Oil stains on concrete need a degreaser. Algae and mildew on a house often require a specialized cleaning solution. And when an exterior looks faded from years of sun exposure, cleaning can sometimes restore its appearance—but true UV fading is a different problem altogether.Understanding the right chemical for the job is one of the biggest differences between simply washing a surface and professionally cleaning it.
 

 

1. Concrete Oil Stains: Use a Concrete Degreaser

 

Oil stains are some of the most difficult stains to remove from concrete because concrete is porous. Motor oil and grease can soak down into the tiny pores instead of remaining on the surface.

That's why pressure washing alone may not completely remove an older oil stain.

A concrete-safe degreaser is typically used first. Degreasers are formulated to break down and loosen petroleum-based oils so they can be removed more effectively during the rinsing process.

A professional cleaning process may look something like this:

1. Apply the degreaser directly to the affected area.

2. Allow it to dwell long enough to break down the oil.

3. Agitate the stain with a stiff-bristle brush when necessary.

4. Pressure wash or hot-water rinse the area to flush away the loosened oil and residue.

Hot water can be particularly useful on stubborn grease and oil because heat helps improve the cleaning process.




 

Can every oil stain be completely removed?

Not always.

Fresh oil spills are generally easier to treat than stains that have been sitting in concrete for months or years. Deeply penetrated stains may only lighten rather than disappear completely.

That's why treating an oil spill as soon as possible is important.

 

2. House Stains: Algae, Mold & Mildew

The dark green, black, or gray staining you see on house siding isn't always ordinary dirt.

Many exterior stains are caused by algae, mildew, mold, pollen, and other organic buildup.

For these types of stains, professional exterior cleaners commonly use sodium hypochlorite-based cleaning solutions, often referred to as SH in the pressure washing industry.

Unlike simply blasting the siding with high pressure, the chemical does much of the work by breaking down organic growth.

This is especially important on siding because excessive pressure can potentially damage the surface or force water where it doesn't belong.

A soft-washing approach uses cleaning chemistry and lower pressure to remove organic buildup while reducing the need for aggressive mechanical force.

Why chemical cleaning matters

Imagine trying to remove years of algae from a house with nothing but water.

You could increase the pressure, but that doesn't necessarily address the root of the organic growth.

The right cleaning solution can break down the buildup first. Then the pressure washer becomes the rinsing tool rather than doing all of the cleaning by brute force.

3. What About Black Streaks on Roofs?

Those black streaks commonly seen on asphalt shingles are another example where chemistry matters.

Roof cleaning generally calls for a low-pressure soft-washing approach, rather than blasting the shingles with high pressure.

A properly selected cleaning solution can break down algae and organic staining while minimizing the need for aggressive pressure.

The important takeaway is that more PSI doesn't always mean better cleaning.

The right chemical, application method, dwell time, and rinse can be much more important than simply increasing pressure.

 

4. What Chemicals Help With Sun-Faded Exteriors?

Sun fading is a little different from a normal stain.

Years of UV exposure can break down pigments in paint and siding materials. Exterior surfaces can also develop oxidation, which may appear as a chalky or dull layer on the surface.

This is where it's important to understand the difference between dirt and actual color loss.

If the surface only looks faded because of dirt, algae, oxidation, or chalky buildup, cleaning may make a dramatic difference.

But if the actual pigment has been permanently degraded by years of UV exposure, no cleaning chemical can simply put the original color back.

Depending on the material and condition of the exterior, restoration may require specialized oxidation removal, a coating, or repainting rather than traditional pressure washing.

 

5. Why You Shouldn't Use the Same Chemical for Everything

One of the biggest mistakes homeowners can make is assuming that one cleaning chemical works on every surface.

Oil isn't algae.

Algae isn't rust.

Rust isn't oxidation.

And UV fading isn't dirt.

Each problem requires a different approach.

Using the wrong chemical—or using the correct chemical at the wrong concentration—can potentially damage siding, concrete, landscaping, paint, or other surfaces.

That's why professional exterior cleaning involves more than just equipment. It requires understanding surface type, stain type, chemical selection, dilution, dwell time, pressure, and rinsing technique.


 

The Pressure Washer Is Only Part of the Process

A pressure washer is powerful, but professional cleaning isn't simply about PSI.

The best results often come from combining the right chemistry with the right amount of mechanical cleaning.

For concrete oil stains, that might mean degreaser + agitation + pressure washing.

For algae-covered siding, it may mean appropriate soft-washing chemistry + low-pressure rinsing.

For a faded exterior, it may mean determining whether you're actually dealing with dirt and oxidation or permanent UV-related color loss.

The goal isn't to use the strongest chemical or the highest pressure.

The goal is to use the right cleaning method for the surface and the problem.
 

Final Thoughts

If your driveway has stubborn oil stains, your house has green algae or mildew, or your exterior looks dull and faded, don't assume everything can be fixed with more pressure.

The chemical treatment is often just as important as the equipment.

A professional exterior cleaning service can identify what is actually causing the discoloration and choose an appropriate cleaning method to restore the appearance of the surface as safely as possible.

The right chemical + the right technique + the right pressure = a much better clean.