11.21.2013

Concrete Counters - Prep & Pour

After spending the previous weekend installing our IKEA cabinets (here and here), we spent this last Saturday pouring our concrete countertops! I didn't document this at all when we did it last year in Breck with the help of a bunch of friends (on our fifth wedding anniversary!) because I was busy grouting five bathrooms that day. And this time, on Saturday, I left at 9:30am to take our dogs to get their annual shots and when I got home less than two hours later, the concrete was already 95% poured. Bummer! But I managed to catch a few more steps at least.

Our kitchen looked like this the Sunday prior. Cabinets were in and Curt cut 3/4" plywood sheets to fit the shape that we planned on pouring our concrete counters, and screwed them into place. 



This time, unlike last year, he also put plastic sheeting over the plywood. Apparently this helps prevent moisture from seeping into the plywood, which could cause cracking. We did have two hairline cracks appear in our counters in Breck on a very narrow strip of concrete behind a sink, so I guess this is a good idea. We didn't fasten the sheets, just laid them over the plywood. An advantage of the plastic sheeting is that you can extend it down to the ground, protecting the cabinets themselves during the messy pouring and finishing steps. Another recommended method we read about online was using cement backerboard, which would also work to not draw moisture out of the concrete and cause cracking, as well as provide a super sturdy and solid surface to build on. 


Curt had already cut a hole on the plywood for the sink, but he also needed to add 1x4 edges around the hole. We didn't need to use the plastic edging from Z Countertops because the edges didn't need to be nice here - the sink has a slight lip around the three sides which covers up those edges. Curt used the same 1x4s to make butt end forms for the sides of the stove and the refrigerator where the edges didn't need to be 100% perfect.




But to back up, as you can see above, he already put the plastic edging all around the plywood bases. We used Z Counterform products for our counters in Breck and have been extremely happy with them, so we ordered the same materials this time (except the concrete mix itself, which I think came back to bite us). They offer multiple styles of edging though I prefer the chunky plain square edging myself. They ship you long strips that you trim to fit and screw into the plywood to hold them into place. The forms themselves need to be completely level also, because they determine the height of the concrete. It's also important to get the corners mitered well at 45 degrees. A few of our corners took multiple tries with the saw to get them perfect. Curt added duct tape outside the corners so they don't shift at all when you start spreading heavy, wet concrete up against them. These plastic edge molds just break off when you're ready to remove them. I was shocked when we removed these forms last year to find glassy smooth and shiny concrete sides with super sharp edges. They were smoother than anything we could have achieved by sanding.

Smooth and shiny once you break them off!
The next step is to cut wire mesh to fit into your edging. This is similar to what you'd do for any other concrete pour - it adds strength. In the photos above and below, you can see that we added a pretty big overhang to the right, where there was previously a half wall. This caused Curt some concern because we didn't know how it would turn out. Would we need to use brackets underneath for support? Would it be too much weight? When he researched this online, there was not a whole lot of info. Our overhang is about 10.5 inches which affords enough room underneath to sit comfortably on our stools.




So, we used 6"x6" mesh along with 3/8" pieces of rebar (you can see the thicker pieces of rebar in the photo above) added to the overhang area in the hope that combined, they would add enough structural support. The pieces of rebar were attached to the wire mesh using wire ties. We also propped up the corners of the overhang with 2x4 supports because the plywood was leaning down, and we wanted everything to be level. We're planning on leaving those supports there for 28 days - the full length of time concrete takes to cure. At that point, we're hoping not to need brackets or corbels of any kind underneath to support the counter. 

After all that prep, Saturday was finally the day to pour! This was what it looked like when I left for the vet with my dogs.


And this was what it looked like when I got back home, less than two hours later!


We bought 15 80-lb bags of concrete mix from Home Depot ($16 per bag) but only used 11 bags. Curt did not use a standard mix that has pea gravel, he used a mix that is much stronger and meant for counters.  We borrowed an electric barrel mixer like we used last year. Funny story - Curt picked up the mixer Friday night from our friend who lives a mile away. When he went to set it up Saturday morning, he couldn't find the detachable legs. He backtracked in the car and found the legs on the side of the road, thankfully! They must have fallen off the trailer the night before. Curt should have been on Sanford & Sons...


Curt mixed two bags of concrete mix at a time. We also used Quikrete liquid concrete color like we did last year. We used very little dye last year because I wanted light gray counters and I got exactly what I wanted. Curt was hoping they'd be darker so he decided to use more color this time around. Our counters are still not dry so we're not sure exactly what color they will be! In order to get the color consistent for each batch of mix, you mix the dye into water first, then concrete, so the proportions are the same each time. We used one bottle per five gallons of water. Each bag of mix, according to its packaging, should get 1 gallon of water. Even though Curt added an extra quart of water per bag of mix, our concrete was still maybe too dry when it was poured, which is we think what caused the texture problems like bumps and air bubbles/holes we're watching come out as it dries. Boo.

While the pour itself didn't take long, there is more to do after just getting the concrete into the forms. It needs to be "worked" and smoothed and troweled for quite a long time to get it looking good. Curt put an ad for a concrete finisher on CL and he found the guy pictured below who had only done floors, not counters. Smoothing concrete is the same no matter where you put it, so I don't think it was his fault that we have some flaws. He charged Curt $100 for about 4 hours total of work so it wasn't a huge loss either way. But he really struggled with the concrete as large bubbles appeared throughout the surface. Usually air bubbles appear at the edges, and you use a vibrating sander to shake them to the surface. Curt did use a sander but I think our concrete was a little bit too dry for it to be super effective. Most of the edges look nice and sharp but the most prominent edges on the outside of the bar and where you enter the kitchen are not solid - they're full of air pockets. The vibrating part was supposed to be my job and I wish I had been home in time so Curt would have been more able to closely monitor the concrete mixing itself.










Later Saturday evening, after the surfaces were hard to the touch, we covered the concrete with more plastic sheeting. We didn't do this last year but it's supposed to slow the drying process and prevent cracking while it slowly cures. It's been interesting to see how it's started drying over the week because some portions have dried quickly (probably close to our floor vent) while others are still damp under the plastic. At first I thought the color was way too dark but I think as it dries it will be the lighter gray color I wanted. The same thing happened last year and then it just finally dried to a super light gray.








We took the sheet off this side because we just couldn't wait any longer, and it's getting closer to the final color, and more even
The bumps throughout the concrete are going to be interesting to tackle. The concrete surface itself is very smooth, but it just has mounds the size of a quarter or larger all over the place. I'm assuming once I start sanding that these will pop and then we'll have craters. This is common in concrete countertop projects - at least with DIYers! - and we've read that people have had lots of success making a slurry of wet concrete to patch the holes. While we didn't have to do that last year, we are going to have to give it a shot this time around. We can also reattach the plastic edges to the sides that are full of holes and see if we can bulk them out a little more. My biggest concern is matching the color, but I've read there is a lot of room for error and that it takes a LOT of dye to make drastic changes in the color of the concrete. So, we shall see what happens when I started sanding these suckers...



1 comment:

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