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Author: Subject: metal salts to color concrete

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[*] posted on 11-1-2004 at 12:34
metal salts to color concrete

I hope some of you guys have some ideas and information...
I'm a very hands on builder that is in the process of converting an old warehouse into loft apts... I'm casting concrete countertops and using all polished concrete floors... I know the "acid stain" to produce the stained or colored concrete is really just an acid to "open up" the concrete and "metalic salts" are used to produde the color (sprayed on with the acid water mix) to react ot the lime in the concrete..... ref: Preview Stained Floors, Acid Etch Staining - The Concrete Network
what i'm looking for is: can i make my own stain (they are really proud of it $$$ if you have to buy it from a supply house) and what metalic salts would i use to get each color... where would i buy them? i don't have to get any exact color... it's loft warehouse units... and nothing has to be "perfect" but browns/greens/yellows would be cool... i play with precasting alot of concrete stuff so these are things i'd like to know ...
anyway... thanks in advance for any and all help


There's no need to put your email address underneath your posts. Why should only you benefit from the replies? Rather egoistic.

[Edited on 11-1-2004 by vulture]
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Vicious like a ferret

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[*] posted on 12-1-2004 at 07:27

have you considered using metallic oxides, you can get some spectacular colors that way.

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[Edited on 12-1-2004 by Ramiel]
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Biochemicus Energeticus

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[*] posted on 12-1-2004 at 17:32

Exactly, I remember that Fe2O3 (red iron oxide) is used to colour asphalt, ever noticed bike tracks etc that are in a red/brown colour? Thats the stuff :) (Although I am sure they dont use this these days anymore, due to some obscure health hazard such as iron poisoning :D)

In addition, pottery supplies provide MANY coloured oxides. I am sure some of them can be used for colouring concrete - at least in concrete they dont have to withstand temperatures above 1000 deg C, plus the reactions that might occur at this temperature!

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International Hazard

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[*] posted on 13-1-2004 at 06:44

There are many dyes you can ADD to concrete, mostly inorganic stuff like iron oxides and soot. You can mix with cement for a superficial layer or mix with the concrete itself for coloring the whole piece, with loss of structural strenght.

I think the poster wants something to stain the concrete. Something you "paint" on concrete and it penetrates a few mm or less, changing its color. Should be inorganic for stability. Not toxic. Can't be washed by rain.

That is tough.
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Hazard to Self

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[*] posted on 30-6-2009 at 14:35

The most common acid used with concrete is Phosphoric acid H3PO4. Phosphoric acid is made by mixing sulfuric acid with Tricalcium phosphate Ca3(PO4)2. Sulfuric acid can be bought at any Napa auto store because sulfuric acid is used in car batteries, it will be labeled "battery acid". Tricalcium Phosphate is the product of the total decomposition of animal bones. It also occurs naturally in Morocco, Israel, Philippines, Egypt, and can be purchased on the internet.

I have never heard of "metal salts" being used to dye the surface of concrete, however I have heard of metal oxides being commonly used for this purpose. The most common metal oxide used with concrete is Iron(II)Oxide Fe2O3 commonly known as rust. Rust can easily be made by the electrolysis of iron, or by placing steel wool in a mixture of 2 parts bleach and 1 part vinegar.

I know this because I make thermite with the iron oxide I extract from concrete dyes, however, I boiled the dye only to receive a solid block of Iron oxide. This is probably because I didn't mix it at all during the boiling process. i can't even get it out of the glass container I boiled it in. It's stuck in there like glue.

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[*] posted on 30-6-2009 at 15:59

Fe2O3 should produce a brick red color in concrete. I grew up in a Spanish style house that had floors of this material. They also had a satin finish that was maintained with paste wax.

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[*] posted on 30-6-2009 at 17:44

Natural weathered iron oxides are used for red, buff, to yellow, and brown, iron + manganese for dark brown to black, and Cr2O3 for a darkish unsaturated green.

Of those ferrous sulfate solution will produce a reddish-brown that's difficult to control the final colour of, iron and manganese sulfates for dark brown. Chromium is SFAIK usually mixed into the concrete as Cr2O3.

Carbon blacks are also used, as is cobalt coloured glass for blues.

What you are after is the same thing as the commercial concrete stains. These are of two families, the first being dilute HCl and salts of Fe, Mn, Co, Cr, and perhaps others, the second is water based acrylic stains similar to acrylic wood stains.

The metal salt type takes some experimentation to get the desired colours, or even a reasonable uniform colour that doesn't resemble WC bowl contents. The blues and greens can be difficult to achieve, they tend to go muddy or grey. Using the commercial products means someone else has already done that experimentation for you. Besides that the choice of salts is done to avoid weakening the concrete as much as possible, all salt-based stains do so to some degree.

You can also scatter or dust fresh concrete with the oxide mixes, then work those into the wet concrete surface. This takes much less of the colour agent as you are only colouring a layer a fraction of a cm deep; the colours are often a bit brighter as well.

As for cost, iron salts are cheap, manganese a bit more expensive, chromium and cobalt are costly.
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[*] posted on 30-6-2009 at 19:16

Copper will make a green or bluish-green, may or may not fade over time. I don't think you could successfully get a blue from inorganic copper; azurite is well known to decompose to malachite (green) over time. Copper phthalocyanine is easy to make (if that's what you're aiming at) and is extraordinarily blue.


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[*] posted on 30-6-2009 at 22:10

I am familiar with a local firm in my area, Stevensons, that makes a variety of concrete pavers and blocks. They use Fe2O3 or FeO(OH) to color its products various shades of yellow or pink or orange or red, MnO2 and/or Fe3O4 to color them various shades of gray, and basic Cu(II) carbonate (malachite) to color them green. A possible green alternative may be Cr2O3. I have not seen them make blue products; however, if azurite or Cu(II) phthalocyanine are not sufficiently stable in a strongly alkaline cement environment subject to weathering, a possible alternative could be CoO, which is used in glass (smalt) and glazes to impart a deep "cobalt blue" color.

Other possible substances that could be added to concrete as pigments are the oxides of vanadium, CrO3 (yellow) and NiO (blue-green), and chromates and vanadates. To lighten its color, TiO2 could be added.

[Edited on 1-7-09 by JohnWW]
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Mr. Wizard
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[*] posted on 30-6-2009 at 22:19

This guy has done some work at home on the subject:
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[*] posted on 1-7-2009 at 11:50

Years ago, I added copper to a HCl/H2O2 mix and the reaction mix erupted out of the beaker when I left momentarily. I returned to notice the limestone rocks under my bench where nicely colored seafoam green. Go find some broken concrete and pour a strongly acid mix of CuCl2 and muriatic(HCl) acid on it and let it set. Leave the pieces to the elements a few months to see if the color holds up.

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