Precast Concrete Countertops

FIVE: DEMOLD THE COUNTERTOP

There are a few simple, but essential, rules to follow when de-molding a concrete countertop. Since the concrete is only a few days old at this point the risk of cracking the countertop is high and we need to be careful of where we pry and lift to insure the countertop slab is not stressed to the point of breaking. Avoid lifting the slab by its corners and prying directly against concrete surfaces with metal pry bars and screw drivers.

We strongly recommend wearing rubber gloves to avoid leaving marks on the concrete surface. The oils from your hands and fingers can soak into the concrete surface and leave recognizable handprints on the final project.

Step 1 – Remove the Form Walls

  • Grind away any concrete lapping over the form wall tops before loosening the forms to prevent spalling the concrete.
  • Grind off any high spots or stones protruding above the form walls flush with the top of the forms to insure the countertop will lay flat upon installation.
  • Pry against the form walls, not the concrete edges, to avoid chipping or spalling the concrete.
  • Use a 60-100 grit diamond hand polishing pad to ease any sharp corners or edges before rolling the countertop over.

Step 2 – Remove the Faucet Knock-out

  • Remove any plumbing or faucet knock-out with a pair of flat screw driver.
  • Remove the screw that attaches the knock-out to the form base.
  • Since this is the underside of the countertop it’s ok to pry against the concrete here.

Step 3 – Roll Countertop

  • Slide the countertop, while still attached to the form base, to one side of the casting table.
  • Place equal thickness foam sections 12” apart and adjacent to the countertop section to be rolled.
  • Gently roll the countertop up in one edge. Make sure there are no stones or debris between the countertop and casting table when you roll it. These will cause damage to the countertop edge.
  • If possible roll the countertop on the edge that will be against the wall and unseen after installation.
  • Carefully lift the form base off the top of the countertop. If the form base doesn’t immediately release from the concrete, one or two flathead screw drivers can be driven into the edges of the form base and used as lifting handles.

Step 4 – Remove the Sink Knock-Out

  • Remove the sink knock-out by standing the piece on edge and punching it out.
Previous: Pour the Concrete

The concrete mix used in this pour was low-slump and required heavy-duty vibration. Add more water to your mix if you don’t have table vibrators like these.

Next: Polish the Countertop

Wet-polish with coarse diamond polishing pads that expose aggregate by cutting deep into the concrete, or use a finer pad for a more uniform finish.