A concrete floor is a very economical and useful way to finish a shower room or bathroom. Drains can be built in so that thorough cleaning is easy. Since it is a solid surface, there is no worry about water getting under tiles or leaking. However, concrete is porous and will absorb water if it is not treated properly and will stain over time. Painting concrete floors results in a sealed surface as well as an aesthetically pleasing floor. Knowing how to prepare the floor so that the paint adheres properly is a process that many people pass over resulting in peeling paint after a few weeks or months.
Check to make sure your floor is dry. If you have already been using the shower and are redoing the floor, it would be wise to shut off the water to the shower, close off the room and install a dehumidifier for a few days. Hopefully, your concrete is not waterlogged from the ground up. A simple check can be done after running the dehumidifier by taping down a square 3-by-3 sheet of plastic. Wait twenty-four hours to see if there is any condensation under it. If it is dry, continue with your project. If it is damp, you will have to find another floor covering method besides painting.
Clean the floor surface of any loose debris by sweeping. If you have old paint on the surface, give it a good scrubbing with a wire brush to remove as much of it as possible. Since concrete is water-based, to get a good bond between the paint and the concrete, it will need to be porous. Old paint or sealers will fill in all the little air pockets and large areas may need to be cleaned out with a solution of muriatic acid. Vacuum to remove any fine dust.
Etch the concrete surface with muriatic acid by getting the floor damp, applying a 1:3 (acid to water ratio) solution of the acid evenly to the whole area and allow it to bubble up for a few minutes. it is recommended that you only work in an area large enough to handle without areas drying out. Note: never use muriatic acid without proper ventilation, eye protection, gloves, rubber-soled boots and a respirator if necessary. Neutralise the acid by hosing it down with water or by applying a solution of baking soda and water: 1 pound per gallon of water, one gallon of water per twenty-five square feet of floor surface. The floor should dry thoroughly for at least 24 hours and should feel like medium grit sandpaper.
Apply a heavy duty epoxy garage paint. There are different kinds on the market, but you can ask at your local home improvement store for their advise. Do not apply any oil base paint as it will not adhere. Some brands to look for are Epoxy Shield, Armor Clad, Color Chips, or Rustoleum Concrete Saver. Most of these are epoxy paints that will be a two part activation product. Roll on as recommended by the manufacturer.
Cure the surface by allowing it to dry thoroughly before using. Use fans and dehumidifiers and do not walk on the surface for at least 24 hours. Some manufacturers recommend waiting a week before heavy usage. Your shower floor should be beautiful with its new finish and resistant to water and soaps.
Add some fine sand to your paint to reduce the chance of slipping in the shower.
Never use muriatic acid without proper ventilation, eye protection, gloves, rubber-soled boots and a respirator if necessary.