Monday, October 24, 2011

Concrete Counters Part 5: the reveal!

After the countertops were set into place, next was to sand and polish them. Ideally, you would do this in another room (like a garage or outside) and not with them in place. But since we poured them in our second story kitchen, we were not going to carry them downstairs and back up. It also would have been good to have them on a stand away from the brand new drywall, but they would have been in our way of doing other work.

When we flipped the countertops over, they looked generally hole-less except for a few areas like this:

Notice how some of the holes are partially covered by a hardened film. To expose the holes fully (so I could patch them), I used a wire brush on the whole counter. That's when my heart sank.

The entire countertop was full of holes. Even the areas that looked perfect like this:

The wire brush revealed thousands of holes ranging from pin size to pea size. Not only is this a cosmetic issue, but also a sanitary issue. The holes would get full of food and germs. We were expecting some holes and were prepared to patch them one by one. All the other bloggers had experienced the same problem, but we had too many to count.

You might be thinking, why didn't I just leave them covered up instead of revealing them with the wire brush? Well, during the sanding/polishing process they would be exposed anyway, so we wanted to get that part over with and get them filled.

You can see an area below that had a lot of holes. Sorry I don't have a close-up picture.

We don't really know what happened to make this many air holes. We vibrated the forms a lot (or at least I though it was a lot). Maybe our mixture was too dry. But we intentionally made the bar piece wetter to cut down on the holes. If we had it to do over, I think I would rent a professional concrete vibrator. Also, instead of pouring them in forms that were on the floor, we probably should raise them up on saw horses or something so that we can vibrate them from underneath.

I did my research on how to fill the pin holes when they are too small to fill by hand (and too many). The tips I found suggested mixing a cement slurry. Instead of using concrete mix (which consists of cement, sand, and gravel) to patch it, use a watered down solution of just cement. The sand in the concrete mix was too large to fall into the holes. Cement is a fine powder.

The idea was to water it down enough so you can brush or spread it onto the surface and it will fall into the holes. I tried this (and added my pigment to the mix to color match it to the countertops). It didn't work. There was too much water tension on the small holes and it wouldn't fall into them. Also, cement wouldn't take the pigment like the concrete mix did, so it was a different color.

As my slurry was drying/evaporating into a mud and I was at a breaking point of frustration, Matt started pushing the thickened slurry into a hole with his finger. It worked!

So that's what I did. Mushed it around with my fingers.

Looking back, I really wish I had put on a latex glove because while cement is usually just very drying to the skin, when it sits on there for an hour, rubbing and scrapping along a surface, it really starts to burn. By the end, I had 4 or 5 little chemical burns on my hand and for the next week my skin was peeling like I had Elmer's glue all over it.

I didn't fill the holes in the sides of the counters because I really love the way they look. It's rustic industrial and doesn't pose a sanitation issue. Once the slurry was cured for 24 hrs, it was time to start sanding.

I have a mouse palm sander of my own. Matt as another palm sander. His dad has a random orbit sander. And we found a orbital sander/grinder with 7 in. attachment on craigslist which we thought would be perfect. We also decided to just use regular sandpaper from the home improvement store. Ideally, you should use diamond grit sandpaper/polishing pads, but they can be very expensive.

I tried all 4 sanders. I spent days and days sanding away. The counters did get smooth. That wasn't really the issue. The issue was the discoloration. The deeper you sand, the lighter the color got and the more aggregate showed (aka the little rocks). That stuff is supposed to show. Like when you add glass chips to the concrete and want it to look like sparkly granite. You have to sand past the top layer to reveal them.

The sanding was so inconsistent and splotchy looking. I was so upset about it and beginning to regret not investing in those diamond grit pads from the start. So we finally bought them. I found some on that were 4 in. pads (much cheaper than 7 inch). I got this whole set for around $25. 7 inch pads are around $25 EACH!

They start at 50 grit and move up to 3000. 50 and 100 grit remove the most material and 800-3000 really bring out the aggregate and give it the feel of granite.

These pads changed my life! That may be a bit dramatic, but they did. Messing around with the sandpaper and different sanders was such a pain! I wish I wouldn't have wasted that much time when the concrete was still "soft" those first few weeks.

In one afternoon I used all 7 pads (actually I skipped a few). But they it still didn't look right to me. Still looked splotchy too me. I remembered that a video I watched said these pads work better then they are used wet. We don't have one of those fancy grinders that has a water feed to it, so the next day I just used a jug of water and kept wetting down the surface. The grinder sprays the dirty water EVERYWHERE on that plane. Which meant my stomach and the kitchen walls were covered with dark grey mud (sorry, no picture). But it worked. And that's what counts. Repainting is not a big deal.

The next step was to clean off any residual powder and particles from the countertops and let dry thoroughly. The next day I rolled on high gloss concrete sealer with a 4 inch foam roller. This prevents water and stains from soaking in once you are using your countertops. I only did one coat, but the other day I put my cold drink down on it and it left a water ring which soaked in. So, I'll probably put another coat on before we move it. And I also need to wax it. But it's basically a usable countertop now, and I have to say I am loving it! I don't think I've ever worked something so hard in my life!

I haven't added up the receipts yet, but I think this project fell somewhere in the neighborhood of $300. Professionals charge around $5,000 (granted, theirs look much more high end). And to get laminate countertops would have been around $1,200. I still think it was worth it. I would even do it again, especially after learning what not to do.

And now for the reveal. I will be painting the cabinets white, so don't let the two-toned wood distract you.

To go back and read the whole process click here:
Research and brainstorming: Concrete Counters Part 1
Building the Forms: Concrete Counters Part 2
Pouring the Concrete: Concrete Counters Part 3
Flipping and Installing the Counters: Concrete Counters Part 4


  1. OMG!! I love them!!! Your hard work paid off, it looks amazing!! Can't wait to see you (and maybe the house) soon!!

  2. They look great! I would say not using a professional vibrator caused the holes. Years ago I worked in a dental lab making crown molds and after you prepped the wax mold you would surround it with a cement/sand product and vibrate it to remove any air bubbles. (the you melt the wax part and fill it with the gold) You would be surprised how much you had to vibrate the mold to remove the air bubbles. I remember when I was learning I ruined an entire 'tree' of castings because of air bubbles.

  3. LOVE those!!!! What a lot of work. Good for you for hanging in there. They look great.

  4. I'm getting ready to make concrete countertops for a wet bar in my basement. Thank you for taking the time to tell your story. It will save me time! Not sure if you're still monitoring this blog, I see the last post was from a couple of years ago. I'm curious about the line that was created from the melamine board seam. I'm surprised it's still visible with all the sanding you did. Any thoughts on that? My bar will have both an "L" shaped section and a "U" shaped section, so my plan is to make it in several sections. I'm a little worried about the seams and wondered if you had any suggestions. I'm also planning to stain it, so maybe that will hide the seams? Thanks again for taking to the time to show us your project. Turned out really nice!!

  5. Yes, I'm still monitoring the blog (comments get emailed to me and we still use it regularly to share photos). Not sure if you read through all 5 parts to making the countertops, but the seam line was caused by caulking the two pieces of melamine together. Apparently, it wasn't water tight, and the water caused the particle board to puff up, resulting in a separation at the caulked seam. It's a physical indentation, so I don't think staining the concrete would help. Before assembling the forms, you could try sealing the exposed cut edge of the melamine by pressing caulk into it. Wipe smooth, then assemble forms, then caulk again. Thus preventing the expansion of the particle board. Just make sure the caulk on the seam is as thin as can be! A few other tips: rent a professional concrete vibrator to remove air bubbles (can't stress this enough), buy the fancy diamond grit polishing pads (as mention in one of the posts), wear latex gloves, and research the sealer before you buy (might want to check out Cheng products). I assume you found me via Young House Love today, so you saw what I mentioned about citric acid damage. We also wax the countertops a few times a year with carnauba wax. Thanks for reading! Hope that helps!

  6. Did you use a standard one-speed grinder? Everything Ive read about those pads say most residential grinders spin twice as fast as what the pads are rated for. I poured my countertops on sunday and have only a few holes like you had (for now!)

  7. We used a polisher that had a max speed of 1600 rpm.

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  9. Good to see these helpful information here,Thanks lots for sharing them with us.
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  10. did you use a concrete bonding agent with the Portland cement slurry mix?

  11. Concrete Contractor Perth, Benchmartk Concrete offer a range of quality products and services. Honed and Exposed Aggregate, Liquid Limestone honed aggregate



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