roofing surface question


what's the stuff called that is used in the deep south on flatdeck reroofs, small pebbles that look like grey and white stones, attached to surface of the topcoat and also thrown onto the melted tar ?
while the tar was still liquid the crew throws a little of this sand like substance over the top coating.
does it serve a cosmetic purpose or is it functional in reducing sun exposure to the surface?
if rain washes away some of this from the surface, is it worth reapplying?
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jack wrote:

Pitch and gravel.
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dadiOH
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dadiOH wrote:

Also crushed marble.
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so I should be able to find crushed marble at local HD or Lowes ?
if rain washes away some of this from the surface, is it worth reapplying?
is it cosmetic or functional (ie. reducing surface temperature) ?
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jack wrote:

The main function of the gravel is to reduce UV radiation. UV radiation degrades the tar.
The light color of the gravel also reflects visible light and tends toward a cooler roof.
Usually gravel completely covers the roof, but some doesn't contact the tar and, with nothing to hold it in place, washes off.
To answer your question, re-applying gravel will help. Don't walk directly on the roof - use wide boards to spread your weight as you maneuver to the area you want to re-seeding.
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what is used to make the new marble/rock crush adhere to the dried surface? epoxy?
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jack wrote:

When the tar gets hot, it get sticky.
I guess, if you want, you can glue each pebble in place. Epoxy is good.
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jack wrote:

Maybe not at the big-box, at least not at a decent price. Local commercial roofing supply, and/or landscape supply, will have marble chips. (they are also used to top-dress planting beds, sometimes.) And on a hot-mop roof, the white chips do reduce the heat load, and disperse the impact of raindrops. If rain washes it away, your roof sloping and drains were not done correctly, or the layer of chips is way too thick. At most, once a year or so, you may need to scrape the high spots over to the thin spots. The bottom layer of chips should bond to the top layer of tar on the first few hot sunny days- that is why walking on the stones is supposed to be kept to an absolute minimum, with walkboards used for any places on roof that have to be visited on a regular basis. Any other spots on the roof, you wear soft tennis shoes rather than work boots, and walk gently.
Note that in current commercial use, they have mostly switched over to light-colored membrane roofs that do not need any additional topping material. Just painting the whole roof with a special sealer stuff every few years, to refresh the fake rubber, and seal the micro-cracks that the UV creates. More expensive up front than hot-mop, but lasts longer, and fewer leaks and failures if properly applied. The in-house repair guys can usually handle the recoating.
-- aem sends...
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that's what this job apparently used but the light colored membrane has microfine white rocks on the surface. heavy rain washed off parts of it into a small sand pit under the gutter spout.
I supposed a white rubberized elastomer would also do over the exposed black tar areas, ie. the exposed areas are very small
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Around here its called a "Tar & Gravel" roof
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