Measure your shower surround wall; you should have 3 sides or wall panels. Take the width and height measurement of each wall.
Purchase materials from your home improvement store or order marble shower surround in kits online. Either way, you should make sure to give them your correct measurement with some allowance. You may have to wait several days for special orders to fit your measurement.
Some custom cultured marble panels can be ordered up to 84" x 120".
After you have ordered your materials, you can start the demolition of your old shower surround. If you are using the bathroom, don't start the demo until your materials have arrived and you are ready to get started. Use safety goggles and work gloves when you do your demolition job for protection.
Install your cement board or dry wall board. Make sure that they are plumb, square and flat. Paint the dry wall with white flat paint to ensure that the color would not show through the marble.
Drill holes for the plumbing fixtures. If you are planning on using a cultured marble surround that has recessed accessory pieces such as shampoo or soap holder, ensure that you cut out holes on the dry wall or cement board.
Drill the matching holes for the plumbing fixtures on the marble surround piece that would be used for the wall facing you as you take a shower. You can use a saber saw to adjust the sizes of each panel. Each wall piece must be "dry fitted" and clean before installation.
Use 100 percent clear silicone caulk adhesive to attach your cultured marble onto the dry wall. You may need an extra pair of hands to help hold the panels firm against the wall until the adhesive starts to dry and the panels are held securely.
Once the 3 panels are secured on the wall, you can add the corner edges to hide the seams which gives your installation a clean finish. Apply beads of silicone caulk and spread with your forefinger for a smooth finish.
Install your shower fixtures and apply silicone caulk to prevent water seepage.
Wait 24 hours to allow adhesive to cure before using.