I’m planning on pouring a concrete countertop soon. And have been toying with the idea of replacing the aggregate that I’d normally use with sand. But I’m not sure what the implications of this would be. My intuition tells me that the slab will be more prone to cracking and possibly have less compressive strength but I’m not sure. The reason I thought about doing this is because I don’t care for the exposed aggregate look I get when polishing the surface and the finer look of just exposing the sand is more of the look I’d want to achieve.
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I believe ... and I'm no expert here ... that the aggregate is essential to the strength of the material. As I see it, the cement and lime are there only to hold the aggregate together.
I imagine the stones act to spread a load out ... a force applied to one stone is transmitted to the three or four stones it rests upon, which transmits it to other stones, etc. This is, I suppose, where the "compressive strength" comes from.
However, there is no reason you have to use the usual mish-mash of mismatched bits of grave as your aggregate. Indeed, there are countertops made that consist of an epoxy binder, with finely chipped and matched stone as the aggregate.
Perhaps you can get a result you like by using other types of aggregate. Marble chippings from a stone company, aquarium gravel, even glass beads might work out for you.
Ted,
While I've done several concrete countertops, I'm noooo concrete expert. So take this with a grain of ummm... sand. The mix you're describing is more like mortar than concrete, and won't have nearly the strength needed for a countertop. If you're trying for a polished surface and seeing too much aggregate, I suspect you're not floating the surface properly. If I want a really glossy surface, I cast upside down into a formica lined form, it comes out like glass. If that won't do for your application, I'd respectfully suggest you reexamine your floating technique... Have you gotten Cheng's books? They're invaluable IMHO.
Good luck,
Paul
Yeah I have Cheng's book. It has indeed been invaluable. This is my second countertop. And for each one I've pretty much followed Cheng's advice verbatim. Only this time I've thrown in a few curve balls like a beveled edge, Bigger radius on the sink knockout, and playing around with mixing different pigments as opposed to using a prepackaged pigment.
As you know the poured in the mold method yields a very smooth surface on the bottom of the mold. So floating the surface is not an issue. What I want is a ground surface without exposing too much aggregate. I can achieve this effect if I grind lightly with nothing finer than 220. But the problem is if I have inlays of some sort they often get buried a little in the cream and I end up having to grind them out, thus exposing aggregat around the inlay.
Like you say I thought a complete sand mix would be kind of crumbly myself. I guess the only real way to tell is to do a test.
Has anyone tried the new countertop mix by Quikrete?http://www.quikrete.com/ProductLines/CountertopMixPro.aspwhoops, nevermind, just noticed the "available soon" part.
Ted, are ya sure you want a concrete counter top?
Anyone here have one, or know someone that has had one for more than 2 years and is happy with it?
Anyone?
Bueller?
Bueller?...
Well this will be the second one I've done. I was happy with the first one. But we had a flood in our kitchen and in the process of replacing the floor and cabinets that got water damaged one thing led to another and now we'll be replacing the countertop because we can't find a stainless sink that'll match the hole in the existing concrete countertop.
Overall I've been pretty happy with the concrete countertop after five years. It has a couple of stains but they're not all that noticable. There are some faux pas that I made being that oit was the first one I made and hopefully will not repeat the second time around. When we first put it in I was afraid to spill anything on it for fear of stains. But the sealer and wax have done a pretty good job of protecting the surface. And the stains that it does have are masked pretty well by the exposed aggregate. Which ironically this time I don't want so much.
I built my first one about 6 years ago in (at the time) my retail store. Stood up great even in very heavy use, and people used to literally come in because their friends told them to check it out... good return on a investment of a few sacks of concrete ;)
do you have one you don't like - whats the story...?
Treat every person you meet like you will know them the rest of your life - you just might!
The smaller the aggregate, the more the shrinkage. That aside, most of the architectural precast is made with a mix as you describe, mostly to keep the finish smooth and details sharp. What if you were to add some non shrink grout to the mix, which has some metalic compounds that counteract the shrinkage?