I suggest that you abandon the idea of applying the cleaning solution
with the sprayer. The cleaning solution needs to reside for a period of
time on the deck surface before you pressure wash. I prefer to apply
the cleaning solution with a hand sprayer (one that will tolerate the
chemicals you're using) and then pressure washing.

3200 psi is quite a bit of pressure if the nozzle is anywhere near the
deck. If you aren't very careful you will remove pith from the wood and
be left with a corrugated surface. I turn mine down to 800 or at most
1000 psi when working on most wood.

Oxalates are good and appropriate if you have iron (rust) staining
because oxalic acid reacts with iron to create water soluble iron salts.
I find that most of my deck stains are mold and just plain dirt.
For this Clorox (5 or 6% calcium hypochlorite) is enough when diluted at
a ratio between 4:1 to 6:1. Commercial deck cleaning products are
usually around 10:1 but I find the higher concentration to be more
effective.
The dirt can be addressed quite effectively by using trisodium
phosphate, not the fake TSP sold so often now. The down side of real
TSP is that it is like topical steroids applied to fungus...watch them
grow! Phosphorous will cause algae to bloom, especially in bodies of
water so you need to be very careful. When I use TSP on my deck I first
saturate the soil under it with an aqueous solution of lanthanum
carbonate. That way most, if not all of the phosphorus is bound up and
not available to damage the water in the harbor.

If you really want to hit the mold the addition of a substited phenol,
such as is found in Zinsser's Jomax works well to prevent reassurances.

B

Michael Bushey wrote:
I recently bought a North Star Washer, 3200 psi with a 9 Hp Honda Engine and
a Cat Pump. The manual that came with it is very incomplete in explaining the
use of the machine. I have used it for some small jobs it seems very well
made. I have some questions though. I want to wash my deck with a deck
cleaning solution, mine is an oxalate solution. The bottle has several
dilutions it recommends but says to refer to your users manual. The manual
only says what nozzle to use and to put the siphon hose in the solution. I
take that to mean undiluted solution but am not sure. The injector appears to
be after the qwater passes through the pump so I am not to worried about
damaging the pump itself.

There is also on the top of the pump a "pressure adjustment knob". The manual
makes no mention of how this is used. Do any of you North Star owners have
advice.

I asked if there was a better manual somwhere and the customer service rep
while very nice said wysiwyg.