By no means should this be considered the standard, we are not experts on wood but this works. Please leave suggestions in the comments if you have alternative methods and help out the community.
I prefer to start washing the deck with a downstream application. Our injector pulls at a high ratio, so we can apply 1.5%-2% application when down streaming straight SH. We try not to have any surfactant in our mix. Surfactant essentially has 1 job, help chem stick. We do not want chem to stick to the wood, it becomes nearly impossible to rinse all the surfactant off the deck.
Multiple applications and dwell times may be necessary however, you should see an improvement with each application. If you do not see any improvement, then unfortunately down streaming is not going to be strong enough.
This is when you would proceed to apply chem directly with a pump-up sprayer or a dedicated pump such as a 12v. You should never have to go stronger than a 2%-2.5% strength application for wood. Anything higher, you risk causing sever furring of the wood which may irritate certain clients.
Heavily infested wood may need a fan motion cleaning with a 45-degree tip. Keep spray pattern on 1 or 2 boards at a time and move wand in a constant sweep motion. The goal is to not stop when spraying with high pressure on the wood – you risk leaving lines.
We always use a pump-up sprayer on railings. They need to be sprayed from the outside of deck. Spray in every nook and cranny. Left, right, up, down, upside down, right side up, side to side, get the picture…? It is extremely easy to miss spots when applying chem to the railings. Once you do the outside, you will need to do the inside the same exact way. Inspect railings from different angles to make sure you got it all. I typically have one of the guys on the crew dedicated to hitting railings with the pump up for the duration of the job.
Once deck is washed, clean, and green free, go ahead and give it another rinse down. You can never rinse too much, that is really my golden rule for any power washing services we offer. I always tell my guys rinse, rinse, rinse especially when it comes to windows and wood. We typically consider the job complete at this point however, there is a next step that should be taken.
Apply oxalic acid, let dwell, and rinse. This brightens the deck up and brings the PH levels back to the proper levels in the wood. Our clients seem to not care so much about that and would rather just have a cheap deck wash. But every market is different. Keep in mind this is how JOHN LANGE cleans decks in his business. This is not necessarily the correct way – this is just what works for us.
Warning (Wood cleaning is a tricky task to get down especially if you are trying to learn it all on your own. It will tend to “fur” the wood. Some guys do not use SH at all, and only use wood stripper. We have not attempted that method yet.)