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Tuesday, May 11, 2010

Tar verus Asphalt Roofing

Remember how the fresh tar gummed up your bicycle tires. To add insult to Schwinn, the tar gathered pebbles until the bike was a huge mess. Mom was mad. You even aimed the bike at the tar like a kid jumping in mud puddles on his way into Kindergarten. I now inform you that this was not tar but asphalt.

Tar is mined and asphalt is cracked. Tar is from plants, asphalt is made in plants. Tar won’t get brittle with time like asphalt. It will run and spread on hot days forever while asphalt will eventually lose its ductility. Tar stinks and asphalt smells good, at least to me. We old roofers love the smell of melting asphalt. Melting tar is bad because of all the creosote. Tar killed the dinosaurs, asphalt, or oil more specifically, is endangering our species.

When roads, which use higher grade asphalt than roofs, are repaired the asphalt is very viscous. On hot days a thermoplasmic migration or slow boil of the asphalt slowly brings the material in contact with oxygen. This softening leaves the granules susceptible to damage or scuffing when the new shingles are hot. On a steep roof the roof need only to be warm. That’s why roofers steal the foam cushions from defunct couches on the side of the road. The pads make excellent steep roof anti-scuff tools.

As asphalt oxidizes it becomes more of a solid and less of a frozen liquid, the natural state of asphalt. The color changes from black to light grey. Fresh asphalt will not adhere to aged asphalt unless it is treated with a topical primer because the old product is no longer a liquid. Merging the two is like trying to caulk glass. It can't be done. That's why glass is glazed, which is a pressure seal like a cork. As the process continues the oils flash out of the material and it becomes brittle. This is one of the many reasons ventilation is so important. Slow down the flashing of oils.

One day I’ll talk about the difference between emulsions and coatings or flash versus evaporate.

When flat roofs are made of tar, and I haven’t seen one in Dallas for a long time, the perimeter must be enveloped or the material will run down the walls on hot days. I saw large lugs of tar at a supply house in Garland that had melted all over the parking lot. The last time I saw a tar roof in Irving it was on an old building in the downtown section. Old tar has a bluish color and smells like a telephone pole.

If you try to repair either of these products with the other you will fail. They are enemies. The ancient versus the modern, the smelly versus the not so smelly, these are battles that will continue until time ends. If you put an asphaltic roof system over a coal tar pitch roof the new roof will blister from the gases and the tar might start running everywhere, and I mean everywhere, because you nailed through the containment.

The test for asphalt properties is ASTM D312, and I’m not looking to see if it has changed. The old ring and ball test checks for ductility and penetration, which determines what grade of asphalt that is being tested. On one end of the scale is “dead level” asphalt. It is like coal tar pitch only worse. If you look at it on a warm day it will attack you like the Blob did Steve McQueen. If you’re not as tough as he was, then you’re a gonner. Better start smoking and scraping asbestos off pipes.

On the other end of the spectrum is “type IV” asphalt which can be mopped on an inclined roof and will stay put like a Gurkha. Phych! Not really. More like a piece of gum on the sidewalk that is there to teach all who may pass that the spitter was a jerk.

The cost of asphalt has risen dramatically over the last several years and not because oil has gone up. The culprit is demand for gas and jet fuel. With the new cokers, not cookers but basically doing the same thing, the oil behemoths are able to squeeze more gas and jet juice out of asphalt. If the roofing giants want it they’ll have to pay.

The raw crude is put in a barrel and heated. Gases flash off. All kinds of substances like butane to heating oils are captured, leaving the trash that will soon be on your roof, and I’m not auto-referencing. The material, not the man, is the illusion here.

The gases are captured in trays above the mixture as it is heated. What’s left is residuum. Boy does that sound bad. “Want some residuum on your roof?”

After catalysts are added to the bubbling crude remains, the chains of hydrocarbons are mutated into whatever the chemist can coax from Mama Natural.

The rising price will eventually lead to a change in the types of roofs you see in America. We may end up with more traditional European style roofs like metal, concrete, and clay. I’d love a synthetic thatch roof myself. I’ve never seen one in Dallas or anywhere in Texas. I did see palm leaf roofs in Arlington, Texas.

I thought I thaw a puddy tat. Time to take the long chain hydrocarbons like the doctor said I mean they even make vitamin E and medicine from this glop.

Those soon to fail plastic synthetic roofs you see all over Colleyville, Fort Worth, Bedford, and Las Colinas, are also from petroleum. Plastic is just treated asphalt.

In conclusion, pitch is not used on pitched roofs but flat ones and if you don’t use us to put on your roof it’s your own arse-fault.

Sorry about that but I love the asphalt molecule and would go on further if left to do so.

If you really need to know more check with ARMA. Asphalt Roofing Manufacturers Association .

Jon Wright