Finish for concrete forms?

[Edward Clarke]

Ok, I know that this is going to sound stupid and many of you are going to think that I'm trolling. I promise that I'm not...

I need to make four wooden forms to produce concrete (actually quick setting mortar) building blocks to make garden beds. Two forms will be six feet long by eight inches wide by two inches high and the other two will be the same but three feet long each. A long form or two of the short ones will take exactly one bag of quick setting mortar. Each of the forms will be put together with stainless steel bolts, washers and inserts. You can see what I'm talking about in this YouTube video:

https://www.youtube.com/watch?v=x7jz96MDvyo

But I'm going to be making a bunch of these - perhaps fifteen or twenty sets. I want to use 6/4 poplar for the bottom and 3/4 poplar for the sides. The wooden parts need to protected from the mortar - which is vicious stuff if you've never mixed it yourself. The forms need to last until I finish them all. This will take two or three weeks at one set per day. What do you suggest for a finish? It's not for looks - even some kind of paint is acceptable.

[Jamie Buxton]

"Release agent" is the google phrase you can use. Many years ago, used motor oil was common. But maybe that's not what you want to put in your garden bed. Nowadays there may be a more environmentally-friendly stuff.

[glenn bradley]

Yep, release agent. A waxy, soapy slime in this case. I made forms for some cap stones.

cap-stone-3-web.jpgcap-stones-in-place.jpg

[Tom M King]

Diluted dish soap will work.

I cast replacement window sills out of concrete, in textured forms. For those, I use a Lecithin release agent by CRC. I'm not saying the Lecithin is best, but it worked like I wanted it to, trying it first, and stuck with it. If you search "concrete release agent", both on Google, and Amazon, there are Many commercial offerings.

You can buy some nice texturing rollers off Amazon, if you make the forms out of concrete. I have used those, but for replacements for old, wooden window sills. I make the plug for what I want the sills to be out of Yellow Pine, burn the surface with a propane torch, and go over it with a soft wire wheel on a side grinder, to make the texture come out to look like old wood. The pourable, flexible form stuff is poured in over that wood plug, and becomes the form, inside a wooden "box" to pour the concrete into