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“BIGGER Hole in the wall…”

April 25, 2013
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After researching historical terra cotta construction details online, I decided that we needed to investigate further into how our terra cotta parapets were constructed. Fortunately, we have an old portion of exterior wall, with the same terra cotta details, accessible by standing on the roof, because they had been enclosed by a later building addition.

The outline of original building can be seen on roof.

The outline of original building can be seen on roof.

This terra cotta was once an exterior wall

This original parapet terra cotta was once an exterior wall

I could safely punch a hole all the way through this wall with no danger of having building pieces falling 40’ to the sidewalk and street below.

I finally came to the “We Need a Bigger Hole” conclusion after reviewing an amazing collection of terra cotta drawings online. It is a collection of hand-drawn plates from the National Terra Cotta Society U.S.A., and the 100+ year old drawings are exquisite. They’re available online: click here

It was details like the one below that led me to question how our terra cotta was anchored and held in place. The section with the blue dashed outline is pretty close to the terra cotta pieces we have in our parapet; one lower row embedded further in the wall, then an upper row sitting further out but on top of the first row.

Beautiful Vintage Drawings of Terra Cotta

Beautiful Vintage Drawings of Terra Cotta

Spending more time looking into this, even if I come to the same conclusion as I did with the previous hole, is not really wasted when the future of BAB is at stake; if we ruin, destroy or otherwise weaken the terra cotta parapet wall, it’s possible it could fail during one of our big storms or tornadoes. Replacement cost could be just as much as the cost of the whole building. That’s not even considering what or who might be damaged or injured by falling terra cotta.

So on to more demo! And like many other unusual tasks at BAB, I talked Eric into helping.

Just like with the previous hole in the wall, there was a seam of open joints that made the first few bricks easy to remove.

Eric pulls out some loose bricks.

Eric pulls out some loose bricks.

The layers of mortar surrounding the metal angle, er, what USED to be the metal angle, were all loose and crumbly. Not good news.

Loose and crumbly.

Loose and crumbly.

There was a short section of angle that was still recognizable – it was loose inside and not doing any good being in there. (Left photo) The remainder of the steel angle was just a ghost of itself: as soon as we touched it, it crumbled to pieces of rust. This wall has been breaking down a LONG time.

Remnant of steel angle left

Remnant of steel angle left

Ghost angles that crumble

Ghost angles that crumble


The bricks without failing joints were hanging on tighter and needed convincing to come out. At first we used ordinary mason chisels and hammer. Those bricks just holding on at their top faces popped off easily after a few blows.

Eric with hand chisel

Eric with hand chisel

tets

Bricks above pop off easily

After a couple more bricks fell, Eric noticed sunlight peeping through a hole. ANOTHER bad sign.

Sunlight at the center

Sunlight at the center

The light was coming through a joint between two large pieces of terra cotta. Without mortar or other sealant in those joints, moisture from rain & snow can get inside the wall; causing metal to rust, and when the moisture freezes, causing failure in the brick and mortar.

These open joints in the terra cotta are obviously one source of the troubles in our parapet.

Then we found that whole bricks had been grouted solid into the openings or “cells” of the terra cotta. At first we weren’t sure why, but then figured out that these bricks placed half-in/half-out were part of the anchoring of the terra cotta.

A whole brick mortared into a terra cotta cell.

A whole brick mortared into a terra cotta cell.

(Before moving on, in the last picture notice the rusty threaded rod sticking up in the foreground. THAT is the short end of a long rod embedded into the wall below – it was used to bolt down the steel angle and hold it in place.)

Since most of the weight of this terra cotta piece was at the front (exterior) and hanging over the edge of the piece below, the back of the terra cotta wanted to raise UP. By anchoring a brick into each cell, it allowed the weight of the bricks above to counteract the upward force of the terra cotta. In effect each terra cotta piece was “toothed” into the brick wall.

But we needed to take those out too to continue this investigation. The pneumatic hammer and chisel were needed.

Eric breaks out the big gun (air hammer with chisel bit)

Eric breaks out the big gun (air hammer with chisel bit)

Eric had to leave soon, so I took a break, and stood back to see how things were going.

Hole is gettin' bigger...

Hole is gettin’ bigger…

That last picture reminds me that I didn’t explain that Eric & I were working on the upper half or row of the terra cotta. There is a lower row that has its back edge exposed (but it’s got tar covering a lot of it.) You can make out the outlines of the terra cotta cells through the black tar – look across the bottom of the last picture. I’m sure I’ll be posting pictures of this area in the future when the tar is removed.

I was finding lots of thin twisted wire. They were tied and twisted through holes in the terra cotta.

Twisted wire found inside wall

Twisted wire found inside wall

Combining this with information from the smaller hole made a few weeks ago, I concluded that the wire went through the hole and then around the steel angle, for the purpose of temporarily keeping the terra cotta from tipping over while the remaining bricks were placed behind and above the terra cotta.

There’s also a thicker piece of steel sticking out of that hole – not sure what that is yet.

So while enlarging the demolished area, I popped off a brick at the top of the opening and it fell with a thud on the new brick ledge. I was surprised to see a straight smooth recess in the mortar; like the kind left by a piece of steel…

Weird mark on fallen brick

Weird mark on fallen brick

Sure enough, I looked up at where the brick fell from, and square piece of steel was visible, still embedded in the mortar on the brick above.

Embedded steel show by dashed outline

Embedded steel show by dashed outline

Eager to see more, I chiseled out as much mortar as I could without taking down more bricks, thinking that heavy hammering might disrupt the steel, and I wanted to see it intact as much as possible.

Removal of the mortar revealed that these were “Z-shaped” anchors, with one end in the hole in the terra cotta and the other end sticking up into the bricks.

Two Z-anchors visible

Two Z-anchors visible

With that figured out, it was okay to take out the next row of bricks at the top of this hole. (My goal was to get an opening all the way through the wall, and if necessary, remove one or more of the giant pieces of terra cotta.)

Running horizontally in the middle of the last photo is a darker hard-edged material. I put the air chisel directly on in it and it wouldn’t budge or chip; I began to worry that it was another steel angle on the top of this terra cotta row, anchoring it much like the lower row was anchored on its top. That would make this demolition (and future reconstruction) quite complicated.

So I eventually got the next row of bricks down and that resolved the riddle of the hard darker material: they were the iron spot bricks used on the exterior face of BAB. I’d finally made it through to the last layer of bricks in the wall.

Some different bricks as the next layer

Some different bricks as the next layer

At the right side of this opening, I could see daylight around the darker brick. Again, not good. Another place where water can get in and deteriorate this wall.

Light peeks around this brick

Light peeks around this brick

But you know what? Why not take advantage of the gappage and make THAT brick be the hole through the wall? So I whacked on it with a hammer (I didn’t want to break it with the air chisel) and it came free in six licks.

Finally through the wall!

Finally through the wall!

Here’s the view from the other side. You can even see a view of the ponding roof water through the hole.

Only one loose brick on the other side.

Only one loose brick on the other side.

The task was now completed; enough brick has been removed. I have a good understanding of the terra cotta construction and feel that there won’t be any “big surprises” for the masons.

I stood back for an overall picture – while it IS a BIGGER hole, I feel there is going to be much bigger brick demolition in my future. (And you can see the lower row of terra cotta too.)

Presenting: The BIGGER Hole in the Wall.

Presenting: The BIGGER Hole in the Wall.

Since we’re entering the rainy season, the next day I bought a very large tarp and draped it over the whole wall to keep rain out of the big hole, and weighed it down with the ballast on hand.

Hole covered to keep rain out.

Hole covered to keep rain out.

If you think this whole roof thing is taking forever to get done, I agree with you!

Next step: get the tar and asphalt removed from these walls… just in time when the warm weather will make it all melty and sticky.

3 Comments leave one →
  1. Avik permalink
    July 30, 2013 9:51 pm

    Very cool post, Tom! I like the amount of research you’ve done before bustin through this thing and how thoroughly you documented your process. How much/what kind of work has to be done on the entire parapet in general? Do you fear that pieces could fall to the street without quick action given the conditions you found some of the metal angles and gaps in this section?

    • Tom permalink*
      July 30, 2013 11:52 pm

      Thanks Avik!

      The parapet needs reconstruction of six rows of bricks about where that angle is; the top terra cotta copings need sealing at their joints (easily done with a ladder on the roof); and the terra cotta cornice pieces also need joints sealed but they’re only accessible with a boom from the ground. Then some general tuck pointing and finally a coat of breathable sealer on the inside.

      Our structural engineer believes (and I agree) that the parapet has been in very slow decay and that the majority of the joint decay has been due to moisture getting to the steel angle and the resultant rusting & flaking has been expanding/forcing the bricks and mortar towards the inside. So “quick action” is relative; that parapet has been up for 100 years; the deterioration has been going on for decades; and action should be taken within 5-10 years or there could be trouble. There is a lot of weight still sitting on the terra cotta keeping it from flipping out; so the masons will have to deliberate with how much brick they remove at one time. I’m going to instruct them how to stagger and phase the rebuilding. If not, a continuous horizontal removal of brick at the angle location could act like a “zipper” on the back of the wall and weaken it. Of course that’s a whole ‘nuther post in itself…

  2. Tom permalink*
    July 30, 2013 12:53 am

    (For those of you that are subscribers, no, you’re not crazy; you may have received notification about this post in July though it’s dated as an April post… I’m just behind!)

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