Concrete mould release agent, whats cheap n easy ?

GodofPecking

Songster
Dec 16, 2015
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141
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

Crowing
Sep 23, 2019
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Pembroke North Carolina
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

Songster
Dec 16, 2015
617
218
141
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.
 

Rachel Taylor

Crowing
Aug 17, 2017
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Virginia
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
 

Rachel Taylor

Crowing
Aug 17, 2017
3,315
5,568
402
Virginia
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
 

Rachel Taylor

Crowing
Aug 17, 2017
3,315
5,568
402
Virginia
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.
 

archeryrob

Songster
Aug 3, 2018
371
545
147
Western Maryland
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.
 
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