How to remove mortar from salvaged vintage marble window sills

MichaltheGirlMay 30, 2012

Hello, All! DH and I are renovating a turn-of-the-century gabled ell in a historical neighborhood. I stopped in a nearby salvage place last week and they had marble window sills removed from a nearby school. Looks like Carrara marble to me--white with fine gray veining.

On the underside of each sill are 2 or 3 blobs of mortar which held the window sills in place. Some of the mortar blobs also have a single nail sticking out. How can I remove the mortar? Should I use acid? Should I try to chisel it off?

More info: I got these sills for $15 each, they're about 4' by 6', 3/4' thick. They will look perfect if I can use them as open shelves in my kitchen (I plan to use aged brass brackets to support them). The tops of the sills are polished (glossy), the bottoms are smooth but not shiny (honed?). Because it is an old house and we're selectively remodeling, I don't mind if they don't looke brand new when I'm finished with them. If I have to use some sort of acid on them, I don't mind if they eat away at the marble a bit. I just want a simple solution, but one that won't destroy them. In fact, if my 'solution' left them with a honed instead of polished look, I'd love it. I prefer honed to polished, especially for this house.

I took a picture of the sills to post, but I'm not sure how....

Thanks!

Here is a link that might be useful: Our Crumble Abode

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Sophie Wheeler

Chisel off the old mortar very carefully. Not only will an acid solution not remove blobs of mortar, it will etch the marble badly, leaving it difficult to clean properly and with holes in it if you leave it in contact long enough. Be very sure that your brackets are sturdy enough and are fastened into the studs. Marble shelving is quite a bit heavier than wood shelving.

    Bookmark   May 30, 2012 at 10:46AM
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millworkman

other than chiseling there is no simple solution.

    Bookmark   May 30, 2012 at 12:59PM
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MichaltheGirl

Alright, then, chiseling it is. Any suggestions on what sort of chisel to use? What sort of surface should I place the marble on when I try to chisel it? Something to absorb some impact? Wood?

Don't worry, we'll be sure to screw the brackets into studs. And these are beast studs, too. We tore through the plaster on the other side, and these are very thick, oak studs.

    Bookmark   May 30, 2012 at 1:19PM
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brickeyee

"other than chiseling there is no simple solution."

You can also just cut off the edges.

Marble is not as hard as granite (or any number of other stones) and carbide tooling with water is often adequate.

    Bookmark   May 30, 2012 at 1:51PM
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sombreuil_mongrel

If you start chiseling, you're going to find out right away if they are sturdy enough to be shelves. Shocks from chiseling are going to be a good test.
Personally I could not see a marble shelf narrower than 8" having sufficient strength to support itself for very long, let alone any weight. Marble lacks flexive/tensile strength unless reinforced by "rodding"..
I think a diamond grinder wheel would be the best removal method.
Acid will eat marble faster than mortar.
Casey

    Bookmark   May 30, 2012 at 7:59PM
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VictoriaElizabeth

Oooh. Sounds like a lovely find. Personally? I would only use one tool for the job-- my husband.

Here is a link that might be useful: We too have a crumbling abode

    Bookmark   June 5, 2012 at 9:11AM
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lazy_gardens

Get an old wood chisel, or a stonemason's chisel. It should be dull, but with a nice beveled edge.

Also get a small iron hand sledge - 2 or 3 pound will do.

Hold it loosely in your hand at a very shallow angle (almost parallel to the marble) and tap it from bare marble into the blob of mortar. Vary the angle of the chisel if nothing happens.

If you are lucky, most of the mortar will pop off.

    Bookmark   June 5, 2012 at 8:09PM
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