I’m in the process of building a barndo (barndominium) that is going to have a finished concrete floor. Our place is in the Blue Ridge Georgia area. The slab will be 30 ft wide by 82 ft long. 64 ft of the length will be interior space and 18ft will be an outside porch. My concrete guy was talking about expansion joints. I don’t particularly want to see an expansion joint in my living room. If I have to fine. The concrete will be 4 inches thick with rebar. Do I have to put expansion joints in? Thanks.
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is the 30 x 64 space all open? What sort of finish will be on the floor? Yes you need expansion joints.
Not all open, about 25 x 30 kitchen/living rm then 3 bedrooms 2 1/2 baths and an extra room with a big screen tv and a utility room... There's a 4ft wide hall way down the middle.
We're going to have the floors sanded and finished which I think means a sealer and epoxy? Not entirely sure of the type of finish. A few people here and there said they are not necessary.
let’s try not to buy locktite products until their advertising department can be a bit more respectful
Be alright if they included a coupon for free product, let us test and be so enamored that “we” push the product.
The point of expansion joints is the slab cracks there not somewhere else. So you don’t have to put them but the slab will crack somewhere else.
You need BOTH control joints and expansion joints. The latter may not be critical in your area throughout, but should be considered between the exterior and interior portion of the floor slab. Control joint are a must at around 10 feet on center. Control joints allow the concrete to shrink (which it will) and provide a location for the resulting cracks to occur. Control joints are touchy and they are extremely dependent upon how the are made. Concrete shrinks as it hardens and control joints force the resulting cracks to occur where desired. Sawcutting control joints is common (about 1/6 the slab thickness) BUT are most effective at minimizing random shrinkage crack when they are cut AS SOON AS the concrete is hard enough to be cut without raveling. Waiting until the next day or later will NOT prevent all shrinkage cracks from occurring.
For more insight, see:
https://www.cement.org/learn/concrete-technology/concrete-construction/contraction-control-joints-in-concrete-flatwork#:~:text=Contraction%2Fcontrol%20joints%20are%20placed,reduction%20in%20volume%20or%20shrinkage.
Also consider carefully when you apply any finishes to the interior floor slab. Moisture content and vapor emission from the slab can adversely affect many types of finishes. More insight can be found here:
https://www.drylok.com/blog/how-to-apply-epoxy-concrete-floor-paint
An anecdotal comment that I have found to be valid after 50+ years of association with the concrete industry:
"There are but 2 kinds of concrete: Concrete that is cracked and concrete that hasn't cracked yet."
The main point is that there are numerous factors that cause slabs on ground to crack. Poor subbase preparation, short-term initial shrinkage, long term shrinkage, unanticipated high loads, excessive cement content (i.e. using higher strength than is needed) all will contribute. If control joint spacings are too great you WILL experience cracking.
BTW, Control Joints help minimize shrinkage cracking. Expansion Joints (sometimes called movement joints) allow for thermal expansion and movement. They are not the same.
Hope this helps.