Under-Subfloor & Under-Tile Waterproofing FAQ

Under-Subfloor & Under-Tile Waterproofing FAQ

Protect your interior flooring from ground moisture and vapor drive with Liquid Rubber. This system is designed for applications beneath tile, concrete screed, and subfloors to prevent mold and moisture damage in grade-level or below-grade spaces.

Product Selection & Sub-Surface Planning

  • Which products do I use for undercoating? Use Liquid Rubber Foundation Sealant. If applying to wood or concrete within 6 ft of grade, you must also use Multipurpose Primer and Geo-Textile.
  • Do I need a primer? Yes. Primer is critical for any substrate on or near grade (within 6 ft) to mitigate moisture vapor drive and ensure a permanent bond.
  • How much should I buy? For undercoating projects, Foundation Sealant is applied at 1 gallon per 20 sq ft (1.85 sq/m). Example: A 200 sq ft area requires 10 gallons. Apply in multiple coats until all material is used.
  • Can I walk on the finished surface? No. Foundation Sealant remains tacky and is not a final walking surface. If you want a finished, walkable surface instead of tiling over it, use Polyurethane Deck Coating.
  • Will I need a slip sheet? Some flooring materials (like certain laminates) may stick to the tacky coating. You may need a slip sheet between the cured sealant and your final flooring; contact our technical team to discuss your specific materials.

Surface Preparation & Compatibility

  • How do I prepare Concrete or Wood?
    • Concrete: Must be cured with less than 5% moisture. Use Concrete Etch to remove laitance and efflorescence before priming.
    • Wood: Scuff the surface to increase mechanical bond and clean with Multipurpose Cleaner.
  • Should I use Seam Tape or Geo-Textile? We recommend Geo-Textile for undercoating as it provides a lower profile than Seam Tape, making it easier to install flooring over the top.
  • Will it fill cracks? No. Prefill cracks and joints (1/8" to 1/4") with Adhesive Caulk before applying Geo-Textile. Larger voids in concrete require a suitable patching material.

Expert Application Tips

  • Can I coat over old paint? Yes, if it is well-bonded. However, if the underlying paint peels, our coating will peel with it. Always perform an adhesion test first. Remove any oil-based or high-solvent coatings before application.
  • What tools do I need? Most applications require standard paint brushes with nylon bristles and 3/8" microfiber rollers.
  • Saving your tools: Between coats, wrap your brush or roller in a plastic bag to prevent it from curing, allowing you to reuse it for the next layer.

✅ Project Checklist: Undercoating Essentials

Item Why You Need It
Foundation Sealant The primary moisture barrier beneath your subfloor or tile.
Multipurpose Primer Mandatory for on-grade surfaces to prevent bond failure from moisture vapor.
Geo-Textile Provides structural reinforcement for joints and cracks without adding bulk.

Technical Documentation: View our Under-Coating Application Guidelines for full instructions.

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