Original Air Date: 07/25/26 Episode Number: 469Episode SummaryA listener question about painting aluminum siding kicks off the show, and Dan splits the answer across two segments with a detour in the middle: a full conversation on how to identify and safely clean biological growth off the exterior of your home -- algae, mold, mildew, moss, and lichen. The aluminum siding answer wraps up at the end with product recommendations and a strong case for always doing two coats. Moss and lichen get their own episode next week.Timestamps
- [00:00] -- Show Kickoff
- [00:30] -- Listener Question: Aluminum Siding
- [01:44] -- Oxidation and Prep Basics
- [03:58] -- Wash, Scrub, Rinse
- [05:42] -- Hand Test and Inspection
- [07:21] -- Primer or Not
- [08:11] -- Switch to Algae Topic
- [08:53] -- Brick Recap and What Triggered This
- [12:20] -- What Growth Is It?
- [13:32] -- Algae, Moss, Lichen, Mold
- [16:16] -- Efflorescence Sidebar
- [17:29] -- Moisture Causes First
- [19:01] -- Cleaning Safely Tease
- [20:01] -- Moss vs. Mold Distinction
- [21:00] -- Golden Rule: Gentle Cleaning
- [22:47] -- Pick the Right Cleaner
- [25:50] -- Prep Before Repainting
- [27:09] -- Hose, Not Pressure Washer
- [29:53] -- Why Not Straight Bleach
- [31:22] -- Protect Plants from Runoff
- [32:41] -- Fix the Moisture Root Cause
- [33:56] -- Aluminum Siding Paint Picks
- [34:45] -- Two Coats Really Matters
- [36:33] -- Best Benjamin Moore Options
- [38:54] -- Temperature and Wrap Up
Listener Question: Aluminum Siding [00:30]A listener wrote in asking about painting their tan aluminum-sided house a darker blue. They wanted to know what prep was involved, whether one-coat coverage was possible, and what products to use.Dan splits the answer into two segments. The short version on the one-coat question: two coats, always. The longer version on everything else follows below.Oxidation and Prep Basics [01:44]The single most important thing to understand about painting aluminum siding is oxidation. If you've ever rubbed your hand across older aluminum and ended up with white chalky powder on your palm, that's the original factory finish breaking down from years of sun, rain, and weather. That chalk has to come off before any paint goes on.Paint bonds to a surface. If that surface is a loose layer of chalk sitting on top of old factory finish, the paint is bonding to the chalk -- not to the siding. When the chalk lets go, the new paint goes with it. This is the most common reason aluminum siding paint jobs fail, and it's entirely avoidable.A pressure washer alone won't get you there. It'll knock off dirt and cobwebs, but it doesn't automatically remove oxidation. Dan compares it to washing your car with only a pressure washer after an entire Michigan summer of construction zones and dirt roads -- you'll get some of it, but you won't get all of it.Wash, Scrub, Rinse [03:58]Start with a good exterior house cleaner that's built to break down dirt, grime, mildew, and oxidized residue. Apply it, and then physically scrub the surface -- a soft-bristle siding brush on an extension pole makes this manageable. Work in sections so you can scrub and rinse before the cleaner dries on the siding.You can use a pressure washer for rinsing, but keep the pressure reasonable and always direct the spray downward the way rain would naturally hit the siding. Shooting water upward beneath the panel laps can drive moisture into the wall. The pressure washer is a rinsing and help-with-cleaning tool. The scrubbing still has to happen.Hand Test and Inspection [05:42]Once the siding is dry, perform the hand test: rub your palm firmly across the surface. If it comes away clean, you're good to move on. If there's still a chalky residue on your hand, keep cleaning. The surface doesn't need to be microscopically perfect, but you should...
