Tag Archives: historic pres technology

fuses

(written Dec 6, 2011, as i studied for an exam)

I just learned something else. (Thanks to Ching’s A Visual Dictionary of Architecture and not to paying attention in class or doing the study guide or anything)
Did you know that FUSES are “a device containing a strip of fusible metal that melts under the heat produced by excess current, thereby interrupting the circuit”? So basically, a fuse is a safety switch. These days we have breakers which do the same thing—act as a safety switch, flipping off when too much voltage runs through—they just are reusable unlike the fuses that had to be replaced.

Now, that grounded wire. I get what it DOES and why, I just don’t get HOW it does it.


how insulation works

I have recently rediscovered the “Preservation in Mississippi” blog and am trying to read it when i get a chance. This morning I delving into the concrete block construction fad in Vicksburg (this relates to studying for my test tomorrow i swear) and was curious as to why they claimed to provide excellent insulation. Some readers were curious too and one guy had an answer:

“The blocks used for the cap of the low wall show some playfulness with the block machine. The manufacture used a form for the short side of the block that was half the size of the block they were making. This gave it a half rockface, half smooth finish to the block.

“[The concrete block construction] claims are 100% valid. The continuous dead air space they refer to in the article is a pretty good insulator since dead air does not transfer temperatures. With modern insulation like fiberglass bats or spray foam (gasp, boo, hiss) its not the product insulating the structure but the dead air space the insulating material tries to create. Like Malvaney said air infiltrating the space will negate the value of a cavity.

“Well maintained this method of construction is fairly efficient. Although temperature transfer through walls is pretty low on the list of concerns. Walls are fourth on the list behind roof, floor, & openings(doors and windows).”

Dead air space provides insulation?! This was something I didn’t know but it makes sense of course. The “loft” of your sleeping bag or comforter keeps you warm (and when you loose that loft cause you washed it, you’re not warm anymore). I sought to verify this with a trip to howstuffworks and learned that the purpose of insulation is to retard the transfer of heat and since air is poor conductor of heat it is probably the most basic, effective, and accessible form of insulator. This would also explain [to me] why all these new thermal fabrics and such are so full of “technology” because they have to get around the most basic rules of insulation.


not exactly related, but this is a picture of the very uninsulated (and drafty) attic of Sunshine. You can imagine how all that hot hot air in the summer transfers DOWN into the house!


nerding out at the Cobb house

back in July when i was in Athens to get my hairs cut and have dinner with RT, we walked by the TRR Cobb house which was moved back to its hometown during my last semester at UGA. It has now been fully restored, landscaped and is a house museum in-progress as the curators work at furnishing it. It was evening and no one was home when RT and i peeked in the windows of this funky pink monstrosity. The re-relocation of the TRR Cobb house has earned a fair share of protests from it’s bold hue to the fact that Mr. Thomas Reade Rootes Cobb is probably “best known for his treatise on the law of slavery titled An Inquiry into the Law of Negro Slavery in the United States of America (wiki). We’ll get to the pink color later.

So, the house, located originally at 195 Prince Ave was originally built in the 1830s as a basic I-house, in the 1840s it was added onto by TRR who was apparently making plenty of money as a lawyer and probably a little from his father-in-law as well (lumpkin) who gave him and Marion Lumpkin the house at their marriage.

The building was put on the National Register in the 1970s and in the 1980s, was moved to Stone Mtn Park where it was slated to be restored and become part of the Antebellum Village. This never happened however and it sat in the woods, mothballed, for 20 years. When they moved it back to Athens (you have to watch this clip and rebuilding timelapse!!). For probably the last 100+ years the house was white, typical antebellum house color of choice. But back before the Civil War (because TRR Cobb was fatally wounded early on), one of the Cobb’s young daughters, Lucy, died and there was a painting done of her with the house, in full octagonal pepto-bismal regalia. I kind of like it (:

for a good brief history but more thorough than mine go to the TRR Cobb House site.

—–
But I need to get to the point of why I am writing this post at all. When RT and I approached the sparklingly clean building (a pressure-washer sign out front indicated it’d just been cleaned) the first thing we noticed was the horrid state of the sidewalk. Newly laid of course and not historic (thank goodness i guess), the surface of the bricks was chipping like crazy. I couldn’t help it, i took pictures, wondered why it was like that and put the thought aside. A week later however, at the GA Trust I came across the word “spalling” and looked it up:
“Spalling is the deterioration of concrete by crumbling or flaking. The main cause of spalling is water. When brick is exposed to water consistently, some of the water is absorbed through the porous material of the brick. When this water freezes and thaws repeatedly, it causes the brick to fall apart.
Other sources of spalling are high pressure washing, water hitting the wall directly by driving rains, water from downspouts, gutters and roofs and water seeping up from the soil.”

it is funny how things come together sometimes. Also, in class (i couldn’t help it, i shared the pics) Ed point out that it looked like those bricks probably were not made to be surface bricks anyway and i’m betting he’s right. In any case, I guess they won’t be pressure washing that sidewalk again!