Concrete Counter Sanding and Parging

[JAG]

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

[Dino_Pizza]

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.

[JAG]

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

[christo]

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

[Dino_Pizza]

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

[Neil2]

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."

Splatgirl is right. I have done a few counter tops of polished concrete. I generally let it sit for 3 days and do the initial surface cut to expose the stone and do any shaping required. I then let it cure for at least 21 days (well wetted) before starting the polishing.