Ask the Remodeler: Condensation issues on brick and piping

Send your home improvement questions to [email protected].

Can efflorescence, that white coating on brick, be prevented?

By Mark Philben -- Globe Correspondent

January 3, 2024

Q. Efflorescence is mysterious to many. Does it ever stop forming? My brick three-family is about 120 years old and has an exposed brick wall in the back stairwell. I have lived in the house for 45 years, and efflorescence has always appeared on the east-facing interior wall. Does this ever become a serious problem? What should I do about it?

G.H.

A. Efflorescence is a constant annoyance here in New England. Not necessarily a problem, just an annoyance. As most people with older homes know, it is caused by water-soluble salts of various types carried to the surface of the brick and deposited when the moisture evaporates. It typically happens on east- and north-facing walls. Your best hope is to stop the moisture from getting into the masonry in the first place, which is nearly impossible. Ground water, rain, melting snow, any number of things can be the cause. Being too aggressive in removing it can create a bigger problem. Improper sandblasting can damage the brick face and mortar, which will make the surface more porous and open it up to more efflorescence. Trying to apply a sealer to the inside of the brick after cleaning the efflorescence can trap the salts just below the surface. These salts will expand when trapped and cause the face of the brick to spall (chip off). You do not want that. Brick and mortar need to breathe, so regular cleaning with a proper masonry cleaner is the best long-term approach. The bricks will be fine.

Q. Thank you for your excellent column. I have learned so much from it. In 2019, I had a new 80 percent-efficiency gas HVAC unit installed in my attic. For two years, I have noticed a white powder around the exhaust vent pipe. I never had this problem with my previous 23-year-old gas HVAC attic unit. During the annual inspection, the service technician told me condensation of the furnace exhaust gas created this powder. I searched the internet and found several articles confirming this explanation. Is this a problem that needs to be corrected?

J.P.

A new gas HVAC unit is creating this powder. Is there a problem with the system?

A. That powder you are seeing is formed from condensation. Most likely the reason you are seeing it now is because the new system is more efficient, so the flue gases are cooler. I am also guessing that the attic is not insulated around the unit, so it is exposed to more extreme temperature differences. In any event, the buildup is not terribly detrimental to the performance of the system as long as it is checked during routine maintenance. It can be eliminated by changing the single wall flue pipes to a double wall B-vent. Part of the system in the pictures you sent show B-vent and no scaling around those joints. It forms only around the single wall pipe. That is a fairly routine project for your service company.

Mark Philben is the project development manager at Charlie Allen Renovations in Cambridge. Send your questions to [email protected]. Questions are subject to editing.