lemonhope
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chalk project prep
I do this project from time to time in front of my house where I'll lure rubes into contributing to the community gingerchalk project. I've been
doing various small-scale experiments, and found the most pronounced effect on "cleaning up" the cement (a nice, clean, uniform canvass, or as best as
I can get) is to lay down epsom salt on the ground before adding small amounts of muriatic acid.
I've been surprised at the lack of information on the actual [HCl + MgHSO4] reactions, although there's quite a bit on JUST Mg a well as basic
equation balancing.
There are various types of cement on the sidewalk, many tiles having been replaced at different times. My current target is cement that has
particulates (pebbles and stones more-or-less about the size the eraser on a pencil).
Ideally I'd like to try and get a fairly uniform surface and color for the various tiles; think of using a piece of chalk on a smooth vs rocky piece
of pavement, and why a "uniform" (ish) color for the pavement might be valuable for this.
Any ideas? Will I have to "level" out the stones mechanically, or is there an acid-ex-machina useful on this kind of scale? And how exactly is the
Mag Sulphate Septahydrate interacting with the HCl?
Thanks for your time everyone! Long time listener, first time caller. Oh, and one more thing....I kind of have a thing for acids, I just love that
proton exchange. Really. But I also don't want to mess with my beautiful neighborhood and the general welfare.
DFTBA!
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Sulaiman
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I think that any chemical composition capable of quickly cleaning concrete should not become part of a street artist's tools.
Personal and public risk, damage to property, waste etc.
Could you consider a cordless (battery powered) sander ?
You could create a nice/smooth/even/polished surface worthy of your art,
and it may be cheaper the chemical route over time.
The time-honoured approach ? https://en.wikipedia.org/wiki/Gesso
CAUTION : Hobby Chemist, not Professional or even Amateur
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CharlieA
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MgHSO4 is not a valid chemical formula. Epson salt, magnesium sulfate heptahydrate, is MgSO4.7H2O.
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macckone
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epsom salt is MgSO4 not MgHSO4
And muractic acid and epsom salt do not react to any significant degree.
Now muratic acid will dissolve cement (calcium carbonate) forming calcium chloride.
Calcium chloride and magnessium sulfate (epsom salt) form calcium sulfate and magnesium chloride.
This turns the cement to plaster (calcium sulfate) which gives a smoother surface
but the surface is very soft and somewhat water soluble (~1g / L).
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kulep
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Quote: Originally posted by macckone  | epsom salt is MgSO4 not MgHSO4
And muractic acid and epsom salt do not react to any significant degree.
Now muratic acid will dissolve cement (calcium carbonate) forming calcium chloride.
Calcium chloride and magnessium sulfate (epsom salt) form calcium sulfate and magnesium chloride.
This turns the cement to plaster (calcium sulfate) which gives a smoother surface
but the surface is very soft and somewhat water soluble (~1g / L).
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Calcium sulfate is also shaped into cylinders known as chalk sticks 
I think you're better off mixing some portland cement with fine sand and applying a good coat, you can even add some pigments to get a better suited
colour
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lemonhope
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Thanks to all for the responses!! I too thought the H looked out of place -- I had purchased it cheaply and the clear translation errors for basic
words kind of astonishes me; hadn't looked too much into it. The H was actually on the package, I really wonder whether it's a poor Chinese
translation or general IUPAC translation!
It seems that applying a coat rather than stripping one away seems best all around.
If anyone has fun ideas for coloring cement or the like, I'd love to hear it!
Thanks again!
Don't Forget To Be Awesome!
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Sulaiman
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Thermochromic pigments
Just search eBay, Amazon etc. for "Thermochromic"
CAUTION : Hobby Chemist, not Professional or even Amateur
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