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Old 09-24-2007, 12:23 PM
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Default removing forms from concrete countertop

I poured my concrete countertop yesterday afternoon and it turned out pretty good. I have a question for all you concrete experts. The eat-up bar is cantilevered 12, with rebar, diamond lathe and fiber reinforced concrete sandwiched between regular premixed concrete. How long do I have to wait to remove the forms? I'd hate for the 12 inch bar to crack after all that work. I attached 2 pictures for you to see. I took the sides off the forms to see how the edges looked. I'd like to start filling the voids in a day or 2 but won't be able to do the underneath edge until the forms are removed completely. Karen
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removing forms from concrete countertop-concrete-countertop-poured-001.jpg   removing forms from concrete countertop-concrete-countertop-poured-002.jpg  
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Old 09-24-2007, 02:23 PM
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Default Re: removing forms from concrete countertop

Here is small discussion on this subject.


http://www.fornobravo.com/forum/f28/...rete-2591.html (Time to Cure the concrete.)


I pulled my side forms on the 4th day.

But I'm leaving the forms underneath and under the cantilever for a month.
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Old 09-24-2007, 07:14 PM
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Default Re: removing forms from concrete countertop

That was a great thread. I don't know how I missed that one. Had me laughing. After all that you still decided to keep the form under the cantilever for a month, huh? I guess I'll wait till I can't stand it any longer. I really wanted to stain my patio before that and I have props resting on it that will be in the way. I guess I could figure out a way to attach them to the cabinet so they'd be off the patio. Thanks for the link to that thread. Karen
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Old 09-25-2007, 06:39 AM
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Default Re: removing forms from concrete countertop

You are an inspiration, Karen. Im pretty handy - I do auto work, some carpentry work, but Ive never ever dabbled in concrete. I guess I could do it but Im too scared of messing it up. The thought of bringing in a jackhammer to break up my mess-up is a deal breaker for me.

Keep up the great work. Keep the pics coming.
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Old 09-25-2007, 07:32 AM
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Default Re: removing forms from concrete countertop

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Originally Posted by Brauma View Post
I guess I could do it but Im too scared of messing it up. The thought of bringing in a jackhammer to break up my mess-up is a deal breaker for me.
You could always build a small form out of a small piece of plywood and 2x4s.

Maybe 2' by 2', and practice your technique until you feel comfortable.
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Old 09-26-2007, 06:27 AM
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Default Re: removing forms from concrete countertop

Thanks for the kind words Mark. It's not really as hard as you probably think it is. My work has definitely improved though over the last couple years. 3 years ago I decided I could make my own kitchen countertops and found these 2 websites with directions that I combined. I made a small table first, then my square countertops, then the one with the sink and then a round table, etc. My outdoor kitchen countertop is already looking much better than my indoor ones. It would be fun to see how a professional does it. I don't want to pay the price though.

I feel the same way about working on cars as you do about concrete.
Karen
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Old 09-26-2007, 10:09 AM
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" I guess I could figure out a way to attach them to the cabinet so they'd be off the patio. "


I would wait at least a week before even doing this. With all that reinforcement in there the concrete is pretty thin surrounding it. When you replace the braces I would do so one at a time and use screws not nails to avoid the vibration. After the slab is set up I would seriously consider some under bracing. If you fabricate some metal "L" brackets and put a triangle brace in the bend they will be almost invisible. Like wise you could get some nice prefab decorative bracket that would go nice with the decor of the kitchen. Either way that overhang may not survive its first encounter with excessive downward force. Its better to add the insurance factor.

BTW it looks very nice. To clean up the edges you can mix up a slurry of washed play sand and pure cement and paint it on the edges. To get it really smooth as this is setting up go back over it with just pure cement and water paint it on a section at a time (careful it dries quickly) then go back with a steel trowel and smooth it like the top. Likewise you can use the sand and cement to do it then go over the whole counter top with a sander to make it really smooth.
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Old 09-26-2007, 11:54 AM
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Default Re: removing forms from concrete countertop

I've decided to wait the 30 days before moving any of the support for the cantilever. The more I look at it the more nervous I get about it. I also think I'll do the L brackets and/or build 2 decorative legs. You're right, I'd be sick if something or someone dropped on it and it broke. It's about 2 inches thick.

Yesterday I made up a slurry of portland cement, pigment and water and filled the voids. I didn't think to use sand. I'm pleased with the way it looks except I can't figure out how to smooth down the bottom outside edge. There's quite a bit of aggregate there that creates an uneveness and the slurry dried and chipped out. If I used sand in my mixture maybe it would have stayed. Maybe you can see it in the pictures.

I'm curious, Unofornaio, would you have used both the diamond lathe and rebar for the cantilever or just one of them? Thanks for your advice.

Karen
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Old 09-26-2007, 01:21 PM
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Default Re: removing forms from concrete countertop

I've decided to wait the 30 days before moving any of the support for the cantilever. The more I look at it the more nervous I get about it. I also think I'll do the L brackets and/or build 2 decorative legs.

>the L brackets hidden or exposed will be fine for support, having a legs would be in the way kinda and not really necessary. I mean if it looks ok to you legs certainly would look nice but again not necessary.

Yesterday I made up a slurry of Portland cement, pigment and water and filled the voids. I didn't think to use sand. I'm pleased with the way it looks except I can't figure out how to smooth down the bottom outside edge. There's quite a bit of aggregate there that creates an unevenness and the slurry dried and chipped out.

> the cement slurry is very brittle and really should be used for a "light coating" to fill voids. what you have done is fine so far. For the edges what I'm assuming from the pics (not real clear) you are talking about is the underside and bottom edge?
What you need to do with this is make the sand mixture into the consistency of stucco or drywall compound. Into this mixture add some "concrete bonding adhesive" looks like Elmer's glue, available for HD or Lowes in a quart or gal about 9.00 for the gallon. you can add this in place of the water for an extremal strong mix but it may alter the color so do a test first. if it changes the color just use a portion of it it still will be very good.
Now before applying this mixture paint the surface it is going to be applied to with the adhesive with a brush just follow the manufactures directions.
THEN apply the cement mixture in thin layers. 1 coat to cover the real rough stuff let it get hard enough to accept the next layer (not dry) the put the next layer building up and shaped the edge as you go.
The best tools for this is going to be a steel trowel and a margin trowel.
Once you get the first coat on underneath take the steel trowel and place it against the new coat (trowel handle will be facing the ground) using the margin trowel take the cement mixture and apply to the section where the trowel is. Using the 2 trowels will create a nice clean sharp edge that will look like the to edge..ya with me?? Do this down the entire edge moving the steel trowel as you go. It you do not get it perfect you can always go over it again with just the cement and color mixture as you did before. Keep in mind doing this in thin layers will make it easier you you to control and bond much better. You can really make it too thick because your voids just are not that thick to begin with. the point is just go slowly.


I'm curious, Unofornaio, would you have used both the diamond lathe and rebar for the cantilever or just one of them? Thanks for your advice.

>It depends on how you did it. most counter top overhangs of the past were just rebar and some still are the fad now is carbon fiber because of the weight. I suppose if you put the rebar and then layed the lath on top of it as long as it is in the middle of the thickness I'm sure its fine. Most structural concrete that is subjected to a span of some sort decking, bridges, etc. is usually of matrix of steel "covered" in concrete. By that I mean the steel to concrete ratio is pretty close.

Get back to me if you have more questions..

Last edited by Unofornaio; 09-26-2007 at 02:47 PM.
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Old 09-26-2007, 01:32 PM
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Default Re: removing forms from concrete countertop

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Originally Posted by Unofornaio View Post
>It depends on how you did it. most counter top overhangs of the past were just rebar and some still are the fad now is carbon fiber because of the weight. I suppose if you put the rebar and then layed the lath on top of it as long as it is in the middle of the thickness I'm sure its fine. Most structural concrete that is subjected to a span of some sort decking, bridges, etc. is usually of matrix of steel "covered" in concrete. By that I mean the steel to concrete ration is pretty close.

Get back to me if you have more questions..
You sure know your concrete!
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