Can You Reuse Stone and Brick Mortar?

When you have too much paint or drywall mud compound, the way to preserve it is to put a lid on top and keep the air out.  But stone mortar is a completely different product, as it contains portland cement and silica sand, and preservation of mixed mortar could yield different results.

The Project

I wanted to see if excess stone mortar can be saved instead of being used up or thrown away.  The reason is because the polymer-enriched Laticrete mortar I was using was very expensive, and I didn’t want to have to purchase extra bags simply because I threw away much of the mixed mortar.

When using mortar, you are supposed to spread only enough mortar that can be covered with veneer within 15–20 minutes.  This indicates that mortar that is left standing past 20 minutes is quickly becoming unusable.

Execution

After mixing the mortar at room temperature (70°F / 21°C), I placed two margin trowel scoops each into a two Zip-Loc bags.  I vacated the air from the bags.  I left one bag in the work area at room temperature.  I placed the other bag in the freezer.

Success Rating

The experiment was not much of a success.  The room temperature bag hardened after about 3 hours.  This was an improvement, though, over exposed wet mortar, which will stiffen within an hour of so.

The frozen mortar fared better.  It did manage to freeze solid, but thawing was a problem.  It took well over 4 hours to thaw.  While length of thawing time was not much of a problem, the real problem is that the mortar is concurrently stiffening as it thaws.  So, if you can manage to hit the perfect sweet spot–thawed enough to be pliable, but not thawed long enough to stiffen–then you can preserve mortar by freezing and thawing it out.