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Dino_Pizza 02-09-2010 10:34 AM

Concrete Counter Sanding and Parging
I just poured my concrete counter in the front my oven yesterday and the top came out nicely. The sides and front face require some parging near the lower portions of my 4" pour. I used an "edging/rounding" float tool along the front edge take the sharp angle away, but it was only partially successful. I'd like to round it a bit more in some places.

Will an inexpensive orbital grinder work to take some sharp corners off the counter? What grit works for this?

I'm NOT looking to turn the concrete top to a glassy finish, but can an orbital sander keep the smooth look and just make it consistent or will I have to use it on the entire counter-top surface?

If my counter front and sides need minor parging because of the wood form that was against it and a few holes, should I do it within a day or 2 while it's still quite moist?

Thanks in advance, Dino

Tscarborough 02-09-2010 01:21 PM

Re: Concrete Counter Sanding and Parging
For minor cleanup an orbital sander with 80 120 200 but be aware that you may expose aggregate by doing so. You should do any touch up ASAP after pulling the forms.

Dino_Pizza 02-09-2010 05:53 PM

Re: Concrete Counter Sanding and Parging
2 Attachment(s)
Thanks, I got home and parged right away. I have 90 grit sand and portland cement and added a little of some of the counter top mix I used so it would be closer in color and rubber-floated the mixture in. Seems to be an improvement. Here's the before and after pics. Small difference but still that's all it needed. I'll see after a few days of curing if the concrete colors stay close enough and if I need to do any polishing.
Cheers, dino

kebwi 02-09-2010 06:06 PM

Re: Concrete Counter Sanding and Parging
I'm so jealous of everyone else's concrete.

Tscarborough 02-09-2010 06:30 PM

Re: Concrete Counter Sanding and Parging
When you are placing the concrete, if you use the orbital sander (without sandpaper) against the form, it will eliminate those bugholes. Sealing or wetting the wood will also help. As a rule, you should remove the edge form within a couple of hours of concrete placement, as soon as the water sheen disappears from the surface. A good way to judge this is to form a test sample of your concrete while placing in (sealed/soaked) wood that is about 6x6xdepth of counter top. Remove one side at a time, and when you can pull the side off with out noticeable slumpage, it is time to wreck the edge forms on your counter top and finish the edges.

Another thing as an aside is that is is easier/better to extend the form out beyond the face, then screw the vertical form down to that surface. When you remove the vertical form, do so by sliding it along the face of the counter top.

PlanoPhil 02-13-2010 03:13 PM

Re: Concrete Counter Sanding and Parging
I recently saw an episode on DYI call House Crashers where they created a concrete table top that was smooth as glass and all they did to it was seal and polish it.
They built a mold using MDO plywood, lined it with either wax paper or plastic wrap and pored a very soupy looking cement (might of been some special formulated stuff) 1.5 inches deep. The next morning they removed the sides of the mold and picked the slab up, pealed the plastic off and voila they had a beautiful colored (forgot to say they added color to the soup) top as slick as a babies butt. Very Cool.


Neil2 02-13-2010 05:08 PM

Re: Concrete Counter Sanding and Parging
The right tool is an angle grinder. A 5 inch angle grinder preferably. The smaller 4 inch ones are much lighter duty tool but will work with smaller jobs.

Get a grinding stone for it. Or, for more bucks a diamond cup grinding disk.

Everyone should have an angle grinder in their toolbox. A very versatile tool.

Jaronimo 02-14-2010 08:25 AM

Re: Concrete Counter Sanding and Parging
I used a 6 inch air grinder and a hose so i could keep it wet. Felt a lot more comfortable with an air powered tool than I would have with a electric tool mixed with all that water. I was able to control the speed by turning down the air pressure a bit.

It was wet and messy, but it was better than dusty and messy. Plus the sandpaper cuts better if you use water which continuously washes away the debris.

splatgirl 02-14-2010 08:33 AM

Re: Concrete Counter Sanding and Parging
If you want to use power tools on it, you should let it cure for at least a week, possibly more depending on the conditions, or you'll just knock/tear the aggregate out of the matrix and end up with holes and deep scratches.
For changing the edge profile or overall shape of a piece, an angle grinder with a diamond cup works great. Make sure you get a cup that can be used dry unless you have a wet grinder. Depending on the age of the concrete, these can take of a ton of material riteawayquick, so be careful especially if you're using it on a fairly green slab.
If you want to polish, get a couple of diamond hand pads. They need to be used wet, and the fineness you'll need to start with depends on the level of finish you put on the slab when it was wet. A good steel troweled finish will let you start with as high as a 400 grit diamond pad. If you only floated it, you might need 120 or 200. If you want aggregate exposed, start with the grinding cup or a lower grit hand pad, like a 60 and work your way up.
I like to slurry to fill voids as soon as I can after the initial pour. With a cast in place slab, this can be almost immediately after you've stripped the form. I always leave my molded slabs in the mold to cure for a week+ and then slurry after I've set them.

Dino_Pizza 02-14-2010 10:16 AM

Re: Concrete Counter Sanding and Parging
Diamond hand pads, that sounds interesting, I'll check them out.

I filled my small holes and re-touched my "rounded" corner edges with a slurry mix of 1/3 super-fine sand (#90), portland cement and 1/3 of the quikrete counter-top mix I originally used put it thru a sieve removing 1/8" gravel out. I put it on within 2 days of the pour and now a week later, it looks fine.

I just bought a $70 Rigid HD 5" Random Obital hand sander. I bought 60 grit hook & loop (is velcro copyrighted?) and 220 grit pads. I plan to sand dry (could I add water to the counter using a "dry sander"?) and I'm NOT looking for a granite-like finish, just a smoother, shinier but natural concrete finish.

Do you think this will work? I've only got a 6' long counter just 10" deep and a 4" face. I know I'll go thru pads but I hope it'll work for this little counter. Also, I know you can get 1000 grit and up pads on-line so maybe I'll try the 220 grit (available everywhere) then see if I want a brighter polish.

thanks, Dino

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