Thread: Efflorescence on exterior brick of chimney

What tends to cause the efflorescence noted in the pictures on this masonry chimney and is it a concern? This was a woodburner until switched to a gas log. Chimney cap had cracks. Squirrel cage was installed. Thank you for your replies.

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When moisture gets into the chimney structure it will eventually wick to the exterior surface and evaporate. As the moisture migrates out it will carry salt with it from the masonry work. The salt is left as a white deposit. The cracks in the crown is one way water enters the chimney. Another way is where the edge of the crown is. If the crown does not overhang the brick as seems to be the case here, water can run off the edge of the crown and travel back underneath it and into the structure. There can be other possibilities but the crown in your picture certainly needs attention - as in replacement.

That chimney needs a new crown to prevent water entry, which as already noted caused the leeching of minerals out of the mortar joints.

Hi Jody, good pic's. as stated before you need a new cap on there. and while they are installing it a through check up on the rest of the chimmy is advised. the squirrel cage is in great condition but shows someone did the install with out taking care of the rest of the problems while there. which leads us to ask what else did they take short cuts on?? maybe nuthing but good reason to check further. good luck with it

Hello Jody,
Yes Eric is quite right. The efflorescence is the dried salts of the lime in the mortar which is being diluted and washed out with moisture ingress through the top. So yes, it's concern, as the lime is the "glue" in the sand, cement and lime mixture of the mortar between the bricks.

To rectify, it needs a capping that will overhang the top by a good 50mm with preferably a drip edge, and the cracked joins should be chased out and epoxy(2 part epoxy resin) filled as the mortar is now weakened.

Cheers

Keith

See attached:

Nice diagram Michael. If only I could find such a crown. I have never ever seen an isolation joint around the liner. I think that it's one of those "in your dreams" installations.

Originally Posted by Jody Humbert

What tends to cause the efflorescence noted in the pictures on this masonry chimney and is it a concern? This was a woodburner until switched to a gas log. Chimney cap had cracks. Squirrel cage was installed. Thank you for your replies.

When operating the gas logs there is a lower flue gas temperature and it is condensing thoses gases in the flue. That moisture is migrating through the masonry and carrying the salts that are evident on the exterior.
The wash does appear to be another [potential source of water entry and the overhanging drip edge should be incorporated in the repair for the best long-term benefit.

Ashley Eldridge
CSIA Director of Education

Originally Posted by Ashley Eldridge

When operating the gas logs there is a lower flue gas temperature and it is condensing thoses gases in the flue. That moisture is migrating through the masonry and carrying the salts that are evident on the exterior.
The wash does appear to be another [potential source of water entry and the overhanging drip edge should be incorporated in the repair for the best long-term benefit.

Ashley Eldridge
CSIA Director of Education

So you feel the clay tile is cracked?

Originally Posted by Bob Elliott

So you feel the clay tile is cracked?

That is not the only option, there could be missing mortar between the tiles. In other cases the tile liners are offset so much that there is a gap that would allow the condensed moisture to escape the liner. What is clear is that the liner can no longer contain the products of combustion and should be closely inspected and repaired. It is indicated by the fact that the efflorescence did not show before the gas logs were installed. The wash is clearly another entry point for water.

Ashley Eldridge
CSIA Director of Education

Originally Posted by Ashley Eldridge

That is not the only option, there could be missing mortar between the tiles. In other cases the tile liners are offset so much that there is a gap that would allow the condensed moisture to escape the liner. What is clear is that the liner can no longer contain the products of combustion and should be closely inspected and repaired. It is indicated by the fact that the efflorescence did not show before the gas logs were installed. The wash is clearly another entry point for water.

Ashley Eldridge
CSIA Director of Education

OK that was a better answer.

Originally Posted by Ashley Eldridge

That is not the only option, there could be missing mortar between the tiles. In other cases the tile liners are offset so much that there is a gap that would allow the condensed moisture to escape the liner.

Ashley,
Would you elaborate on the above a bit? I'm just trying to further understand.
Would there be missing mortar because it has all leached out? What are the tile liners being offset from? Each other? Thanks. -Luc

Originally Posted by Luc Lamarche

Ashley,
Would you elaborate on the above a bit? I'm just trying to further understand.
Would there be missing mortar because it has all leached out? What are the tile liners being offset from? Each other? Thanks. -Luc

Luc,
The missing mortar could be from washing out due to a lack of a rain cap or it could have never been placed between the tile liners in the original construction. Both issues are not uncommon. The offset tiles means that they are not aligned directly above each other, not plumb. In offsets within the chimney the liners often do not marry up well and there is a tremendous potential for holes to exist allowing moisture and flue gases to escape the liner. Another common practice is to use bricks to space the top liner, leaving openings into the chimney cavity.

Ashley Eldridge
Chimney safety Institute of America
Director of Education

This looks like a 2 part problem; when they switched to a gas fireplace they didn't take into consideration the size of the terra-cotta flue liner, bet there is damage from condensation at the liner mortar joints additionally water enters the cracks in the crown and at the flue penetration. Good case for recommending a qualified chimney sweep to inspect and repair the fireplace, flue liner and chimney components. In my market most flue liners are metal type with flame arresters and metal crowns, biggest problem is no one inspects them routinely and they will rust out rather quickly. Water damage results to the roof framing and in many cases shows at ceiling above the fireplace. Had one case recently where it rained during the inspection; the water streamed down the face of the brick fireplace, the owner of course said that was the first time, right!!!!

You have multiple issues here. One, you have a damaged cap allowing water intrusion to the systems. Two, you have a gas log system in a wood burning fireplace which creates multiple other possible areas of deterioration. Three, did not find any comment on dampener or smoke shelf. Typically during an inspection you do not have the time or ability to determine what all of the possible causes are. You know of two or more right from the get go. There are going to be many more internal to the entire system. My recommendation in this case would be a complete review and repair by a qualified chimney contractor.

Catching up on a backlog of reading and have an observation not discussed.

The photo shows efflresence presenting itself only through mortar not brick. The mortar does not appear to be crumbling at joints? Your photo only shows the upper section of the chimney and only one side. I would assume from this efflorvesence is not present lower on the chimney or on other sides. The side in the photo is in shaddow, is it perhaps the Northface we are looking at?

It clearly needs a proper cap, but the raincap & cage look relatively new, no smoke stains, heat discoloration, no twigs or debris. With all the leaves on the trees, it is clearly not winter, so I wonder when was the last time the fireplace was used? Given that the efflorvesence is presenting itself in segmented yet undisturbed patterns, can I assume that side is not subject to extreme wind driven rain or snow?

Water is absorbed by the brick continually and flows down and our througsh capillary action working it's way down it will only flow laterally and outward if something is blocking downward movement or an easier escape route presents it'self. The cap cracks and lack of overhang show us a primary entry
point for water but there is more going on.

Is it possible that someone other than a brick mason recently did some tuckpointing, perhaps the same person who installed the rain guard? Is it possible that they did not use a compatable mortar mix and what they used was far to pourous with a high lime content? Is the area in question the North face, with no sunlight to dry brick or mortar? Is the driving wind coming at the chimney from behind?

To make a proper diagnosis ( even though determining causal relationships are not an inspectors job) answers to questions above might give you answers beyond the obvious issues with the cap or liner.

Hi Jody, another question which has not been addressed or seriously commented on is has the chimmy got a liner in it installed when the gas logs where installed or was it a straight convertion at the fire place with no work being done to the liner and just a cap put on. some have mentioned a metal liner like ss or so could have been installed, but you have not shared those details and we can't see from the pic's. thanks. also there are no details on the gas log configuration too. is it an insert or what set up do they have?