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Community and Q&A

Sealing Brick Veneer…or not?

user-958947 | Posted in General Questions on

I have a modular masonry fireplace. The chimney has a brick veneer with a small gap between the brick and the masonry blocks. I initially had a small leak through the brick and onto the chimney’s built-in brick ledge (in the attic) during a rain. This seems to have stopped based on observation during subsequent rains. It has been recommended that I spray the chimney brick with a sealer.

1) Do I need to do this? Why did it leak at first and now it doesn’t? The mortar wasn’t fully cured at the time of the initial leakage—would that make a difference?

2) Separate, but related issue—–My painter suggested that I spray a sealer on the brick veneer of the entire house to seal it off and save the white mortar from discoloring over time. Would eliminating the permeability of the brick (on the walls of the house) create drying problems to the outside, or is the air gap sufficient to handle any moisture load seeking to escape to the exterior? I’ve read EEBA literature suggesting that painting brick is a bad idea (for lots of reasons). Spraying on a sealer seems to be akin to painting the brick.

HH climate —zone 2B. 2×6 walls, plywood exterior sheathing, 1″ gap, brick veneer, oc spf insulation, non-vented attic.

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  1. GBA Editor
    Martin Holladay | | #1

    Can you provide more information on the construction of your chimney? If I understand correctly, your chimney construction consists of a metal flue surrounded by masonry blocks. Is that correct?

    Do I understand correctly that the bricks do not extend from the footing to the chimney top (as for a traditional brick chimney) -- rather, the bricks begin in the attic. Is that correct?

    My guess is that your chimney was never flashed properly. Brick veneer always leaks, so flashing is required to direct the water that leaks through the brick veneer to the exterior. Your chimney probably needs a type of flashing called "through-chimney flashing." For more information, see this article: Keeping Water Out of Brick Veneer.

  2. user-958947 | | #2

    1). There is no metal flue. This is an Isokern modular masonry fireplace. It's assembled on site from precast blocks. The chimney has an inner and outer set of blocks---I assume for safety reasons.
    2) The chimney bricks do not start at slab level. They begin at a brick ledge just below the roof line. The brick ledge is cast into a special masonry block at that elevation. So the brick ledge is visible in the attic.
    3)The flashing consists of sheet metal inserted into saw cuts in the brick, and then caulked. The saw cuts in the brick are 1/2" to 3/4" deep. So this is definitely not a through-chimney flashing. This is pretty much the standard for my area----not to say it's right, but that's how its being done.
    4) Short of tearing down the brick and starting over, would the sealer be a reasonable alternative?
    5) As I said, it's not leaking anymore (at least not at the brick ledge or any other place that I can detect). Why do you think that is?
    6) See attached photos. Note that leakage is coming from between brick and brick ledge. This was after a fairly light, but sustained rain about a week after the bricks were set. The photo was taken prior to spraying in the roof insulation.

  3. GBA Editor
    Martin Holladay | | #3

    The problem you describe is common. Few roofers and few masons understand how to flash brick chimneys.

    Brick veneer always leaks -- the water usually runs down the back side of the bricks after a rain -- so if there is no flashing system that is designed to get the water out to the exterior above the roof line, then of course the water will enter your house.

    You have three choices;
    1. Don't do anything. This is called "watchful waiting."

    2. Try a sealer. Most brick experts hate sealers, because they sometimes do more harm than good, but this option is cheaper than tearing apart your chimney. If you want to try a sealer, choose a siloxane product.

    3. Tear the chimney down to below the roofline and hire an experienced mason to rebuild the chimney with copper through-chimney flashing.

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