The pitfalls of pressure washing wood

Pressure washing wood surfaces is a topic that causes

alot of consternation amongst painters and DIY'ers.

When force propelling water at high speed (2200 psi)

into wood, you inject the wood capillary layer with

way too much moisture which ups the moisture

content way past 14%. Wet wood does not hold

coating properly over the long-term and usually

leads to premature coating failure. What to do then ?

The best surface preparation is to always leave water

out of the equation and powersand/abrade wood surfaces

with a high speed sander (belt or try the new B&D tongue

sanders). Set up your sander with 60 grit and you will

see how fast coatings and the dead fiber layer on decks

and window trim are sanded off. Now you have a perfectly

dry and profiled surface which will accept primer

perfectly.

If the surface is very wet, allow a full 2-3 day dry out period

after sanding before priming and you will get a 10 year paint

job on trim and about 5 years on deck finishes.

Overuse of pressure washers and TSP are a leading cause

of paint adhesion and early coating failure. TSP is basically

salt and salt and paint do not get along, force this into wood

at high speed and now you have guaranteed paint failure

waiting to happen.

TSP is overmarketed and oversold and people who use it

often allow it to dry into the surface under the hot sun - ICI Paints

has a number of large claims documented where TSP overuse was

the root cause of the coating failure. If you decide to use it, you must

always flush hot water rinse the surface completely and it is really

only practical to use it inside on surfaces that are not absorbent.

One of the best surface preps can be home made - add 2tbsp of

Tide non-softener powder detergent to hot water and throw in a

capful or two of bleach. Cost ? Negligible. Results - perfect for

removing atmospheric pollutants, bird doo, leaf litter etc.

Don't fall for the TSP hype ;)