Concrete mould release agent, whats cheap n easy ?

[GodofPecking]

I've done a sort of slab with a round slightly tapered hole in it for a hatch, like a manhole but half the diameter, and want to just put concrete into the hole so that it IS it's own mold. But I need the new piece to come out when required...

What can keep the cement separated from the mold, what is EASIEST. I was thinking of using spray olive oil from the kitchen, it would discourage the new cement from joining the old cement, but would it effect the setting of the cement ? Fat mixed into cement will stop or seriously delay setting, but what about oil, or what else can I use that is as easy, what kinds of things have people used with success ?

 

[Ted_Harrell]

I was going to suggest saran wrap. It is thin enough not to affect the outside size of the hole and would allow it to release later on. I just don't know how much of a pain it would be to keep in place while you are pouring the plug...

 

[GodofPecking]

I had thought the same thing, there are plastics and stretch plastics but holding them flat rather than having a wrinkle in the concrete. don't know.

 

[RoosterML]

Any used or new oil will work from motor oil the vegetable oil.

 

[Birdsong 82]

What type of forms are you using? If you're using wood forms like we usually do at work honestly if the forms are wet prior to the concrete being placed that works. But most of the time oil

 

[Birdsong 82]

From what I understand and I don't know how much but the components and motor oil may break down the concrete overtime faster. I think a mineral or vegetable oil would be better Plastic on the inside of the forms may delay the setting. But just as a suggestion putting plastic over the top while it is curing can help it from cracking

 

[Birdsong 82]

I feel silly don't know how I missed the part where it is it's own mold. Keeping concrete from bonding to concrete pretty difficult. I don't know how big the whole is but a lot of concrete precast companies that make manholes and drain inlets actually have plugs that are rubber or plastic that they provide when they sell their products. They may give or sell you some. And these plugs are used in manholes and drainage structures for interstates so they're definitely strong and it helps allow for expansion and shrinkage of the concrete between hot and cold temperatures.

 

[Deleted member 551573]

Just use an aerosol cooking oil, I make concrete sleepers in a latex mould for my garden and that's all I use

 

[archeryrob]

Any oil will work, as long as its not old and dirty, like motor oil used. Dirty oil will stain your concrete. People use new diesel, motor oil and cooking oil. When I built the roof for my smokehouse fire box I oiled the plywood base form with used kitchen oil before building the rebar. Walked away for a minute and came back and found the dog licking the plywood clean. Had to oil it again.

 

[Flame80]

Don't know if this helps but...I build a lot of concrete benches and other yard items from plastic molds. IALWAYS spray PAM on the molds very heavy and never have trouble removing the mold from the dried concrete.