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How to Seal the Bottom of Stucco

Most homeowner's apply an elastomeric paint to a stucco surface to waterproof the wall but do not consider sealing the bottom edge. Unless a sealant is applied to seal the bottom of stucco, moisture will enter from the bottom and rot the stucco from the inside out. The sealant needs to be applied in such a way as to form a barrier between the outer edge of the stucco and the wall of the foundation, covering the stucco backing board and mesh as well.

Stucco must be completely sealed to withstand the elements.
  1. Expose the bottom of the stucco. Use a shovel to clear any dirt away if necessary.

  2. Score a line a 1/4 inch up from the bottom of the stucco using a straight edge and box knife. Cut off the bottom strip by guiding an angle grinder along the score line making sure to cut through the backing board. This creates a clean edge to seal.

  3. Use a scrub brush to clean any dirt from around the edge so it does not contaminate the sealant. Make sure that where the backing board meets the foundation is free from debris so the sealant will adhere to the foundation.

  4. Apply an elastomeric sealant or caulk between the foundation and the lower edge of the stucco. Completely fill the space between, making sure that the bottom of the backing board is covered as well. Use a caulk gun if necessary, although some sealants come in a tube that can be hand squeezed instead.

  5. Shovel the earth back over the bottom edge of the stucco when the sealant or caulk is dry if necessary.

Warning

  • Use caution when applying the sealant. Stucco is applied over a wire or stiff plastic lathing that can cause cuts.