Wood – Is sanding hardwood floors really necessary

I hate to be the one to tell you this, but there is really no magic putty or filler for shallow scratches and gouges in hardwood flooring. Even though there are a lot of colored wood fillers on the market, they are not designed for high traffic flooring or nuclear dogs. If it was just a couple of scratches you might be able to sneak by with a filler, but not for a refinishing job in a larger area as you describe. Most engineered flooring has 3/16" to 1/4" of hardwood veneer over a plywood base. If the scratches have not gone through the veneer, then you can sand the scratches smooth, stain to match, and refinish with 3 to 4 coats of urethane. I would recommend an oil based urethane. Apply 3 to 4 thin coats rather than 1 or 2 thick coats. Remember, the veneer is fairly thin and usually can only be sanded and refinished 2 or 3 times at best. Once the scratching penetrates the plywood base, your floor is unrepairable.

My advise would be to protect the floors with area rugs, runners, etc or keep the dog's nails cut short, or better yet, train them to behave in the house.

(Bona fides: I sanded my house and a friends' about 10 years ago, and two rooms in my new house last year. I then went with a pro for the rest of the house — it's crappy work and not something I wanted to do again.)

Drum sanders are the fastest but also take a deft hand and careful attention — they can dig a groove in the floor pretty quickly, especially where you drop and pick them up on each run.

An orbital or vibrating sander is a lot easier for novices to handle, I would recommend these if your floors have already been sanded several times.

If you take on this job yourself, you should be aware of a few things:

• Sanding floors takes a lot of time to do properly. 1500 sq. ft. will probably take a week. There's the initial prep (removing molding, furniture, nails, and cleaning), three passes with different grades of sand paper, staining/sealing, screening that finish, then polyurethane three times, screening between each one. And lots of waiting time between applications of stain and poly. You'll also need hand sanders (a small drum sander works best) to get around the edges of the room, the floor sanders don't go all the way to the wall. Then you have to replace the molding.
• This is dirty work. Even the sanders with nice vacuum bags are going to leave dust all over the place and you should wear a mask. And hearing protection, depending on the type.
• Rental sanders vary in quality. Some rental shops take care of their equipment, but many do not. Best case, this can result in trips back when the sander is DOA. Worst case, the sander may sand unevenly and create grooves or circular patterns in the floor. Keep a close eye on them.
• If the floors haven't been sanded in a number of years, the older varnishes (and the wax buildup on top of them) is very hard to get off the floor and you'll burn through a lot of sandpaper (it gums up the paper and you have to replace frequently).
• Most rental places will let you return unused sandpaper for a full refund. Take advantage of this and buy 2–3× what you think you'll need, because those same rental shops probably aren't open on Saturday night or Sunday morning when you run out.