222) Concrete Countertops – Prototype

by Gail on February 16, 2015

house with metal roof.jpgWell, I know I declared This Green House finished in 2014, only 5 years after we started building.

But, the truth is: there will always be more tasks when you build your own house – some of them fun, and some of them fraught with difficulty. Concrete countertops fall into the second category for me.

It was always my intention to replace the temporary plywood countertops with concrete countertops I make.laundry alley before

I am ever-so-slightly risk averse, not-to-mention a scaredy cat. (Is that the same thing?)

Making 23 lineal feet of concrete countertop is a big deal.

But, I have a couple of test projects. One is the very simple countertop in our laundry alley, above the two pull-out (dark and light) laundry drawers. It measures 35″x 25.5″, and has no sink or knockouts of any kind.laundry counter before

Piece o’ cake, right?

Well, maybe not piece o’ cake, but about as simple as it gets for a countertop. A good learning exercise.

To start, I read this bible of countertops cover-to-cover:concrete countertop book

I have come to the conclusion that most of the YouTubes and blogs filmed and written about most any subject are not offered by experts. Some of the info is downright erroneous. And some dangerous. At the very least, they will make my DIY job more difficult. They are written by people like me, who have tried something once or twice and are telling our stories. But, we’re hardly experts.

So, I go to the experts. One of the experts is my supplier of the concrete mix: StarPatch Concrete. I visit their showroom and call them whenever I need advice, and they patiently answer my questions.

I still make mistakes. But that is how I learn.

So, here’s my experience for this learning piece, complete with the lessons I’m learning.

I used the temporary plywood countertop as my template, because it’s already been cut to fit. Since I planned to prepare a mould rather than casting the countertops in place in the kitchen, I turn it upside down and mark the front of the mould. On the table saw, I cut strips of what we call Melmac, although I think there are other brand names for similar plastic-coated pressboard. The width of the strips determine the thickness of the countertop – in this case 1.5″, plus 3/4″ for the plywood base = 2.25″.

After drilling pilot holes for the drywall screws, I screw the strips onto the plywood template with drywall screws, making sure each upper edge has a screw at the corner so the concrete won’t push the top of the mould apart.

Then, I apply tape on either side of all the joins, about 1/4″ away from the join, so that when I apply black silicone caulk, the edges will be perfectly straight after I smooth it out with a gloved finger or a caulk applicator.

After the caulk has dried, I pull off the tape.tape and silicone

In my prototype, I wanted to make a surface treatment with some agate slices and concrete colourant. This is the part that can go badly wrong, and I would say it did, to some degree. I applied a very thin layer of black silicone to the agate slices, and adhered them to the bottom of the form, which is, of course, the top of the countertop.removing silicone tape on countertop mould

Then, I sprinkled some mocha and black colourant in a not very planned design. Didn’t love the way it looked, so I took a small paintbrush to spread it around differently. I truly didn’t know how this would work.

Next, I cut a 2×2 wire grid to fit inside the mould, about 1/2″ away from the sides and back, and about 1.5″ away from the front of the form (these wire strengtheners can ghost through to the concrete surface, so I kept them away from the visible parts of the finished countertop.) With small wire hooks, I suspended the 2×2 wire about 1″ from the bottom of the mould.countertop mould ready for concrete

With the mould ready, I turned my attention to mixing the concrete.

By my figuring and the estimator on the StarPatch site, for my .8 cubic foot volume I needed 1.5 bags of the countertop mix (50 lb bags). I mixed each bag with a flow kit (a powder from StarPatch) and 4 litres (4 quarts) of water. One bag worth easily fit into a 5 gallon bucket (sorry about mixing Imperial and Metric measurements. Such is our lot in Canada.) The mixing paddle fits on a 1/2″ drill.mixing countertop mix in bucket

Now I wish I had mixed it in the wheelbarrow with a hoe, as I did whenever I was mixing mortar for the stonework on the house. It’s easier to get a good mix. IF I decide to do the kitchen countertops, I will rent a cement mixer. The goal is thick like oatmeal, not runny. The drier the mix is, the stronger the bond.

By the trowelful at first, and then, when the pail became lighter so I could lift it, I poured it into the mould, pushing the concrete into all the corners and voids (or so I thought.) I have no photos of this step or the next two, because it is such a hectic time. Turned out I had to mix more mid-pour, which made me all the more anxious. My total to fill the mould ended up being 1.75 bags.

To settle the concrete into the mould and eliminate voids (again, so-I-thought), with a palm-sander, I vibrated all around the mould 3 times, plus banging the whole mould down on the table once or twice.

With a board, I screeded the full mould to level the concrete, and then let it sit undisturbed for about 30 minutes.finished wet concrete in mould

Then, I used a rounded metal trowel to “float” the surface.

When it was “leatherhard”, after about 90 more minutes, I used a metal trowel to trowel the surface smooth, and an edging trowel to curve the edges of the concrete.

I left it to cure for 5 days. SOOOOO curious, but I couldn’t peak until it was cured.

Took out all the screws holding the mould together:remove screws in concrete mould

Pulled off the sides strips of the mould, and then, with my cousin Chris and D for muscle, turned it upside down and carefully pried off the plywood base.

To reveal…….

Ta! Da!

A gawdawful mess – yuck. unmoulded countertop

You can see all the voids, and the concrete colourant looked like a dog’s breakfast.

Here’s a closeup:unmoulded concrete bug holes

And, it was at this point that I somehow changed the borrowed camera’s setting to a “tint”, which means that some of the next photos are black and white with a feature colour tint (what the heck?)

My response to the great unveiling was to walk away until the next day, when I decided to experiment with it. I could hardly make it look worse.

First, I dipped a cloth in water to wipe away the powdered colourant that was just sitting on the surface. It just made a mess as I wiped it off. Worse, it revealed even more faults, surface cracks and discolouration.

But then I started noticing how the colour settled into surface imperfections, and the whole surface started to look like a combination of marble and pitted sandstone! I was beginning to warm to the look.concrete slab before repair

So, I decided to fill the “bug holes” with a slurry to see how that would look. My go-to guy at StarPatch suggested I sift out the fibre and the larger sandsifting concrete mix for a slurry

and mix the resulting powder with water and a bonding agent (1:4 with water) to fill the holes. In retrospect, I should have used a finer seive, because the slurry is too granular.

applying slurry to concrete countertopI pasted the whole surface with a gloved hand, and then scraped it off, so that it looked hazy like grout on tile.

Impatiently, I started wiping it down, first with water, then at the suggestion of a YouTube video, vinegar. It did get the slurry off, but the bug holes were somewhat depressed because it hadn’t hardened enough before I started cleaning it (and still granular.) Goodness, this is a lot of rash decision-making, kind of panicky.

I blundered on.

Decided it was time to grind and polish with my wet grinder.wet grinding concrete countertop

As I started to polish, I noticed the only part I was liking (the marbled look) was being ground off to reveal the pure white underneath. So, I stopped grinding, and put some more powder on my cloth to re-colour the surface imperfections.

There comes a time in any artist’s project that she needs to decide when the work is “finished.” Seldom easy for me. But, this is the point where my experimentation ends with this prototype countertop. I decided to leave well enough alone, and stop working on it.

So I scraped the black silicone off the agate slices, cleaned the surface with water and let it dry overnight.

I still have half a bucket of Broda Clarity sealer left from finishing our concrete floors, and applied three coats with a micro-fibre cloth. You can see the first coat started here, and the difference between the raw concrete and the sealant applied.before and after concrete sealerIf this were a kitchen countertop, it would not be acceptable, because the depressions would trap bacteria. As a sealed laundry countertop, it will work.

A real learning piece for me, and beautiful in its own way. The jury is still out on whether I will attempt the kitchen countertops. I will apply what I learned to a bathroom countertop next, and gain more confidence before I commit.

Here’s the finished countertop, and the before and after.

finished laundry concrete countertop


before & after laundry counter

Thank you for hanging in there until the end! (The countertop saga to be continued.)concrete counter with colour added

Sharing with these link parties:

Cozy Little House , Boogieboard Cottage, Lavender Cottage, Home Stories A – Z, Dwellings – The Heart of Your Home, Elizabeth & Co, Savvy Southern Style (Featured!DIY By Design



{ 9 comments… read them below or add one }

Joy@aVintageGreen February 16, 2015 at 5:30 pm

Creative Gail, good flow patterning. Works with your cabinets and walls. Looking forward to seeing the bathroom countertop.


Gibson Doug February 16, 2015 at 5:33 pm

So….it took slightly less work than the Pyramid of Cheops, then?

Very cool to see Grandpa’s drill being used, still answering the call to duty.


Gibson Doug February 16, 2015 at 5:40 pm

“…the concrete colourant looked like a dog’s breakfast.”
Actually, it looks like the dog’s breakfast AFTER HE FELT UNWELL.

This posting reads like a Christmas Newsletter by a certain famous Christmas Newsletter Writer. What could possibly go wrong?


Carol Schuld February 16, 2015 at 7:30 pm

Hi Gail,
Love to see what you are doing. From the photos I cannot see flaws, looks wonderfully unique. Makes me wonder why I just hired a carpenter to do my work rather than struggle something on my own. Oh well, I’ll just enjoy your undertakings.


Judith @ Lavender Cottage February 17, 2015 at 5:13 am

This is quite the project and since a concrete countertop is new to me, I found your process very interesting. It looks nice and you have the gratification of knowing that it is a one-of-a kind.
Thank you for linking to Mosaic Monday and sharing your creation.


Brenda Young February 17, 2015 at 8:02 pm

Although the finished texture with depressions may not be what you were after, I must say I love the finished color with the agate pieces. All and all a very pretty product, this process would look great as a repurposed top for a piece of furniture!


Kim February 24, 2015 at 5:20 am

That is really pretty and I am featuring it at Wow Us Wednesdays tonight.


Sherry February 25, 2015 at 8:13 am

This looks amazing! I love the idea of adding the agate to the counter top, I have always wanted to try making a concrete countertop. Thanks for showing how to do it!


Chatlie February 26, 2015 at 5:22 pm

Wow! I think you did an awesome job! I understand the mid project panic. I have experienced the same on many occasions. Learning can be stressful. :o)


Leave a Comment

Previous post:

Next post: