Why you still need 6mil moisture barrier?

 SPC is waterproof from above. Concrete releases moisture from below. This barrier blocks the moisture before it reaches your floor. 

Concrete slabs leak vapor every day, forever. Without a barrier, that moisture creeps into your SPC floor and causes: 

🔸 Cupping and gapping

🔸 Click-lock failure and squeaks

🔸 Mold and odor under the planks

🔸 Voided warranty — most SPC brands require a barrier over concrete

A 6 mil barrier stops it 

Use It On 

• Concrete slab (ground floor) 
• Basements (passing moisture test)
• Any concrete subfloor 
• Crawl spaces with sealed concrete below

Do Not Use It On 

• Wood subfloors upstairs — traps moisture, rots the plywood  
• SPC planks with a built-in vapor barrier pad — check your plank's spec sheet 
• A wet slab — fix the leak first, a barrier won't save you 

How to Install 

• Clean the slab. Patch any cracks wider than 1/8 inch.
• Roll it out, printed side up, along the longest wall.
• Overlap seams 6 to 8 inches using the white guide line.
• Tape seams with moisture-resistant seam tape (sold separately).
• Run the barrier 2 to 3 inches up each wall. Trim after baseboards go in.
• Do not puncture. Cut around obstacles, do not tear.

My SPC is already waterproof. Why do I need this?

SPC blocks water from spills above. This barrier blocks vapor from concrete below. Two different jobs.

Installing upstairs over plywood — do I need it?

No. Skip it. A vapor barrier over a wood subfloor traps moisture and will rot the plywood.

Can I just use plastic sheeting from a hardware store?

Same thickness, but no printed grid, no overlap guide, and no quality control for flooring use. Misaligned seams are the number-one reason barriers fail.