Brick Delamination

I've been doing a lot of repointing and masonry work ahead of the porch build because I need to make sure the walls the porch will tie into are solid. While I was up on the scaffolding yesterday, I took a picture of some delaminating brick above a 1st floor window in proximity to where I'm currently working.

What is delamination, you might be wondering? It's when the layers of something start to come apart. In this case the inner wythe and the outer wythe have become separate entities, which has resulted in the outer layer bowing out.  

In a 2-wythe wall, there's an inner layer of brick and an outer layer of brick. Each layer is a "wythe". Every few rows ("courses") of brick, the bricks are rotated 90°and, in effect, tie the inner wythe and the other wythe together. The mortar between the bricks holds everything together, and those rotated bricks provide structural stability. In theory, the whole assembly should look something like this:   

Unfortunately, the section of brick above the window in question doesn't have any courses of rotated brick. Strike 1. On top of that, at some point water was getting into the wall. Strike 2. Drag that out over a long enough period of time...strike 3; delamination.  

Making a long story short, when water gets into the wall it works just like gravity indicates it should: it heads towards the ground and does so along the path of least resistance. In brick walls that aren't properly maintained, it's not uncommon to have bed joints - the horizontal mortar - be relatively intact while the head joints - the vertical mortar - be garbage. Why? Because water tends to run vertically more so than horizontally. Given enough time, particularly when talking about lime-based mortar like what was commonly used back when my house was built, water will make the mortar turn to dust. 

When the mortar between the wythes is eroded away, and with no header course, the end result is a giant mortarless void between the wythes. But the mortar doesn't just evaporate or disappear, and that's part of the problem.

Like I said before, the mortar turns to dust. That dust either falls down into the wall due to gravity, or it's carried there by the water. I won't get into the physics of it, but that accumulated mortar dust exerts pressure in both the downward and sideways directions.

If the interior wythe is relatively solid, maybe because there's a layer of plaster covering it all on the interior side, or maybe because the bed joint mortar is still decent, or maybe because there's more modern framing and drywall keeping it from going anywhere, not much damage happens in that direction. 

Likewise, not much damage happens in the downward direction because the mortar dust isn't of a sufficient enough weight put a hole in the earth. That leaves the other sideways direction, towards the exterior wythe, the wythe that's already subject to rain, snow, wind, etc.; that's where the problems show up. 

The weight of the bricks combined with reduced structural stability due to water-casued mortar erosion, plus built-up piles of soggy, eroded mortar inside the wall putting lateral pressure on the wythes, causes the wall to bow. It'll only get worse with time and eventually it'll fall apart. Currently, the wall above the window - which I suspect has been rebuilt, poorly, at least once in the past - has a bow of maybe 3/4". It's not a lot, but I don't want it to get any worse. 

In project management terms, dealing with this is outside the original scope of the project. But I'm there, the scaffolding is there, and while I don't entirely know what I'm doing in terms of fixing it without having it all come crashing to the ground, a case could be made to address the situation right now. I put a poll on the 'gram to see what others might do - fix it now, or come back to it later - and the results were pretty one-sided.

I was probably going to go ahead and fix it now, but the masses have spoken and that's now the official plan. I'm not a mason and I don't have a ton of experience with this kind of work but between years and years and years of building and fixing things and the limited masonry experience I do have, my gut is telling me to tread lightly. The wall is in that bad of shape. 

I'm going to attempt to rebuild the arch first, maybe in 2 or 3 separate sections. I'll feel much better about things if I can make that solid and coplanar with the corners of the wall, which haven't seemed to have moved any. From there it'll be more of the same: rebuild in sections, a course or two at a time. If there weren't 2 cornices and the entire parapet above this I wouldn't be so cautious, but there's a lot of brick in precarious positions above me and if it all comes down, it'll hurt at a minimum and take me on a 15' ride to the ground on the other end of the spectrum. I want to experience neither thing, so I'm all about slow and steady winning this race.

So far, this is how things have shaped up (and you better believe I deconstructed things in the most delicate way possible):

That's the delamination void, or space between bricks where mortar should be. Given how the rest of the walls seem to have been constructed, those 2 bricks should be a LOT closer together. The innter wythe hasn't moved, the outer wythe...that's what I hope to put back in its rightful place. 

See those black marks on the brick above the section I removed? That's to help me get the bricks lined up, when I reset them, in a halfway orderly fashion. Building these arches isn't as easy as it may look, and a little help to keep them evenly spaced won't hurt. This ain't my first rodeo.

That's where things stand now. I need to stop typing get to wall-rebuilding.