Washing before painting

From prep to final coat. Discuss it here

Moderator: Pacificpainters

Post Reply
PDT Armour Coatings
Posts: 5
Joined: Sat Nov 23, 2013 8:13 pm

Washing before painting

Post by PDT Armour Coatings » Wed Feb 26, 2014 12:23 pm

I know that we all know, that for a good paint job, we need good prep (also, a good surface really doesn't go a stray too). However I am wondering about other businesses preperation methods.

At PDT Armour Coatings we have a number of large 15Hp Pressure washers, and I am looking at buying either a 30Hp or larger unit soon. Pressure is not an issue for us. However I am amazed at the number or painters who look at me dumbly when I ask how they wash down exterior before they paint, with the look on their face, 'why would you wash the house?'

Contrary to what a lot of people think it is not pressure that cleans, order of importance generally is:
  1. Flow Rate
  2. Chemicals used
  3. Pressure and Temperature
A big machine allows you to get great flow and high pressure.
Our exterior house wash entails 2 x 15Hp, 4000PSI 18LPM pumps sucking water out of a 200L Buffertank through 1-1/8" suction hose. Buffer tank fed from house by 30m 3/4" hose with 18mm hose connections (like standard, but twice the size) that goes through a high-flow float valve.
Our pressure washers also have a remote on/off, and start function to prevent them from being damaged by heat build up by being left in by-pass for too long.
This comes out of 60m 3/8" Wire braid hose, each, then to the lances and out 040 fan tips or 045 turbo heads.
This is all trailer mounted for ease of set up, which is:
Connect to mains water
Run out pressure hose
Start machine

We clean roofs and houses before all painting works, and also do contract cleaning for other painters who cannot or will not clean it themselves.

The best way I have found to clean a house for paint prep is:
1) Pre wet house and garden areas with water before starting, it is best to get the client to give the lawn and surrounding gardens a good soaking the day before you come to clean the house.
2) Using black nozzle, or soaper nozzle, downstream at low pressure your cleaning chemical onto the areas to be cleaned. (cleaning chem mix given later)
3) For walls, or other surfaces that may be damaged by high pressure, get a long painters extension pole, Something like 8-16' long and put a soft bristled broom head on it. If you buy the right one, it is the same thread
4) Broom all surfaces while still wet, and watch the black, brown and green stuff fall off the house.
5) Using a fan tip, rinse surfaces clean with ample water.

If you are washing a hard surface like a roof or concrete, don't worry about the broom, just hit it with full pressure to remove all laitance and debris. Cleaner is better when you have to warranty your coating for 10 Years.

The cleaning chemical mix is
12.5% Sodium Hypochlorite (Pool Chlorine) 3L
100-200mL Koala Care car wash soap, or Bunnings Dishwashing liquid from the 5L bottle
Half a cup Trisodium Phosphate
Maybe a litre of water depending on your pressure washers downstreamer rate, and hose length.

Don't waste money buying expensive 30seconds. Read the label, active ingredient, Sodium Hypochlorite, depending on the container size, strength can be from 2.5%-5% (25-50 /L)
Pool chlorine is $0.80/L and 3 times as concentrated. 30 Seconds is up to $10/L

I know we may go overboard with cleaning prep, however we have got to a pretty fine art with our machines and set up, and Myself or another operator with an apprentice can get a roof and exterior done in as little as 3Hrs, from the time we turn up to driving away

n.b. Sodium Hpypchlorite will 'burn' or even kill plant life and grass if you are not careful, that is why the first step is to pre-wet everything and final step, is wash throughly.
Use biodegradable soap,
Sodium Hypochlorite evaporates cleanly, without residue or stain
Trisodium Phosphate can also be used as a fertiliser, however it can burn foliage if not washed off/ watered in.
Caution, mixing SH, TSP, and soap together it EXTREMELY alkaline, don't be an idiot with it. It does burn if you leave it on you.
Make sure your soap is safe to mix with SH and TSP
NEVER, EVER mix SH and Ammonia. EVER. it can make a substance, hydrazine, the nasty stuff that explodes to power space shuttles.

I in no way, expressed or implied take any responsibility for people mixing chemicals without adequate training or supervision.

Any way, now that is done, How do you guys prep for exterior repaints?
Also, if you want exterior house wash done for a repaint, and don't want to do it yourself, give us a call, or contact through our website, http://www.pdt-coatings.com.au

James Thompson
PDT Armour Coatings

Posts: 55
Joined: Mon Feb 13, 2012 9:57 am
Location: Fiji

Re: Washing before painting

Post by Pacificpainters » Thu Feb 27, 2014 6:29 am

Great information, thanks James.

Post Reply