Paint difficulties can be resolved by scraping and priming with a shellac or oil based primed. I prefer the polyurethane based construction adhesives for strength and toughness. Their down side is cure time (overnight)
Another scheme would be to cut back the plaster to 75% of the baseboard height with a diamond blade in an angle grinder (yes, very messy: floor to ceiling tarping, shop vac.. ) Then place 1x or thicker wood and blue screw (one brand of masonry screws are blue and need only a pilot hole (also comes in counter sinkable flat heads))(Tapcon brand, GRK and Spax are also good) it to masonry. Overfill with setting joint compound to flush surface. Nail baseboard normally.
Not afflliated with either company. Have used both.
Your question is concerning two things:
1. Proper fitting (wood planks to masonry wall).
2. Proper wood treatment (anti-moisture).
So that's how will my answer look like. Let's look at this.
1. Proper fitting.
I would advise preparing additional support planks going vertically with - say - 1 meter space (that spacing requires additional insight on how much planks will weight, what wall you got and what kind of bolts you will use; use your aptitude and experience or ask a prO). These support planks will be bolted to the wall on all wood-wall height and have only supportive purpose (don't need any beautiful finishing or something). The spacing also determines if (or HOW MUCH) your wood-wall would deform over time. Shorter spaces mean less visible deformations (in short).
Your proper planks - THE planks you want to see as a decorative - will be attached to these supports I mentioned before. That will make support planks perpendicular to these decoratives. Also, I would leave some few centimeters (or, preferably, more) space from the floor to avoid water to be in contact with planks (due to water from shower or cleaning tools) and to let air circulate between masonry wall and wood-wall. Similiar space would be needed up near ceiling.
2. Proper wood treatment.
This will require appropriate info on what you got in stores - all of these chemicals that render your wood water- and moisture-proof (at least for some years...). On that I advise to talk to some shot helper that seem to have proper knowlege.
EDIT concerning question edit :)
The space between masonry and wood is to be kept, I'm afraid. Here are some reasons:
- it allows air (and often steam) to travel op the wall; moisture has an occasion to evaporate
- using supportive planks lets you not to drill that many holes in a wall (cuz you will connect decorative planks to supportive planks with screws)
- it allows planks to deform, avoiding some of tensions that would lead to look bad/destroy it
I'm aware that it may not look as intended with this visible difference between wood and tiles, but you may try either to neutralize that view or use it to your benefit (better visual effect). You can achieve that whatever you like (covering first line of tiles with last line of wood; plaing decorative hangers and so on...).
Of course, You can glue/attach wood to the wall with some glu-ish adhesive, but I guess that wood will 'work' and deform over time. If, later on, You would decide that any refinishing is to be done, it would be easier to unatttach the screws than tearing down (un-glue) all of them.
I would also wait for other DIY-ers to give their opinions as well. Mine is one of many, and I know it :)
Best Answer
I visited my local paint shop and got a handful of paint cards to match against the current paint. I selected the paint and had it mixed up to good quality. It is a dark grey which is common in my area. I brushed off any loose sand from the stone before painting. Areas that were falling off in lumps I put PVA glue mixed with a small amount of water on it.
You can then paint over that area if need to. I will have to keep on top of painting the lower part of the wall. It will protect against rain and wind.
The problem was the stone was going soft and flaking off. I wanted to know how to protect the stone from the weather. This seems to work. It is worth paying for the paint because it is very expensive to have to outer wall rebuilt. The wall was down the side of the house with a walkway so you do not see it. It was the bottom that got the worst of it.