Spalling brick

Kinda reminds me of some conditions I observed a few years back on a high rise apartment building’s exterior wall in minnesota near the top 100 feet up and also a few years after on a commercial shopping center in south carolina exterior wall + conditions on chimney

Been seeing this many years Juan.
Improper cap does cause this as main reason in this case.

Without being there this is the issue that is seen.
Mason can examine the rest in regards to liner and mortar.

Chimney cap.jpg

Great post and link Marcel, thanks!

If the problem is related to the use of high-compression mortar, wouldn’t the mortar act as a capillary break, or at least a major impediment to capillary flow?

I’m with Bob on this one. Having a gas appliance without a proper liner would deteriorate the chimney from the inside.

No as wouldn’t you think that a foundation wall would be a capillary break? With the way forms are pulled so quick, curing is compromised along with additives. So we have to add a break.
So when you seal the inside of the basement where does the moisture go… up.

As Juan said if this is used as a gas vent then there is moisture in the flue area and if it not lined then for sure it is getting into the brick and mortar. Therefore the brick is compromised as the mortar is harder than the brick.

Think about the cap, if it is a problem wouldn’t it be more of a problem toward the top as far as moisture soaking in than at the lower portion.

How about this as an explanation:

                 This type of damage can occur when the compressive strength of the mortar exceeds that of the brick, and moisture is absorbed. It happens like this:

Mortar is typically made up of three dry components: a binder (portland cement), an aggregate (sand), and hydrated lime. The ratio of these three ingredients determines the strength- and in turn the ASTM classification- of the mortar.

Bricks are laid in mortar, both of which absorb and release moisture. When absorbed water freezes, it expands, and during expansion it can increase in volume as much as 12%. So as mortar and brick expand, even minutely, either the brick or the mortar must give.

If the bricks are harder than the mortar, the mortar will give, often without cracking or falling apart or leaving any visible record of this slight failure. And if the mortar joints do fail, it’s much less expensive to repoint masonry than it is to rebuild with new brick.

If the mortar is harder than the bricks, the bricks faces will spall, crumble, or peel loose from the rest of the brick.

The source of moisture can vary. It may be rain, a leaking chimney cap, moisture spreading or rising through capillary action from a source above or below, or an unlined chimney, sometimes made worse when the chimney is used to vent a gas-burning appliance like a water heater. Gas-burning appliances produce exhaust gasses with a high moisture content.

A good mason will be able to design a repointing mortar that will not damage the brick. If the color or texture are more challenging, there are firms available online that will custom match mortar samples relatively inexpensively.

Here’s an example in which brick and mortar have deteriorated at an almost even rate, with deterioration pretty uniform over the entire house. I found two widely separated houses like this in Boulder.

" This type of damage can occur when the compressive strength of the mortar equals or exceeds that of the brick, and moisture is absorbed, and then freezes.

Mortar is typically made up of three dry components: a binder (portland cement), an aggregate (sand), and hydrated lime. The ratio of these three ingredients determines the strength- and in turn the ASTM classification- of the mortar.

Bricks are laid in mortar, both of which absorb and release moisture. When absorbed water freezes, it expands, and during expansion it can increase in volume as much as 12%. To accommodate this expansion, either the brick or the mortar (or both) must give.

If the bricks are harder than the mortar, the mortar will give, often without cracking or falling apart or leaving any visible record of this slight failure. And if the mortar joints do fail, it’s much less expensive to repoint masonry than it is to rebuild with new brick. If the mortar is harder than the bricks, the bricks faces will spall, crumble, or peel loose from the rest of the brick. If brick and mortar are close to equal in strength, they may both be damaged or deteriorate, such as is the case here.

A good mason will be able to design a repointing mortar that will not damage the brick. If the color or texture are more challenging, there are firms available online that will custom match mortar samples relatively inexpensively. This only matters if damage has just begun to show. Once deterioration is this extreme, damage is permanent, although repointing may help stabilize this condition.
"

:shock::shock:

Looks like you have it covered. :wink:

I see spalling all the time here in Bmore, not just on chimneys, on lots of brick surfaces.
With and without overhangs.

Sometimes just a few bricks exhibit spalling, sometimes quite a few.

Mostly I attribute it to “manufacturer defect”, of course a brick yard from a hundred years ago isn’t going to have the same quality control they have now.
And as we all know a brick yard from any era can have errors which make the brick less weather resistant and prone to spalling.

I am a HI and you still lost me.

Bob, I didn’'t understand until I read Marcel’s link. But if I lost you, then it’s bad writing and I need to re-write, because this is for the flash card project mainly geared toward newer inspectors and it needs to be really clear.
I’ll try again tomorrow.

I just found this tonight Kenton it’s good reading as well.
http://buildingscience.com/documents/insights/bsi-011-capillarity-small-sacrifices

The Building Science Corporation stuff is excellent Ken, thanks for posting that link.

Not sure if that was geared towards a Home Owner Kenton.
Seemed long winded.

I am a simple man so keep it simple.:}