Luan plywood under brick

Saw this today. It looks like 1/4" luan plywood between the brick window sill and brick wall veneer. The sills are obviously loose due to this.

I haven’t seen this before, have any of you?

Whatever it is, if it’s wood I’d say the exterior siding is insufficient to protect wood structure and refer it.

possibly a type of required flashing

Cavity Wall: Brick Veneer/Wood Stud

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Agree with Joe. If it were sealed in, there would be some hope that it would remain stable, but exposed to the elements, failure is not a question of if, but when, and you are already seeing that taking place. Really bad practice. Shame on the mason.

OP, that is a thin angle iron. Not plywood.
Why is the angle iro there. Poor brick/masonry bond.
Once the iron was exposed, due to degraded/ing mortar, mortar does not bond to steel, the sun heated the steel deforming the angle iron shape, while increasing the likelihood for rapid mortar degradation. Result. The bricks shifted.

Never liked rowlock brick window sills. The mortar/masonry fails faster, and most times masons do not take capillary break, a 15% sill angle/offset for the window sill to shed water, and the brick/masonry bond is not considered when it should be.
Too bad. So sad.
Masonry veneer it an expensive veneer to install, and maintain. Masonry is durable and last ><100 years, when erected properly and good materials are considered.

Always used concrete sills when I could and took any brick/masonry bond into consideration. 6"X 5" Concrete window sills had the best results. (Weight)

*OP, likely the mortar bond loss of each lower window with rowlock sills. Sufficient Caulking Seal, or lack thereof, is an issue as well. Inform the client!

In my opinion, having a bit of experience in masonry, the masons did not take mortar/masonry bond into consideration. The short/thin angle iron was introduced to offset the masonry bond loss.
Poor thinking by the lead mason.

Observation: (Exterior Section)
Masonry: Shifted rowlock window sills.
Exposed deformed steel angle iron.
Cracked, Degraded mortar.
Exterior: Windows: Cracked, degraded, split caulking.
Immediate Concern/s: Water intrusion at all windows.
Recommendation: Masonry: A licensed masonry contractor; (1) Correct masonry bond deficiencies at window sills. (2) Reset / rebuild / repair / replace all window sills. (3) Tuck point degraded missing mortar. Time: Immediately.
Exterior Windows: Caulk all window frames.
Limitation: Masonry, Brick Veneer, Wall, Ceiling, Flooring assemblies.

The running bond is the most used bond and is composed of stretchers offset by 1/2 brick per course as depicted by the image below provided by, Archtoolbox.
standard running bond.JPG

Below edited illusion., component context.
standard running bond illustration.JPG

Below image, OP posted image.

1: Compare the running bond standard. I hope you see the defects.
Deformed angle iron.

Below image, deformed angle iron.

Hypothesis. Heat, load, thickness/dimension coupled with substrate inconsistencies, surface not flat, lead to the demise of the component in question, the angle iron, and what is situated on top. Rowlock brick window sill.

Robert, I appreciate the info, good stuff. My recommendations basically identical to yours.

The material was indeed wood. I wasn’t sure at first, then I was able to pull some loose and it definitely is wood.

Wood is hygrostatic. When it rains the wood will wick moisture content from the masonry and swell.
Shifted rowlock window sills.
Refer a licensed masonry contractor replace the sills.

Rob did you mean hygroscopic…?..

Much thanks for the correction.

Maybe I should use it for Questions of the Week

This is an older thread. Done just a little bit of masonry over the years myself. Whys they would’ve put wood in there in the first place, who knows, probably trying to take a short cut to fill the spacing, it obviously has chipped out. Another sore point for me is angle iron over windows, door, etc on brick veneer almost never gets primed. I would hit mine with a coat of red oxide before it went up. Once that was on there the angle iron wouldn’t run rust down the windows and could be painted later if desired. Even if left unpainted the red oxide would partially blend in with most all but tan brick.