ARDEX MRF Moisture-Resistant, Rapid-Drying, Skimcoat Patching Underlayment is a new, weatherproof patch and the very first of its kind available in the marketplace. It’s fully moisture-resistant and can submerge in water for any amount of time, which makes it suitable for use under moisture control systems and moisture resistant adhesives and flooring. It provides a smooth surface and is suitable for use over a variety of interior and exterior substrates. Thanks to its rapid-drying formula, the installation of most floor coverings is possible in only 30 minutes. ARDEX MRF does not require primer or a latex additive for most substrates.