I just finished powerwashing the concrete patio in my backyard and
after it dried I noticed some swirl marks which I guess were from where
I pointed the nozzle. I was careful not to use it too close and I used
a fairly wide spray. But there was no damage to the concrete,
everything looks and feels flat with my hand. Do these marks eventually
dissipate? Are these marks characteristic of using a powerwasher?

your swirl marks just indicated areas that are cleaner than the rest

Mikepier wrote:
I just finished powerwashing the concrete patio in my backyard and
after it dried I noticed some swirl marks which I guess were from
where I pointed the nozzle. I was careful not to use it too close and
I used a fairly wide spray. But there was no damage to the concrete,
everything looks and feels flat with my hand. Do these marks
eventually dissipate? Are these marks characteristic of using a
powerwasher?

They will even out in time. They are just spots that did not get as
clean as others. You can go back over it, a little slower this time, and
reduce or eliminate it. I find it tends to become a lot less noticeable in
a day or two.

--
Joseph Meehan

Dia duit

If you clean large flat surfaces often, then you should consider
purchasing a powerwasher attachment designed for such
applications. Otherwise, you need more practice in using the
typical wand that comes with a powerwasher. Swirl marks
indicate that you aren't making good lateral passes.

When using the wand, I powerwash the same way that I would
use a power painter to paint a large flat surface. The wand is
ALWAYS perpendicular to the surface and the wand moves at a
uniform rate across the work. Modest overlay is maintained on
each pass. The wand is ALWAYS at exactly the same distance
from the work. Etc.

That is a slow process and difficult for some to master. So two
other options are possible. First is a larger power washer which
enables a larger area to be cleaned on each pass. Better yet is a
"hover-craft" style surface cleaning attachment which provides an
extremely uniform surface cleaning. Karcher makes one for $50
called the "T-Racer Wide Area Surface Cleaner", and 2.640-508.0
is the part number.

Check out this site:
http://karcher-usa.com/accessories.php

I bought the Karcher accessory and I'm extremely happy with it.
It is faster than the wand and does a better job. It has 2 rapidly
rotating jets which are just inches above the surface (their height is
adjustable). Just be certain that the attachment will work on your
particular brand of powerwasher. I don't own a Karcher, but I phoned
them and determined that this attachment would work with my
powerwasher.

This unit has two different sets of jets, based upon the power range
of your power washer. Also, the very easy to use jet height adjustment
makes it possible to power wash concrete as well as washing wood
flooring without damaging it. My teenage son learned to use this
attachment properly in just minutes and has made quite a bit of money
cleaning concrete, decks, siding and other flat surfaces for neighbors.

Good luck,
Gideon