Subfloor Preparation & Moisture Control
Subfloor inspection standards, moisture testing methods, leveling compounds, vapor barriers, concrete cure requirements, and moisture barrier primers.
- Identify the tools used for measuring subfloor moisture content
- Explain the purpose and placement of vapor barriers under flooring
- State the maximum subfloor variation allowed for hardwood installation
- Describe concrete cure time requirements before flooring installation
- Explain the purpose and application of leveling compounds and moisture barrier primers
Leçon 1
Subfloor Inspection & Flatness Standards
Why Subfloor Preparation Matters
Every successful flooring installation begins with the subfloor. A subfloor that is uneven, dirty, damp, or structurally unsound will cause every flooring type to fail - hardwood will buckle, tile will crack, vinyl will telegraph, and carpet will wrinkle. The Red Seal exam places heavy emphasis on subfloor preparation because it is the foundation of the entire trade.
Flatness Standards
The maximum subfloor variation allowed over 10 feet for hardwood installation is 3/16 inch. This is a critical number you must memorize. If the subfloor exceeds this tolerance, it must be corrected with leveling compound, grinding, or plywood overlay before installation begins.
Vinyl flooring has an even tighter tolerance because it is thin and flexible - every bump and dip in the subfloor will show through. This defect is called telegraphing, where subfloor imperfections become visible through the finished floor surface.
Types of Subfloor
| Subfloor Type | Common Uses | Key Concerns |
|---|---|---|
| Plywood | Most residential installs | Check thickness, moisture, flatness |
| OSB | Budget residential | More moisture-sensitive than plywood |
| Concrete | Commercial, basements | Moisture, pH, cure time, flatness |
| Existing flooring | Overlay installations | Adhesion, height clearance, condition |
Inspection Checklist
Before any flooring goes down, the installer must verify:
- Flatness within tolerance using a 10-foot straightedge
- Structural integrity - no loose sheets, squeaky areas, or soft spots
- Cleanliness - no dust, paint, drywall compound, or debris
- Dryness - moisture within acceptable limits for the flooring type
- Fastener condition - all screws or nails set flush or below surface
The maximum subfloor variation for hardwood installation is 3/16 inch over 10 feet. If the subfloor does not meet this standard, it must be corrected before installation begins.