Just for clarification, this thread is around 4 years old… I only bring that up so that you know the age of the advice at the beginning of the thread. That doesn’t mean it isn’t accurate, though.
No offense to midwestwaterways, but the guys recommending bleach at the top of this page (everett, rpetry) are two of the biggest names in the wood cleaning industry. There IS a bit of debate about using bleach on wood, but i believe that was mostly in the past. These days it’s generally ‘approved’ for use, at least from what i have seen. Shane Brasseaux is a huge wood guy too, and he uses it.
However, like everything, you must use it properly. Used incorrectly, bleach can produce a bad result.
Now, the recommendation to use 50/50 (which would be 6% if using 12.5 bleach)? I’ve never seen a pro recommend that strong of a mix, as rpetry pointed out. Generally 2% is recommended, although rpetry says 3% max.
So if you want a 2% mix and you are using 12.5% strength, you add water to dilute it down to 2%.
When figuring mixes, a lot of people just use 10% in the calculation, because it’s easier to figure, and unless the bleach is brand new, there’s a chance it’s down around 10% anyway, because of how fast it degrades. Using 10% in the calculation, you add .2 gallons of SH to .8 gallons of water for a 2% mix. So 5 gallons of 2% would be 1 gallon of SH to 4 gallons of water.
If you want to use 12.5% in the calculation, you would use a little less bleach.
F8 and F18 is another great combo to use. This is generally used when stripping a stain, however, it is also pretty effective when you dont have to strip… you just have to be careful with how strong you make it, and how long it dwells, as it will fur the wood if left too long.
Use appropriate nozzle to produce around 6-800 (ish) PSI for cedar, and 1000-1200 PSI (ish) for pine.
Full disclosure: I’m no expert, I learned this information from reading the input of others, like @Racer, and practicing on old wood.
This can get you headed in the right direction, but you need to do a lot more research… there are tons of discussions on the web that will answer your questions. It’s going to take more than an hour on youtube. Join some of the Facebook groups, and search for ‘deck’ or ‘fence’… there are many many conversations about wood there.
Also, find some old pallets to practice on. Nothing beats experience.