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Old 06-26-2011, 11:13 AM   #1
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concrete form release


I'm constructing a poured concrete retaining wall and I've completed the footing and am now building forms for the wall. The forms are plywood and I want them to come off easily after the concrete is poured. People around here usually use diesel. However, I'd also like to "fill in" some of the roughness of the plywood, so the finish on the wall is smoother. I was wondering if, say, a cheap latex paint might work as a form release agent. If not, any other suggestions? Thanks.

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Old 06-26-2011, 11:46 AM   #2
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Latex paint is not going to be much of a release agent. There are all kinds of release agents you can put on for concrete form release---even over fillers you have used to even out defects in the form surface. Check to see what your building supply company has availed.

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Old 06-26-2011, 02:12 PM   #3
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Personally, I'd skip the paint. It could very well end up coming off of the forms & sticking to your walls, creating one more step than necessary.

Diesel is OK, as long as it's mixed about 50/50 with a heavy oil IMO. Otherwise, just about any thin oil will work, including vegetable oil you already have in the kitchen.

If you want a smoother finish you'll probably have to either sand the plywood first, or rub the wall out later.
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Old 06-26-2011, 02:19 PM   #4
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Any depression in the plywood that would require fill would result in a protrusion in the poured wall if not filled in the plywood. (basic)

so...
Why not leave it as-is, go ahead and pour the concrete, and then remove the forms as soon as practical and rub the wall's surface with a rubbing stone while it is still green?
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Old 06-26-2011, 06:55 PM   #5
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Put some 4mill poly on them before assembling or spray them with sugar water mix before pouring. Don't spray anything on the stub steel or re-bar, though. Gives more time to trowel smooth right after stripping.

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Old 06-27-2011, 11:54 AM   #6
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Put some 4mill poly on them before assembling or spray them with sugar water mix before pouring. Don't spray anything on the stub steel or re-bar, though. Gives more time to trowel smooth right after stripping.

Gary
Plastic sounds like a good solution. And then I could leave the forms on for a couple of weeks to help with the curing. Is there any potential problem with this? Btw, the wall is about 6' high, if that makes a difference. Thanks.
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Old 06-27-2011, 04:12 PM   #7
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Plastic film will transmit any imperfections that may exist in the plywood. The longer you wait to break forms the harder it will be to correct the wall's appearance. If you break the forms ASAP the wall can be uniformly scuffed/rubbed overall for a nice finish. If you wait a couple of weeks the task will change and not for the better. If you think you have to slow the cure of the wall for more strength then bust the forms ASAP, rub the surface, then cover it with plastic for a couple of weeks if you think there is something to be gained by doing so.
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Old 06-27-2011, 05:04 PM   #8
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Diesel as a release agent is probably not allowed in all the 50 states.
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Old 06-27-2011, 08:29 PM   #9
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As Bud brought out correctly in post #7. Jeremy, you must have skipped this from my answer "Gives more time to trowel smooth right after stripping." You obviously can't wait more than an hour, depends on weather, ingredients, etc.

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Old 06-27-2011, 08:35 PM   #10
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concrete form release


Stop by a concrete contracters yard and offer $10-$15 for a gal. or two for form oil. I think deisel fuel would work fine or you could mix it with kerosene.........I think canola would work fine also, as long as you strip your forms the following day.

As far as smoothing out the surface I'd just plan on skimming the wall with mortar the day you strip. That will fill in all of the "honeycomb" or air that doesnt get vibirated out of the mix, it will give a even color also.
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Old 06-27-2011, 08:37 PM   #11
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You obviously can't wait more than an hour
I've never seen a wall form striped the same day it was poured much less within hours.
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Old 06-27-2011, 09:26 PM   #12
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I've never seen a wall form striped the same day it was poured much less within hours.
I've never actually seen it either, although my Dad insists he poured and stripped a basement in the same day many moons ago.........

It's certainly not something I would suggest for a DIY trial though. A curb, maybe, but not a 6' high wall.
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Old 06-27-2011, 10:31 PM   #13
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Quote:
or air that doesnt get vibirated out of the mix
Oh Lordy! Wish you hadn't brought that up.
A concrete vibrator in the hands of the inexperienced can result in disaster.

Sh-h-h-h-h-h! He'll be fine as-is, no vibrators.
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Old 06-28-2011, 09:37 AM   #14
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I've seen forms striped the same day ... but these where some skinny columns in between block wall not a 6' retaining wall.

I think if you strip em down next morning you will still be able to scrape some of the stuff of.

I've seen plastic used in couple occasions...it will leave surface perfectly smooth in the areas where is stretched out but man will it leave a mess if it gets crumpled up or concrete gets behind it.

I've actually spent few weeks fixing a ceiling that was poured with plastic visqueen over the forms (Europe).
I was not there while they where pouring that ceiling but my "guess" would be that they didn't secure the plastic to the plywood and stuff got all crumpled up in between rebar.
You guys wouldn't believe how bad did that ceiling look like.

There are different grades of plywood.. if you are going to use a CDX ply for the forms there is no "oil" or paint on this world that will cover all of those holes.

Use one smooth side plywood ,oil and VIBRATOR and you will achieve some very satisfying results.

Oh Lordy!
Wish you hadn't brought that up.
A concrete vibrator in the hands of the inexperienced can result in disaster.

Sh-h-h-h-h-h! He'll be fine as-is, no vibrators.


What is going to happen if he uses a shaft vibrator?

Skim coating over newly poured stuf will work but you are looking at the work that can be avoided now using better plywood.

AC or BX ply its only 20% more than CDX and unless you are doing a mile long retaining wall that is a money well spent.
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Old 06-28-2011, 09:49 AM   #15
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Steel Toes this site has some fairly nifty features for quoting and stuff like that. You should learn to use them. It would make your comments easier to understand.

Quote:
What is going to happen if he uses a shaft vibrator?
You have never seen wall-forms blow out from the over-use of a vibrator have you? It's not a pretty sight, and it's not easy to clean up. He doesn't need a vibrator necessarily.

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