Products : CustomTech Flooring Prep : Patching : Silk™ Patching & Finishing Compound

Silk™ Patching & Finishing Compound

A fast-curing, calcium aluminate based, patching and finishing compound that provides a smooth finish to a variety of substrates prior to the installation of floor coverings. Formulated with Controlled Cure Technology,™ Silk helps eliminate installation problems of bond failure, crumbling, mildew and staining of resilient flooring due to free-moisture found in traditional underlayments. Its rapid setting formula allows installation of most floor coverings in as little as 30 minutes.

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Key Features

  • Superior mixing and handling
  • Excellent for skim coat patching applications
  • No additives required
  • Apply from featheredge to 1"
  • Install flooring in as little as 30 minutes


Suitable as an Underlayment for:

  • Carpet
  • Wood and parquet flooring
  • Luxury Vinyl Tile/Planks (LVT/LVP)
  • Vinyl composition tile (VCT)
  • Sheet vinyl and rubber flooring
  • Laminated flooring
  • Ceramic, mosaic, quarry or cement body tile
  • Impervious porcelain and glass tile
  • Cement-based precast terrazzo
  • Natural stone tile
  • Terrazzo


  • Quick-setting formula permits floor covering installation in as little as 30 – 90 minutes
  • Smooths the finishes on interior subfloors
  • Patches and levels concrete and plywood from feather edge to 1" (25mm)
  • No additives required


Applicable Standards

  • Silk™ Patching & Finishing Compound meets the requirements of ASTM F710 Including compressive strengths >3000psi without the use of additives

ASTM International (ASTM)

  • ASTM C109 Standard Test Method for Compressive Strength of Hydraulic Cement Mortars (Using 2-in. or (50-mm) Cube Specimens)
  • ASTM F1869 Standard Test Method for Measuring Moisture Vapor
  • ASTM F710 Standard Practice for Preparing Concrete Floors to Receive Resilient Flooring
  • ASTM C627 Standard Test Method for Evaluating Ceramic Floor Tile Installation Systems Using the Robinson-Type Floor Tester
  • ASTM F2170 Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using in situ Probes

Resilient Floor Covering Institute (RFCI) Recommended Work Practices for Removal of Resilient Floor Coverings

Tile Council of North America (TCNA) TCNA Handbook for Ceramic Tile Installation, TCNA Method EJ171.

American National Standards Institute (ANSI) ANSI A108.01 and A108.02 of the American National Standards for the Installation of Ceramic Tile

Conformance to Building Codes

Installation must comply with the requirements of all applicable local, state and federal code jurisdictions.

Composition of Product

Silk Patching & Finishing Compound is a blend of cements, inorganic fillers and polymers.

Environmental Consideration

Custom® Building Products is committed to environmental responsibility in both products produced and in manufacturing practices. Use of this product may contribute to LEED® certification.

Suitable Substrates

  • Absorbent concrete
  • Gypsum-based underlayment (meets ASTM F2419)
  • Exterior grade plywood & OSB / APA or CANPLY Group 1 
  • Flooring manufacturer’s approved wood underlayments
  • Existing ceramic tile
  • Resilient flooring
  • Embossed vinyl
  • Cutback adhesive residue
  • Primed cement terrazzo
  • Approved and prepared moisture control membranes

 *Special preparation or primers may be required

General Surface Prep

USE CHEMICAL-RESISTANT GLOVES, such as nitrile, when handling product.

All surfaces must be structurally sound, clean, dry and free from contaminants such as grease, oil, dirt, dust, curing compounds, waxes, sealers, efflorescence, or any other foreign matter. Concrete must be fully cured and absorb water. Smooth concrete surfaces, existing glazed tile, terrazzo, or polished stone may need to be roughened or scarified. Refer to Custom TechPrimeTM A Acrylic Primer technical datasheet for use in lieu of mechanical preparation or when applying over Custom TechMVCTM Moisture Vapor and Alkalinity Barrier. For increased performance in demanding applications, concrete surfaces can be mechanically profiled and prepared by shotblasting, sandblasting, scarifying, diamond-grinding or other engineered approved methods (reference ICRI CSP 3 standards for ideal profile height). Any existing flooring must be well bonded and stripped of old finish.

CUSTOM® products may be used in assemblies over concrete with high moisture vapor emission levels provided that other materials such as finish flooring, adhesives or membranes are approved in these conditions. Consult the manufacturers for their limitations and requirements. Additionally, any sources of moisture are to be limited to initial concrete placement and not from sources such as water intrusion or from a lack of an effective vapor retarder/barrier.

Assembly mockups will determine suitability for these conditions on specific projects. Contact CUSTOM Technical Services for product information (800) 282-8786

Bonding to Concrete

In addition to general surface preparation requirements listed above, concrete must be free of efflorescence and hydrostatic pressure. Concrete surfaces must have a tensile strength in excess of 200 psi (1.4 n/mm²). Concrete that was treated with curing compounds must be evaluated for suitability or mechanically removed

Bonding to Plywood and OSB Surfaces

Plywood floors, including those under resilient flooring, must be structurally sound and must meet all industry guidelines. For questions about proper subfloor installation, call Custom® Building Products.

Bonding to Gypsum Surfaces

Gypsum-based underlayment must be solid and structurally sound, achieving a compressive strength >2000psi (13.8 MP) Remove any unacceptable surfaces. The underlayment must be sufficiently dry and properly cured to the manufacturer’s specifications for permanent, non-moisture permeable coverings. Substrate deflection not to exceed the current industry standards.

All Gypsum surfaces are required to be sealed or primed prior to leveling. Apply TechPrime A Acrylic Primer directly to the gypsum or over gypsum manufacturer’s sealer. Dilute TechPrime A 3-parts water to 1-part primer with clean, potable water. Apply a second application of primer diluted 1:1. Drying time depends on site conditions, but is normally less than 1 hour between coats.Leveler can be applied to the primed surface after primer dries.

Gypsum based underlayment used in tile or stone applications may require waterproofing or crack isolation. For these applications we recommend applying RedGard® Waterproofing and Crack  Prevention Membrane over leveler once cured.

Health Precautions

This product contains Portland cement. Avoid eye contact or prolonged contact with skin. Wash thoroughly after handling. If eye contact occurs, flush with water for 15 minutes and consult a physician. Use with adequate ventilation; do not breathe dust and wear a NIOSH approved respirator. If ingested, do not induce vomiting; call a physician immediately.

Limitations to the Product

  • Interior use only.
  • Do not bond to plank hardwood, particleboard, parquet, cushion or sponge back vinyl flooring, or other dimensionally unstable substrates.
  • Not for use as a finished surface/wear layer.
  • Do not use under moisture mitigation systems. 
  • Do not use when substrate temperature is below 50°F (10°C).
  • Not for use in areas with continuous water exposure (ie: showers, swimming pools, spas, water features and fountains).
  • See Flooring Manufactures recommendations for Relative Humidty limitations and Moisture Vapor Emissions limitations.

Bonding to Cutback Adhesive

Adhesive layers must be removed. Use extreme caution; adhesives may contain asbestos fibers. Do not sand or grind adhesive residue, as harmful dust may result. Never use adhesive removers or solvents, as they soften the adhesive and may cause it to penetrate into the concrete. Adhesive residue must be wet-scraped to the finished surface of the concrete, leaving only the transparent staining from the glue. To determine desirable results, do a test bond area before starting. Refer to the RFCI Pamphlet, "Recommended Work Practices for Removal of Resilient Floor Coverings", for further information.

Mixing Ratios

Combine 2 parts powder to 1 part water.

Mixing Procedures

Mix 1.5-1.75 quarts (1.4-1.65 L) clean, cool water to a 10 lb bag of Silk™ Patching & Finishing Compound. Slowly add powder to liquid while mixing with a high speed drill (650 RPM or more) and mixing paddle to a lump-free consistency. Mix amounts that can be applied in 10 minutes.

Application of Product

Apply material into all voids up to 1" (25 mm) thickness using a broad knife or trowel and finish flush with surface. For skim coating, use a smooth edged trowel to flatten the surface area. Only spot patching should be done on wood surfaces. If an area more than 5 ft. (1.5 M) in diameter is required, use an appropriate CustomTech™ self-leveling underlayment.

Curing of Product

LVT, LVP, VCT, sheet vinyl and carpeting can be installed when surface can be worked on without damage (usually about 30 - 60 minutes). Parquet, athletic flooring and flooring requiring special adhesives (such as epoxies and urethanes) which can be sensitive to the presence of moisture can be installed after 16 hours. Drying time depends on ambient conditions and thickness.

Cleaning of equipment

Clean with water before material dries.

Product Maintenance

Properly installed product requires no special maintenance.

Ordering Information


10 lb (4.5 kg) Bags

Warranty Information

Product Warranty

Custom® Building Products warrants to the original consumer purchaser that its product shall be free from defects in material and workmanship under normal and proper usage for a period of one year following the date of original purchase. Custom's sole liability under this warranty shall be limited to the replacement of the product. Some states, countries or territories do not allow the exclusion or limitation of incidental or consequential damages, so the above limitation or exclusion may not apply to you. This warranty will not extend to any product which has been modified in any way or which has not been used in accordance with Custom's printed instructions. Custom makes no other warranties either expressed or implied. This warranty gives you specific legal rights, and you may have other rights that vary from state to state or from one country/territory to another. For details and complete warranty information, visit

Product Videos

Coverage Chart

SQUARE FOOT COVERAGE PER 10 LB BAG (SQUARE METER PER 4.5 KG). Coverage will vary depending on the texture of the surface being smoothed.

As a Skim Coat 100 ft² (9 M²) 300 ft² (27 M²)
1/8" (3 mm) 33.3 ft² (3 M²) 35.9 ft² (3.3 M²)
1/4" (6 mm) 16.6 ft² (1.5 M²) 17.9 ft² (1.6 M²)
1/2" (12 mm) 8.3 ft² (0.7 M²) 8.9 ft² (0.8 M²)
1" (25 mm) 4.1 ft² (0.3 M²) 4.4 ft² (0.4 M²)

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