MRS101 Moisture Resistant Skim Coat 

DESCRIPTION 

PrepWorx MRS101 is designed to create smooth, even surfaces on a variety of substrates and is perfect for environments with high moisture, up to 100% RH. Suitable for both interior and exterior applications, it can be installed in temperatures as low as 40°F (5°C). Easy to mix with water, it applies smoothly to a true feathered edge, and floor coverings can be installed as soon as 30 minutes after application. 

AVAILABLE SYSTEM 

When PrepWorx MRS101 is installed as directed as part of the approved system below, it qualifies for applicable system warranty coverage, making it a reliable and efficient choice for moisture control.  

APPROVED SUBSTRATES                                

  • Interior and exterior use for residential and commercial applications 

  • Produces flat, smooth surfaces for installing textile, resilient, ceramic, and engineered wood floor coverings 

  • Suitable over: 

  • Structurally sound concrete 

  • APA Exposure Type 1 plywood, OSB, or equivalent subfloors 

  • Well-bonded hard surface flooring (e.g., terrazzo, ceramic tile, stone, epoxy coatings) 

  • PrepWorx moisture control systems 

  • Well-bonded, non-water-soluble adhesive residues (including cutback adhesive) 

  • Gypsum (not suitable for strengthening weak gypsum surfaces) Must prime with PrepWorx QBC300. 

  • Minor substrate preparation under moisture mitigation products in isolated areas, but not as a substitute for mechanical preparation. 

  • Do not use over chemically abated substrates. ​               

                  

                  

SUBSTRATE TESTING 

  • No moisture testing requirement 

  • Refer to substrate moisture limits per flooring installation requirements. 

  • If RH exceeds acceptable levels, apply a moisture control system like PrepWorx MCS310 or PrepWorx VBS311. 

  • Install when substrate, product, mix water and ambient temperatures are a minimum of 40°F (5°C) 

SUBSTRATE PREPARATION 

  • Substrates must be structurally sound, clean, and surface dry. 

  • Substrate must be free of dust, dirt, oil, grease, paint, curing agents, concrete sealers, loosely bonded toppings, loose particles and any other substance or condition that may prevent or reduce adhesion. 

  • Any weakly bonded or soft surface material, such as loose patching compounds, leveling compounds, floor coverings, or coatings, must be removed. 

  • Do not use sweeping compounds.   

Concrete Substrate: 

  • Concrete and cementitious substrates must be fully cured and free of hydrostatic pressure and topical moisture.  

  • Clean surfaces using mechanical methods and avoid using acid etching or sanding, which will not provide adequate bonding preparation.   

  • Ensure all expansion, isolation joints, and moving cracks are properly treated 

  • For dormant cracks wider than 1/32” (0.8 mm), PrepWorx CJR400 may be used to repair. 

  • It is recommended to fill dormant cracks and saw cuts deeper that 1”, using Prepworx MRS101 or QVR110. 

  • Ensure all moving joints, including expansion and isolation joints, as well as moving cracks, are properly addressed and accounted for throughout the entire flooring system, including the finish layer. No flooring material should be installed over these areas. 

  • If no moisture control system is needed, prime the clean surface with PrepWorx QBC300. 

Wood Substrate: 

  • Wood substrates must provide a rigid base and be securely fastened without excessive vertical movement. The surface of the wood must be clean and free of oils, grease, wax, dirt, varnish, shellac, and any contaminates that would impair adhesion. 

WARNING! DO NOT SAND, DRY SWEEP, DRY SCRAPE, DRILL, SAW, BEAD BLAST ORMECHANICALLY CHIP OR PULVERISE EXISTING RESILIENT FLOORING, BACKING, LINING FELT , ASPHALTIC “ CUT BACK” ADHESIVES OR OTHER ADHESIVES. These products may contain either asbestos fibers and/or crystalline silica. Avoid creating dust. Inhalation of such dust is a cancer and respiratory tract hazard. Smoking by individuals exposed to asbestos fibers greatly increases the risk of serious bodily harm. Unless positively certain that the product is a non‐asbestos‐containing material, you must presume it contains asbestos. Regulations may require that the material be tested to determine asbestos content and may govern the removal and disposal of material. See current edition of the Resilient Floor Covering Institute (RFCI) publication Recommended Work Practices for Removal of Resilient Floor Coverings for detailed information and instructions on removing all resilient covering structures. For current information go to www.rfci.com. 

APPLICATION INSTRUCTIONS AND COVERAGE RATES 

Read and follow the product specific installation guidelines for layout, design and any special instructions for installation. 

Mixing 

  • Product strength and performance are dependent on exact mixing ratios: 

            3.25 parts powder to 1 part water by volume.
            For a 10 lb. bag, mix with 1 3/4 quarts (1.65 L) of clean water. 

  • Mix as much as can be installed in a 15-20 minute time period. 

  • Pour water into the container first, and then add powder while mixing. 

  • Mix with a heavy-duty drill (min. 650 rpm) for 2-3 minutes to achieve a smooth, lump-free consistency.  

  • Do not overwater the mixture, as additional water weakens the material. 

  • For small batches, mix by hand with a margin trowel and stir again before application.  

Application 

  • Use a flat, steel trowel to spread MRS101 to a smooth level surface. 

  • Pot life is approximately 15-20 minutes depending on site ambient conditions. 

  • For exterior applications, use a maximum thickness of 1/4”; for interiors, up to 1/2”. 

  • Product can be remixed without water to maximize pot life. 

Curing 

  • Drying times vary depending on environmental conditions. 

  • Typically, the product is ready for floor covering in 30 minutes, but for wood floors or high-performance adhesives, allow up to 16 hours. 

  • Foot traffic and installation of most floor coverings can begin in 30-60 minutes depending on the thickness and substrate. 

  • Always refer to floor covering guidelines for installation over cement-based patch products. 

  • Ensure proper ventilation to speed up the drying process. Do not apply fans or other forced air to surface. 

Coverage Rates 

Coverage rates are approximate values. Actual coverages may vary according to substrate conditions and thickness of the application. 

Application Depth Approximate Coverage per 10 lb bag 

  • Skim Coat 200 - 250 sq ft (18.6 -23.2 m2) 

  • 1/8” (3 mm) 28 sq ft (2.6 m2) 

  • 1/4" (6 mm) 14 sq ft (1.3 m2) 

  • 1/2" (12 mm) 7 sq ft (0.65 m2) 

PRODUCT CHARACTERISTICS 

Weight 

10 lbs / bag 

Pallet Quantity 

52 cases / 208 bags 

Pallet Weight 

2197 lbs 

Physical State 

Dry Powder 

Color 

Gray 

Shelf Life 

1 year from manufacturing date (unopened package) 

Storage Conditions 

Store away from direct sunlight in a well-ventilated, cool, dry area. If storing after opening, remove all air from packaging and seal tightly. 
Freeze/Thaw Freeze thaw stable

Compressive Strength (ASTM C109) 

3200 psi 

Cleaning Instructions 

While still fresh, wash hands, tools and equipment with warm soapy water. 

Traffic / Installation

  • Traffic: 30-60 minutes 

  • Installation: LVP/LVT/Sheet Goods - When Hardened (average 30 minutes 

  • Installation: Engineered Hardwood/ Epoxy or Urethane Adhesives: 16 hours  

WARRANTY 

Standard product warranty is 1 year.  When combined with certain PrepWorx moisture management and flooring adhesive products the term of warranty is extended ranging from 10 to 20 years.  See Shaw System Warranty (Warranties) for complete details. PrepWorx Floor Preparation 1 Year Limited Warranty

PRECAUTIONS 

Carefully read and follow all precautions and warnings on the product label. For complete safety information, please refer to the Safety Data Sheet.

Revision: 03102026
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