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Step 6Curing and Finishing
There's a window of time that is ideal to take advantage of if you're going to be grinding and polishing your countertop. After 4 days, the concrete is stiff enough to break the mold. After 10 days, the concrete has reached 95% strength and will be more difficult to grind. Concrete reaches full strength after 28 days. I made sure that all my grinding and polishing was done within that 6 day period which made my job easier.
After 4 days of curing, I started unscrewing all of the screws in the mold. Make sure that you get all of them and it should go fairly smooth. Don't put any pressure on the green concrete by prying against it, as you will risk chipping or cracking. Once you get all the sides off, you'll need at least one other person to lift it off the bottom of the mold. It should pop of the bottom fairly easily, then prop it up on it's edge. I then laid down strip of the styrofoam and laid the countertop right side up on top of it. This props the countertop off the bottom so you can get your fingers under it and it also makes it easier to grind the edges.
If you want your countertop to be a solid color, you can skip the grinding process and move right on to polishing. Both processes require using diamond coated grinding pads with a wet grinder, however there's less time involved in polishing. I wanted to expose the aggregate and glass in my countertop, so I chose to grind first. There's ways to get around using a wet grinder, like using a regular grinder/sander with the diamond pads and having someone else use a hose, or poking a hole in a gallon jug and letting the water run out as you grind. If you choose to take shortcuts, PLEASE make sure you are on a properly grounded electrical circuit and you're plugged into a GFCI socket. This is an extremely wet process - you will be soaked from head to toe - and as we all know, water and power tools don't mix.
There's also the option of using air tools to avoid the problem of electricity which I thought was the perfect (and cheaper) solution. So I bought this air wet grinder. It seems like a great little tool, but I never got a chance to use it because I failed to realize it requires 8 SCFMs to operate. For those of you who aren't up on your air compressor lingo, which I obviously wasn't, that's ONE BIG HONKIN' AIR COMPRESSOR. The only air compressors I could find that could push that much air were in the $550 to $800 range. My little pancake compressor wouldn't even get close. The good news is that for anyone who does have an air compressor that can push 8 SCFMs, I'll sell you my air grinder....cheap.
So I went the pro route, I bought a Hellcat Wet Grinder. Not only did this make a rather time intensive job much easier, but it's double insulated from water and has an additional GFCI on it for added protection. Of course, you'll need a set of diamond pads, which I found very cheap here. The only pads didn't use were the 3000 grit and buffing pads, so I found this to be a really good value. They will also last for multiple projects, so you may want to talk a buddy who also wants new countertops if he wants to split the cost of the grinder and pads. I tried that with Mr. P but he didn't fall for it...curse him for his evil geniusness.Mr. P Note-Beelzabubba didn't raise no fool.-
Again, this is an extremely wet process. Water mixed with ground concrete dust flies everywhere, so I chose to move the countertops outside. You'll want to wear rubber gloves and rubber boots to give added protection from shock.Mr. P Note-Some people consider this a fashion forward look, not many, but some do.-
I started grinding with a 50 grit pad. I slowly moved it forward and backward, then from side to side. Almost as soon as you grind, you'll start seeing aggregate being exposed. The first pad is the most difficult because your grinding down the most with it. Continue grinding until you have the desired aggregate exposed. One thing that is important is to keep your grinder as flat as possible on the surface, especially with the rougher grit pads. You can get some deep marks in the countertop if you don't keep it level.
I then went with the 100 grit, then 200 grit, then 400 grit. 400 grit is considered to be the last pad that's considered "grinding". Finer pads start adding more of a sheen to the countertop. I then used a concrete slurry to fill any holes or tiny gaps that were in the countertop. This slurry came with the Cheng Kit and was colored the same as my countertop. I just mixed it up with a bit of water and used a putty knife to apply it on the countertop, wiping off any excess with a damp sponge. After it dried, I then went back over it with a 400 grit pad.
I finished out the last 2 pads, which were the 800 and 1500 pads. Even though I had the 3000, Cheng doesn't recommend using it, as the sealer that comes with the kit needs a little bit of "tooth" in the countertop to penetrate and adhere. By the time you seal it and polish it with wax, it has the same or more sheen than using a 3000 grit pad.
The grinding and polishing is done! Almost.
After 4 days of curing, I started unscrewing all of the screws in the mold. Make sure that you get all of them and it should go fairly smooth. Don't put any pressure on the green concrete by prying against it, as you will risk chipping or cracking. Once you get all the sides off, you'll need at least one other person to lift it off the bottom of the mold. It should pop of the bottom fairly easily, then prop it up on it's edge. I then laid down strip of the styrofoam and laid the countertop right side up on top of it. This props the countertop off the bottom so you can get your fingers under it and it also makes it easier to grind the edges.
If you want your countertop to be a solid color, you can skip the grinding process and move right on to polishing. Both processes require using diamond coated grinding pads with a wet grinder, however there's less time involved in polishing. I wanted to expose the aggregate and glass in my countertop, so I chose to grind first. There's ways to get around using a wet grinder, like using a regular grinder/sander with the diamond pads and having someone else use a hose, or poking a hole in a gallon jug and letting the water run out as you grind. If you choose to take shortcuts, PLEASE make sure you are on a properly grounded electrical circuit and you're plugged into a GFCI socket. This is an extremely wet process - you will be soaked from head to toe - and as we all know, water and power tools don't mix.
There's also the option of using air tools to avoid the problem of electricity which I thought was the perfect (and cheaper) solution. So I bought this air wet grinder. It seems like a great little tool, but I never got a chance to use it because I failed to realize it requires 8 SCFMs to operate. For those of you who aren't up on your air compressor lingo, which I obviously wasn't, that's ONE BIG HONKIN' AIR COMPRESSOR. The only air compressors I could find that could push that much air were in the $550 to $800 range. My little pancake compressor wouldn't even get close. The good news is that for anyone who does have an air compressor that can push 8 SCFMs, I'll sell you my air grinder....cheap.
So I went the pro route, I bought a Hellcat Wet Grinder. Not only did this make a rather time intensive job much easier, but it's double insulated from water and has an additional GFCI on it for added protection. Of course, you'll need a set of diamond pads, which I found very cheap here. The only pads didn't use were the 3000 grit and buffing pads, so I found this to be a really good value. They will also last for multiple projects, so you may want to talk a buddy who also wants new countertops if he wants to split the cost of the grinder and pads. I tried that with Mr. P but he didn't fall for it...curse him for his evil geniusness.Mr. P Note-Beelzabubba didn't raise no fool.-
Again, this is an extremely wet process. Water mixed with ground concrete dust flies everywhere, so I chose to move the countertops outside. You'll want to wear rubber gloves and rubber boots to give added protection from shock.Mr. P Note-Some people consider this a fashion forward look, not many, but some do.-
I started grinding with a 50 grit pad. I slowly moved it forward and backward, then from side to side. Almost as soon as you grind, you'll start seeing aggregate being exposed. The first pad is the most difficult because your grinding down the most with it. Continue grinding until you have the desired aggregate exposed. One thing that is important is to keep your grinder as flat as possible on the surface, especially with the rougher grit pads. You can get some deep marks in the countertop if you don't keep it level.
I then went with the 100 grit, then 200 grit, then 400 grit. 400 grit is considered to be the last pad that's considered "grinding". Finer pads start adding more of a sheen to the countertop. I then used a concrete slurry to fill any holes or tiny gaps that were in the countertop. This slurry came with the Cheng Kit and was colored the same as my countertop. I just mixed it up with a bit of water and used a putty knife to apply it on the countertop, wiping off any excess with a damp sponge. After it dried, I then went back over it with a 400 grit pad.
I finished out the last 2 pads, which were the 800 and 1500 pads. Even though I had the 3000, Cheng doesn't recommend using it, as the sealer that comes with the kit needs a little bit of "tooth" in the countertop to penetrate and adhere. By the time you seal it and polish it with wax, it has the same or more sheen than using a 3000 grit pad.
The grinding and polishing is done! Almost.
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