You need to build temporary wood walls in order to support the concrete for bottom of the house. When the sement hardens you take down the wood exteroir. This is a very important step because if the cement can break through the wallls the damage is expensive. You need to have soild concete foundation in order to start building a house.Snap ties are the most inportant part of cribbing. They keep the boards square so the cement is straight also adds as a reinforment.