#11  
Old 02-14-2010, 10:32 AM
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Default Re: Concrete Counter Sanding and Parging

You will need a couple steps between the 60 and the 220.
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  #12  
Old 02-14-2010, 10:46 AM
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Default Re: Concrete Counter Sanding and Parging

I have always mixed my own slurry of straight cement powder and water. The sand component you added is unnecessary and I'm not sure how this will affect the finial finishing other than to say that a surface coat of anything is mostly moot if you want to polish.
A well floated and troweled slab has a surface coat of "cream" meaning a layer of 100% cement that can be polished up with very little effort and ends up being baby smooth and shiny almost all on it's own. That is the type of surface that can be worked starting with 400 or even 600 or 800 grit pads to get something like glass.
If you intend to polish your slab after the fact, you will be removing most or all of what you've just applied to the surface whether you like it or not. Since your slurry included fines (the sand), you will want to let that cure VERY well (for several days to a couple of weeks) or, as I said before, you'll end up just tearing those particles out of the cement matrix instead of polishing and smoothing off their peaks.

Right now, what you have is like unfired clay so yea, sandpaper will work on the softer elements but it's effect on the aggregate is going to be just about nothing (can you sand down a rock with sandpaper?). Personally, I would return the $60 sander and order up 3 or 4 diamond hand pads in a range of grits (check Ebay, the should be less than $10 each). Leave what you've done alone for TWO WEEKS, at which point you'll have the hand pads and can spend an hour or two with those and a bucket of water and you'll get a super smooth surface that then just needs to be sealed and it'll be shiny like glass. If you must have power tools, a $20 harbor freight angle grinder is more useful.
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  #13  
Old 02-14-2010, 10:46 AM
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Default Re: Concrete Counter Sanding and Parging

Dino, I have a 6 inch DeWalt random orbital sander and it is better at not cutting "smiles" in the surface, but will still tend to leave the surface with a gentle undulation. The pad still flexes and the softer material is cut away quicker than the harder. However, if you want a really flat surface there's a modification to the disc of a sander/polisher that allows one to sand larger surfaces remarkably flat. Although you area is small I would think it would be worth the time to build such a disc especially if you wanted a flat surface from one end to the other of your counter. And once you have one of these discs you will it quite useful for other projects. I expect these modifications will never be OSHA approved as they will leave one major bruise if you are sanding floors and manage to contact your knee (been there, done that). When one tries to tilt the sander the square corners force the sander back flat against the surface. One simply cannot cut a smile. Since the disc surface is flat and inflexible the surface is cut away uniformly, evenly no undulation. Use silicon carbide paper attached by feathering disc adhesive. Of course wear good eye protection and mask and be sure to wait at least a week for the concrete to be hard.

Hope this helps,
Wiley
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  #14  
Old 02-15-2010, 09:24 AM
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Default Re: Concrete Counter Sanding and Parging

Hey Wiley, that's a pretty cool jig on your sander. My counter is so small, I don't think I'd make one but I'm hoping my deft touch and experience in painting will somehow keep my sanding level .

Splatgirl, I used the 50/50 recommendation on this forum for parging (thats half portland/fine sand) and it's mentioned a few times here. I just mixed in the special counter mix that has plasticizers and fibers in it cuz it seemed like the right thing to do. My counter top remains untouched; just my lame attempt at a smooth finish with a new steel trowel.

I'm going to wait 2-3 weeks before I attempt to lightly polish the counter. I'm going to check out diamond buffing pads online too and I'll pour myself a square block of my concrete mix to experiment with my polishing options to see how it'll turn out.
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  #15  
Old 02-15-2010, 04:16 PM
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Default Re: Concrete Counter Sanding and Parging

keep us posted! The fun thing about concrete is you can never completely predict what you're going to end up with. A nicely finished slab is beautiful no matter what, IMO.
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Old 02-16-2010, 02:27 PM
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Default Re: Concrete Counter Sanding and Parging

Here are some pics of my pour in place concrete counter. I spent several months reading up on the process and was convinced that the pour in place would not yield the appearance of form made tops because the nice colorful aggregaqte sinks in the wet mix to deep. With that in mind after troweling I added black, blue and white tumbled glass nuggets to the wet surface and tamped them down just into the top surface of my pour.

To get that top skim layer off and expose the glass I used a grinder with a diamond cup and for the polishing I used a Porter Cable R/O sander with 60-500 grid diamond pads. I applied water by hand as needed. I also used A GFI circuit for this process. As I had read the larg aggregate had settled to deep to see so I was very happy that I added the glass to the top surface. There was some aggregate present for polishing but it was very small and There was no way I was going to get that beautiful aggregate finish you see in the mags. To get a super nice polished surface you really need to wet sand with diamond pads.

The relief I molded into the counter will be home for cobalt blue tile that wraps aroound the whole oven. Unfortunately I didn' get finished before winter hit.

John
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  #17  
Old 02-16-2010, 10:10 PM
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Default Re: Concrete Counter Sanding and Parging

Beautiful counter John! The blue and white colors in the counter are great. The whole look of your wfo is pretty nice. How much do you have to take off to expose the aggregate? That Porter Cable unit looks like it's a good sander for concrete finishing. Thanks for sharing the pixs.
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Old 02-17-2010, 03:45 AM
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Default Re: Concrete Counter Sanding and Parging

Thanks Dino,

For the initial polishing I used a grinder with a diamond cup and applied as little pressure as possible, actually I tried to almost hold the grinder up, probably from fear of digging in those pesky little smiles you can get when your grinder catches an edge, but the top material I removed to get to a pretty layer was minimal. It is kind of tricky starting out with the grinder, it likes to grab a little on the roughness from troweling. It was much easier to control the grinder and really get down to the appearance I was looking for after I got past that initial surface roughness.

After that, I switched to the porter cable and wet sand diamond pads and that is when it started to get real smooth. These diamond pads do come in a hand held version, I believe Splatgirl mentioned it, but my surface area was to large and it takes a whole lot of elbow grease using hand held.

John
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Old 02-17-2010, 07:18 AM
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Default Re: Concrete Counter Sanding and Parging

Coming in late on this - Sorry -

I poured my benches, columns and then column caps with varying degrees of success - the next one was always better. Beat the crap out of them with rubber mallets, rubbed the body of my HF grinder to it - (with a bolt through one of the holes of the cement griniding wheel to make it out of balance and vibrate). Finished up by an ages old rockwell vibratory sander that made my hands numb.

12 hours or so in the forms and removed them - For the blemishes - I did took mortar mix and filled holes in - not good - the sand knocked away and I still had blemishes -

I then went to what splatgurl said earlier - portand - no sand - but rubbed it in over 100% of the surface - not just the blemishes.

I let that set one more day and took a hand sanding block with 220 grit sand paper to the whole thing. Any blemishes I repeated the portland and sanding process. I waited 3 days (total 6 days after initial pour) and took the orbital sander with 220 to it. Used lots of paper as the concrete was pretty hard by then. I did not expose much agregate - pretty much only on the corners. I opened a few voids while sanding and filled only the voids with portand mix applied by toothpick and touched it up a few days later with the sander.

When I was done I had satin smooth capstones, with voids hardly noticible anymore (columns and portland were tinted dark gray and really look like slate). The benches were not tinted and the portland was a slightly different color than the concrete mix but I don't even notice the marks anymore.

I was not looking for a shiny terrazzo-like finish for these non food prep areas - a satin finish with sealer is working great. I have not sealed the benches - I wonder if I should. Even with 220 grit I have no noticible sander marks.

The capstones have gone through fall and a good part of winter and I'm not seeing leaf stains on them - so the sealer is doing its job. This is the 2nd winter for the benches and they are holding up like new.

Christo
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  #20  
Old 02-17-2010, 10:37 AM
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Default Re: Concrete Counter Sanding and Parging

Your cement work is impressive Christo. I'm going to TRY to do what you've done except I wont fill the very few imperfections on my counter side. I'm glad to hear that someone used a orbital sander with some success. That's my plan too.
I also just received my diamond sanding blocks. I'm going to experiment with them as well. I may have gotten them too fine a grit and they be a waste of money. I got a block of 660 and 2 blocks of 1500 I think. They look like a 50cent foam block with white, rubber dots glued to them. The dots feel like smooth rubber. Again, I don't know what I'm doing but I appreciate all the feedback from this forum. Thanks, Dino
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