Recently noticed while in my attic mounds of granular “sandy” particles over by my chimney which is still used for venting a gas furnace (but in the old days had a coal fired octopus venting through it). My house is a 1930’s house.
Anyways, found out that the mortar between the bricks is disintegrating. I can lightly touch it and and it’s crumbly and breaking into fine “sandy” particles.
The entire chimney is about oh say 28 feet tall. So, not knowing much about brick mortar, should I be worried, concerned, or is it just the outside mortar aging but the “meat” of the mortar is still ok and my chimney will stand?
Replies
Have it checked out. Water is getting into the mortar and the chimney.
That water can be coming from cracks in the chimney crown (fairly common and usually a minor repair) or from condensation of the water vapor in the flue gases inside the chimney, which is potentially deadly if the mortar deteriorates enough and flue gases (which can contain carbon monoxide) get into the house.
Have a competent heating contractor check it out as soon as possible.
Location can affect the likelihood of the various possible problems - where are you located?
Is the chimney on an exterior wall or does it run up through the interior? What kind of furnace do you have now? Does it have a draft inducer on it? Or a draft hood? (A draft inducer is a little motor connected to the bottom of the metal flue leading into the furnace, about the size of a fist - a drafthood is usually a box at or near the top of the front of the furnace with a big opening on the bottom.)
Things to look for which can indicate drafting problems (and possible CO poisoning problems:)
Drip marks or rust stains on the metal flue between the furnace (or water heater) and the chimney, especially at or below elbows.
A lot of rust under a drafthood (see "drafthood" attachment) and or heat stains on the front of a drafthood. (The drafthood is the box at the very top of the picture.) Or rust under the waterheater flue bonnet on the top of the water heater.
Rust or water marks on the bottom of the draft inducer (see "draftinducer" attachment)
A furnace with a draft inducer where the flue goes into a chimney on an outside wall and where there isn't a flue liner: look for a metal flue cap sticking out of the top of the chimney to evidence (not prove) the existence of a flue liner.
A plastic flue running into a masonry chimney
If the problem is condensation of the flue gases (one problem caused by a poor draft) the usual solution is running a metal flue liner up the chimney, usually not too expensive for gas appliances.
As Bob says, a flue liner solves your venting problems. But not your chimney's structural problem. Tuckpointing works for a while, but you realize that you then only have 1/2"-3/4" of good mortar, but better than none, I suppose. Poured-in-place flue liners turn your chimney into a structurally sound edifice again, assuming that it doesn't explode (from expansion pressures) in the process.
BTW, I think the mortar deterioration was caused by sulphuric acid which condensed out of combustion gases.
A checkup by a masonry professional is in order. Gas appliances should not be vented in unlined masonry chimneys because the combustion products are acidic and eat away at mortar. It's not uncommon, though.
Here in Southern California ALL the 50 year old plus mortar is crumbly and can be picked out with a finger. The mortar was like that due to the use of lime when it was originally mixed. All the used bricks that were recycled from old buildings were very easy to clean, cant recycle bricks from newer buildings.
If your brick is not subject to weather, the joint is not more than 3/4" deep, your not in earthquake country or you don't have kids picking at it - just wait and watch.
Otherwise , it can be redone (repointing), so long as the brick is sprayed with water before being done.