concrete forms

Old 11-19-07, 08:24 AM
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concrete forms

Hi all! happy Thanksgiving.
I have a question about what material i can use to make a form for a bench / retaining wall. I want it to butt to the pool deck (4"thick) the wall/bench is going to be 44'long X 13" high X 8" thick, i purchase some fiber board house siding for the long straight pieces, however its not pliable enough to make the bends that follow the pool deck. Can i go to something as thin as door skin? or will the weight of the cement break it? also should i put a thin piece of plywood at 3' intervals to prevent cracking? or will the re-bar hold it? (This is my first real cement job so i hope it turns out. I bought a cement mixer so that will help) any info you can provide will be greatly appreciated!
Thanks, Juice
Old 11-19-07, 10:17 AM
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Double layer of door skin and lots of support/staking will work.
Old 11-20-07, 03:02 AM
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To make radius forms, depending on how tight the radius is, we use fiberboard lap siding (like masonite). It is made of compressed wood pulp and bends quite easily. I've used it to make curved walls up to 2 feet tall, but we had to stack the pieces to do it. However, no matter what you use, keep in mind that wet concrete weighs a lot and exerts a LOT of lateral pressure. You must be sure to brace the forms well and OFTEN (every 18 inches or so). If you don't, your forms will bulge and quite possibly break under the weight, spilling all that concrete on your pool deck.
If the radius isn't too tight, plywood would be a better option. Use the thickest grade possible that will still make the bend. Be VERY sure to firmly attach the spliced joints so the form won't break at the joint.
Lastly, mix the concrete as per the instructions on the bag. It will seem too dry, but don't add extra water. People mistakenly "pour" concrete all the time, when in fact it should be "placed". If you can pour it, it's usually too wet. Of course I'm speaking of normal bagged concrete without plasticizers, etc. Good luck.


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