Do-It-Yourself Concrete Countertops - Part 2
How one do-it-yourselfer tackled the project!
Our appreciation to DECORATIVE-CONCRETE.NET for allowing us to reprint this reader's submission to their site. Unfortunately, their webiste is no longer available. This article is both instructional and painfully honest presentation by a dedicated do-it-yourselfer and his experiences in making his own concrete countertops. Hope it is as inspiring for you as it was for us! To read Article 1, click HEREs.
The Whole Messy Process... one person's experience building a concrete countertop
Since many have asked, here is how I went about making my countertops. This is by no means the only way to do it, just my way. I searched the net, made phone calls and asked all the people I could find about the subject. I ordered the back issue of Fine Homebuilding with the concrete countertops on the cover - this was useful even just for the pictures of how the guy set up his saw horses and supports. (Fine Homebuilding/Taunton Press have a home page with info on ordering back issues. Look for Issue No. 90 Sept 1994) GET THIS ISSUE!
I started with several test pieces about 1' square and an inch thick. I used plywood for the bottom of the forms and 2x2's for the sides. I lined each piece of wood with some 6 mil poly and then screwed the pieces together. I wanted to first, learn how to work concrete, and second, see what looked better - the side I finished with the trowel, or the side that faced the poly. My first few attempts at the troweling were pathetic. I did get the hang of it however, all it takes is enough patience to wait until the surface water is gone before doing the hard troweling.
The side that faces the poly does come out smooth like glass but I did end up with small air bubbles, the concrete picks up any folds or ripples in the poly, and overall it looked like something that was manufactured instead of man-made. So I decided that I would build my forms right-side-up and I would hand trowel the finish. I wanted a jet black counter and searched high and low for pigment. The smallest amount of powder pigment I could find around town was 50 lb bags. I only needed a couple of pounds so I looked for liquid pigment. I found some but then the supplier ran out and no one else within 1000miles had any (that may be an exaggeration but I don't think so). So I bit the bullet and bought a 50 lb bag of black iron oxide for $90CDN.
You will need to do a little math and experimentation to make your color
work. From what I've read, a good rule of thumb is "the MAXIMUM amount of colorant
should not exceed 7% of the cement content of the concrete". In
my case I was using 50 lb. bags of ready-mix concrete. I phoned the manufacturer
and they said that the cement content of the mix was 15%. So I have 7.5 lbs of
cement per bag. So 7% of that allows me to have up to 0.525 lbs of color per bag
I had lots of room indoors so that's where I set up my supports. (I was in the middle of renovations and didn't feel guilty about getting a plywood floor dirty.) I made them almost exactly like the supports in the Fine Homebuilding article; two sawhorses with 2x4's laid across them edge up. Put down lots of tarps or poly or do it outside because it does get messy! Duh...
I started with the island which was approximately 4' x 4' x 1.5", with plywood for the bottom and 2x2's for the sides, all lined with poly, of course. I made it in one piece and, in hindsight, would probably have made it in two pieces. Moving around a 275 lb. slab of concrete is not my idea of fun! I cut some stucco wire to fit with about a half inch of room between the stucco wire and the form sides. I made sure that the wire lay flat on its own (not curling up in the middle or around the edges). I put the stucco wire aside for later.
Reading the directions on the concrete and doing the math led me to 5 bags of concrete for that size of slab. Big mistake number 1: Don't try mixing 5 bags of concrete in a wheelbarrow by hand. PAIN, SWEAT, BLISTERS! Plus it takes too bloody long. My sister thought I was going to die. Spend the $10 and rent a mixer. Even then, mix a little at a time. I found that adding 1/2 a bag of concrete, then a little water, and repeating that until all the bags were in was just about right.
Adding a full bag at a time, I ended up with dry clumps sticking to the bottom of the mixer. You can get them off by stopping the machine and scraping the dry stuff with a shovel, but why make things harder than they need to be. Find out the total amount of water needed for the number of bags you have and have it all standing by in a bucket or jug.
Once you have all the concrete in the mixer and 3/4 of the water, you can add the pigment. Don't add all the water unless you need to. The drier the mix, the stronger the concrete will be. How dry is dry? How wet is wet? I don't know. If you get a bucket full of your mix and you dump it out and it flattens out like pancake batter, well, that's way too wet. It should hold together like a sand castle when you dump it out of the bucket. Sure it's going to "slump" some but it shouldn't "run".
I filled a bucket with the mix and dumped it into the poly-lined form. Then I roughly spread out the concrete. As soon as I had filled the form about 1/2 way up I laid in the stucco wire, then the rest of the concrete on top of that. Push the concrete around with a trowel to generally even it out then take a board and screed the top back and forth to force the concrete into itself and to level it off.
Tamp down the surface with the end of a board or something just to force out more bubbles. Trowel again. I borrowed my neighbors magnesium trowel to bring lots of cream to the surface but that was just because he had it handy. A regular trowel will do. I also borrowed his broken hand sander. It is not great for sanding but it does vibrate like hell. I held it to the sides and bottom of the form and brought a lot of bubbles to the surface. If you don't have a broken sander, I've heard of people using 'personal' vibrators. If the slab is light enough you can gently pick up one end and drop it a number of times and wiggle it back and forth. Or you can just walk around with a stick and tap the edges and bottom.
Since I had the forms inside the house, it took quite a while for the surface water to disappear; about 4 hours if I remember. Once it was gone I laid into the surface with the trowel. You have to push really hard but the results are worth it. The concrete takes on a nice polished look. Each time I did this the concrete seemed to build up a sweat so I'd trowel a bit, wait a while, then trowel again. Finally no amount of troweling would change the appearance and occasionally the troweling started to do more harm than good by bringing up small grains of sand from the surface. I covered the slab with poly, called it a night (1 a.m. I think) and went to bed.
I covered that slab for about a week with poly just so it would dry slowly. My neighbor said that it wouldn't matter but I had read otherwise. Better safe than sorry (and mad at your neighbor). I unscrewed the sides of the form after a couple of days to reveal mistake number two. I thought I'd try something tricky with the form so the night before I poured it I put a bead of latex caulking on the inside edges of the form so that I'd have nice round corners. Well I don't know if the caulking wasn't fully cured, whether the caulking was old, whether it had reacted with the concrete, or what, but it was still goopy and had stuck to the concrete. It dried after a couple of days and did eventually scrape off. I wouldn't do that again... at least not without more experimentation on small test pieces.
I looked high and low for concrete sealers to use. I was almost ready to buy an acrylic sealer when I went into one store and they told me it was a bad idea. They said that all the acrylic sealers contain (xylene?). It is poisonous and that if it was a public heath concern (for a restaurant lets say) then it would never make it past an inspector. They recommended a food safe epoxy. It is what a woman who makes concrete countertops in the area uses. I had seen her countertops before at a home show and thought the finish looked alright. Not wanting to have toxic countertops, I bought the epoxy. If nothing else I'd have a mostly indestructible finish. It wasn't cheap though, 9 liters for $270.00 CDN. That's the smallest quantity they had. I'll probably end up using it all by the time I'm done. (if anyone has more/contrary info on sealers available for this application, I'd be grateful to hear about it!)
I let the island cure for 28 days (the time recommended by the epoxy manufacturer). I set the slab up onto the sawhorses so that each side hung clear by several inches, allowing me to get good access to the sides. I wet sanded the top with 220 paper, using lots of water to clear away bits of sand, etc. I ended up using a belt sander on the edges to smooth them off. I tried using a edging trowel on my test slabs but never did get the hang of it. I let the slab dry for 24 hours before applying the epoxy. The instructions said I could apply it when the slab was damp but my experiments seemed to indicate that more bubbles appeared in the epoxy when the slab was wet. I mixed up 2/3of a liter of epoxy to put on the slab. I poured it out onto the slab and brushed it around and over the edges with a disposable brush. I laid it on in a good thick layer and as soon as I had brushed it out evenly, I left it alone. You don't want to work epoxy too much, this stuff starts to set up in 20 minutes. Besides it smoothed out fine on it's own. I left it alone for about 20 minutes then ran the brush along the undersides to pick up any drips. So my guess was about right, approximately 1/2 liter for the 4x4 slab.
The next day I felt the top of the slab and it seemed waxy. After some reading I found out this is called an amine blush and is a byproduct of the epoxy reaction. It washes off with a little water. I washed the slab then on the next day I did a quick wet sand with 400 grit to get rid of the tiny bumps and dog hair embedded in the first coat. I waited 2 days to sand because the epoxy was still soft (dent-able with a fingernail) after the first day and wouldn't sand well. There were a couple of small spots that were not quite covered with epoxy. What I think happens is that areas of the slab that have a little pit or aren't that smooth, absorb more of the epoxy than the rest so you end up with a dry area. I just made sure that on the second coat I really covered that area.
After the second coat had cured I washed and wet sanded with 600 grit. Now I went a little overboard with the finishing here trying to see how much like a piece of fine furniture I could make the slab look like. I did the 600 wet sand, then steel wool and some wool lube, then some pumice stone, then rottenstone, then auto polish. After all that, for a kitchen counter, I'd say anything more than steel wool is overkill. There is nothing wrong with the finish as it sits with just the unsanded epoxy. In fact it's gorgeous. But I think that over time with scratches and scuffing you will end up sanding anyway. With the Black color I chose, scratches show quite easily. The epoxy is hard to scratch, but it does scratch. I think that with a light color you might never see a scratch. My dad and I were trying to separate 2 boards that had got epoxied together the other day. We banged the epoxy with a hammer dozens of times and it never showed a scratch over the light colored wood.
To protect the island cupboards from damage I covered them with a 1/4" masonite board, stapled down in spots. I put a couple dabs of silicon caulking near each corner and we laid the slab down on top of that. I made it so that there was 1/2 inch overhang on all sides. If I did it again I'd go for a little more overhang. I put a mix of bees and carnauba wax on top and buffed it up. Beautiful.
The rest of the countertops are your basic large "L" shape. I made it in three pieces. One slab is just a straight ahead 5' length of counter. The next is about 6' and has a hole for a cook top. The other is 8' long and has the hole for the sink. A couple of the pieces meet a corner cupboard which is on a 45 degree angle so I had to do some clever form work. I made a cardboard template of the corner and transferred the shape onto the form.
For the cook top and sink cutouts, I layered several pieces of plywood together, covered them with poly, then screwed them in position into the main poly lined forms. Along with the stucco wire I added 4' lengths of rebar in the thin spots either side of the cutouts. Mistake number 3: Measure how big and where your cutouts are about 1 million times. I had the cook top in the right spot but didn't account for the little screws on the side of the cook top. I didn't discover that mistake until the countertop was already set in position. That meant another hour or two with the belt sander and black smelly dust all over my kitchen. I made the mistake of taking my neighbors advice on how far forward my sink should be and ended up adjusting it later on. I had to rent a wet/dry handheld cutting wheel and bloody hell was that a mess. Wet, filthy water everywhere, plus a lot of hard work. We took about an inch and a half off of one side of the hole. At least we discovered that BEFORE we installed that slab. We almost made another mistake in the sink placement. I knew I' would need to drill a hole through the concrete for the tap, but I forgot that I should account for that when I put my rebar in the slab. As it turned out we got lucky and just missed having to go through the rebar.
When epoxying these slabs I hurried too much. I tried doing 2 slabs at once and, as a result, one slab picked up much more dust than the other because of all the dancing around I was doing while putting epoxy on the other slab.
Once these slabs where in place (thanks to all my muscular friends) I needed to fill the joints between them. I called the guys where I bought the epoxy. I told them it looked beautiful and they were glad to hear it. I asked about the joints and they said that I could make a filler out of the epoxy, sand, and the pigment. I taped off either side of the joint and pushed the filler into the cracks. After smoothing off the top I let the mixture set for about 30 minutes before I removed the tape. Once the epoxy had set a couple of days I sanded it. And although it looks a little different than the concrete, it fits right it and makes a nice looking joint.
I put a bead of clear silicon around each opening and put in the sink and cook top. I first put in the cook top and sink and marked all around with tape so that when I put down the silicon then the sink I could just peel off the tape and have a nice clean edge. That idea mostly worked. I also put a bead of silicon along the backs of the cupboards along the backsplash, and up the sides where they met with the oven cupboard.
Those countertops have been in since August and still look great. There are a couple noticeable scratches but nothing that is deep and wouldn't come out with a light sanding. To tell the truth, I don't know what causes the scratches. I've slid big heavy things across the counters and nothing happens, but you shove a cardboard box around and marks appear. Most marks disappear with a coat of wax, so maybe it's just the wax getting scratched? There is also a (less than) hairline crack in front of the cook top. It is not noticeable unless you are looking for it and waxing it hides it completely. Honestly, I think you have to accept the fact that your counter may crack as it settles. I don't think it is anything to worry about. If a big crack did appear I'd just stuff it with more of the epoxy paste I used for the joints.
The counters have not bowed at all since they were cured. I'd say that any 'non-flatness' in the slab was probably there in the form on the day I poured it. The slabs themselves did not shrink noticeably, or bend. The only thing I think I'd do different is I'd make the 8' slab with the sink in it into 2 slabs. I thought the joints would detract from the beauty but they really just become another part of the slab.
I am currently working on two slabs which will be my eating nook. They are just less than 3/4" thick but are remarkably strong. I even embedded a small fossil in the top of one of the slabs but I have no idea how it will look after the epoxy goes on. The epoxy does a good job of hiding scratches - probably fossils too. I also want to redo my vanity top in the master bath. I just need to decide on a color/texture. There seems to me to be a world of possibilities. I borrowed my neighbor's grinding wheel with a concrete grinding stone. You couldn't call the results smooth but it does expose a lot of the aggregate which could look nice. And with a thick coat of the epoxy it would be smooth to the touch anyway.
In total (so far) I've bought for 26 linear feet of counter (1.5 inches thick):
So at around $500 total for 23 feet of counter = $19/linear foot (Canadian