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Discussion Starter · #1 ·
Hello,
I am making a small (1-1/4" x 16" x 40") concrete countertop. I have made several countertops in the past and I have always use Melamine for the forms and they turned out well. This time I used an old piece of plywood. I put a really light coat of paint on the form, so as to ease in the release.
I used (1) 60 pound bag of high strength concrete mix and measured the water (3 quarts) per instructions on the bag. I mixed by hand in a plastic tub and the mix looked good.
I placed the concrete yesterday (3/6/2020) at about noon time. I screeded and troweled the concrete and I shook the form and tapped the edges with a hammer. I let the concrete sit until all of the water disappeared from the top and troweled again. And then again.
Everything looked good, but this morning the concrete is shiny and not very hard - I can easily scratch the surface with a finger nail.
Questions:
Do I need to wait another day for the 'crete to harden?
Should I remove the form edges to facilitate drying?
Will it ever harden?

Thanks For Your Help,
Russell
 

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Discussion Starter · #3 ·
Thanks for the reply.

Right now it is sitting inside at 51 degrees and 57% humidity. Last night it probably got down to 38 degrees.
 

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JUSTA MEMBER
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Add a small fan blowing across the countertop.

It should dry by tomorrow, your temps and humidity are not perfect, but still within reason.


ED
 

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Remodel and New Build GC
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Concrete does not dry...or should not dry....

Concrete cures in a chemical process dependent on water to cure....it is sensative to warmth which speed the chemical process.

I'd give it more time....and I sure would not put a fan on it. Your melamine or painted forms should not have sucked a lot of water out of the mix....that's good.

I'd keep it warm, and maybe through some plastic over it to prevent evaporation.


(There is a situation where you can get "green" concrte/cement ....which I don't understand the chemical issue.....but that would occur from a bad batch plant of cement, and not likely in a bagged product)
 

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JUSTA MEMBER
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He did say he wanted it to dry, but cure is the correct term.

Here in the cold they add a Calcium Chloride to the batch, in winter to cause it to self heat, and cure when it is too cold.

A fan will dry the surface faster than the interior of the slab.

And on a hot windy day, the surface will cure first, then later it will spall badly.


ED
 

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'green' concrete occurs when the mud's not hard yet not plastic any longer,,, you can dent it with a thumbnail on edge,,, typically that's when contraction jnts are diamond sawed,,, never heard the term defined otherwise
 

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Remodel and New Build GC
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'green' concrete occurs when the mud's not hard yet not plastic any longer,,, you can dent it with a thumbnail on edge,,, typically that's when contraction jnts are diamond sawed,,, never heard the term defined otherwise
Stadry.....I've heard green used as you also,,,,as a stage in curing, primarily construction.

Actually, the term I used came from Oil/Gas cementing operations on an oil well
when subsequent testing and cement logging showed uncured cement....often attributed to the cement batch production...but also likely from contamination in the cementing process.
 

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Remodel and New Build GC
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interesting,,, never knew that - thanks !
btw, chemical process is known as 'hydration' & it is exothermic
Ah STADRY....You and your millenials wit h all thode fancy words....I could never typoe those words.

Just kidding.....Thanks....:wink2:

Best
 

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brother, left the millennial age eons ago,,, speaking of eons, wtf ever happened to woody,,, seems to have dropped off the edge of the world
 

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Discussion Starter · #14 ·
My countertop was a total failure. All I can think is that I messed up on the placement - not enough shaking/vibrating after I put the crete in the form.

I thought about trying to fix it with epoxy or Bondo or self leveling concrete, but it's probably easier to buy a piece of Melamine (I think the plywood was not the best material) and start over.

Thanks everyone for the interesting thread.
 

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Premium Member
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Discussion Starter · #18 ·
I made another countertop, this time using Melamine and a little more (maybe too much) water. The top is very smooth, except for a couple of small divots, which I will not worry about The corners are also a little ragged, but I won't worry about that, either. And as you can see, there is some color variation which I attribute to too much water, but I could be mistaken - I am viewing the variation as character. Overall I am pleased with the beast.

Thanks Again,
Russell
 

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Concrete & Masonry
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I've helped a good friend pour a bunch of concrete tops years ago. On conventional tops like yours, he always reserved some of the Portland cement to create a slurry mix to fill the bug holes after pulling them out of the forms. All of the conventional tops received a grind or sanding of some sort.
 
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