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Technical Data Sheet (TDS)

EHS-265 Hydro-Seal

Water Based Epoxy Primer (two component pail)

Special features

  • for use under ULC-500
  • superb penetration of sub floors
  • increases bond of subsequent urethane levelers

Product Description
STAUF EHS-265 Hydro-Seal is a two component, hybrid-epoxy resin based primer for sub floor preparation prior to installation of urethane based leveling compounds. Unlike water or urethane based primer, EHS-265 is not affected by elevated sub floor moisture. It will not foam up or get weaker because of water present in the sub floor. It also has a higher penetration of the concrete compared to traditional 100% solid epoxies which creates a stronger bond. It does however NOT create a moisture barrier but merely reduces the amount of vapor penetration.
EHS-265 spreads easily and creates a dust free surface ready for safe installation of flooring. It increases the bonding of subsequently applied primers, leveling compounds and/or adhesives.
Pre-Installation Checklist
A successful installation requires proper preparation of the sub floor. Read and understand all applicable guidelines and technical data sheets before installation. Follow industry standards and flooring manufacturer's recommendations for sub floor moisture content, design, layout and application of flooring materials. All slab constructions must meet the specific requirements of the floor covering to be installed.
Sub Floor Examination
Do not apply sealer onto a visibly damp or wet surface. Examine concrete sub floor for color, cleanliness, porosity and pre-existing residues PRIOR TO installation (for details see Technical Information #18 @ Concrete sub floors must be checked for any contaminants and/or anti-adherents using the STAUF Epoxy Test Kit (for details see Technical Information #16 @
Prior to installation, the sub floor must be checked according to applicable installation guidelines. It must be solid and sound, clean, free of chaps and anti-adherents, as well as resistant to pressure and tension. Check for missing or compromised vapor barriers and hydrostatic pressure. Perform RH or CaCl moisture tests following ASTM standards. Results of 99% RH or 25# CaCl could indicate that there is a higher moisture content in the slab than what tests can measure and there might be hydrostatic pressure and/or a compromised or missing vapor barrier.
Sub Floor Preparation
The condition of the sub floor will determine which type of mechanical treatment is required (e.g. wire brushing, sanding, grinding or shot blasting). Dust, paint, curing compounds, sealers, residual adhesives or other surface pollutants MUST be removed by suitable means. Extent of sub floor preparation can only be determined at the site by the installer. Clean the surface with an industrial vacuum cleaner, tack or damp mop floor before application. Do not use sweeping compounds as most will contain oil or wax which will act as an anti-adherent and prevent primers, sealers, leveling compounds, coatings and/or adhesives from bonding to the concrete. Cracks and gaps must be treated prior to application of primers, sealers, leveling compounds, coatings and/or adhesives (for details see Technical Information #19 @
Mixing of Components
Lid contains hardener. Pierce all the way through plastic disc in center of lid and the bottom of the lid using a long screwdriver or similar tool. Let the hardener flow into the lower part of the bucket for one minute. All of the hardener must drain into the pail before mixing parts A&B. Open ring, remove the lid and mix both components with mixing paddle for at least 3 minutes. Use an electric drill with less than 300 rpm until an even color is reached. Avoid air entrapment by mixing slowly and using an appropriate mixing paddle. Make sure to mix along wall and bottom-part of the container as well. Temperature of both components should be at least 50 °F before mixing.
Installation Procedure
Mix pail according to mixing instructions. Apply coating undiluted with approved applicator. Make sure coating is spread evenly and up to the perimeters. The spread rate is critical for a successful installation. Do not exceed the minimum or maximum coverage.
When using other than STAUF products in conjunction with STAUF primers, sealers, leveling compounds, or adhesives, STAUF denies any and all responsibility for any ensuing problems and/or damages without prior written authorization from STAUF.
Do not dilute primer/sealer or mix with other products.
In case of accident, injury, spill or exposure, see SDS sheet for information. Consult technical data sheet at for updated information.
Sealer will not prevent moisture damages from hydrostatic pressure, missing or compromised vapor barriers, underground springs, damaged water pipes, sinks, icemakers, faulty plumbing, flooding, etc.
The foregoing representations are based on the results of our most current product and material testing within a controlled environment and are of a non-obligatory advisory nature only. As such, they do not constitute an express or implied warranty of any kind including the Warranty of Merchantability and/or Fitness for a Particular Purpose. Because we have no control over the actual quality of workmanship, materials used and worksite conditions, STAUF USA, LLC. will in no event be liable for any incidental and/or consequential damages. herefore, we strongly recommend that prior on-site testing be conducted to refer to and study the suitability of the product for the intended purpose. With the release of this technical information sheet all its prior versions become invalid. For warranty and warranty disclaimer information please see our Limited Lifetime Warranty @
General Features
  • works under any type of flooring
  • contains no isocyanates
  • contains no chlorinated solvents
  • contains no solvents
  • contains no VOC (calc. per CA Rule 1168)
  • high solids content
  • ozone friendly
  • Freeze/thaw stable
  • contains no isocyanates
Installation Features
  • creates dust free surface
  • very low odor
  • high spread rate
  • excellent penetration of sub floor
  • higher temp & RH will shorten drying time
  • observe pot life during installation
Long Term Features
  • resistant against aging
  • suitable for radiant heat systems
Viscosity [cps]
  • 400
Approved Sub Floors
  • Concrete Slabs
  • Felt backed Sheet Vinyl (well bonded, sanded, asbestos-free)
  • Ceramic Tiles
  • Stone, Terrazzo
  • Wet Concrete Slab up to 25#/24hrs/1,000SF and 100% RH
  • Stained Concretes (well bonded)
Approved Trowels and Spread Rate
  • Foam Roller: up to 470 SF/gal.
Drying Time
  • approx. 2 hours or until clear
Temperature Range during Installation
  • 32-100F
Relative Humidity Range during Installation
  • 20% - 90%
Packing Size
  • 2-1/2 gal. Metal Combo Pail (A+B)
  • 60 per pallet
Density [lbs./gal.]
  • 8.9
  • White
Color Hardener
  • White
Mixing Ratio
  • 1 Part A + 3 Parts B by weight
Pot Life
  • approx. 45 min @ 70 F (21 C)
pH value of concrete
  • resistent up to 14
  • above 32 F, not freeze/thaw stable
Shelf Life
  • 24 Months in original, unopened container
  • above 32 F, not freeze/thaw stable
  • UN 3082 Environmentally Hazardous Substance, Liquid, N.O.S., DOT Class 9
Revision: 2019-02-15 10:35:48

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