Did a retaining wall, concrete, and river rock today and thought I would add something that hasn’t really been mentioned recently about retaining walls. I didn’t want to add it to matchit’s post because that was about efflo.
Before working on the wall, check the block/brick/stone to make sure it is colored throughout or if it is just surface colored. Not all are colored all the way through, especially the older ones that are in desperate need of maintenance. If it isn’t colored throughout, don’t dare touch it with a turbo or heavy pressure as you will remove some of the color on older stones/blocks. Most of the ones that aren’t colored through tend to be more like cinderblock, but that is just my opinion. I love using a turbo on a retaining wall because it is super fast, but I couldn’t do it today. The block was not colored through.
You can check by looking underneath the caps stone at the normally hollow stones underneath. If the inside is grey and the outside is red, you know what you are getting into. If the cap stones are glued down, mortar, held in place with wizardly spells, look for a cracked one or a split one and check the edges, or go the the end of the wall and look at the last one. If it looks like that 99 cent lowes special 9" stone, well, enough said.
Side ramble: If there is river rock/river stone around it, quote to clean that up too. It makes a bigger difference if the now clean wall is surrounded by cleaner river rock. Just be careful of plants. IF it has lichen, set the expectation that it will take more than one treatment and know you are almost going full SH on the rock. If you go almost full/full SH on river rock, be aware that SH smell is going to be strong for awhile and make sure that they keep their pets away from it until it dries. It sounds stupid to say this, but you aren’t soaking the earth, you are spraying the rocks. My .02 and worth everything you paid for it, HW mix will normally do diddly to dirty river rock. Pump up, 12v, racer approved application device (TM pending 
) for application. DS is a waste of time.
I would love to hear other people’s take on retaining walls.
