Tying in a new block wall to an existing one involves properly bonding the two structures to ensure stability and prevent water penetration. Here's a detailed guide:
Steps to Tie In a Block Wall
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Prepare the Existing Wall:
- Remove any loose material, dirt, or debris from the existing wall where the new wall will connect. This ensures a good bonding surface.
- Clean the area thoroughly, possibly using a wire brush.
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Install a Steel Angle (Recommended):
- Attach a steel angle iron vertically to the existing wall where the new wall will meet it. This angle will provide a mechanical connection between the two walls.
- Consider using epoxy anchors or expansion bolts to securely attach the angle to the existing wall. The spacing of the anchors will depend on the load requirements of the wall. Consult a structural engineer if needed.
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Provide a Bond Breaker:
- On each leg of the angle iron that will come into contact with the mortar or block, apply a bond breaker. This prevents the mortar from rigidly bonding to the steel, allowing for some differential movement and preventing cracking. Polyethylene sheeting or a similar flexible material can serve as a bond breaker.
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Prepare the New Blocks:
- Break out the end webs of the new concrete blocks that will abut the existing wall or the steel angle. This creates a void for mortar to fill and mechanically lock the new blocks to the existing structure. This improves the shear strength of the connection.
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Mortar Infill:
- Carefully pack the cores of the new blocks around the angle iron with mortar. This creates a strong connection between the new wall, the angle, and the existing wall. Ensure the mortar completely fills the voids.
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Seal the Joint:
- Once the mortar has cured, seal the joint between the new blocks and the existing wall with a high-quality elastomeric caulk. This prevents water infiltration and accommodates any slight movement between the two walls. Choose a caulk that is paintable and suitable for exterior use.
Alternatives to Angle Iron
While using a steel angle is a strong and recommended method, other options exist, especially for non-load-bearing walls or less critical applications:
- Toothing: Remove blocks from the existing wall in a staggered pattern (toothing). Then, build the new wall, filling the gaps to interlock the two walls. This is labor-intensive and weakens the existing wall.
- Wall Ties: Use metal wall ties embedded in the mortar joints of both walls. These ties provide a mechanical connection. These are typically used in cavity walls.
Important Considerations
- Local Building Codes: Always check and adhere to local building codes and regulations regarding tying in block walls.
- Professional Consultation: For load-bearing walls or complex projects, consult a structural engineer or experienced mason to ensure proper design and execution.
- Mortar Type: Use the correct type of mortar for the specific application and block type. Type N mortar is often suitable for general use.
