the weight of a concrete slab is nominal relative to the force of this expansion.

So when you pour a slab directly on clay you need to be able to control the moisture content of the clay to control the amount of lift. Thats why its best to use a gravel or sand buffer between the clay and the concrete to mitigate the movement. Its best if the depth of the buffer is equal to the frost line of that climate zone.

We have had two winters in a row in the southern piedmont that were colder than anything we have experienced in the last 20+. The typical pattern is a warmer low pressure with precipitation followed by a cold high pressure front which is the perfect equation for frost heave. Because so many owners and contractors cut corners on subsurface prep and inadequate adjacent drainaige there are a lot of pool patios moving up and down to a greater degree than before. If you don't properly facilitate this movement the slabs crack.
 

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