Do Concrete Floors Contract & Expand?

Initial Contraction

• The first time that concrete contracts noticeably is when it is initially poured. As concrete sets and cures, the entire mass of concrete will contract until the curing is complete. Small cracks on the top of the concrete occur frequently during this stage due to that contraction. These cracks are usually not structurally relevant and shouldn't compromise the stability of the concrete, but simply appear as small superficial fractures.

Weather

• For as long as they last, concrete floors will be affected to some degree by the weather. If your concrete floor is subject to extreme temperatures, it may contract somewhat when cold and expand as it warms. Concrete and steel tend to expand and contract in response to hot or cold temperatures at a similar rate, which is why concrete foundations are often reinforced with steel.

Joints

• The expansion and contraction of concrete floors is something that builders need to take into account. They do this by constructing a safeguard known as the expansion joints. This is a border consisting of either a gap or a more pliant material than concrete that surrounds larger slabs of concrete. This allows the concrete to expand without putting undue pressure on the slab itself, which would cause cracking.

Joint Spacing

• The distance between your joints is determined partly by the thickness of the concrete. Take the depth of the slab in inches and multiply it by a factor of 2 to 3. This is how many feet apart your joints should be. You can hide joints skillfully in a home under walls or floor coverings. It is also important to place joints next to walls. That way, if the concrete expands it won't exert pressure on the structure.