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T&G Plywood Flooring: Grades, Thickness, and a Surface That Stays Flat
T&G plywood flooring uses tongue and groove edges to turn a set of sheets into one continuous surface, and that surface carries a finish as well as a load. The grade sets the face you see, the thickness sets the load you feel underfoot, and the edges keep the seams tight as the floor moves with the seasons. This guide covers how to choose and install T&G plywood flooring so the deck stays flat and quiet.
Why T&G Edges Suit a Floor
A floor takes two kinds of load at once: the weight of what stands on it and the traffic that crosses it every day. The T&G edges spread both across the seam rather than letting one sheet carry them alone, so the finish above the deck stays level instead of dipping at every joint. The interlock is the reason a plywood floor performs better than loose panels.
One Deck, Not Loose Sheets
A butt joint relies on the fixings to hold two edges together, and the seam can open as the panels move. A tongue and groove joint holds the edges in line as well, so the deck resists a step at the seam and the finish above it stays smooth. The interlock does the work that fasteners alone cannot.
The tight seam also keeps dust, drafts, and spills from passing through, which matters under a floating finish or over a heated space. The edges then serve the surface as well as the structure.
Movement and Squeaks
A floor moves as the air changes, and a loose seam rubs as it moves, which produces the squeak a homeowner hears at night. A glued T&G joint holds the edges together so they move as one and stay quiet. The glue turns a set of panels into a single floor.
Fastening alone leaves a seam free to rub, so add adhesive along the joint as well as the joists. The extra step costs little and removes the sound that a loose deck would make for years. A glued seam also stiffens the floor across the whole surface, so the finish above it feels solid rather than spongy.
Humidity moves a floor more than temperature does, so a panel laid in a dry season gains moisture and swells as the air changes. The gap at the perimeter gives that swell somewhere to go, and the interlock holds the seams in line while the deck grows.
Choosing Grade and Thickness
The grade and the thickness decide how the floor looks and how it feels, and the two together set the price. A floor that carries the inner grade and a sound thick core holds up underfoot, while a thin utility panel flexes between the joists.
| Use | Thickness | Face grade | Finish |
|---|---|---|---|
| Hidden subfloor | 18-19 mm | Utility | Under a finish |
| Exposed floor base | 18-19 mm | Mid | Painted or sealed |
| Heavy traffic | 22-25 mm | Good | Sealed |
| Over heated space | 18-19 mm | Mid | Sealed both sides |
Face Grade for the Floor
A hidden subfloor takes a utility face because the finish covers the panel, while an exposed floor base shows the face and needs a mid grade at least. Choose the face the finish demands rather than the highest grade on the rack. A clean face then saves sanding while a hidden panel saves money.
Seal both sides of a floor panel that sits over a heated or a damp space, because the two faces take moisture from different directions. A panel sealed on one side alone cups as the other face swells, and the finish above it lifts at the edge.
Thickness for the Load
A thicker panel carries more load and flexes less underfoot, which matters in a hall or a kitchen where traffic crosses a long span. A thinner panel suits a low-traffic room over a tight joist spacing. Read the span rating against the joist spacing before you choose the thickness.
A panel that spans beyond its rating feels spongy and wears the finish above it, so match the rating to the supports rather than guessing. The rating states the widest spacing the panel takes. Where the rating and the thickness disagree, trust the rating, because it reflects the way the panel is built rather than the raw measurement.
A finish that resists flex, such as tile or a thin laminate, needs the stiffest deck the budget allows, because a small movement cracks the surface from below. Build the deck for the finish, and the finish then stays whole. A flexible covering tolerates a thinner deck, so the surface above the panel decides the thickness as much as the load does.
Run the numbers before the order, because a small step up in thickness costs far less than a floor that fails under a heavy finish. The stiffer deck then carries the finish and the traffic without a complaint.
Installing T&G Plywood Flooring
Install the deck so the tongue faces the open side and each new sheet slides into the last, then fasten along the joists and glue the seams. Leave a small gap at the perimeter so the floor expands without lifting, and stagger the seams so no joint lines up across the room.
Layout and Stagger
Stagger the end joints so a seam never lands beside a seam in the next course, because aligned joints form a hinge that lets the floor flex along a straight line. An offset layout spreads the seams across the deck and keeps the surface rigid. The stagger costs nothing and stiffens the whole floor.
Start the first sheet square to the room and work across, because a floor that starts out of square stays out of square to the far wall. A chalk line and a quick check keep the courses true.
Fastening and Finishing
Fasten at every joist and glue the seams, then drive the heads flush so the finish sits flat above the deck. Fill the fixing heads and any gaps with a floor filler before the finish goes down, because a hollow left under a finish becomes a soft spot. A flat deck then takes a paint, a seal, or a covering without a ridge.
Sand light and seal both faces where the floor shows, because a sealed panel resists spilled water and a change in humidity. The seal also keeps the exposed face from staining as it dries. A floor that takes regular water, such as a kitchen or a utility room, earns a heavier seal than a dry bedroom floor.
Framing and Layout Checks
Check the joists for level before the lay, because a floor laid over a high joist rocks and a floor over a low one dips. A straightedge across the frame shows the spot to plane or pack, and the fix there is far quicker than a floor that flexes against the framing. A level frame gives the T&G panel the flat bed it needs to lock into one surface, and the finish above it then sits true.
Plan the courses before the first cut, because the floor works best when each sheet lands so the seams fall over a joist and the offcuts stay useful. A quick layout sketch shows where the sheets meet and turns the order into a list rather than a guess.
Store the panels flat and dry before the lay, because a sheet that takes a bow in storage keeps the bow in the floor. A dry, flat stack delivers a deck that sits true from the first course to the last, and a sheet left on edge takes a curve that no amount of fixing will pull out.
Frequently Asked Questions
Short answers to the questions that decide a T&G plywood floor.
Is T&G plywood good for flooring?
T&G plywood works well as a flooring base because the tongue and groove edges lock the sheets into one flat deck that spreads load and resists a seam step. Choose the thickness for the traffic and the face grade for the finish above it.
What thickness plywood for flooring?
Use 18 to 19 mm for most floors and step up to 22 to 25 mm where traffic is heavy or the span is wide. Match the panel to the joist spacing and the span rating so the deck stays rigid underfoot.
Can you use T&G plywood as a finished floor?
T&G plywood can serve as a finished floor where the face grade is clean and you seal it against spills and humidity. Sand light and seal both faces so the panel stays flat and resists water at the surface.
For flooring panels with the grade, thickness, and edge profile a deck needs, HYY supplies Commercial Plywood, Melamine Plywood, and MDF Board, so the floor arrives ready to fix and finish.