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We'll be casting my first concrete countertops soon. We already talked thickness, reinforcement and sealing with manufacturer of concrete mix we will be using (great guys!) so on that part, we feel safe.

As you can see below, plywood has really smooth finish. I'll seal and round edges with silicone. My question is - do I need to spray form with anything? Or can I just clean it and pour concrete? It looks like it is designed to not need any separating agent, but I prefer to ask before I pour.

We'll be using extra smooth mix designed for countertops and small architectural details, if that matters, and designed thickness is 3cm /(1 3/16 inch).

Photo of smooth finish

  • You don't "need" anything and I'm not aware of any release agent for your application that will help. I am however interested in what the answer will be. – Joe Fala Feb 21 at 13:14
  • @JoeFala what do you mean I don't need? This plywood is supposed not to stick to concrete, obviously, and I probably will remove sides in the process of releasing my countertops. But I want it to be easy - it's not thick slab on construction site this plywood is usually used for. – Mołot Feb 21 at 13:17
  • I'm not a professional with concrete though I do work with it. But yes, it seems a release agent is recommended for your countertop. – Joe Fala Feb 21 at 13:22
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I've seen this done with melamine-coated boards. I would make sure that the plastic veneer of the boards you're using is one solid piece. Family Handyman indicates you don't need any special chemicals to get it out of the form

To remove the form, pry off the long sides and then the short sides. Pry against the form base rather than the concrete. If you have to pry off the form base, use a plastic putty knife; metal will mar the surface

  • It is. It is plywood specifically for casting concrete and plastic coat is guaranteed by manufacturer to be solid, and not easily fractured even by coarse concrete mix. – Mołot Feb 21 at 14:11
  • OK, I tried, I used small amount of WD-40 on the base, but not on the sides and sides released perfectly without any issues. Looks like concrete casting plywood really is enough to cast concrete ;) – Mołot Mar 5 at 13:40

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