Decking · Hot & humid

How a composite deck ages in Mobile, AL

THE SHORT ANSWER

In Mobile, composite won’t rot, but the damp still matters: about 133 rainy days and 79% average humidity mean shaded boards grow surface mildew unless they are washed once or twice a year. Model estimate: 23–30 years of service.

Main threat
Moisture & decay
Climate profile
Hot & humid
Expected life
23–30 yrs
Wash
Spring & fall
Rainy days / yr
133
Days ≥ 90 °F
73
Simulated composite deck in Mobile, AL after 10 years
Year 10Surface mildew in shaded areas
MODEL SIMULATION
Mobile, AL · capped composite boards, south-facing, full sun
Color lossHigh
Surface wearModerate
Mildew / rotHigh
Fails first hereShaded boards (surface mildew)

Storyboard

20 years in Mobile, washed yearly

Composite deck in Mobile, install: Install day
InstallInstall day
Composite deck in Mobile, year 1: Slight early fade
Year 1Slight early fade
Composite deck in Mobile, year 3: Slight early fade
Year 3Slight early fade
Composite deck in Mobile, year 5: Color has lightened, then stabilizes
Year 5Color has lightened, then stabilizes
Composite deck in Mobile, year 10: Surface mildew in shaded areas
Year 10Surface mildew in shaded areas
Composite deck in Mobile, year 15: Surface mildew in shaded areas
Year 15Surface mildew in shaded areas
Composite deck in Mobile, year 20: Surface mildew in shaded areas
Year 20Surface mildew in shaded areas

Mobile’s wear fingerprint

Each bar is scaled to the highest of the 25 cities we cover; the black line marks the median.

Rainy days / yr133.4 · High
Avg humidity79.2% · High
Decay index110.2 · High
UV index (avg)1.5 · High
Freeze–thaw days15.1 · Typical
Days ≥ 90 °F73 · Typical

NOAA station MOBILE DWTN AP (USW00013838, 8.7 km away), 1991–2020 normals · humidity & UV: NASA POWER.

What fails first here

  1. 1Surface mildewComposite does not rot, but pollen and dirt on shaded boards feed mildew — common in Mobile’s damp climate. A wash in spring and fall prevents it.
  2. 2Early color fadeCapped boards lighten in the first 1–2 years, then level off. Stronger here than average: UV rank #8 of 25.
  3. 3Heat underfootAbout 73 days a year top 90 °F; dark composite can get uncomfortably hot in full sun. Lighter colors help.
  4. 4Gaps & fastenersBoards expand and contract with temperature; check hidden clips and end gaps every few years.

Upkeep

Mobile maintenance calendar

Built from local normals: bar width is the share of days with rain; composite mainly needs washing.

Jan
Feb
MarWash & check for mildew
Apr
May
Jun
Jul
Aug
Sep
OctWash, clear gaps
Nov
Dec

Same city, other materials

How the alternatives age in Mobile

Cedar deck in Mobile at year 10 (simulation)
Cedar deck
Expected life here: 9–12 yrs · main threat: moisture & decay
See it age in Mobile →
Wood fence in Mobile at year 10 (simulation)
Wood fence
Expected life here: 10–13 yrs · main threat: moisture & decay
See it age in Mobile →

Pin-ready

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The 20-year storyboard as a tall pin, linking back to this page.

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Pinterest storyboard: composite deck in Mobile, AL, new to year 20

Composite decks in similar climates

Miami, FLTampa, FLNew Orleans, LAHouston, TXAtlanta, GA

…and in very different ones

Las Vegas, NVPhoenix, AZDenver, COAll 25 cities →

Questions Mobile owners ask

How long does a composite deck last in Mobile?

Our model puts a capped composite deck at 23–30 years in Mobile, close to typical warranty terms. The boards outlast the look: expect some early fading and surface mildew in shade.

How often should you clean a composite deck in Mobile?

Twice a year — in spring and fall. Mobile’s damp climate makes mildew on shaded boards the most common complaint.

Is composite worth it over cedar in Mobile?

In Mobile our model gives untreated cedar 9–12 years and composite 23–30. In a damp climate that gap is mostly rot you avoid.

Why does wood turn gray or black in Mobile?

Graying is UV plus weathering of the surface; black spots are usually mildew or algae feeding on that grayed layer in damp weather, not rot. A cleaner and a dry-season seal stop it.

Model simulation, not a guarantee: south-facing, full sun, no shade or ground-contact surprises. How it works.