Why lime
It doesn't sit flat. It clouds.
Lime wash goes on in coats like anything else — a minimum of two to three — but it doesn't build a film the way paint does. Each coat soaks into the one beneath it, and what comes out is cloud-like movement across the whole wall rather than one flat, even tone. Over bare masonry or a lime or cement plaster it needs no primer. Over drywall, which is nearly every room in Victoria, it gets a coat of the lime wash primer first, and that step is where lime wash jobs are won or lost.
The material is made in Vancouver. I use 5 Star Finishes for lime wash, Venetian plaster and liquid metal — microfiltered hydrated lime and powdered marble, blended to order rather than tinted out of a tin. It matters for two reasons. It is a day up the road instead of a container from Italy, so a colour that goes wrong is a week, not a season. And their lime wash can be matched to any Benjamin Moore or Sherwin-Williams colour — so the three finishes above are examples of what it does, not the list you have to choose from. If you have already picked a Benjamin Moore colour for the rest of the house, the lime wash can be that colour.
Water is the thing to be careful with, and the answer is the sealer rather than the room. The lime wash I use is made for interior and exterior surfaces, and it can be finished with a penetrating sealer, with soap, with wax, or left bare so that more coats can go on later. Left bare somewhere that gets splashed it will mark. Sealed, it takes a great deal more. It is still a mineral surface rather than a wipeable one, so I will tell you which walls want a sealer and which are better left open — and hand you the data sheet either way.