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Ria
chemical reaction of mortar and glaze
Ria

When our 1929 kitchen was gutted for a renovation, the contractor uncovered a brick chimney that we decided to keep exposed. The chimney was glazed with Minwax Polycrilic, and within a week, the previously gray mortar had changed color to -- there's no good way to put this -- puke yellow/green. The contractor said he had never seen this kind of reaction before with this product, which means that the 1929 mortar is to blame. Does anyone know (a) what 86-year-old mortar could have in it that contemporary mortar would not, and (b) what kind of glaze or sealer we might be able to use that is so stable it won't react with the mortar? Thanks!

Clarence
Re: chemical reaction of mortar and glaze
Clarence

The problem is most likely moisture and chemicals trapped behind the product used to seal it.
The moisture vapors are prevented from migrating thru the mortar joints.
You will have to remove the Glaze that was applied than you could use a Silicate coating that is water resistant and vapor permeable.

Sombreuil_mongrel
Re: chemical reaction of mortar and glaze
Sombreuil_mongrel

Lime mortar + water in the varnish created a caustic that attacked the resin. The label says it is intended for wood, not sealing masonry. I don't know why your contractor tried to substitute that in place of an actual masonry sealer, except to try saving $20 bucks.
Casey

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