How to Prepare Concrete Subfloor for SPC Flooring Moisture Test and Leveling
Concrete subfloors require specific preparation before SPC installation. Moisture from the concrete can damage the flooring over time. An uneven surface causes clicking and locking issues. This guide covers the complete preparation process.
Moisture Testing
Test the concrete moisture level before any other preparation. The calcium chloride test is the most reliable method. Place a test kit on the concrete surface for 60 to 72 hours. The result tells you the moisture vapor emission rate.
Acceptable levels for SPC flooring:
- Under 3 pounds per 1000 square feet per 24 hours: no vapor barrier needed
- 3 to 5 pounds: vapor barrier recommended
- Over 5 pounds: vapor barrier required
If the moisture level is above 8 pounds, consult a flooring professional. High moisture may indicate a drainage problem that needs fixing first.
Surface Cleanliness
The concrete surface must be clean and free of contaminants. Remove all dust, dirt, oil, grease, and old adhesive residues. Use a concrete cleaner or degreaser for stubborn spots.
Sweep and vacuum thoroughly after cleaning. Any dust left on the surface will prevent the underlayment from laying flat.
Leveling the Concrete
Check flatness with a 2 meter straight edge. The concrete surface should not vary more than 3mm over 2 meters. Mark any high spots and low spots with chalk.
Grind down high spots with a concrete grinder or angle grinder. Fill low spots with self leveling concrete compound. Apply the leveling compound according to manufacturer instructions and allow it to cure fully.
Cracks and Patches
Fill any cracks in the concrete with a patching compound. Cracks under 2mm wide can be filled with crack filler. Wider cracks may indicate structural movement.
For large patches or repairs, use a cement based patching compound. The patch must be level with the surrounding concrete after curing.
Vapor Barrier Installation
For concrete with moisture levels above 3 pounds, install a 6 mil polyethylene vapor barrier. Roll out the barrier across the entire floor area. Overlap seams by 6 inches and tape them with vapor barrier tape.
Extend the vapor barrier up the walls by 2 inches. This prevents moisture from traveling up the wall and under the flooring at the edges.
Underlayment Installation
Install underlayment over the vapor barrier. Use a 1mm to 2mm foam underlayment designed for SPC flooring. Do not use thick underlayment that can cause the locking mechanism to fail.
Trim the underlayment to fit the room. Tape the seams to prevent shifting during installation.
Final Check Before Installation
Before starting the SPC installation, do a final check:
- Concrete is dry: moisture test within acceptable range
- Surface is flat: no variation over 3mm per 2 meters
- Surface is clean: no dust, debris, or contaminants
- Vapor barrier is properly installed if needed
- Underlayment is smooth and taped at seams
About PROLEADER provides detailed subfloor preparation guidelines with every SPC flooring order. Contact us for pre installation checklists and technical support.
