Moisture Vapor Barrier

When a slab needs a moisture vapor barrier

Concrete on grade wicks ground moisture up all the time, and it leaves through the top as vapor. Seal it with epoxy and the vapor collects at the bond line until it pushes the coating off. A slab can feel bone dry and still emit too much to coat. The only way to know is to test before you buy resin.

Our concrete moisture testing guide walks through the three tests we run. In short:

• Plastic sheet (ASTM D4263). Free screening. Condensation or dark concrete under the sheet is a fail. A dry sheet is not a pass, it only means keep testing.
• Calcium chloride (ASTM F1869). Gives the moisture vapor emission rate (MVER) in lb per 1,000 sq ft per 24 hours. At or under 3 lb, a standard epoxy system can go down.
• RH probes (ASTM F2170). Reads relative humidity deep in the slab. Most coating makers set the limit at 75 to 80%.

Between 3 and 25 lb MVER, or 75 to 90% RH, is barrier territory: lay the barrier coat, then build the floor on it. Over 25 lb, visible dampness or standing water is a water problem, and no coating fixes it. Correct the drainage or grading, then retest.

South Florida slabs and basements

Around Pompano Beach, slab on grade over a high water table is the normal case, not the exception, and the air is humid enough that the slab has to sit at least 5 degrees F above the dew point while you coat. Test every slab here. More on local conditions at our Pompano Beach supply counter page. Below grade, the basement floor epoxy guide covers testing and building a system on a damp basement slab.

Epoxy moisture barrier or penetrating treatment

We stock two ways to handle a damp slab. Every number below is from the product page and its data sheet.

Which one to use

• EF-160 is the barrier we recommend for residential and commercial floors. Grind, lay it at the full 18 mils, then put any epoxy or polyaspartic system on top. It is built for damp, green or poorly prepared slabs and cold, humid conditions, with 8,000 psi compressive strength under the floor. Do not stretch the kit thinner than 18 mils; that is the thickness the rating is stated at.
• Premera Easy MVB is the low-odor route: zero VOC, one component, sprayed on. It goes on bare concrete, brick, mortar or tile, under FP1 and your coating, or ahead of a polishing job. It may etch glass and dull aluminum, and it is not for acid-contaminated concrete.

Either way, the barrier is the first layer, not the whole floor. EF-160 ambers in sunlight like any epoxy, so it always gets a base coat and a topcoat over it. The rest of the system is on epoxy coatings and primers.

Peeling, blisters and what a barrier cannot fix

Moisture coming up through the slab sits behind most bubbling, peeling and whitening we see, and it is the cause nobody tests for. If a floor is already lifting in sheets, nothing rolled on top changes it: the failed coating comes off, the slab gets tested, and the new system starts with a barrier. Why is my epoxy floor peeling ranks the causes, and epoxy floor problems covers bubbling and white haze.

A moisture vapor barrier is not a waterproofing membrane. EF-160 is not made for high hydrostatic pressure, and standing water pushing up through a crack needs the source fixed first.

Buying a moisture barrier from Latux

• Authorized dealer for every brand we carry. Everflow, Premera and the rest are on epoxy flooring supplies.
• Shipping. Free UPS Ground on orders over $150, and one EF-160 kit qualifies on its own. Pallets go by freight, quoted per job.
• Pickup. 2201 N Andrews Ave, Suite 108, Pompano Beach. Call ahead.
• Contractor pricing. Contractor, Distributor and VIP tiers apply at checkout with no code. Apply for a trade account.
• Help. Send us your test readings and square footage at (800) 413-1427, Monday to Friday 8 to 5, and we will spec the system. Data sheets are on technical data sheets.

Common questions

Do I need a moisture barrier under epoxy?

If the calcium chloride test reads over 3 lb, the RH probe reads over 75%, or the slab is on grade with no vapor retarder under it, yes. Below grade and in South Florida, assume you do until a test says otherwise.

Can I use a handheld moisture meter instead of testing?

No. A meter reads surface moisture and is fine for finding wet spots, but it does not measure emission rate. Confirm with calcium chloride or RH probes.

Can EF-160 go on new concrete?

On concrete cured at least 14 days. For a slab 14 to 28 days old, ask your Latux rep about a deep-penetrating primer first.

Can I put polyaspartic straight over EF-160?

Yes. EF-160 is a primer and base coat, and an Everflow epoxy or polyaspartic system builds on top of it. It has to be covered, because it discolors under UV.

How many EF-160 kits do I need?

One 3-gallon kit covers about 264 sq ft at 18 mils, so a 500 sq ft garage takes 2 kits. The coverage guide sizes the layers above it.