When you do not want to limit your choices among waterproof-only wallpaper styles when redecorating your bathroom, you have other options. You can waterproof any type of wallpaper with decorator's varnish. This product does not contain alkyd resins that can yellow, nor does it contain polyurethane. It contains an acrylic product instead, which is more brittle than polyurethane, but not as plastic-looking. This type of varnish comes in three finishes: gloss, satin and dead flat. If your wallpaper has a sheen, and you want to eliminate it, you can do that with a combination of satin and dead-flat varnish.
Wipe the wall with a clean rag. Make certain to remove any dirt or grease that can mar a varnish finish.
Transfer an amount of decorator's varnish sufficient to cover the wall into a bucket or into a garden sprayer. You can brush or spray the varnish, but rolling it on with a paint roller will not achieve the needed results. If brushing, use a high-quality synthetic-bristle brush, because the product is water-based.
Start brushing at the top of the wall. After covering an area about 6 inches wide by brushing parallel to the ceiling, employ long, vertical brushstrokes. Start each stroke at a point lower than the existing finish line and stroke upwards, finishing the stroke on the existing finish. This helps eliminate drips.
Mask the ceiling with masking paper and tape and cover the floor with plastic if you spray. Pump the sprayer frequently to keep the pressure high and spray with vertical or horizontal strokes. Keep the tip at least 6 inches from the wall to prevent drips.
Wait for the varnish to dry, which takes from 2 to 4 hours, then recoat. Repeat once more, if desired.
Use satin varnish for the first two coats if you want to turn a glossy wall into one with a matte finish. Spread dead-flat varnish for the final coat.