What the Heck IS Terrazzo, Anyway?
"Terrazzo?" you ask. "Yes, terrazzo!" we say.
Well, what's terrazzo? Terrazzo is made up of small granite chips. (Remember the Belgian block? That is a bigger hunk of granite.) There are several steps to laying terrazzo:
1) The crews place a gravel sub-base (bottom layer) between the compacted dirt and the concrete base.
2) They place an epoxy-coated mesh inside the concrete to reinforce it and help prevent cracking.
3) They make forms (boxes) on top of the sub-base. This allows them to properly set the level of the concrete. They do this by shimmying long 2x4s across it -- like how you'd run a knife across the top of a measuring cup of sugar to get it level). This allows the construction crew to work in smaller sections and alternate boxes for a better terrazzo product, and the joints allow for expansion of the concrete to help prevent cracks.
For you true construction geeks out there, here's some more info on laying terrazzo: There are two different ways to lay terrazzo. Yes. Two.
First way is that you lay the concrete, let it dry and come back later for the terrazzo, putting a chemical bonding agent between the two materials (think of it as a really serious glue). The second way is to press the granite chips into the cement while it is still wet.
Market Square will have the second process (see them pushing chips into wet cement in photos above?), which should make it a stronger product, and more resistant to cracking. It will also be laid in 6' x 6' squares. These joints will allow for expansion (more crack prevention), and in the case of any damage, it will be easier to repair.
Once the granite is set in place, the construction crews cover it to let it cure. When laying concrete you don't want it to dry too fast, so they cover it with plastic to keep it moist while it begins the curing process. Sometimes they use burlap (as in the photo above) because they can keep rewetting it and manage the level of moisture and drying time. Once the concrete is set they must spray it down to clean it and then put a sealant on to protect it.
Fun fact: It takes 28 days for concrete to cure completely. You know, like if you dry your clothes on the line... after a couple hours it will be drier than when you hung them, but it takes a good while for them to be completely dry through and through. Well, concrete takes a whole 28 days to reach full strength. If you ever wonder why the project near your house or on your commute looks ready but is still blocked off… it needs time to cure!
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