Hi all,
I am using a form to create a concrete hearth. The form is made of melamine and the hearth is poured upside down, so there is no trowelling of the top. I added a strip of wood trim to create a detail on the top front edge. I sprayed the whole thing with release agent (PAM).
My question is this: What I’ve read so far states that you remove your piece from its mold after three days, but the concrete is not, of course, fully cured yet. I am considering letting it sit in it’s form for a week to let it get that much stronger before releasing it. Does anyone have experience getting concrete out of melamine forms? Does it become harder to remove from its form after three days? Any input would help me make my decision…
Thanks.
-Jeff
Replies
I've poured concrete upside down in melamine. Absolutely no problem getting the forms to release. I didn't coat mine with anything. The melamine does not bond to the concrete. After a day or two, rip the sides off of the form and then just slide the concrete a bit (1/4" or so ) to break it loose off the melamine and then cover it back up with plastic to sit and cure.
Be very sure to use as dry a mix as possible and vibrate well to eliminate air bubbles in the finished surface. You'll just have to fill them later. I used a palm sander to vibrate mine, just hold it against the underside of the form and you're good.
I let mine sit for 2 weeks before attempting to move, but these were 1-1/2 thick countertops with a large sink cutout, so I was very concerned about breaking it at the cutout.
Turned out to not be a problem whatsoever.
Make sure you keep the concrete moist (I hosed mine down every day for 2 weeks) so it doesn't cure up too fast. Keep it covered with plastic.
I flipped mine and installed after two weeks, let everything sit for another two, and then rubbed in two coats of siloxane sealer and then two coats of bees wax. Looks great. Couldn't be happier.
If you want to poilsh the concrete any, even just to cut over the corners, strip after 2 or 3 days, flip in 4-5. Wait too long and the concrete gets to be a bear to grind/polish in my experience
Second that. Do not wait too long if you're going to grind on the surface. I found that using carbide paper on my pad sander worked good for bringing out a bit of sheen and rounding over corners. I can't remember grits, but just play around with it.
Truth is, you can probably pull the forms and flip it in 1-2 days. Just be careful.One more note: Make absolutely sure that whatever it is that you're setting your forms on is VERY VERY sturdy. Do not cut corners or miser up in any way your support. You do not want your forms to settle at all or you'll end up with a warped slab. Happened to a guy I know. He had to repour his counters.
I have had counters warp just because they cured out too quickly, or were installed and finished too early.Its all about timing with the concrete
Thanks a lot for all the great input. I feel much better about coaxing it out of the form now. I was getting nervous after all the time I put into building the form, not to mention handmixing three 80# bags of concrete thoroughly. Won't do that again...
-Jeff