Black Spot remover for patios

Why Your Patio Still Looks Dirty After Jet Washing

You spent the weekend pressure washing the patio.

At first, it looked better. The green slime disappeared. Surface dirt lifted away. Job done.

Or so you thought.

Then, a few days later, the black spots returned. The paving still looked patchy. Some areas even looked worse once they dried.

Sound familiar?

If so, you are not alone.

At Alfresco Exterior Cleaning, we hear this all the time across Oxfordshire. Many homeowners clean their patios, yet still feel disappointed with the result.

So, why does it happen?

The Start – Jet Washing Only Cleans the Surface

Most domestic pressure washers remove loose dirt. Its similar to a hair cut, looks okay but it still keeps growing!

However, many patio problems sit much deeper than the surface.

For example:

• Black spot fungus
• Algae spores
• Lichen growth
• Deep organic staining

These problems grow into the pores of the paving.

Therefore, while jet washing improves the appearance temporarily, it often fails to deal with the root cause.

As a result, the patio quickly starts looking dirty again and often darker in colour as this is the organics coming back to the surface.

Black Spots Are the Biggest Problem

Black spots are one of the most common complaints. The picture used is from a patio clean we completed. Just one slab has the black spots! no others around it! Just one, how can that be?

They appear mainly on sandstone and concrete paving. At first, they seem small. However, over time, they spread across the slabs.

Many homeowners assume normal jet washing will remove them.

Unfortunately, that rarely happens.

Because black spot is a type of lichen, it bonds tightly into the surface. So, cold-water pressure washing usually only removes the top layer.

That is why patios often still look patchy after cleaning.

Cheap Pressure Washers Have Limits

Most home machines are designed for light cleaning. Running maximum of 1200 psi and 6 LPM

They are useful for garden furniture and basic rinsing. However, patios are different.

Professional systems use:

• Higher water flow – upto 25LPM
• Commercial pumps upto 3600 psi
• Professional surface cleaners
• Hot water systems upto 130oC

Because of this, they clean much deeper and more evenly.

In contrast, domestic machines often leave:

• Zebra stripes
• Patchy cleaning
• Uneven colouring

As a result, the patio may actually look worse once dry.

Hot Water Makes a Huge Difference

This is where professional cleaning changes everything.

At Alfresco Exterior Cleaning, we use hot water pressure washing systems.

Hot water cuts through algae, grime, and organic growth far more effectively than cold water alone.

Therefore:

• Black spots improve more
• Algae lifts easier
• Grease and staining break down faster

Most importantly, the results tend to last longer.

Because the surface is cleaned properly, regrowth slows down.

Pressure Alone Is Not Always the Answer

Many people think more pressure equals better cleaning.

However, too much pressure can damage paving.

This is especially true with:

• Sandstone
• Pointing joints
• Resin surfaces
• Decking

In some cases, aggressive jet washing strips away the surface layer.

As a result, patios become rougher and more porous. Then, dirt and algae return even faster.

So, professional cleaning is about using the right method. Not simply more power. With soft washing its the knowledge of the right mix and dwell time to get the best results.

Why Softwashing Helps Patios Stay Cleaner

After cleaning, many patios benefit from softwashing treatments.

This involves applying specialist solutions to kill remaining spores and organic growth.

Because of this:

• Algae returns slower
• Green staining is reduced
• Patios stay cleaner for longer

Therefore, combining hot water cleaning with softwashing usually delivers the best long-term result.

The End – The Difference Proper Cleaning Makes

Picture your patio properly cleaned for summer.

The slabs look brighter. The black spots have faded. The surface feels safer underfoot.

Then, weeks later, it still looks clean.

That is the difference professional cleaning makes.

At Alfresco Exterior Cleaning, we help homeowners across Oxfordshire restore patios, paving, decking, and outdoor spaces using professional hot water pressure washing and softwashing systems.

We do not just clean the surface. We tackle the cause of the problem.

So, if your patio still looks dirty after jet washing, the issue may not be the patio.

It may simply be the method used to clean it.

Even with 30 years of knowledge and experience, we sometimes have to go back to a client and re treat the black spot due to its stubbornness. We want to give our customers the most phenomenal experience ever. Sometimes we have to go back because we didn’t get it right the first time.