What the Black Streaks Actually Are

Drive through any Shreveport neighborhood from Broadmoor to South Highlands and you will see black streaks running vertically down asphalt-shingle roofs, especially on the north and east faces. Most homeowners assume it is dirt, soot, or runoff. It is none of those.

The streaks are colonies of gloeocapsa magma, a cyanobacteria (technically blue-green algae) that feeds on the limestone filler used in modern asphalt shingles. Limestone became standard in shingle manufacturing in the 1980s as a cheap inert filler. The downside: gloeocapsa magma loves it, and Louisiana humidity gives the algae everything else it needs to thrive year-round.

Once a colony establishes, it spreads roughly one to three feet per year and produces a dark protective sheath that protects it from sunlight. That sheath is what you see as black streaks. The sheath also absorbs solar heat the shingle was designed to reflect, which heats the roof deck underneath and shortens shingle lifespan.

Why You Cannot Pressure-Wash an Asphalt Roof

The Asphalt Roofing Manufacturers Association (ARMA) explicitly warns against pressure-washing asphalt shingles. The reason is simple: the colored ceramic granules on top of each shingle are what protect the asphalt underneath from UV damage. High-pressure water strips those granules. Once they are gone, the shingle ages 5 to 10 years overnight under direct sunlight.

Most major shingle manufacturers (GAF, Owens Corning, CertainTeed, Atlas, Tamko) require ARMA-compliant cleaning to keep warranties valid. Pressure-washing your roof can void a 30-year warranty in a single afternoon. We have seen Shreveport homeowners with 8-year-old roofs that look like they are 25 years old because a previous service used a pressure washer.

Soft washing solves this. Instead of relying on water pressure to remove the algae, soft washing uses a low-pressure (under 100 PSI, about the same as a garden hose) application of cleaning chemistry that kills the algae at the root. The next rainstorm rinses the dead growth off.

The Chemistry: What Actually Works

The ARMA-recommended chemistry is a 2 to 3 percent sodium hypochlorite solution mixed with a surfactant. Sodium hypochlorite is the active ingredient in household bleach but at a higher concentration. The surfactant lets the chemistry cling to vertical surfaces long enough to kill the algae before rinsing off.

We apply this with a 12-volt soft-wash pump that delivers chemistry at fire-hose pressure (about 60 to 80 PSI), well below the granule-stripping threshold. The application takes 30 to 60 seconds per roof section, the chemistry sits for 10 to 15 minutes, then we rinse with plain water. Total time on a typical 2,500 square foot Shreveport roof is 60 to 90 minutes.

The chemistry biodegrades within 48 hours. We pre-rinse and post-rinse all landscape beds within the perimeter of the house. Shreveport homes with mature azaleas under the eaves get extra care because azaleas are sensitive to chemistry runoff.

How Often Shreveport Roofs Need It

Every 3 to 5 years for asphalt shingles in Shreveport humidity. North-exposed roofs and homes with heavy tree shade may need closer to 3 years. Sun-exposed roofs in newer South Shreveport subdivisions can sometimes go 5 to 7 years.

If the streaks have been ignored for 10+ years, the first cleaning will dramatically restore the roof to factory color. Subsequent cleanings every 3 to 5 years prevent new colonies from establishing and keep the roof looking new for the rest of its lifespan.

We also offer optional zinc-strip installation along the ridge line. Zinc oxide releases during rain in trace amounts that prevent algae regrowth for 5 to 10 years. The strip is invisible from the ground and adds about $300 to a typical job.

What About Moss, Lichen, and Other Growth

Black streaks (gloeocapsa magma), moss, and lichen are three different organisms that grow differently on Shreveport roofs. Moss grows in thick green patches in shaded valleys and behind chimneys. Lichen attaches as raised crusty spots that resist plain pressure cleaning.

Each requires the same soft-wash method but a different application sequence. Moss often needs a longer dwell time before rinsing. Lichen sometimes requires a manual scrape to remove the dead crust after the chemistry kills the organism. We identify each on the estimate so the bid is accurate.

Common Questions

How long does a Shreveport roof cleaning take?

A standard 2,500 sq ft asphalt roof takes 60 to 90 minutes start to finish. Larger homes with multiple roof planes or steep pitches take two to three hours.

Will the chemistry hurt my landscaping?

No. We pre-rinse, tarp, and post-rinse every landscape bed within the perimeter of the house. The chemistry biodegrades within 48 hours.

How long do the results last?

A single cleaning lasts 3 to 5 years before new colonies become visible. With a zinc-strip ridge installation, results last 5 to 10 years.

Will it kill the algae permanently?

It kills existing colonies. New spores reach roofs by air every season, so without prevention they will eventually return. The optional zinc strip prevents new growth for 5-10 years.

Is soft washing safe for a 25-year-old roof?

Yes. Soft washing is gentler than rain. The chemistry kills the algae and gravity rinses dead growth on the next rainstorm. There is no abrasive contact with shingles at all.

Do you clean tile, metal, and slate roofs in Shreveport?

Yes. Tile and metal use a different chemistry concentration. Slate requires the gentlest possible approach with hand-rinsing. We do not pressure-wash any roof material.

Read more on our Shreveport Roof Cleaning service page, see our recent project gallery, or learn about the team.