Cottage Bath Countertop

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May 17, 2010
After doing three test pieces we decided we were ready to try making an actual countertop. Jay’s mom Pat crushed up some pale green glass to add to the blue canning jar that Peggy had crushed a few days ago. Jay made the mold from melamine, with an oval block in the center for the sink cut-out. We spread the blue and green glass into the mold in wide diagonal bands.

May 20, 2010
After the glass was placed in the mold, Jay added a “chimney” that will form a dropped apron in front of the sink (keep in mind that it’s upside-down at this point). We wheeled it out onto the lanai for the pouring operation.

The countertop takes a little over a cubic foot of concrete, which is hard to mix in a small cement mixer like this without some of it spilling out the front. So Jay added a plywood cover that lets us mix a little more concrete, and also keeps in the dust while mixing the dry ingredients. After weighing out the sand, glass, Portland cement and additives, we mixed it all together without water for about 5 minutes.

Here’s a close-up of the dry mixed material. You can see some of the polypropylene fibers sticking out from the mixer blade. We’re not using steel rebar in this countertop so the fibers help strengthen the concrete. Individually each one isn’t very strong but with about 6 million individual fibers in a countertop this size the concrete becomes much less likely to crack. The glass chips should also make it stronger than concrete made with gravel, because the chips will overlap to form a layered structure.

We added the prescribed amount of water and mixed for about 5 minutes, and did a slump test. It’s too stiff to work so we added a bit of water and mixed some more. The second slump test looked about right so Jay scooped the concrete out into a 5-gallon pail.

While spreading the concrete we tried to disturb the colored glass as little as possible. The mix was already getting stiff so there was no problem filling the chimney and having it stay put. The hard part was working fast enough to get it all placed before it set up. As we added concrete to the chimney Liz placed some colored glass in it so there should be some color showing on the apron in front of the sink.

The photo below shows Jay using the concrete vibrator, which is designed to consolidate concrete and vibrates a lot more than the simpler methods we used in our initial tests. This releases trapped air and makes it flow a bit even though the concrete is quite stiff at this point. We vibrated it for several minutes, working the vibrator over the entire surface.

After placing more concrete in the mold we screeded off the top with a board to level it. Fortunately this will be the underside and it won’t show, because it was hard to get it smooth with all the glass in it. The main thing is to get it flat enough to sit solidly on the base cabinets.

Here’s the countertop in the mold, and it seems not too bad for a first try. We had enough extra to fill the two 12-inch test molds, so we’ll have two test tiles to practice diamond-polishing before we polish the actual countertop. Now we need to let it cure undisturbed for 4 days before we can remove it from the mold and start to polish it.

May 24, 2010
The countertop has cured for 4 days so today we removed it from the mold. It weighs about 200 pounds, which is not too difficult to handle, but the main danger is twisting or dropping it and possibly causing a crack since the cement is not fully cured yet. So we enlisted the help of Jack and Dan to turn it over gently, while Liz positioned foam strips to support it. We could have managed okay with two people but this was good practice for the larger countertops to come.

With the foam strips in place, we carefully flipped it over so that the apron in front of the sink hung over the edge of the workbench.

And finally we removed the bottom of the mold from the top of the counter. It didn’t stick much, so it took only a moderate pull at one corner to get it loose. And with that we revealed the top surface – and a few surprises.

The sink knock-out came out easily, since we had wrapped the edge in 1/8″ foam and duct tape, so a few gentle taps with the rubber mallet eased it out of the hole.

In the photos below you can see the large voids around the areas where we placed the colored glass. Apparently we got the mixture too stiff, and/or we didn’t vibrate it enough to release the trapped air around the colored glass that we placed in the mold. We were hoping to see a solid white surface with glass just below, ready to polish, but this is going to take some fixing!

In order to patch the voids, we mixed up a paste of Portland cement and sand, and spackled it into the holes. Once it has hardened we’ll grind it down with the diamond polisher, and then fill any remaining (hopefully small) voids with a slurry of Portland cement and water. It should look reasonably good when we’re done, but it would have been much less work if we could have gotten all the air bubbles out when it was cast.

We also removed the test pieces from their molds, and one of them had voids similar to the countertop so we filled them in the same way. That way we can try polishing it in a couple of days, before polishing the real counter top. The other test piece was better, with relatively few voids, so we polished it a bit to see how the glass will look. The colors are nice, and just about what we wanted for this bathroom, so we’re optimistic that the real countertop will turn out good once the voids are filled.

May 26, 2010
After the voids were patched and the patching material had hardened for two days, it was time to polish it. Jay started out with the 50-grit diamond disc, grinding away the paste on the top surface to expose the glass and rounding over the edges.

It quickly became apparent that polishing the upturned edge at the back was going to be difficult because the diamond pad is not flexible enough to polish the concave curve. For the time being we just left that area unpolished.

Polishing the sides was not difficult, just a bit messy as the polisher throws a lot of water spray in this orientation.

Here are photos of the countertop after the initial polishing was done. This is only with the 50-grit wheel so the surface is not very smooth yet. We like the colors though, just about what we expected.

Here’s a close-up of the top surface, showing the many small pits caused by bubbles in the concrete. It’s going to take some work to fill all of these.

May 31, 2010
The drip edge on the back of the countertop seemed like a good idea, but it’s just too difficult to polish it with the electric polisher so off it comes! Jay made a plywood spacer a little taller than the height of the countertop on the table, and used it to guide a diamond cut-off wheel to cut off the drip edge. Fortunately it was a breezy day because this dust is very nasty.

After the edge was cut off, Jay went back and ground it flat with the 50-grit diamond wheel. The photos below show the result. You can see that the glass along the edges was oriented more vertically than on the top surface, which creates an interesting effect. Most of this won’t show however, because we’ll add a tile backsplash along the wall after the countertop is installed.

June 6, 2010
Jay polished the surface using increasingly finer diamond discs up to 800 grit. In order to fill the remaining voids in the surface, he applied a slurry made from just Portland cement and water.

June 8, 2010
After letting the slurry cure for two days, it was polished again with the 800 grit diamond disc. The result looks pretty good, but there are still some small voids in the surface so it will need another coat of slurry and more polishing.

June 16, 2010
It took another coat of slurry and a lot of polishing, but it’s finally done! These photos show the final result, after applying a coat of sealer and wax.

Here’s how it looks overall, and after installation:

Second & Third Countertop Tests

May 14, 2010
The results of the first countertop test were pretty good but we wanted some samples of the colors to be used in the cottage bath countertop. The cottage bath has blues and greens in the decorative shower tile so Peggy broke up some blue bottles and arranged the pieces like this:


The first test seemed a bit too sandy so we tried altering the mix by using half as much sand and correspondingly more crushed glass. The result was quite difficult to work with, and even with relatively little water it fell completely apart in the slump test. There seemed to be too much glass aggregate and not enough mortar paste to hold it together and to fill all the spaces in between.

Since the stuff was already mixed, we went ahead and put it into the mold. It didn’t fill the mold completely, and the top looked more like a gravel driveway than a mass of concrete. Obviously the first mix was better but in order to salvage the test we mixed up some more cement and water and poured it over the top to fill in the gaps.

With the second test not looking promising we went ahead with a third test batch, and this time Peggy put in some red glass to see how it will look.

This time we went back to the original recipe. The first slump test was too stiff so we added water, maybe a little too much as the second time it slumped a lot more. This is no problem for a test piece but it would weaken a real countertop to have that much water in the mix.

After filling the mold about half full, we tried a new technique for vibrating the mold to release the air bubbles. Using a reciprocating saw with no blade proved quite effective in vibrating the mold, and made air bubbles rise to the surface. With the mold not quite full, we jammed some pieces of colored glass around the edges. Hopefully they will show after the piece is polished.

The full mold was screeded to level the concrete, then vibrated some more to release the remaining air bubbles (we hope).

May 17, 2010
We diamond-polished the test pieces enough to see how the colors will look. Surprisingly the third test piece showed more glass in its surface even though there was less glass in the mixture. Presumably the more liquid mix and the increased vibration allowed more of the glass to settle to the bottom of the mold. Overall we think they both look fairly good, and this will help us choose the colors for the actual countertops.

First Countertop Test

May 9, 2010
Before making our actual countertops, we decided to cast some small pieces in order to test our mixture and our technique. We made a mold 12″ square and 1.5″ high, which is the thickness that our countertops will be. For this test we decided to try placing some colored glass pieces in the bottom of the mold before pouring in a concrete mixture made with just clear glass. We want to use this technique, rather than just mixing the colored glass throughout, because we only have a little bit of some colors like canning-jar blue and we’ll need to use it to maximum effect. This also lets us control, to some degree, the pattern of glass that will appear on the finished countertop.

We enlisted Liz’s mom to help smash some green glass pieces for the test. It’s not worth using the glass crusher for such a small quantity, so Peggy just broke it up with a hammer on a large flat rock. Then she carefully arranged the pieces in the mold. We also documented the pattern with a top-down photo (not shown), which we will compare later to the finished piece to see how much the pieces moved around as the concrete was placed. The countertop is molded upside-down, so the glass on the bottom of the mold will end up on the top surface.

We mixed up the concrete from white Portland cement, crushed clear glass, sand, and a commercial concrete countertop admixture that strengthens the concrete and reduces the amount of water we need. The concrete mixture needs to have just the right amount of water – if it doesn’t have enough water it won’t flow completely and if it has too much water it will be weaker and more likely to shrink and crack. In order to check the water content we performed a slump test using a plastic cup. We filled the cup with concrete, tapped it a few times to settle, cut a small hole in the top to let in air, and pulled the cup straight up. The resulting cone was nearly as high as the cup; it didn’t slump much at all. Too dry!

After adding a little more water and mixing again, we did another slump test. This time the concrete slumped to about 60% of the height of the cup, which should be just about right.

We carefully placed the concrete into the mold, trying not to disturb the green glass. We only filled the mold about half full at this point.

In order to consolidate the concrete and to encourage air bubbles to rise to the surface, Peggy vibrated the mold by tapping around the edges with a hammer.

After tapping for a minute or so, the concrete had settled and air bubbles rose to the surface. If we don’t vibrate it enough, air bubbles will remain and any that are on the bottom of the mold will become pot holes in the top of the concrete (which we can fill later if needed). And we want the liquid to flow around all of the green pieces that we placed in the mold so they’re well embedded in the concrete. But if we vibrate too much, the solids will settle out of the mixture and we could end up with not enough cement “cream” on the bottom to make a hard surface. The photo below shows what we judged to be about right.

With the first layer consolidated, we placed the rest of the concrete and smoothed it with a stick. We calculated the amount of mixture that should just fill the mold and it came up close but a little bit short, partly due to some material still clinging to the bucket and tools. We’ll add about 10% extra next time.

Here’s the finished piece in the mold after a little more vibrating. We’ll cover it with plastic to prevent rapid moisture loss, and leave it undisturbed for 4 days to cure before we remove it from the mold.

May 13, 2010
After letting the piece cure for 4 days, we removed it from the mold. The first photo below shows the piece as it came out of the mold, and the Makita stone polisher we used. The second photo shows the underside of the polisher, and some of the diamond-impregnated polishing discs that attach to it. The first disc on the polisher is the coarsest, 50-grit, which will remove material quickly but leave a rough surface. The other discs have progressively finer grits up to 1500. The stone polisher has a hose connection and a valve so that it can feed water right through its central shaft and onto the piece as it’s being polished.

As Jay started to polish the piece, the green and clear glass started to appear.

After about 10 minutes, most of the green was visible. Overall it took about 15 minutes to polish the top and the edges with the 50-grit diamond disc.

The first photo below shows the green glass as it originally appeared when Peggy arranged it in the bottom of the mold. This photo is a mirror image, so that it can be compared with the view from the other side after polishing. The second photo shows how it looks after polishing with the 50-grit disc. We can see most of the original pattern, but some of the original pieces are not visible – presumably because they moved upward in the mold as the piece was vibrated. More grinding would reveal those pieces but it would also grind away some of the fine pieces of green glass so we won’t grind it any more with the coarse diamond wheel.

Below is a close-up of the two above photos combined, with the original pattern of glass overlaid on top of the final photo. It lets us see how much the green glass moved around as the concrete was placed in the mold, and how much of each piece is actually visible. We can see that most pieces stayed about where they were, but some of them moved by up to 1/2 inch. This tells us that we can create large patterns this way, but there’s no point in placing each piece of glass exactly because they’re going to shift around a bit.

The photos below show how the edges of the piece came out. They look decent but of course there’s no green on the edges and it seems that it would look better to get some colored glass on the edges somehow. We could just mix it all together if we had enough colored glass, and we have plenty of green to do that but not enough of some of the colors we want to use. So instead we’ll try to find a good way to get some colored glass to stay around the edges of the mold.In these photos you can also see quite a bit of texture from the sand that we used in the mix. It seems a bit more sandy than we’d like so we’ll cut back on the sand and increase the percentage of glass for the next batch.

Building a Glass Crusher

DISCLAIMER: This page documents what we did, but we’re not suggesting that you should do anything like it. This machine can cause severe bodily harm, and if you use this information to build anything then you assume full responsibility for the consequences.

We converted an old clothes dryer into a crusher for crushing glass down to pieces small enough for making countertops. The basic idea is to drill holes in the drum so the broken pieces can fall through, and to make an opening the bottom so they can fall into a bucket below the dryer.

October 3, 2009
The first step was to remove the top and front of the dryer, and then to add some reinforcements to the side of the case. This is a view looking downward, with the dryer laying on its back. The drive belt runs around the middle of the drum and the motor sits behind that, so we decided to put a vertical “fence” made of plywood below the middle of the drum and to enable the crushed glass to fall out in front of that. The fence sits in front of the 2x4s shown in this photo. We added some slanted plywood sides to make a “funnel” that will guide the broken glass to the middle, where we cut a hole in the bottom of the case. Notice the plastic fins inside the drum. These are fine for tossing clothes around but they’ll quickly get smashed once this is full of bottles and rocks so they have to go.

Once we had cut the 8-inch-square hole in the bottom of the dryer and boxed around it with plywood, Dave drilled 5/8″ holes in the drum so the crushed glass can fall through and out the bottom.

We replaced the flimsy plastic fins with square steel channels bolted on to the drum. For the first short test we put in just a few bottles plus a fist-size rock to help smash them up. These photos show the glass before and after running for a minute or so. It works pretty well for a first try!

October 5, 2009
After a few test runs we decided that the holes needed enlarging from 5/8″ to 3/4″, in order to let slightly larger pieces of glass fall through. We also added another steel bar for a total of 4 bars instead of three, arranged symmetrically around the drum. The most significant refinement was to remove the heater from the back of the dryer, leaving an oval opening near the top of the drum large enough to feed bottles in while the crusher is running. Now we don’t have to stop it except to empty the glass bucket at the bottom when it’s full (it holds about 40 pounds of crushed glass).

In addition to letting us feed glass in while the crusher is running, the opening in the back of the dryer allows us to watch the crushing process – and so can you! The following is a video shot through the port on the back of the dryer as the crusher is running. For a realistic sound effect while watching the video, turn your computer’s speakers to maximum volume and then repeatedly slam them together as hard as you can right in front of your ear. It’s louder than that.

In our first production run it produced 70 pounds of crushed glass in about 15 minutes. That may sound like a lot, but our countertops will be about 85% glass and weigh about 18.5 pounds per square foot, so 70 pounds of glass will make roughly a 2-foot by 2-foot section of countertop. We’re going to need a lot more glass! Here’s a shot of the crushed glass we produced, with a dime added for scale. This is all clear glass, but you can see that some of it has light shades of blue and green. The pieces range from dime-sized down to dust, which will make stronger concrete than if the pieces were all of the same size.


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We decided to make our own countertops out of concrete, using recycled glass for the aggregate. We found the book Concrete Countertops: Design, Form, and Finishes for the New Kitchen and Bath to be inspiring and helpful for getting started. Most of that book talks about making countertops out of conventional concrete, i.e. with cement and sand and gravel, but we like the look of glass aggregate. Here are a couple of examples from Vetrazzo that show the general ideal of what we’re aiming for:

Since our property already has some piles of old glass containers back in the woods from prior owners who thought that dumping trash in the woods was a good idea, we decided to clean up their mess and recycle the glass into countertops for the house. Here’s a photo of Liz washing the crates of mostly-broken glass jars and bottles we dug out of the woods.

Concrete Mix Recipe

Here is the final recipe that we used for our countertop mix. These quantities make approximately 1 square foot at 1.5 inches thick, with a little extra, so we multiplied this times the square footage of each countertop to get the final quantities that we mixed up:

Item Quantity
Crushed Glass 11.4 lbs (typically 7.4 lbs clear glass plus 4 lbs colored)
White silica Sand 4.8 lbs
White Portland Cement 3.6 lbs
Cheng Countertop Mix 88 grams
Polypropylene Fibers 2 grams (optional)
Water 1.3 lbs (plus more as needed to make a workable mix)

The amount of water given above yielded a fairly stiff mixture, and then a little more water was added to make a workable consistency. The Cheng Pro-Formula Countertop Mix is available in various colors and we used the base mix but the “platinum” color is similar. It contains additives that improve workability and reduce shrinkage and cracking, including some chopped polypropylene fibers. We added a bit more fibers to our mixture and they’re probably not necessary, but our local concrete supplier sold us a bag for just a few dollars and it was enough for all our countertops.