The Bunnings Workshop community can help with your home improvement projects.
For sealing a wash, try a sealer similar to our Rust-Oleum 887ml Matt Clear Chalked Protective Topcoat. It was designed for use over our Rust-Oleum Chalked range, but would also be suitable over water-based paint.
For a surface which coffee cups are placed on, I would suggest Cabot's Water Based Matt Cabothane Clear Polyurethane Varnish. It's suitable for furniture and is harder wearing than the chalked topcoat.
I recently kept to a budget and used Timber Protect 1L Satin Oil Based One Coat Clear Varnish on a coffee table I built. This oil-based coating was placed over a water-based paint wash effect and is still holding up perfectly six months later.
For step-by-step instructions, check out How to lime wash timber furniture. - MitchellMc
I watered down some white paint that I had for the house, and used a scraper to spread the paint until I got this look. - LePallet
Trial and error using scrap wood, dilute paint, wipe off with a cloth. The colour comes out even better with wax or sealer. - Vicki65
Workshop is a friendly place to learn, get ideas and find inspiration for your home improvement projects