My concrete counter tops

[b_m_hart]

OK, so I've installed my concrete counter tops.  My first attempt was a failure, but I seem to have learned a fair amount from my first try, and come out looking at least OK on my second try!  I still have some shimming to do, and then I need to caulk everything.  Once done with that, I'll use some hand diamond pads to smooth the seam in the middle, and call it a day:
http://b.m.hart1.googlepages.com/home

(lotsa pics, and all far too high resolution to be hosted here)

I used the TS 55, and RO 150 FEQ primarily for this project.  I used the saw to rip cut the mold pieces, including the mitered pieces for the sink knockout.  I used the sander to do all of the polishing work with the exception of a rough grinding on the tops of the pieces.  I used it to do the rough grinding on the edges (with Saphir 24 abrasives) then used a 5" dry 100 grit diamond pad.  Even though it was a bit too small, it worked quite well.  Once done with the diamond pad, I used the Platin 500 through 4000 grits to polish the concrete.  One thing I need to do is to buy a Festool drill if I ever do this again.  Switching between bits would have saved me at least an hour, probably two on my last mold.

Oddly enough, I didn't really use any of the Festool tools on my first attempt, other than to polish a bit.  However, on the second attempt, the accuracy of the saw and the rail system helped me a TON.  I think the difference in results can be attributed to me getting over the hump a bit on the learning curve, but a lot to the better accuracy of the tools I was using the second time around.

Various other tools were used, such as a corded Dewalt drill with a plaster mixing paddle to do a quick "blend" to even out the concrete dye before I mixed each 80 pound bag basically by hand in 19 gallon buckets.  I also used the same drill to drill countersinks and pilot holes for screws every three inches.  I vibrated the concrete by vigorously shaking the table back and forth, and once both molds were full, by pounding on it with a 16 ounce rubber mallot.

I know that the RO 150 FEQ was not designed nor intended to grind / polish concrete, but it held up fairly well.  It had issues with diamond pads, and the vertical surfaces, but the random orbit was HUGE in turning out a nice finish.  There are certainly portions where I could have / should have done a better (as in, more even) job, but I liked the look, so I called it 'good enough'.

The beauty of the Festool products was the cleanup portion.  Now, this isn't the traditional "clean up a bunch of wood chips".  Using the RO 150 FEQ instead of a wet polisher meant I didn't have to stand around with water splashing everywhere, hoping to whatever God you all may wish to pray to that the GFCI worked as it was supposed to if something went wrong.  So, my basement is not a freaking swamp of concrete-muddy water for days.  Sure, I track in concrete dust, but the house is trashed anyway, dust is no big deal, mud still gets the evil eye in a major way.

 

[casmith32]

I'm curious - what did you use to do the initial grinding of the concrete ?  I've already done a couple of countertops and have used wet grinders to do the grinding.  Your mention of using the RO150 has peaked my interest... did you use dry grinding pads ?  I'm wondering if I could use that method to "retouch" my concrete countertops...without all the watery mess...

 

[b_m_hart]

I used a wet grinder (50 grit diamond pad), then went to a 100 grit dry pad.  Yes, a 5" pad on a 6" sander is kinda ghetto, but it worked quite well, and the dust collection holes kinda stick out of the edge on the outside, so there isn't a bunch of dust flying from it.  The rest, I used the Festool abrasives for, and it worked out very well.

I've read / seen a bunch of people saying that they don't like to go past 1500 grit so the wax has something to hold on to, but I had no problems when I polished up to 4000 grit (platin).  Sealer and wax took just fine.

If the concrete is still quite green (as in, two to three days from pour), 24 grit saphir pads will chew into them fairly well.  This works OK, but your back and arms will thank you for just using your wet grinder to get down to whatever level of aggregate you're looking to expose first.  If you do want to give it a go, you'll burn through the saphir abrasives VERY fast.  I mean, two minutes of grinding tops per pad before they've lost their bite.  They're not used up, just aren't very coarse anymore.

 

[Bill Wyko]

Your counters look fantastic. I wonder if you mounted a woofer with a tone generator at a low frequency around 60hz to the bottom of the table if it would bring all the air bubbles to the top? I think it would only take 20 watts or so. I need to build new counter tops pretty soon too but I don't think I'm ready to attempt this. I better not let the LOML see this post or she'll have me at home depot with a flat cart and a trailer for concrete. ;D Again, great job.

 

[b_m_hart]

Haha, I should have thought of that.  It would have been nice to have some music to work to, but it woulda been a royal PITA to set up the computer and attach the sub without getting concrete all over it.

I ordered a concrete vibrator, but because I went for the small cheaper one, it's on back order.  Still.  I figured 'how many times am I going to use it?', before I had to re-do my counter tops.  I'm going to wait for it to get here, because in the next few months I'm going to goof around with making cabinets out of really cheap plywood for practice, then when we add a second bathroom next spring, I'll make the vanity cabinet and top.

 

[Tinker]

Haha, I should have thought of that.  It would have been nice to have some music to work to, but it woulda been a royal PITA to set up the computer and attach the sub without getting concrete all over it.

I ordered a concrete vibrator, but because I went for the small cheaper one, it's on back order.  Still.  I figured 'how many times am I going to use it?', before I had to re-do my counter tops.  I'm going to wait for it to get here, because in the next few months I'm going to goof around with making cabinets out of really cheap plywood for practice, then when we add a second bathroom next spring, I'll make the vanity cabinet and top.

The vibrator I used for small projects like that (I am not in any way belittleing your project.  You have done a great job and learned a lot.  A bigger job where I used power vibrators would have been concrete foundations and concrete decks/ceilings) would have been a momentum piston with an armstrong powered short arc hickory boom.  It is possible you might refer to it as a hammer. 

All you need to do is set up your forms to be very sturdy, mix and apply your concrete and start tapping right away before setting begins.  Be sure your forms are lubricated with a light film of release agent.  There are also additives that will not only slow the set, but aid in strengthening the finished product.  I have been out of the business for nearly 30 years and there are hundreds of newer materials out there that I know nothing about.  The principles are still pretty much the same.

One tool I have in my shop that might possible supply enough high frequency vibration to use around the sides and underneath your forms would be my Fein Multi Master.  You don't need tremendous power to vibrate those bubbles to the surface.  But even trying that, I would keep my hammer handy.
Tinker 

 

[Steve Jones]

I recently did a cabinet job where they had a company molding the countertops in the garage on site, they carefully made a flat table to mount the forms on then suspended rebar and pig wire (4" heavy wire netting) for reinforcement, poured the concreted and used cheap 1/4 sheet hand sanders held (actually clamped) to the underside of the table for vibration.

 

[Tinker]

Any method that will vibrate the forms will work.  You are not trying to overpower the concrete or redistribute the aggregates.  you are just trying to vibrate the AIR out of the mixture so the voluum becomes more dense, and thus much stronger. 

I am not sure what sort of vibrator b_m_hart is planning to use, but if you intend to insert it directly into the mixture, i think you will learn about a new problem.  isolation of materials is a possibility.  As the materials isolate, they will create a mass that will become weaker due to uneven redistribution of aggregates.

You have done a fine job so far.  As I mentioned before, you have learned several lessons.

One thing I learned early on with concrete, it is ALWAYS better to have a little too much mixed for any job where the concrete is to be exposed than to be short, even one shovel full.  For your project, it is much better to have some to throw away than to have to mix just a tad more to get a pannel to come out just right.  Even if you must mix new batch for each pannel.  You don't want to remix for any individual pannel.

Another thought, you may already know about this.  To little water and the vibration won't do much of anything for you.  To much water and you will get way too much isolation of aggregate.  The stone will work its way to bottom of the form.  unless the form bottom will be your actual finished top, you do not want that.

Let us know when you have finally installed your countertop.  I would like to see it.  You are tackling a tricky job and doing very well.
Tinker

 

[b_m_hart]

I used the "rubber mallot hitting as hard as my pain threshold permits" technique.  My right (dominant) thumb was (well, still is) sprained, so I was hitting it as hard as I could, as fast as I could... but something mechanical would have been much better.  Additionally, before my mold was loaded up with 500ish pounds of concrete, I physically moved the mold back and forth on the table.  The only problem with that was, I'm not nearly strong enough to shake 500 pounds back and forth, so that's when I went to the rubber mallot.

I have a cheap-o table mount vibrator on order, but it's been back-ordered for months now.  I guess the boat from China sank or something.