How to replace crumbled mortar

If a mortar mix is old or has been applied using too little water, it may well crumble and affect the stability of the wall or place where it's been applied. Read this guide on how to fix crumbling mortar and rectify this problem.

Level of difficulty

Level 2: Intermediate

What you need

  • Safety goggles
  • Dust sheets
  • Chisel
  • Hammer
  • Cement
  • Sand
  • Wooden board
  • Putty knife
  • Trowel
  • Vacuum cleaner or brush
  • Spray bottle
  • Rag
  • Sandpaper

The steps to follow

  1. Cover your work area with a dust sheet.
  2. Wear safety goggles before starting this project.
  3. Knock out any crumbling mortar with the help of a chisel and hammer. Make sure all crumbling mortar is removed.
  4. Vacuum the hole to remove any loose or crumbling mortar.
  5. Next, make a mortar mixture (one part cement and five parts sand). The mixture should have a firm consistency, enough to be molded. Load the mortar mix onto a wooden board.
  6. Spray a bit of water into the hole to dampen it.
  7. Then, apply a fair amount of mortar mixture into the hole. Make sure you've filled the hole up with mortar.
  8. Let the mortar set but not fully dry.
  9. Whilst the mortar is still moist so that no cracking occurs, flatten the surface with the blade of a putty knife.
  10. Smooth the surface with fine grade sandpaper when the mortar has fully dried.

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