It will be on one of the next videos in more detail, but i'll write the steps anyway
in case of the red walls:
-dark oak stain, let it dry to the touch
-sand with 60 grit until there's only some oak left
-a couple generous coats of isopropilic alchool+indian ink solution (mine is 40 drops to 200ml of alchool), let it dry after the 2 coats
-depending on the look after dry, i might do a 3rd aplication of the alchool with indian ink if i want it the gray to be darker
-matt varnish coat, let it dry
-apply chipping effects layer, let it dry, i use valejo, you can do this with hairspray too, or an other brand of chipping effects i guess
-paint with red, thin layer of paint is better for this, so i use airbrush, it's not mandatory, but makes next step easyer and more controlable
allow paint to dry, now this is important step, the more the paint dries the harder it will be to chip, but if it's not dry enough it will peel too easy, i dry it for 3-4 minutes under the AC, it might take a couple of times to dial in what is our prefered point. Because of this i never work on many pieces at once, or very big areas
-with a brush put water on top of the paint, wait a bit (the more water and the longer it sits there the easyer the chipping is), then with a brush, i prefer harder brushes for this, start poking and scraping the paint and some of it will come out, stop when you like the look of it.
The process will be detailed on one of the next videos, but the videos are always a little bit behind the building process and the build log
You can also chek youtube and do searchs for:
valejo chipping medium
mig chipping effects
chipping with hairspray
All of those will give you a good idea of how this chipping works on plastic models, the difference on wood is that you nead a coat of varnish to prevent the medium and the paint from beeing absorbed by the wood
A similar effect can be obtained with the salting technique, but for me that technique is better for larger areas, not for smaller pieces
forgot to mention, the chipping effects is sticky and shiny even after dry, both go away, don't get scared by it