You might get away with using ordinary ply if you already have it or want to save money but virtually any flat plank or ply should do the job as you say you screw it into the bottom rail from the inside of the garage making sure it overlaps the ply panel above by a few inches.
Repair rotted garage door bottom panel.
Sand down the area of damage and apply a layer of prepared auto body filler to fill in the dent and any voids on the door s surface.
Wooden door dent repair.
Inspecting the garage door for rot signs is very important.
I used a sheet of exterior grade plywood to cut new panels and wedge them into the grooved opening where the old panel sat.
The most susceptible areas to wood rot are the frames and bottom parts of the garage door.
I used 18 gauge brad nails to pin them in place.
Dig out any rotten wood.
Even without damage dampness is enough to cause wood rot.
Then coat the rotted door frame area with wood hardener as shown.
How to use epoxy on wood for repairs.
Caulk around the exterior side of the panel for added protection.
After the filler hardens sand it smooth with the surface.
Paint and prime the new piece of panel.
Mix up two part automotive filler.
Fit the new piece of panel into the hole and use caulk and finish nails to attach the quarter round back around the interior of the panel to secure it in place.
The 2 bottom panels are the most common to get damaged.
Inspect the garage door for wood rot.
With the new panels in place i then applied a bead of glue to the pieces of round molding.
Watch this video to find out more.
To repair rotted door frame first remove rotted wood with a 5 in 1 or other sharp tool.
Replacing the panels on a garage door when.
Mix polyester wood filler or bondo wood filler and press it into the recess with a putty knife.
Fill the void with the filler.
You need to identify the specific parts of the door that are deteriorating.