Why does concrete cure white and portland cement cure grey? - Contractor Talk - Professional Construction and Remodeling Forum

jgray152 · 10-03-2009, 09:02 PM

This is something that has been bugging me and I think it may be due to the extra calcium in the redi-mixed concrete compared to the very little in portland cement??

Anyone know the reason? If I mix portland cement and sand together to get a grout mix which I use for my faux rock retainer walls, it will usually cure a dark grey or mild dark grey where as if I get it delivered from the concrete company it cures very white which is better for acid staining.

CJKarl · 10-04-2009, 05:19 AM

I have found it to vary from....Manufacturer of the cement, quarry that mined the sand and even how much water is added to the mix.

jgray152 · 10-04-2009, 08:33 AM

hmmm. Well thats a bummer. I usually mix my home made concrete mix real dry for strength. Is it possible if using a lot of sand or maybe a lot of silica or another fine filler to allow the cement to maybe not be so dense or turn it white or at least a light grey? I have got portland / sand to turn white after 3-4 days of curing but that is not always the case, I guess I got lucky on that mix.

6stringmason · 10-04-2009, 08:24 PM

Quote:

Originally Posted by CJKarl

I have found it to vary from....Manufacturer of the cement, quarry that mined the sand and even how much water is added to the mix.

Same here.

user50444 · 10-05-2009, 06:04 PM

slag mixes get really white. pretty much every redi-mix producer is either adding fly ash or slag, unless you tell them straight cement.

CaliDesigns · 10-05-2009, 06:27 PM

Your percentage of portland in concrete is a lot less than your slurry mix. That's why a lot of concrete guys add white portland to their slurry mix to wet face steps.

concretemasonry · 10-05-2009, 07:25 PM

Mortar color is highly influenced by the sand color, while ready-mix is not because of the difference in the cement content. The lightest mortar will be a traditional portland/lime mix that has more workability and long term healing from the weather.

naptown CR · 10-05-2009, 07:29 PM

Quote:

Originally Posted by jgray152

This is something that has been bugging me and I think it may be due to the extra calcium in the redi-mixed concrete compared to the very little in portland cement??

Anyone know the reason? If I mix portland cement and sand together to get a grout mix which I use for my faux rock retainer walls, it will usually cure a dark grey or mild dark grey where as if I get it delivered from the concrete company it cures very white which is better for acid staining.

Portland cement comes in two colors white and gray. next time by white portaland.

jgray152 · 10-09-2009, 10:00 AM

I know it comes in gray or white in bags but thats why it didn't make sence that portland in redi-mixed concrete trucks cured white or very very light gray where as portland in backs mixed roughly the same way cured gray or dark gray.

Its just something I will have to keep in mind thats all. White Concrete here is about $22 a bag verses $9.80 a bag of standard portland.

harpomason · 10-29-2009, 11:32 PM

thanks for asking as i have pondered over this same thing. I like my work to be consistant through out the job. Its one reason i try to avoid using dye or powdered color. when i can't talk them out of using it. I will measure very carefully every mix.
The man who schooled me on this trade told me that he remembers when a bag of masonry cement cost him 75cents and portland was $1-$1.25 per bag.