How to Use Exterior Masonry Caulking


Over time, exterior masonry develops cracks or gaps that are unattractive and can lead to further damage. Most damage occurs from water that gets into imperfection or hairline cracks in masonry that then freezes, expands and makes the damage worse. Sealing damaged areas with masonry caulk as soon as you see signs of damage is the best way to safeguard against future problems. Caulk, foam backing rods and other needed supplies are available from most hardware and home improvement stores.

Things You'll Need

  • Broom, brush or vacuum
  • Hose or pressure washer
  • Canned air or air compressor
  • 1/4 to 1/2 inch insulator backing rod
  • Utility knife
  • Expanding spray foam
  • Masonry caulk tube
  • Caulking gun
  • Old large spoon
  • Clean rags
  • Clean the area around the crack or gap using a broom, brush, or vacuum. You may also use a water hose or pressure washer to remove any debris. The area needs to be completely dry before sealing, or trapped moisture may cause problems later. Canned air or a blower connected to an air compressor also is an option to blow away anything from the gap or crack.

  • Cut foam insulator backing rod to fit larger gaps and press it in using a piece of wood shim or your fingers. Try to place the insulation approximately 1/4 to 1/8 inch below the surface of the gap. Spray foam also is acceptable for deep openings, but expands so completely that you may have to carve some away to get it flush with the gap edge to allow you to caulk over it smoothly. For cracks too small for insulation, skip this step.

  • Cut the tip of the caulk tube with a utility knife so that the size of the nozzle is roughly the same as the crack or gap opening and place the tube into a caulking gun. Try to cut it at about a 30-degree angle to allow the caulk to be forced downward smoothly and fill the space thoroughly. Apply the caulk with an even motion in one direction across the opening and use the tip to get it flush with the surface.

  • Fill cracks or gaps at seams between masonry floor and the edges of houses, steps or other structures by beveling the tip upward slightly. Smooth the edge of the opening with the back of an old large spoon. This creates an attractive rounded seam at the angle between the two edges. Allow the caulk to dry completely for the time indicated in the manufacturer’s instructions.

Tips & Warnings

  • Wipe off all tools that come in contact with the caulk using a rag dipped in paint thinner or mineral spirits.
  • Avoid getting caulk on your skin and clothes because it is very sticky and can stain fabrics.
  • Use the caulk only in temperatures recommended by the manufacturer for proper sealing.
  • Clean up spilled caulk quickly with a clean rag and mineral spirits before it hardens and becomes difficult to remove.

Related Searches


  • Guide to Concrete: Masonry & Stucco Projects;” Phil Schmidt; 2008
  • Photo Credit Thinkstock Images/Comstock/Getty Images
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