Uneven colors - How can I correct surface to a uniform colour after demolding?

Hi All,

this is my first attempt at making anything concrete so bear with me.  I am making a concrete table top for a firepit and and used Quikcrete Countertop Mix and the black colour through 3 batches.  When I pulled it out of the mold the flat surface side had 2 distinct colours after drying for 4 days - see attached image.  There is a darker area in the middle and much lighter along the edges (probably from me pouring 2 different batches and not properly mixing them after pouring?)

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I am hoping I can get and hear advice on how to make it a uniform colour now easily.  I am trying to get it to the darker grey if possible or could settle with a uniform grey colour.  Can I apply a slurry mixture across the whole surface and sand? I haven't applied any sealant to it.

Any help would be much appreciated!

Dee

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Thats just hydration...it will become uniform with more time.  Basically the concrete in the center is staying hydrated(a good thing) and the edges are drying out.

Thanks Tom.  The image is after the concrete was left out to dry for over a week now.  I was thinking it was moisture not dried out but the marks have not changed at all.  I did mix colourant in to each batch and worried it may not have been even.  Any advice on anything that can be applied to the surface to coat or make even before I seal it for outdoor use?


Thanks

Tom Fischer- Fishstone,CCS said:

Thats just hydration...it will become uniform with more time.  Basically the concrete in the center is staying hydrated(a good thing) and the edges are drying out.

HI Dee,

When was the picture taken that you shared?  Also, have you seen any evening of the color or has it stayed the same the entire week since you de-molded it?

Keep in mind concrete takes 28 days for full cure and on darker colors with basic mixes it can take a month for it to even out more.

Try giving it a light sanding or cleaning with Clean & Etch.  Both of these things can help.

For color it is most likely to all go to the lighter color.  You can use an enhancing sealer like U-Seal which will enhance the color(make it darker),will help with color uniformity and is breathable for exterior use.

Tom

www.concretecountertopsupply.com

Hi Tom,

the picture was taken 4 days after demolding but after a 10 days it still looks the same as the image and the darker area has not changed.  Do you know if I can apply a slurry over the surface to coat and apply an even colour and sand/seal this?

Thanks,
Darryl

Tom Fischer- Fishstone,CCS said:

HI Dee,

When was the picture taken that you shared?  Also, have you seen any evening of the color or has it stayed the same the entire week since you de-molded it?

Keep in mind concrete takes 28 days for full cure and on darker colors with basic mixes it can take a month for it to even out more.

Try giving it a light sanding or cleaning with Clean & Etch.  Both of these things can help.

For color it is most likely to all go to the lighter color.  You can use an enhancing sealer like U-Seal which will enhance the color(make it darker),will help with color uniformity and is breathable for exterior use.

Tom

www.concretecountertopsupply.com

Hi Dee,

I wouldn't recommend staining or coating to make the color uniform as this usually is just a band aid to the problem and will rear it's ugly head down the road.  I still think it will even out if you simply sand the top surface....If not I would suggest re-pouring.  It looks like a very big piece and easy to re-pour and chalk it up as a school day.

With all that said...sure you could put a microtop (slurry) over the entire piece and seal

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