Water – How to know when the wooden floor has fully dried out post-flood

Plywood to build up the wood floor height is an appropriate way to address this problem. For use under carpet some regions may allow use of other products for this purpose such as particle board but plywood is still the best.

Installation of the plywood also gives an opportunity to firm up the floor and work at eliminating any possible squeaking in the old floor. It is best to screw down the plywood into the original floor joists. You can probably find where these are by looking where the old boards were nailed. It can be handy to apply some masking tape to the bottom of the adjacent walls and marking the location of the joist center lines so that after you lay down the plywood it is easy to locate the joints and snap chalk lines across the plywood for a screwing guide.

You may still need to do some special work at the plywood to concrete transition zone because there may still be some minor height variation after the plywood is installed. This can be handled by troweling in a layer of an appropriate floor leveling compound and feathering it out away from the transition zone.

NIOSH (National Institute Of Safety and Health) does not manufacture respirators or dust masks, they conduct research and make recommendations for prevention of worker injury/illness. If their name is on a respirator it means they approve of it's use for the manufacturer's stated purpose.

Generally. you should wear a particulate mask or respirator when sanding, mostly because of the chance for lead in old coatings. For old varnish the chance of significant lead exposure is slim and no volatile organics will be released.

However, you should wear a N99 dust mask or P100 particulate respirator anyway because breathing airborne dust when you don't have to is dumb. Ever blow your nose after working in a dusty field? Do you really want that stuff in your respiratory tract?