Various woods require various techniques. Each situation even requires various techniques. Every individual wood material will react differently to certain chemicals. Your Exterior Cleaning Contractor needs to know the majority if not all of these situations and substrates. When cleaning wood, you don’t want to bleach out the grains and give them a pale wood look, you want all it’s rich tones to come forward. The goal is to clean the organic matter and remove all the wood’s old grey dead fibers and expose the new ones. Bleaching the wood will also hinder the staining process. If you are wanting to maintenance clean the wood, use light chemicals and only let dwell for 10 minutes max. If you are wanting to strip the wood to refinish, then you will heat the mix up a little and let dwell for 30-45minutes to remove paint, stain & connect oils. I do not promote products but after trial on all the Big Box stores wood cleaning products, the best I’ve found was 30 second Outdoor Cleaner. This is my opinion only!