The
Dangers of Pressure Washing Stone and Masonry Surfaces
Frederick M. Hueston
Stone Forensics
Pressure washing is a fast and easy way to clean concrete,
sidewalks, driveways, and other surfaces, but when it comes to stone and
masonry, pressure washing can cause damage. Anyone can purchase a pressure
washer and claim to be qualified to clean exterior stone and masonry. One
should always opt to have a professional stone restoration contractor to
achieve safe, lasting results.
Oversaturation Can Cause Efflorescence
Pressure washing can remove the natural protective patina of
stone and masonry surfaces. It will also remove any coating or sealers. This
opens up the pores in the surface, allowing water to seep deep into the stone
or masonry. The higher the pressure, the more water the stone or masonry will
consume, and the more saturated it will become. Oversaturated stone or masonry can
cause a condition known as Efflorescence, a white powdery residue that
accumulates on the surface. This powder consists of salts originating from the
stone and the setting material. The salts are dissolved from the water and
deposited on the surface. In many cases the salts will deposit into the pores
without making their way all the way to the surface, causing pitting, flaking
and delamination.
Figure 1
Efflorescence
Scaring/Gouging
In order to get difficult soiling removed, many contractors
will intentionally not place tips on their pressure washers. This can cause
severe scaring of the surface. It is easy to recognize scaring by deep patterns
carved into the surface of the stone or masonry.
Figure 2 Scaring by
zero tip Pressure Washer
Chemicals
In addition to pressure washing, unqualified contractors
often use inappropriate chemicals in an attempt to help remove the soiling.
These chemicals are applied before and during the pressure washing process. The
chemicals can be driven deep into the stone with the high water pressure, causing
etching and other damage. Common chemicals are acids, bleach, and high alkaline
cleaners, which if not applied and neutralized properly, can cause irreversible
damage.
Figure 3 Damage
caused by chemical application
Missing Grout and Point
Grout on interior surfaces and point on exterior surfaces
can be removed by pressure washing. As grout and point become soft, weak, and
crack with age. Using a pressure washer accelerates this process through
oversaturation.
Figure 4 Missing
Grout
The Proper Use of Pressure Washing
Not all pressure washing in damaging, but whoever performs
it needs to be aware of the following:
1.
The surface to be cleaned should be inspected
and evaluated to determine the softness of the material.
2.
Grout and point should be examined carefully
before washing.
3.
Never use a pressure washer over 1000 PSI.
4.
Never use a zero-point tip. Only fan tips should
be used.
5.
Do not use bleach, acids, or high-alkaline chemicals
on stone or masonry surfaces.
6.
The pressure washing tip should be at least 12
inches from the surface of the material being cleaned.
In order to avoid damage to your stone or masonry
always consult with a professional stone and masonry restoration contractor.
