How to Patch Chips in Cinder Block

Cinder block chips require repair.

Cinder block is a hollow, lightweight masonry block used largely for foundations, garages and retaining walls as well as other projects that require large blocks. Their lightweight nature makes moving and placing easier. Cinder blocks, cast from cement, fine gravel and sand or aerated concrete, are commonly referred to as foundation blocks, cement blocks or concrete masonry units. Generally, after foundation installation, cinder blocks require a waterproof coating that stops moisture from penetrating through the porous block. Chips on cinder blocks allow moisture to find a way into a basement or through a wall and require an immediate repair.

Things You'll Need

• Wire brush
• Paint brush
• Hydraulic cement
• Putty knife
• Nylon scrubber or towel
• Waterproofing primer
• Waterproofing paint

Instructions

1. Use a wire brush to brush away loose bits and pieces of the cinder block.

2. Brush away excess dust and debris with a paint brush.

3. Mix hydraulic cement, according to the package directions, in a bucket.

4. Use a putty knife to apply a thin layer of hydraulic cement and press it deeply into the chip.

5. Apply a second layer of hydraulic cement over the first, building the second layer up so it sits flush with the surface of the cinder block. Feather out the edges of the patch as you work away from the chip, making the layer thinner and thinner as it moves away from the patch.

6. Before the patch dries, blend the patch by dabbing at it with a wet nylon scrubber or a wet towel to create a finish similar to the rest of the cinder block.

7. Allow the hydraulic cement to dry thoroughly, usually 12 to 18 hours.

8. Apply waterproofing primer to the patched block and allow it to dry fully.

9. Apply two coats of waterproofing paint over the primer.

Tips & Warnings

• Wear safety glasses, gloves and a dust mask.

• Properly ventilate the area when working with waterproofing materials by opening windows and using large fans.

References

• "Masonry"; Time Life Editors; 1977