In this article we explore the demould process.... BUT before we do there is a bit of work to do to ensure your concrete comes out as expected!
If you’ve cast your GFRC concrete as per the instructions so far, you should have infront of you your concrete poured into a mould that is now covered with plastic and blankets!
You now have a little finessing to do. The good news is you can uncover the concrete. Pack those blankets away for the next project and fold up that still wet plastic neatly.
Where you’ve cast your lips, downstands etc. you will want to sand off the tops within the mould to neaten them off. Plug in your orbital sander, attach it to your hoover and put on your PPE. Now start sanding off the lips.
Now It IS time to demould!
Again a warning. If you’ve reached this section too early, thinking you can somehow cheat the system and try to demould too early be warned. Be afraid! The author (hello!) in the early stages of his concrete career did just that.
SNAP!
Then you'll have to be even more creative...
So be patient. Stick to the curing times (approx 15 to 18 hours minimum).
So time to demould.
Before you do anything have walkthrough. Think about where your hands are going to be holding the concrete where you’re moving it to etc. Most likely you’ll be flipping the concrete to a location nearby. You’ll be putting the concrete onto trestles the right way up. Your first view of your new baby!
You don’t want to be moving it too far because it WILL be heavy. This will be a minimum 2-person job if not more.
You may be wondering why the trestles are important. Up until now, the concrete has been enclosed on all sides. Moisture loss has been even from all surfaces. If you now flip your concrete and place it right way up on a solid surface moisture will leave the upper air-exposed surface faster than the enclosed lower surface. During this secondary stage of the curing process the concrete can still move and will curl if the moisture loss is not even. The trestles will ensure that a pretty much equal surface area on the underside will be exposed in comparison to the upper surface.
Time to get started. Knock off the melamine formers encapsulating your concrete. Clear the excess snots of concrete, glue and remaining bits of melamine stuck to the casting table around the concrete. Why? Because you’re most likely going to be sliding the concrete off the casting table and any excess bits stuck the the table will scratch the surface of your concrete.
Gently lift the concrete away from the tabletop. DO NOT use scrapers or chisels etc to try and lever up the concrete, you’ll just damage it. Grab a corner and pull horizontally. This is where the Water-Based Release Agent will do it’s magic. It’s still there and it’s providing a thin film of “anti-friction” between the table and your concrete. Be patient. The concrete will move eventually.
When it does, slide it to the edge of the casting table, raise it up... actually. Forget the verbal description. Watch the process in action. In the video below, the team are remoulding a small section but the same applies to larger pieces as well.