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Question DetailsAsked on 7/27/2017

how to get white film from mortar when it has dried on rock fireplace

Put in a rock fireplace and the mortar in several places has turned white

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1 Answer


If new construction, just warm water scrubbed with a sponge or sometimes needs stiff bristle brush (like a horse brush) can remove a light film - use white vinegar (though that can etch soluble rocks) for a heavier or more resistant film, or if this is leaching from moisture in the chimney. Though if new fireplace construction, the contractor should have removed the mortar film off the fireplace - typically after several days to a week of mortar curing, commonly using a weak muriatic acid wash followed by a fresh water sponging down.

Note if this is not new construction, new white laittance buildup on the stones indicates (unless your interior humidity is near 100% mcuh of the time), that free water is getting in there, leaching the lime and cement out of the mortar, so you should be looking at having a Chimney Sweep inspect the chimney for leakage - either down inside the chimney, or down around the outside past the flashing and caulking.

Here is a previous similar question with answer which should help:

Answered 3 years ago by LCD

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