You will certainly find it very annoying if your self-made patch fades after one year and moss or algae have spread in the joints. You could have slightly avoided this worsening of the condition if you had sealed your plaster right at the beginning. However, almost everyone neglects this investment, the impregnating agent is expensive.
If you now start this cleaning, you can cause damage if you do it the wrong way. Not every remedy is suitable for every patch and some false information circulates on the internet. So how do you proceed?
Variant 1: Scrape out with the screwdriver
This method is very laborious and strains your back. They scrape all joints with a screwdriver and scrub stone by stone with water.
Risk of mechanical damage to the joints and algae coverages. Do not completely remove them. This form of cleaning is therefore unsuitable.
Variant 2: the high-pressure cleaner
For composite paving without joints, the high-pressure cleaner (92.17 € at Amazon) can be very efficient. However, if you have a pavement with open joints filled with gravel or chippings, rinse out the top layer of this material. The joints are therefore deeper and provide dirt and weed only a very safe breeding ground. So only with cobblestones without joints use.
Variant 3: Chemical agents
For each plaster material, ie for concrete, natural stone or clinker paving, there are individually designed cleaning preparations (18.92 € on Amazon). If used properly, you will kill algae and moss, clean the stone surfaces, and then simply brush off the dead plant parts thoroughly.
Variation 4: potassium permanganate and soda
These two options are often touted as home remedies. However, potassium permanganate is highly toxic. It worsens the condition of the joints and contaminates the groundwater. So steer clear of this remedy.
Soda unfolds with a correspondingly long exposure time of at least 6 hours a very good effect. Following this, however, the paved area must be sealed, which is also necessary for professional agents.
An additional note: Never clean the joints of the natural stone plaster with acidic household cleaners. The acid destroys the joint material and a renovation is required.