Removing mortar from joints, often called raking out or grinding out, is typically done to prepare the area for repointing. The primary goal is to create a clean, stable surface for new mortar to adhere to.
The Process: Grinding or Chiseling
The process involves mechanically removing the old, deteriorated mortar from the joints between bricks or stones. You can achieve this using various tools, primarily either grinding or chiseling.
- Grinding: This method uses power tools like angle grinders with special tuckpointing blades. It's often faster, especially for long, straight joints, but requires careful control to avoid damaging the masonry units.
- Chiseling: This method uses hand tools like cold chisels and a hammer, or power tools like pneumatic hammers with chiseling bits. It offers more control, particularly in irregular joints or sensitive areas, but can be more labor-intensive.
Determining the Correct Depth
A crucial step in preparing joints for repointing is ensuring the old mortar is removed to the correct depth. According to best practices:
You should grind or chisel out mortar joints to a depth of 2-2.5 times the width of the joint or deeper until sound original mortar is located.
This depth range (2 to 2.5 times the joint width) provides sufficient space for the new mortar to bond effectively and create a durable patch. Removing only a shallow layer won't allow the new mortar to key into the joint properly, leading to premature failure. You must continue removing material until you reach solid, intact mortar, regardless of the initial depth calculation, if the deterioration goes deeper.
For thin joints, there is a minimum required depth: The minimum depth of thin joints is 3/4″. Even if 2-2.5 times the width is less than 3/4 inch, you should still remove mortar to at least this depth to ensure a robust repair.
Depth Guidelines Summary
| Joint Width (Example) | Target Depth (2-2.5x Width) | Minimum Depth (If Applicable) |
|---|---|---|
| 1/2 inch | 1 inch - 1.25 inches | 3/4 inch (applies here) |
| 3/4 inch | 1.5 inches - 1.875 inches | 3/4 inch |
| 1 inch | 2 inches - 2.5 inches | N/A |
Note: Always remove deeper if necessary until sound, original mortar is reached.
Practical Steps for Removing Mortar
- Preparation: Clean the joint surface of any loose debris, dirt, or vegetation.
- Select Your Tool: Choose between grinding or chiseling based on the joint type, accessibility, and your experience level.
- Start Removing: Carefully begin removing the old mortar. Work methodically along the joint.
- Grinding: Guide the grinder steadily along the joint line, maintaining control.
- Chiseling: Place the chisel at an angle to the joint and tap gently with a hammer (or use a power chisel), breaking the mortar away in small pieces. Work from the sides towards the center.
- Check Depth: Periodically check the depth of the joint to ensure you are meeting the 2-2.5 times width requirement or the minimum 3/4″ for thin joints, and that you have reached sound mortar.
- Remove All Material: Ensure all loose and deteriorated mortar is removed from the joint.
- Clean Thoroughly: After removing the mortar, brush out the joints to remove dust and debris. Using compressed air or rinsing can help ensure a clean surface for the new mortar.
Safety First
Removing mortar creates dust and flying debris. Always wear appropriate personal protective equipment (PPE), including:
- Safety glasses or goggles: To protect your eyes.
- Dust mask or respirator: To avoid inhaling mortar dust.
- Gloves: To protect your hands.
- Hearing protection: When using power tools like grinders or pneumatic hammers.
Proper ventilation is also important, especially when working indoors.
By following these steps and ensuring the correct depth is achieved, you create an ideal surface for successful and long-lasting repointing.
