Concrete patio w/o expansion joints - DIY Chatroom

TrentJA · 07-23-2009, 12:45 PM

I hired a contractor to install a stamped concrete patio. I came home from work to find they didn't install an expansion joint where the patio meets the house foundation.

How concered should I be? Do I need to insist they rip it out and intall a joint?

jomama45 · 07-23-2009, 01:06 PM

Obviously, an expansion joint up to a foundation is ideal, but is far more important in some scenarios than others

Couple of questions: What part of the country are you in/ climate? What did they pour against, concrete or block? foundation insulation? ground break? wood ?

concretemasonry · 07-23-2009, 02:20 PM

Depending on your patio size, you should also have control joints sawed to control the cracks that will eventually appear.

The joint you are concerned about is a separation or control joint since the slab and the home are on different soils. Concrete has little "expansion" and has a long tern shrinkage that should be accounted for.

TrentJA · 07-23-2009, 02:23 PM

I'm in Northern California, Sacramento area. 100+ summers, mild winters with highs in 50's and 60's, only occasional bouts of freezing.

One edge of patio is poured along the concrete slab foundation of my home (10' in length). The other side of patio (15') is along existing concrete sidewalk. The other two sides are completely open.

If the worst thing that will happen is the patio may end up with more cracks I'd be disappointed but could live with it. More concerned it might create problems for my concrete slab foundation of the home.

itsreallyconc · 07-24-2009, 03:54 PM

i'd be more concern'd there aren't contraction jnts sawcut or formed in the surface,,, 1 on ea horizontal plane at right angles to each other

TrentJA · 07-24-2009, 04:00 PM

There are contraction joints, one horizontal in the middle on through the vertical middle and it has a band around the edge seperating the stamped area from the smooth concrete area so shouldn't be an issue with that.

I did check with local building code to be sure expansion joints aren't required and they're not so I guess it'll work as-is.

Daniel Holzman · 07-24-2009, 04:21 PM

See http://www.johnbridge.com/control_joints.htm for an interesting discussion on expansion joints, contraction joints, and construction joints. In your case, it sounds like you have the contraction joints covered, but you really should have an expansion joint between the slab and the foundation of the house. The expansion joint would normally consist of a space at least 1/2 inch wide, filled with a flexible material that was watertight, such as cork, silicone caulk, butyl rubber, or similar material. The purpose of the joint would be to avoid exess buildup of stress in the concrete of either the patio or foundation when the concrete expands during the summer heat.

Note that the johnbridge site claims that concrete will expand 2/3 inch per hundred feet of concrete per hundred degrees F rise. In you case, the temperature difference between summer and winter is some 50 degrees, hence 1/3 inch per 100 feet of patio. Since your patio is about 20 feet, that is about 1/15 inch of movement, so you would not need a large expansion joint, only about 1/8 inch in theory, so you could in principle saw cut it if you could get a blade that close to the foundation. There may be an offset saw that could do it, I have never seen one, but there are lots of unusual tools out there.

itsreallyconc · 07-24-2009, 05:28 PM

danny, that's almost probably more'n even i wanna know

good link, tho, & thanks for posting it,,, i'm only aware of a flush diamond blade which's specific to wall saws,,, would almost bet slab shrinkage's compensated for the lack of exp jnt mtl.

i'd bet the 'band' is the trowel track on the perimeter,,, its not common for exp jnt mtl to be removed to accommodate jnt sealant on residential work but, as you're probably aware, the reason for most hgwy slab failure's the lack of properly-spac'd jnts together w/proper sealing to resist the intrusion of 'incompressibles' which cause slab blow-ups.

thanks, AGAIN ! ! !