Best Mold and Mildew Cleaners for Exterior Painting Prep: Our Top Picks

Let’s get this out of the way: painting over mold is asking for trouble.

Think about it—mold is alive. It grows, spreads, and clings to surfaces like a parasite. Slapping paint over it doesn’t kill it. It just traps it… and gives it a cozy place to keep thriving underneath your brand-new paint job.

So when that fresh coat of paint starts peeling, bubbling, or changing color within months? Mold is often the culprit. And the sad part is—it was preventable.

We’ve heard it from homeowners time and again:

“I thought I cleaned it well enough before painting.”
“I didn’t know mold needed a special cleaner.”
“It looked dry, so I figured it was safe.”

Spoiler: dry doesn’t always mean clean. Mold spores dig deep—especially into wood grain, porous stucco, or old paint. If you’re investing in a paint job (whether DIY or pro), prep work is half the battle.

Let’s take a closer look at what you’re really dealing with.

Mold, Mildew, and Algae: What’s Growing on Your House?

They might look similar at first glance, but not all discoloration is created equal.

Here’s a quick cheat sheet to help you identify the troublemakers:

Mildew tends to be surface-level, easy to wipe off. Algae is common in humid areas, especially on vinyl. But mold? Mold means business. It embeds itself in porous surfaces and needs more than just water and elbow grease.

How to Choose the Right Mold & Mildew Cleaner

Choosing a mold cleaner isn’t just about brand names or price tags. It’s about matching the product to your home, your climate, and your comfort level with chemicals.

Let’s break it down.

Some cleaners rely on bleach to zap stains and kill spores. These are fast-acting and effective but can damage nearby plants, fade colors, and require heavy rinsing. Others are bleach-free, safer to use but slower to show results. If you have pets, a garden, or allergies, non-toxic formulas are often the way to go.

If you’re dealing with raw wood or unsealed stucco, you’ll want a cleaner that can penetrate deeper. And if you’re in a warm, wet zone like Florida or the Pacific Northwest, long-lasting formulas that help prevent regrowth are worth every penny.

Our Top 5 Mold & Mildew Cleaners (Tried and Tested)

We’ve seen what works—and what’s a waste of time. These five picks are homeowner favorites, contractor-approved, and proven to prep surfaces properly for paint.

1. RMR-86 Instant Mold & Mildew Stain Remover

Speed Demon

If you need instant results and you’re not afraid of a little chemical kick, RMR-86 is your go-to. It removes mold stains from siding and decks in under 30 seconds. But be warned—it’s strong. You’ll want gloves, goggles, and good ventilation.

2. Wet & Forget Moss, Mold & Mildew Cleaner

The Low-Maintenance Champ

This one’s for folks who’d rather not scrub. Spray it on and let the rain do the rest. It’s bleach-free, gentle on surfaces, and ideal for large areas like siding and roofs—just don’t expect overnight results.

3. Concrobium Mold Control

Eco-Friendly & Preventative

More than just a cleaner, Concrobium also stops regrowth. It doesn’t bleach stains, but it kills spores and keeps them from returning. Great for homes with kids, pets, or sensitive lungs.

4. Krud Kutter Mold & Mildew Stain Remover

Budget-Friendly Workhorse

Mild, effective, and safe for most surfaces, Krud Kutter is ideal for regular maintenance. You’ll need to scrub a bit—but it won’t damage paint, and it won’t kill your plants.

5. Spray & Forget Exterior Cleaner

Set It and Forget It

This slow-release formula works over time and continues to protect. One application can last for months. Great for roofs, patios, and out-of-reach walls—just don’t expect it to clean up a mess before the weekend BBQ.

Step-by-Step: How to Use Mold Cleaner Before Painting

Here’s the simple process we follow before any exterior painting job:

1. Inspect the surface
   Look for streaks, fuzz, or musty odors. Pay attention to corners, shaded areas, and anywhere moisture lingers.

2. Choose your cleaner wisely
   Match the product to your surface type and level of infestation. When in doubt, test a small area first.

3. Apply according to the label
   Don’t wing it. Whether it’s spray-and-rinse or no-rinse, follow timing and safety guidelines exactly.

4. Let the cleaner sit
   Most products need a dwell time of 10–15 minutes. Walk away, grab a drink, and let the formula do its work.

5. Rinse thoroughly (if needed)
   If the product calls for it, rinse every nook and cranny. Leftover cleaner can block primer from sticking.

6. Let everything dry completely
   Moisture left behind is the enemy of good paint adhesion. Give it 24–48 hours, depending on weather.

7. Inspect again
   If stains persist, repeat or switch to a stronger cleaner before moving on to primer.

Common Cleaning Mistakes That Ruin Paint Projects

Let’s be honest—most paint failures don’t come from bad paint. They come from bad prep.

A few common blunders:

• Rushing the drying time

• Using a household cleaner not designed for mold

• Forgetting to rinse off bleach

• Ignoring mold on trim, eaves, or behind shutters

• Painting the same day as cleaning

These mistakes might seem small, but they add up to peeling, bubbling, and costly redos down the line.

When to Call in the Pros

If your home is more than one story, has years of mold buildup, or just feels overwhelming—don’t wing it. Call a professional painter or remediation team.

Here’s what the pros bring:

Hiring a pro may cost more upfront, but it saves you from redoing the entire project a year from now.

The Right Start Leads to a Beautiful Finish

Prepping your exterior for painting isn’t just about looks—it’s about longevity, health, and value.

Cleaning away mold the right way ensures your paint job lasts longer, looks better, and doesn’t hide any surprises underneath.

A quick recap:

• RMR-86 is your fast-acting stain remover

• Wet & Forget is perfect for low-effort maintenance

• Concrobium helps prevent mold from coming back

• Krud Kutter offers affordable, reliable results

• Spray & Forget gives long-term protection with minimal effort

Whether you go DIY or hire a professional, taking the time to clean your surfaces properly is the single best investment you can make in a successful exterior paint job.

Ready to paint with confidence? Start with a clean slate with us. Literally.