Install cement backerboard inside the shower enclosure. Secure the boards in place by hammering finishing nails through the boards into the wall studs or shower frame studs. This water-resistant material makes it suitable for shower walls.
Measure the wall in the shower. Have the 1-by-4-inch pieces of wood cut to the wall specifications. Lay out the boards on the floor to map out the stones before you attach them to the backerboard.
Prepare the Type-S mortar in the large bucket according to the manufacturer’s instructions. Mix one bag at a time to ensure the mortar does not begin to dry and set before you add it to the wall. You can find this kind of mortar at home improvement stores.
Mix the mortar with the mixing attachment on your electric drill. Test for the right texture by scooping a thin portion up with your trowel and holding it at 90-degree angle. The mortar should remain on the trowel.
Don your work gloves. Scoop up a handful of mortar and place it on the wall. Smooth the mortar over the wall in a 1/2-inch layer. Continue applying the mortar in this manner until you cover the entire wall
Drag the notched side of the trowel over the mortar to create grooves. Let the mortar cure or dry for 48 hours.
Put on your work gloves again and prepare another batch of mortar in the bucket.
Add a thin layer of mortar to the wall with the trowel beginning at the bottom right corner of the wall. Put a layer of mortar onto a river rock and press it to the wall. Continue adding the rocks in a row until you cover the entire wall. Let the wall cure for 48 hours.
Seal the shower rock wall with a water-based masonry sealer. Use a paintbrush to apply the sealer to the wall. Let it dry according to the manufacturer’s instructions, usually 24 to 48 hours, before you use the shower.