Subfloor Prep
Subfloor Preparation & Leveling for LVP
Subfloor prep is the part of a flooring job that nobody sees and everything depends on. A rigid plank floor is only as flat, dry and quiet as what it sits on. We offer prep as its own service because plenty of Idaho homeowners and contractors need the substrate fixed correctly — whether or not we are the ones installing the finish floor.
Flatness, not level
These are different things and the distinction matters. A floor can be perfectly out of level across a room and still install beautifully; what breaks a rigid plank floor is local deviation — a dip, a hump, a ridge at a plywood seam. Manufacturers publish tolerance as deviation over a span, commonly 3/16 inch in 10 feet. We map the room with a straightedge, mark every failing area, and correct only what actually needs correcting.
Self-leveling underlayment and patching
Small dips get feathered with a cementitious patch. Larger or more numerous deviations get a poured self-leveling underlayment over a primed substrate. On wood subfloors this requires the correct primer and often a reinforcing detail; poured over an unprimed or dusty surface, SLU debonds and you have made the problem worse.
Moisture testing and mitigation
Concrete: in-situ relative humidity probes per ASTM F2170, because surface calcium chloride tests tell you far less than the industry once believed. Wood: pin or pinless meter readings compared against the flooring manufacturer's allowable range, plus a look at the crawlspace, because a wet crawlspace under a vented Idaho foundation will keep re-wetting the subfloor no matter what you install on top. Where readings are out of range we specify a mitigation system or, honestly, a delay.
Squeaks, deflection and old material removal
Squeaks are movement between subfloor and joist and are fixed from above with structural screws before new flooring hides them forever. Excess deflection between joists needs blocking or an added layer, not thicker underlayment. Old tile, thinset ridges and cutback adhesive have to be mechanically removed and the surface brought back to a bondable condition.
What's included in this scope
- Straightedge flatness mapping and documentation
- Cementitious patching and feathering
- Self-leveling underlayment over primed substrate
- ASTM F2170 concrete relative humidity testing
- Wood subfloor moisture metering and crawlspace assessment
- Squeak elimination and subfloor re-fastening
- Tile, thinset and adhesive removal
- Plywood underlayment installation
Questions about subfloor prep
- Do I need leveling, or is my floor fine?
- We check rather than guess. A 10-foot straightedge across the room in several directions answers it in about ten minutes. Plenty of houses need nothing; plenty of others need three small areas addressed, not a poured floor.
- Can you do prep only, without installing the flooring?
- Yes. Subfloor prep is available as a standalone service for homeowners installing themselves and for contractors who need the substrate handed over ready.
- How long does self-leveling underlayment take to dry?
- Most products are walkable within hours and ready for a floating floor the same or next day, but glue-down installs generally need longer and the specific product data sheet governs. We schedule around the real number.
Get a written LVP estimate
We measure, check the subfloor, and put the scope in writing — including the prep work most quotes leave out.