Pro Tips

Pro Tips for Moisture Vapor Barrier Installs

Objectives: The objective of installing a moisture vapor barrier product is to minimize the chances of MVE related coatings failures.


  • Insufficient absorption
    • A CSP of 3 or greater is absolute necessity, not only for, mechanical bond purposes but particularly to maximize the porosity of the slab cap. Porosity and absorption are directly related to one another. For example, vinyl seat covers are great for when you have toddlers because they are not porous. So that chocolate milk and grape juice is not absorbed into vinyl. Cloth seats on the other hand are exactly the opposite. In the coatings industry absorption is a desirable thing for our first coat of product, particularly when that product is intended to serve as a barrier to moisture vapor. A CSP of 3 can be achieved with 24 grit diamond on a grinder. But, if you, fail to set a measurable objective “like CSP 3” and hit it, you are wasting your time. Just “saying” you ran a 24 grit diamond might make you feel better for now, but the objective is to hit a surface profile of three or greater. If you do not have a surface profile meter then you need to lean towards the side of excessive prep.
    • One good test we like to do is save one spot of the slab un prepped then once we have achieved the correct surface profile, we pour water on both areas. The prepped area should absorb water more rapidly and more of it than the un prepped area. If this is not the case then you are probably wasting time and money installing your moisture vapor barrier product.
    • If absorption is desirable then you need to account for some % of your product disappearing into the slab, and as it does it will displace air “and the air is going to move to the surface”.
  • Insufficient Millage:
    • IF you created enough porosity with your profiling, then you are going to have a hard time getting more than 120 sq. ft. per gallon out of a good moisture vapor barrier product. Why? Because a significant percentage of the material is not absorbed into
      the slab.
    • If you are able to roll out a good moisture vapor barrier to 150 sq. ft. per gallon than you probably have not prepped the slab thoroughly.
    • This begins us to the next hazard
  • Outgassing/Bubbles:
    • Outgassing is a direct result of your product displacing air in the pores of the slab. THIS IS A GOOD THING! If your product does not displace the air in the pores of the slab then you are not going to establish and adequate bond nor an adequate barrier to moisture vapor.


  • Prep/Profiling:
    • Shotblasting is the most effective way to achieve maximum porosity and ensure mechanical bond and absorption. That does not mean, however, that you can not adequately prep a slab with a diamond grinder.
    • All of the usual fundamentals apply “cracks properly chased and filled, shot holes filled, contaminants removed, edges/perimeter of penetrations profiled”.
    • If you prep the floor with grinders, the residual dust will your worst impediment to absorption of the moisture vapor barrier! Read that again. Why go to all the effort to achieve the CSP 3 and then blow it by not removing all the fine dust from the pores you opened up.
    • If you vacuum wand attachment is not sticking to the floor from suction as you pull it across the floor then you are not removing the residual dust.
    • Do NOT allow the floor to get wet while it is dusty because it will turn that dust to mud and embed it into the pores where your vapor barrier needs to go.
  • Mixing:
    • Set Up Staging Area for Materials, Tools, & Supplies
    • Set up a Mix station with adequate room and light to be able to move and mix without knocking things over. Also, have enough room to be able to see and work around all your Part A’s and Part B’s.
    • Mix product only when all personnel and equipment are in place ready for application.
  • Application:
    • Skim/Primer Coat:
      • This one step will mitigate the hazards of inadequate absorption as well as outgassing/bubbles when done correctly. It does take a little extra time.
      • Using either a steel trowel or a pole scraper spread the product slowly as thin and tight as you can. You will need spikes if you are using a pole tool. If using a steel trowel you need to focus on dragging every square inch three to five times with the product. The objective is to saturate the slab “ to rejection” much like we teach broadcasting to rejection. The more porous the slab the more time
        you will have to spend to get slab to rejection. But we are only talking about an extra hour per 1000 sq. ft…if that much.
      • Once the slab is loaded to rejection with your moisture vapor barrier you can then begin the roll out to achieve the proper coverage rate.
      • On a moderately pores “normal slab”, you can expect 1/10 th of your total product loading the slab to rejection “skim coatings”.
      • Rolling out then becomes fast and easy. Additionally you will notice the consistency of your roll out is much better.
      • During the roll out keep a window squeegee handy so that if and when you notice any bubbles or fish eyes you can use the window squeegee to “scrub” the area with fresh material which will help force the product to displace any remaining air.
      • After your roll out you will need to stick around for at least 30 minutes to address any outgassing spots via squeegee scrub and roll out.

Post Application Repairs:

  • In the event that the product did outgas after you left the project and you have bubbles cured into the floor they will need to be addressed prior to an subsequent coatings.
  • Abrade the bubbled area with 60 grit sand paper, vacuum, and apply a tight fill Bondo with a steel puddy knife. This will cure within 15-30 minutes depending on temperature and be sandable and ready to coat.


  • Moisture vapor barrier epoxies “full resin” are by nature thick “viscus”, slow curing membranes.
  •  The application of moisture vapor barrier epoxy is not a good “shortcut” step for time. It is very similar to prep work. Do it correctly and invest the necessary time, and you will reap the rewards later on in the installation and for the year of the life of the product you are putting down.
  • These Pro Tips are intended to be a helpful guide and are not exhaustive installation instructions.
  • For further details or specific questions about installations or products please call your local RFS representative.

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