How to Repair an Outdoor Slate Wall

Lead Image
  • 2-3 hours
  • Intermediate
  • 100-200
What You'll Need
Oxygen bleach
Thinset mortar
Masking tape
Non-sanded grout
Rubber float
Natural stone sealer
Roller or spray
Injectable epoxy
Grout saw
Replacement tiles

An outdoor slate wall, exposed to many environmental factors, can get damaged over time. One of the main problems that need to be repaired is algae and mold growth. There are also instances where the individual tiles break, due to exposure, moisture, and extreme heat. Here are some ways to repair any damage.

Step 1 - Clean Organic Growth

Oxygen bleach can solve discolorations caused by organic growth, such as molds and algae. Scrape or brush off fresh algae. Mix the oxygen bleach with water in a plastic container according to the manufacturer’s instructions. Use a sponge or a spray bottle to apply the solution to the wall. Leave the solution for about 10 minutes. Brush the surfaces to remove the solution. Rinse with water thoroughly.

Step 2 - Repair Damaged Tiles

Use epoxy to patch cracked and broken tiles. Epoxy is a very strong compound and is resistant to water, stains, and mold growth. Remove any loose debris from the cracks using a vacuum cleaner. Prepare epoxy mix and inject the epoxy into the holes. For smaller cracks, use a toothpick to fill the cracks with epoxy. If the cracks are not patched or bonded, the cracks will worsen and might result in serious chipping. If this becomes the case, the broken tiles need to be replaced with new ones.

Step 3 - Replace Damaged Tiles

Scrape the grout around the damaged tile to loosen it from its place. You can use a thin chisel to remove the grout.

To remove the damaged tiles, insert the sharp edge of the chisel into the underside of the tile and tap lightly with a hammer. If the tile will not budge, try chiseling from the center to break the tile. Continue breaking the tile until it comes off completely. Chip away the mortar underneath it as well, to provide space for the replacement.

Mix a sufficient amount of thinset and apply it at the location of the removed tile. Push the replacement into the hole. Check if it is level. Surround the tile with masking tape to keep the tile in place. Allow the thinset to harden for 4 to 6 hours. You can also use a cement tile adhesive or use a mastic tile adhesive if the mortar is a bit heavy for wall use.

Mix non-sanded grout and fill the gaps around the replacement tiles, using a rubber float. Let the grout cure. Follow the same procedure for other broken tiles in need of replacement.

Step 4 - Seal the Slate Wall

Seal the wall to give it protection from moisture. A membrane-forming sealer is perfect for tiles that are exposed to heavy rains and snow. This type of sealer repels water and helps in prolonging the life of the stone. Apply the sealer according to the manufacturer’s instructions. Use a paintbrush or paint roller, or spray the sealer directly. Layer several thin coats of sealer. Wait for the sealer to dry and you're done.