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When to early strip concrete post form

1680 Views 5 Replies 4 Participants Last post by  pritch

Normally, I work on carpentry projects, but I've been asked to replace a damaged light post made from exposed aggregate concrete. I've made a form from a 18" sonotube with wooden spines fastened around the inside to create a fluted concrete post about 3' above ground level forming a base for a decorative streetlight. The top of the form has multiple pieces that cause the post to neck down to a 6" diameter. The plans call for an exposed aggregate finish. This, of course, will mean that I have to early strip the form in order to wash the fines and expose the limestone aggregate. My question is how do I know when to remove the form. I'm concerned about damaging the flutes if I strip the form too early and, of course, if too late, I won't be able to. With sidewalks, it's easy to test the cure point. In this case, the form and the Any suggestions?
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There are several variables that need to be considered. Air temp.,humidity,in full sun,shade,slump of concrete (water in mix).

Just maybe,your best bet would be to pour a small test sample under conditions you expect to work with.
Yes, I agree with those variables. After more thought, I was considering removing the top form rings early which would expose the top of the post and allow me to prod the poured concrete to see how stiff it is. Assuming I follow that line of thought, how do I know when "set up" is "set up" enough? If I use a pick, how far should I be able to drive it into the concrete fines?
Here is just a few more ideas that may help. Lets say you wait a touch to long,a soft brush may have done the trick with perfect timing. A stiffer brush could now give you good results,if need be,a pressure washer on stand by may save the day.

Hope this helps.
Are you planning to spray the insides of the form work with a retarding agent? That will help you a lot.
Have you considered sandblasting it after it has cured properly? Maybe look for a plastic form-liner to put inside the sono tube. I don't know if I would use wood, but if you do make sure it's tapered and sealed against moisture. The wood will swell up and quick! That's a tough detail, either way.

Maybe just pour really stiff and don't vibrate, that'll expose the aggregate!:whistling:blink::no:
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