First, you will need to sand the sheet down to make it smooth for applying the primer with multiple coats, then let it dry. You can also apply a resin filler, wait for it to dry and then sand it down again. If you want to apply a primer over the resin filler you will need to prime it twice.
The rougher side of the sheets are kept upwards, but structurally it makes no difference which way it goes.
To apply a sealing coat, soak the paintbrush in your chosen sealer and brush it over the OSB all over making sure to coat the edges. Allow this to dry for 12-14 hours.
Apply a thin even coat of satin on the flooring. If you require it to be darker, apply a second coat and allow it to dry.
The most common thickness for flooring is 18mm, for walls, it's 9mm, and for roofs, it's 11mm.
OSB panels that get wet or moist can swell up around the edges.