R540 Moisture Barrier/Primer by Bona

New Product Professional Use

5 L
In stock
Free Delivery
Quebec, Ontario · More info

Bona R540 is a polyurethane reactive primer that is compatible with the entire Bona Adhesive System. It is specially designed to mitigate vapor transmission on absorbent and non-absorbent floors, including Gypsum-based underlayment.

Only one coat needed when used with 1250G or 1500G trowel and any Bona Adhesive. Two coats required in all other installations when the above criteria is not met.

  • Helps mitigate potential moisture issues, like cupping, originating from below the membrane, in new and existing construction
  • One coat can be used for damp proofing concrete subfloors up to 95% RH & 18 lbs.
  • Dries fast allowing nail-down installation immediately
  • Easy to apply with a roller
  • Suited for underfloor heating
  • Radiant heat systems will have a maximum moisture protection of 6 lbs or 80% RH

For Professional Use Only

Directions for use


Moisture testing

For concrete slabs, conduct moisture testing per ASTM test methods F1869 “Test Method for Measuring Moisture Vapor Emission Rate (MVER) of Concrete Subfloor Using Anhydrous Calcium Chloride”, and/or F2170 “Test Method for Determining Relative Humidity in Concrete Floor Slabs Using in Situ Probes”. Contact ASTM International to obtain copies of the test methods before proceeding. Use one of Bona R540 Moisture Barrier Sealer at a coverage rate of 400 square feet per 5-liter jug prior to installation of hardwood flooring with a Bona adhesive and the 1250G or 1500G trowel when MVER using ASTM F1869 (Calcium Chloride test) exceeds 12 lbs/24 hours/1000 square feet or when using ASTM F2170 (RH probe test) exceeds 85% relative humidity. The maximum moisture content should not exceed 18 lbs/24 hours/1000 square feet or 95% relative humidity. When using a Tramex measuring device to identify moisture levels in cementitious based substrates, use the Tramex measuring device to find the highest reading in the area to be installed and then run the CM testing method where you have recorded the highest reading. As a general guideline for floors with no infloor heating system, if the Tramex is below 4%, the Bona R540 will not be necessary and between 4% and 6%, Bona R540 will be required. However, the CM method must be used to make final determination of concrete moisture levels. As a moisture barrier where Bona Adhesives in conjunction with the 1250G or 1500G trowels will not be used, Apply two coats of R540 at a coverage rate of 400 square feet per 5-liter jug. The maximum moisture content should not exceed 18 lbs/24 hours/1000 square feet or 95% relative humidity for moisture content and quality of substrates, the guidelines of the wood floor manufacturer must be observed. Wood subfloor MC not to exceed 20%. Do not use more than one coat of R540 on any wooden subfloor system.

Acclimation and site conditions

Building climate control systems must be functioning with a temperature of 65°- 80°F and maximum relative humidity of 70% for 72 hours before flooring is installed, during installation, and for 72 hours after installation. Acclimate flooring according to manufacturer's instructions. Acclimate Bona R540 Moisture Barrier Sealer and Bona R851 or R859 Adhesive to the room temperature of installation; usually overnight.

Substrate preparation

Substrate must be clean, smooth, dry, free of loose material and structurally sound, with the surface slightly textured for best adhesion (similar to a light broom finished concrete). Remove adhesive residue, paint, concrete curing compounds or other contaminants that may affect adhesive bond. Sandblasting, shot blasting or scarifying may be necessary to completely remove some of these residues. Surface cracks, grooves, depressions, control joints or other non-moving joints, and other irregularities must be filled or smoothed with a Portland Cement-based patching and/or leveling compound. Substrate must be level to 3/16” in a 10-foot span. Slab temperatures must be between 55° and 95°F. NOTE: If a concrete slab needs to be leveled, Bona R540 Moisture Barrier Sealer should be applied to the slab prior to application of the leveling compound. Dry sand should be broadcast into the last coat of R540 (while wet) prior to the application of leveling compounds. Always refer to leveling compound manufacturer’s recommendations for detailed installation instructions. Other suitable substrates include wood and radiant heat flooring (refer to manufacturer’s recommended installation instructions).

Product limitations

Bona R540 is designed to reduce moisture vapor emissions that originate from below the membrane only. It does not affect other issues originating from the top, sides or ends of flooring (water leaks, puddles, hydrostatic head, etc.) nor does it eliminate other moisture or installation related issues such as improper acclimation of flooring or the effects of jobsite temperature and humidity.


  • On wet, contaminated, or friable surfaces
  • Over concrete curing compounds, sealers or other surface treatments that could affect adhesion
  • On areas subject to hydrostatic head
  • On cutback residue, or over vinyl/VCT/LVT
  • On chemically treated woods (stain, preservatives, etc.)
  • As a leveling compound
  • As an adhesive


Working out of a paint tray, pre-saturate a roller with Bona R540. To minimize product set up, work in 4’ by 10’ sections, and no more than 4’ x 20’ sections. Pour a 3-4” puddle of product spanning the width of the area you wish to seal, about 2’ from starting wall. Roll out Bona R540 in 4’ sections, 2’ on either side of the poured puddle. Work across the floor until section is complete. Repeat, pouring a new 3-4” puddle 2’ from the previously rolled section. Be sure to overlap into previously section. Continue working in this manner until the entire floor is sealed. As a primer, roll Bona R540 evenly to the substrate using a high quality ¼" nap roller, or similar, at the rate indicated in the chart on page 4 of the product Technical Data Sheet (available on this page). Avoid the formation of puddles, or heavy spots. Allow to dry to a transparent film. If used as a moisture barrier over cementitious substrates, and a second coat is needed, apply within 24 hours. When used as a vapor retarder for nail down installations only, allow R540 to dry 1-2 hours or when dry to the touch. When using R540 in conjunction with Bona R850T, R851, or R859 adhesives, whether as a nail-glue assist or full trowel, dry time of R540 is a minimum 16 hours and a maximum of 48 hours.(For R880, dry time of R540 is a minimum 4 hours and a maximum of 48 hours.) Higher temperatures and higher relative humidity may decrease dry times while lower temperatures and lower relative humidity will increase dry times.


Classification Wood Glues
Brand Bona
Size 5 L
Sold Since July 6, 2022
SKU BR54002200USBO
UPC 737025016227
Drying Time

1-16 hours - See application information
Cure Time : 24 hours


Per 5 L jug:

  • When used as a vapor retarder on unsealed wooden subfloors: 1 coat at 300-400 square feet.
  • When used as a primer on sealed subfloor systems: 1 coat at 400-600 square feet (test for compatibility).
  • For moisture barrier protection (up to 18 lbs or 95% RH) on concrete: 1 coat at 400 square feet (when used with Bona 1250G or 1500G trowel and any Bona Silane Adhesive).
  • For any other installation not meeting the above criteria, apply two coats, each at 400 square feet.

0 g/L




Brown transparent liquid


Store in a climate-controlled environment. Keep from freezing. Do not store for extended periods above 32°C (90°F)

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