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Recipe For a 3/4" Concrete Shelf

1269 Views 11 Replies 6 Participants Last post by  RustyRealtor
Hello Everyone,

No matter which side of the divide you are on, I hope you are all safe, healthy and prospering.

It is a beautiful day here in Nashville and I have much for which to be thankful.

I am going to attempt a concrete shelf which is 3/4" x 14" x 31". I bought a sack of Portland cement and a sack of sand and I'd like to use broken glass for the aggregate. And I plan to dye the crete black. My questions are:

Is there a better recipe than the standard 1-2-3 ratio for such a thin slab?

Should I use a liquid polymer in lieu of some of the water?

Is broken glass an acceptable aggregate?

If glass is acceptable, how the heck am I going to smash the glass without a huge mess? (Somewhat rhetorical.)

Thanks Very Much,
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By using Rockite you won't need be concerned with the 1-2-3 mix but only the amount of water and add the glass on top of the pour at the correct time.

Glass for aggregate, i haven't a clue, but it can be broken inside a 5 gallon bucket with a sledge hammer without making a mess.
I am going to attempt a concrete shelf which is 3/4" x 14" x 31".
What you can do is sandwich the glass between two pieces of cardboard.
You may be able to contain the mess and check out the progress by lifting up the top piece. It won't be easy to get it to break evenly or into pieces that are useable. And regarding the do you plan on supporting it?
Are you going to add any reinforcement within the shelf to keep it together?
Perhaps some wire mesh?
I am skeptical of the strength of a 3/4" concrete shelf, but if you are willing to try, go for it.

I have read about competitions where they are challenged to build the best concrete canoe. I think this is most common in engineering schools. You might be able to search out their techniques for achieve strong concrete in thin sections.
how're you going to support this conc shelf ? the shelf'll be fine if you don't overload it,,, carbon fiber mesh 1/2way thru it,,, you can buy glass already sized for this project,,, either that or smash away & screen out all the undesirable pieces,,, i'd stay under 1/4" but not less than 1/8"
You can make "lightweight" concrete....sounds like an oxymoron to me, by adding perlite to the mix.
The recipe I found is 8 parts sand, 8 parts cement, 8 parts perlite to 5 parts water.
I do not know if that will have the strength you need but you can start your research along those lines.
If it is just decorative, why not use styrofoam and just stucco it?
forgot this - we have used a drill & mixer to break up glass thru a covered 5gal bucket,,, turned out to be a pita spinning the mixer, screening thru hardware cloth, adding more bottles, repeat,,, the table top turned out ok - we just could've saved lots of time ( $ ) by buying the graded glass
trowel into surface after screeding for best results
Thanks for the replies, everyone.

SeniorSitizen, I've never heard of Rockite. I looked it up and I think it is 98% gypsum and 2% Portland. It hardens in 15 minutes. Might be just the thing.

Missouri Bound, I will try the cardboard trick for breaking the bottles. If it doesn't work I will try the 5 gallon bucket and a hammer. As Stadry noted, it will likely be a huge PITA. Might not be worth the trouble. I will see if I can find broken glass online.

Staydry, the shelf will be supported on the two 14" ends and one of the 31" sides. It is going under a bathroom sink.

I am going to put some sort of reinforcement in the form. I have stucco mesh - I might use that.
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Make sure you come back with pics of the finished product.
I've been wanting to pour a concrete or Rockite hour glass shaped shooting bench to accommodate both R and L hand shooters so i'll also be interested in your results. thanks
I will see if I can find broken glass online.

I am not sure if it will suit the look you are going for but you can get cut glass for an aquarium in many different colors.
I will post some pics. I am installing kitchen backsplash at the moment. I wii start the shelf in a day or two.

Thanks For The Replies,
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