Concrete Won't Dry

1720 Views 26 Replies 7 Participants Last post by stadry, Mar 15, 2020

RustyRealtor

Discussion Starter · Mar 6, 2020

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

1 - 20 of 27 Posts

Bondo

· #2 · Mar 6, 2020

Will it ever harden?

Ayuh,.... In what temps is it sitting,..??

give it somemore time, never seen concrete Not cure,....

RustyRealtor

Discussion Starter · #3 · Mar 6, 2020

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.

de-nagorg

· #4 · Mar 6, 2020

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

RustyRealtor

Discussion Starter · #5 · Mar 6, 2020

OK.

Thanks a lot!!

Reactions: 1

ClarenceBauer

· #6 · Mar 6, 2020

Keep the temp above 45 Deg. & keep it moist 70% humidity would be perfect.

Reactions: 2

MTN REMODEL LLC

· #7 · Mar 6, 2020

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)

Reactions: 1

de-nagorg

· #8 · Mar 6, 2020

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

Reactions: 1

stadry

· #9 · Mar 6, 2020

'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

Reactions: 1

MTN REMODEL LLC

· #10 · Mar 7, 2020

stadry said:
'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.

Reactions: 1

stadry

· #11 · Mar 7, 2020

interesting,,, never knew that - thanks !
btw, chemical process is known as 'hydration' & it is exothermic

Reactions: 1

MTN REMODEL LLC

· #12 · Mar 7, 2020

stadry said:
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

stadry

· #13 · Mar 8, 2020

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

RustyRealtor

Discussion Starter · #14 · Mar 8, 2020

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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Reactions: 2

stadry

· #15 · Mar 8, 2020

appears as if the plywood sucked all of the moisture out of your plastic mix - no wonder it didn't cure - not enough water

Reactions: 2

de-nagorg

· #16 · Mar 8, 2020

That looks terrible.

Too dry, to have cured.

Patching it is not advised, it is too weak to be used.

ED

stadry

· #17 · Mar 8, 2020

this is how we gain experience in life,,, if it were to have properly cured, you wouldn't have learnt nothing/anything :vs_laugh:

Reactions: 1

RustyRealtor

Discussion Starter · #18 · Mar 12, 2020

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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Reactions: 2

de-nagorg

· #19 · Mar 12, 2020

If you polish it, most of the divots, and discolored parts will disappear.

I am glad that you tried again.

ED

jomama45

· #20 · Mar 14, 2020

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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