Natural or artificial waterfalls can make any backyard garden or pool soothing and inviting. These decorative features aren't just limited to homeowners who love natural, rustic decor. You can paint waterfall rocks for a colorized, contemporary take on the traditional waterfall. Special types of paint also limit algae growth on rocks for a cleaner, low-maintenance waterfall surface.
Shut off your waterfall if possible. Artificial waterfall rocks are the easiest to paint, because you can control the flow of water. For a natural waterfall, divert the water flow with plastic tubing or tarps. If the waterfall is too large to divert, then you'll need to remove the rocks from the waterfall. Remove one rock at a time and replace the painted rock before moving on to the next one.
Put on rubber gloves.
Clean the rocks with a muriatic etching solution and a rag. This solution removes excess grime, and the muriatic acid also conditions the stone surface for painting.
Prime the rocks with masonry primer using an airless spray gun. Hold the spray nozzle about one foot from the surface and keep the nozzle moving. If you don't have a spray gun, you may use a paintbrush, but sprayers provide the best coverage on bumpy rock surfaces. Wait for the primer to dry.
Paint the rocks using general purpose exterior latex paint or elastomeric exterior latex paint. Algae needs a porous surface to cling to as it grows, so a slick rock attracts less algae build up. Elastomeric paint fills in divots for a smoother finish and less algae growth. If you want to retain a natural, rough surface, general purpose exterior paints work well. An airless sprayer is your best choice for both options, but you can use a paintbrush if you do not own an airless sprayer.
Turn back on the water or return the painted rocks to the natural landscape after 24 hours.