How to Use RedGard With Marble

RedGard prevents substrate movement from cracking marble surfaces.

RedGard, a waterproofing and crack prevention membrane, prepares interior and exterior substrate surfaces for marble tile installation. Suitable substrates for RedGard include concrete slabs, lightweight concrete, cement backerboards, gypsum-based underlayments, exterior-grade plywood and exterior decking. If an installer bonded marble directly to a substrate, the marble would crack when the substrate settles or shifts. RedGard fills settlement cracks and provides an isolation barrier for the marble. A RedGard membrane stretches slightly if the substrate moves, preventing cracks in the marble or the marble's setting material.

Things You'll Need

• Hammer
• Drill
• Broom
• Dust pan
• 3/16-by-1/4-inch V-notch trowel
• Water
• Bucket
• Paint brush

Instructions

1. Inspect the substrate surface for movement and repair as needed. Drive any loose nails into the substrate's surface with a hammer. Countersink any raised screws with a drill.

2. Clean the substrate with a broom and dust pan. Remove all debris from the work area.

3. Pour a small amount of RedGard along the cracks in the substrate. The amount of RedGard needed depends on the width of the cracks.

4. Force the RedGard into the cracks with the flat side of a 3/16-by-1/4-inch V-notch trowel. The flat edge of the trowel should scrape the excess RedGard off the substrate's surface. Fill all of the cracks in the substrate before continuing.

5. Coat lightweight concrete and gypsum-based underlayments with a RedGard primer, using a paint brush to spread the primer. Allow the primer to dry for one hour before continuing. To make a RedGard primer, mix 1 part RedGard with 4 parts clean water in a bucket.

6. Cover the substrate with the RedGard, using the notched side of the trowel to spread the material. Flatten the ridges in the RedGard with the flat side of the trowel.

7. Let the RedGard dry until the material turns an even shade of red, usually less than 1 1/2 hours.

8. Apply a second coat of RedGard to the substrate with the V-notch trowel. Apply the second coat in a perpendicular direction to the first coat.

9. Allow the second coat of RedGard to dry before installing the marble with a marble-approved thinset mortar.

References

• Custom Building Products; RedGard Waterproofing and Crack Prevention Membrane Technical Data Sheet; September 2000

Resources

• Realtor: Installing Marble Flooring