float tricks- smoooth finish?


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Old 05-17-06, 12:38 AM
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Talking float tricks- smoooth finish?

hey everyone,
i was wondering if there were any special tricks to floating and getting a perfectly smooth finish? i used a magnesium float on my little slab, but i couldn't get it perfectly smooth. the edges of the float would leave lines, and occationally as i would be pulling it along, leaving a smooth surface, the float would catch the concrete and pull it up ever so slightly leaving a pattern. it was one of those things where i'd keep going back over it, and then i'd make an imperfection somewhere else.

i'd like to get really good so i can make a concrete couter top. i've noticed when melamine is used as the frame, the concrete has perfectly smooth surfaces where it was touching the frame. when wood was used, you could see pits and aggregate. is this usually true? would a heavyer layer of mold release work like melamine?

also, in my little slab the next morning - i noticed a crack, in trying to rub it out i made it even worse. did it crack because i didn't cover it with plastic?

thanks for all the help guys and gals.
max
 
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Old 05-17-06, 02:49 AM
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A float is used only for initial smoothing of the concrete, whereas a steel trowel is used for subsequent passes. The trowel makes it smoother. After floating, let the slab sit for about 1/2 hour or so and hit it with the trowel. Repeat trowelling, waiting 15 minutes to 1/2 hour between passes. Depending on how good your technique is, eventually, the slab will be smooth.
More form release will not make the edges smoother. Pouring the top on melamine is the way to go for a smoother face.
The crack was almost certainly caused by pouring the concrete too wet. Being able to rub it out and mar the surface the next day is a very good indication of this. Follow the mixing instructions on the bag. I know it seems very dry when doing so, but that's how it's supposed to be. Using a better grade of mix like Quikrete 5000 will help as well. Even better is to use several pieces of #3 rebar tied into a grid (or just laid in) in the countertop, and don't move the top for a few days after pouring. If you pour less than 1 1/2 inches thick, the concrete doesn't have much tensile strength and will crack when you try to move it. Good luck.

Pecos
 
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Old 05-17-06, 06:38 PM
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Yeah a high early strength mix like Quikrete 5000 has a higher portland percentage in the mix so you get more "cream" for smoothing the top.
 
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Old 05-17-06, 10:53 PM
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whats "cream"
 
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Old 05-18-06, 02:36 AM
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Cement paste, as opposed to the rocks it encases.
 
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Old 05-18-06, 11:48 AM
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Originally Posted by Pecos
and don't move the top for a few days after pouring.

Pecos
pecos, which top were you refering to here?


also, its not possible to build the frame out of melamine and close the top in with melamine too so the top of the couter has the perfectly smooth melamine finish to it right?

should i be able to get the concrete just as flat and smooth with the trowel and the right technique?
 
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Old 05-18-06, 01:29 PM
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I meant don't move the countertop for a few days. You can get the counter just as smooth with a trowel, if you know what you're doing. However, some folks who aren't as good with a trowel pour their countertops upside down on top of melamine or glass, so the top is extremely smooth with no trowelling at all. You can use caulk, modeling clay, or plaster of paris to round the corners where the sides of the form meet the bottom (which will actually be the top of the countertop). This gives you a nice, rounded edge profile without having to use a concrete edger.

Pecos
 
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Old 05-18-06, 01:35 PM
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To see some photos of concrete countertops/bartops I've done (all trowelled, no upside down pours), click on my name on this post and follow the link to my homepage.

Pecos
 
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Old 05-18-06, 05:31 PM
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Pecos, you left off the most important instruction: Leave it alone! Don't overwork the finish.
 
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Old 05-19-06, 02:04 AM
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Well, it depends. Certainly don't work water back into the surface, but I keep trowelling mine (with a cut trowel) until they're burnished. This creates a much smoother finish and the blackening makes for some nice mottling effects when stain is applied. These are interior pieces that won't be subjected to weather, so overworking isn't a problem like on exterior concrete.

Pecos
 
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Old 05-19-06, 01:14 PM
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pecos you do beautiful work!!!

i love how shiny the counter tops are. you don't add any sort of plastic or epoxy to the cement for that? thats just the effect of your perfect trowling and burnishing? great job. i've been wondering how concrete gets that shiney look. in the meuseum here there's some concrete benches that i swear have some sort of epoxy layer over them because they're so shiney.

when you do the multiple colored stuff, like the green countertop with brown edging, is that two pours? or are you just matting it off and then staining it after its poured? (not to ask you to divuldge your trade secrets, just curious)
 
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Old 05-19-06, 08:25 PM
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Thanks for the compliment, however there IS concrete sealer over the finished product. Concrete is a porous material, so to leave a countertop unsealed would be a huge mistake. Any spill or splatter would immediately stain the surface.
To answer your other question, the countertops are done in one pour, then stained different colors afterwards.

Pecos
 
 

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