Moisture from the ground can ruin flooring months after a project closes. The vapor barrier is the cheapest protection, if it is installed right.
In this article
Why it matters
Moisture from below damages flooring and adhesives and can cause odors and mold.
Material
Use the thickness and class specified for the project.
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Laps and seams
Overlap and tape seams according to the manufacturer.
Penetrations
Seal around pipes and conduits with boots or tape.
Protection during the pour
Repair punctures from rebar chairs, foot traffic and equipment before concrete arrives.
Inspection
Walk the barrier before the pour and photograph it.
Coordination
Plumbers and electricians must know the barrier is in place.
Getting started
Add a vapor barrier walk to the pre-pour checklist.
Common mistakes
Untaped seams, unsealed penetrations and punctures left unrepaired.
Example
A general contractor added a photographed vapor barrier walk before every slab pour. Flooring moisture complaints on later projects dropped sharply.
Pre-pour walk checklist
Seams lapped and taped, penetrations sealed, punctures repaired, edges turned up where specified and photos taken.
What to track
Repairs found during the walk and flooring moisture issues reported later.
Talking with the trades
Remind plumbers, electricians and rebar crews that the barrier is in place and that any puncture must be reported and repaired before the pour.
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Frequently asked questions
Why is a vapor barrier needed under a slab?
It limits moisture moving from the ground into the concrete, which protects flooring, adhesives and indoor air quality. Damaged or poorly sealed barriers lose much of that protection.