How Best to Whiten Mortar on Old Fireplace

Recently I asked a question about how best to brighten brick on an old fireplace and now have a good database on that subject. But now I would like to know how to brighten dingy, smoke-discolored mortar, which may require a different approach (??) I have tried the standard, non-reactive cleaners and they don't work. I have also heard that muriatic or phosphoric acid solutions may work, but I wanted to consult the experts before trying anything. Could someone set me straight on this? (Whatever is suggested, I am prepared to take all necessary safety precautions, but I want to avoid "wimpy!") Thank you for your help. Frank
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frank1492 wrote:

Muriatic acid is for brick cleaning....I think it breaks down the mortar or something.
I would try some muriatic acid and a stiff brush but I wonder how far that smoke has embedded itself in the concrete....it may have over the years "stained" the mortar making it near impossible to remove without getting off a thin layer of the mortar itself.
Have you tried a product such as greased lightning or simple green...maybe try some vinegar on the mortar...you probably have some at home so you could make a quick test.
Im just offering suggestions....no actual experience...
I have removed heavy cigarette residue from bar equipment before...20-30 years worth but it was from wood and metal surfaces....used greased lightning and it worked well
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Ive used muriatic acid inside and out, its dangerous enough outside because it fumes and burns your lungs. If you want to do it get a fume respirator, realy a paint respirator, several fans to remove air fast outside, use a nylon broom-brush on a pole to apply it and leave fast, and let it work for 15 minutes or so, then scrub with a stiff nylon brush on a pole. Now you need to rinse it clean with gallons of water, and of course you have protected the floor and absorbed everything with old towels you put in a garbage can, take outside and dilute the acid with water.
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Thank you all. Any of the conventional detergents will NOT work. I have a product in a spray can designed to clean brick and, while it brightens the brick somewhat it won't touch the mortar. Whatever will get the mortar clean will have to react with it, not just sit on the surface. I am expecting I may lose a tiny bit of the surface in the process, but I assume that can be controlled by the dilution ratio. Nobody ever mentions phosphoric acid which it seems might be less caustic than muriatic. Yet I have seen a couple of products on the net which SEEM to address the grout problem. I keep hoping some comments about phosphoric will turn up here. Anyway, thanks again and I am prepared to try muriatic if I don't come up with other suggestions. Frank P.S. Can't I stop the acid with some kind of base to neutralize it rather than just plain water? Suggestions?
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How about ammonia, for example?
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frank1492 wrote:

I think soot is mostly carbon. According to the CRC Handbook the only thing in which carbon is soluable is liquid iron and then at less than 1% (that's how you turn iron into steel).
I'll bet you have to either mechanically remove it (wire brush, etc.) or cover it with something else (paint or more mortar).
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I think the trick is to find something that actually "attacks" the lime in the mortar. If the top surface of the mortar bubbles away, the soot will go with it.
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++++++++++WARNING DO NOT ADD AMONIA TO MURATIC ACID++++++++++++
the color of your joints will be the least of your worries...Regular hosehold white or cider vinegar will neturalize muratic acid..But muratic acid it not a stain remover persay it will remove cement based stains and once you get the soot and other crap off of the joints you can paint on a dilution of it with a small paint brush and it will brighten it a bit. I have had good luck with (powered) T.S.P the liquid seems worthless...
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That is what I was planning to do, with a toothbrush. True TSP (trisodium phosphate) is almost impossible to find as it has been replaced with a "substitute" (sodium metasilicate.) I think that's what the liquid contains and that is why it doesn't work.
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As to your warning, I quote:
Scrub off any remaining residue with a stiff brush while rinsing thoroughly with water. There are long handled masonry brushes ideal for this job. To neutralize any remaining acid, you can spray a neutralizing rinse of one (1) cup household ammonia to one (1) gallon of water.
See http://www.naturalhandyman.com/iip/infxtra/infmur.shtm
Ammonia is a base and bases neutralize acids, as I understand it.
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You have a few idiots here recomending BS, Vinegar is an acid, not a neutraliser. Amonia is just as bad for your lungs as acid, try to use the least toxic way to harm yourself. Muriatic works but contact Detrict Chemicals out of Minnesota or Wisconsin, all they do is make stone and brick acid cleaners. Detrich usualy only sells 5 gallon lots, but try them. Sure you can neutralise it but it still must be diluted with a water wash, I have done it with finished oak floors, no harm done.
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