Reused old form boards as roof sheathing 100+ years ago

I was in a DC attic recently and noticed that every one-in-five or so of the roof decking boards had a cement coating.

The boards looked just like our modern day forms boards after being dirtied from use. This roof framing is original to the house. At the time of construction of much of DC row homes, concrete (and therefore concrete forms as well) was not yet in use. So, I had to think and try to figure out where the boards could have been used.

After spending a few minutes thinking it over I realized the boards weren’t concrete forms at all, they were likely scaffold planks used by the mason who built the demising walls (probably not the front lumper).

Tabby construction in DC?

We were on a jobsite last month where there was a section of concrete paving. The concrete paving was old and largely broken up. I wasn’t expecting this but I found old mollusk shells in the concrete, similiar to the old tabby walls common on the shores of the Carolina’s.

Tabby concrete construction is a method of building using fired mollusk shells to create a lime cement. Together with the resulting lime binder the shells themselves also were kept in the concrete as an aggregate.

Old rat slab

The photo below shows an example of an old rat slab, a thin layer of concrete applied on top of a dirt floor cellar in historic times.

These old slabs were intended for just three purposes:

1. Minimize dust of a dirt floor.

2. Keep rodents, like rats from boring through as quickly.

3. Reduce some of the subgradr moisture permeability.

A close look at at electrogalvanization

The picture below zooms in on a panel of electrogalvanized corrugated sheet metal, in this case used as a siding material.

The exposed layer of the metal panel shown in the photo above is zinc. The panel itself is steel, likely grade-5 mild steel which is easy to cut and less expensive than grade-8 or higher tensile strength steel.

In this case the zinc galvanization acts as a sacrificial anode to protect tge cathode, the steel substrate. Essentially the zinc coating protects against oxidation, rusting, when exposed to precipitation or air moisture, humidity.

Some obvious advantages of this type of steel protectant process are:

1. Electrogalvanized steel has lower cost than hot dipped steel, in most cases depending on batch process mill run lot sizes.

2. Thinner plating of electrogalvanized steel allows for better and tighter fit between mating parts.

3. The aesthetic of electrogalvanized steel has a cleaner, brighter, shinier look.

However there is one downside as well, the thinner coating of zinc in electrogalvanized process offer lower restance to corrosion than hot dipped process.

Concrete remains show structural subcomponents of California’s Sunken City

It’s a beautiful sunset looking south into the Pacific from California’s Sunken City, an incredible seaside terrain.

Looking closely at the stony land at the edge of the sea below the the unstable cliffs, it becomes clear that the stone is not a natural formation. The cement where broken in jagged edges and worn away with time exposes the aggregate among the cement, a clear sign this stone is actually the ruins of relatively modern concrete constuction.

Whispering you can see the mangled heavy where are outside of the structural steel construction mixed together embedded in concrete. Together these heavy materials laced ruin upon the beach in liver ruins of construction from almost 100 years ago.

At the time of the seaside collapse, in the late 1920’s this site was the location of hundreds of homes, most of which were relocated and a few which actually collapsed with the eroding Cliffside. From a structural engineering prospective, it’s clear today that many mistakes from need the time in the nineteen twenties. There is no record of proper geotechnical subgrade survey or survey report. A massive area of bentonite clay which is common in the decomposition of volcanic ash, was later identified below the area of the structural subsidence and failure, but this apparently was not properly diagnosed or recognized at the time of construction. Also, end result of this massive engineering failure, it was the leader identified that the construction was missing proper structural wall stabilisation at the cliff side.

In construction beyond a bearing point which exceeds the law of repose degree particular to the class of subgrade soils, we use retaining and hold back system such as sheeting and shoring, deadmans, pilings, or even a cantilevered base.

Calcium carbonate to calcium oxide

We put together a few videos and a lot of info below to explain the process of chemical conversion calcium carbonate calcium oxide. This process is more commonly known as firing of limestone to create quicklime. Quicklime as many know is the key active ingredient in historic lime mortar.

Doing a little backyard chemistry, we burnt limestone to create quicklime. This is an extremely small batch process just done for the purpose of learning the chemical process. In real production masons most often create a comparatively massive batch of quicklime.

The videos below has a detailed description of the burning and associated chemical conversion process through burning with the addition of h2o.

What’s in your pipes??

Piping and tubing has led to the development of societies overall. We’ve been using piping for thousands of years. However, over time our piping and plumbing methods have changed significantly.

(Interestingly, the word plumbing comes from the Latin root word for lead.  Plumbers essentially are/were lead-ers.  Because at the time of the origin of the name, plumbers made and installed pipes from lead.)

The example of lead piping used in Rome is well known. It was used extensively, and it helped the civilization develop so that people could live in city centers.

Old corroded steel pipe, rotten out on the inside

However, even with the significant development over the past millennia, even in the last hundred years our methods of piping and tubing have changed significantly. Many old houses on Capitol Hill still have steel pipes such as the ones shown in the photos above.  (Many houses still have lead service lines as well, an issue DC and other cities are trying to slowly address.) At the time of installation, these pipes were one of the best methods available. Annealed copper, CPVC, and PEX used today were not a real option at that time.

But, just looking at this photo, you can see some of the problems with steel piping. The corrosion shown in these pictures is a perfect example of the corrosion typically found in steel pipes in Capitol Hill.