control joints

EHH week 14: concrete floor topping

The finished floor upstairs will be a polished concrete topping.  At just 2 inches thick, the concrete has pea gravel aggregate and is reinforced with steel mesh.  It was pumped into the house, then screeded and troweled to a smooth, flat surface.  Flat is crucial for the floor polishing to look good.


The subfloor is red!  The color comes from a waterproof coating sprayed over the entire plywood subfloor.  Since concrete is wet at first, we did not want all that water to soak the plywood that Model Remodel so carefully protected from rain all summer.  The coating also acts as a bond breaker, allowing the concrete to shrink and move independently of the plywood.


Since the finished floor will be “cast in concrete” it was crucial to lay out all the floor penetrations before the concrete is poured.  Items like electrical outlets, heating grilles, and some plumbing pipes were blocked out to the precise size of each recessed item.


The pour was done in two halves on two different days with a “cold” joint between.  After the concrete had hardened, control joints were saw cut into the surface using a wet saw and a vacuum to limit dust.  These joints are intended to control the surface cracks as the concrete dries so they fall in nice straight rectangular lines, instead of unsightly jagged cracks.  Both these joints will be filled with caulk to match the color of the concrete once it is polished.


A week after pour day, still no cracks!