Here is how I have dealt with a similar situation. The POs were covering up damage on oak hardwoods with area rugs. I am guessing that in addition to their petÂs accidents, they shampooed the area rug in place which further damaged the floors. We found out about the damage two hours before closing on the house during the final walk-through. This is a very temporary solution and is not the correct way to fix the damage; the experts on this board can advise you how to do that. Wash the floor on your hands and knees (or sitting on the floor using a small amount of water, MurphyÂs oil soap, scrub brushes, scrubbies, and old terry towels- whatever it takes to clean the floor. Do a small section at a time, and rinse with clear water using a clean towel and dry each section thoroughly as you go along. Be careful with the waterÂdonÂt pour it onÂyou donÂt want to cause more damage than is already there. This will take a long time as you will be crawling around the floor. With a damp sponge mop using water and vinegar, rinse again. Remember while you need the water to clean the floor, water also damages the floor. DonÂt let pooling water sit on the floor. Dry it with a towel. On the stains you can try several things to at least lighten the color of the damaged spots. I used a combo of lightly sanding and household bleach. The stains have not disappeared, but they are lighter and cleaner. Wait till the next day or several hours to be sure the floor is completely dry and temporarily fill in the spots where the poly is gone due to damage of pet stains, water and sanding/bleaching by judiciously using a small amount of wipe-on-poly. Wipe-on-poly is for furniture and is not recommended for floors, but a small amount can fill in and blend the areas where the floor poly is completely gone. After the poly is completely dry, use a shine product. I used Holloway House Quick Shine for about $9.00 (Orange Glow does not work). I have added a few throw rugs and the floor looks about 50% better and will get me buy until I can have the floors refinished.

Get it as smooth as you can with the sanding. I don't think you can use a pad under 3/4" flooring. Your best bet is get it as flat as you can and put a plywood rated for underlayment on top of that. Underlayment plywood has no voids to give or flex like Luan or reguar 1/4" plywood will. You can put a paper or even roofing felt under it. I think the proper installation of that wood will be either nail or glue. If you glue, you shouldn't use anything but the underlayment under the wood. Glue wouldn't stick. Your best bet would be go to the manufacturer's website and look for installation instructions or help. If you can't find that, try to get a number. Flooring manufacturers look for any reason to dishonor a claim for adjustment. One thing done wrong and even if it has nothing to do with the defect, and they will usually disallow the claim. I laid floors for @ 15 years, but have been retired for 5 and I have never bought a floor because I made sure to do everything the way they said. When I didn't agree with them, I got pictures and kept them. You can't go wrong doing what they say...just keep records that you did it their way.

I realized after I posted that I just added more issues to think about; but you are correct there are tons of info and misinfo out there about floors in general. Nail polish remover is acetone, and what you removed was probably old-fashioned varnish which I think is soluble in acetone. I'm not sure acetone dissolves shellac - alcohol does that. It's not un common to have multiple different types of old finishes, for various reasons, (You might try some denatured alcohol, or vodka. I use grain alcohol which is the nuts, though sometimes hard to obtain because of laws trying to prevent people from misusing it. I actually have to leave NY and buy mine in VT, by preorder from a State source.) The cracks you see in August (and still now) are likely the narrow ones! Wait until late March rolls around after a full winter of heating. I can lose Bic pens in some of mine. That's when they are easiest to clean out, though. I wouldn't try anything other than emergency washing until the cracks are clean as there is no point moistening that junk in there. It's important that at the end of the season that the gaps are clean as they begin to swell back up. Dirt and debris trapped in the cracks as they close can compress the edges of the floor board, causing increasing gaps the next season. Of course old houses weren't built when there were effective vacuum cleaners so there's a lot of debris down there. As to washing: Murphy's has long been a standby, but has also acquired some (perhaps innaccurate) reputation as being hard to fully remove from floors prior to using poly urethane finishes. I will say this: about a decade ago I was visiting Montpelier, Pres. James Madison's plantation, (he was comtemporary pal of Thos. Jefferson) in VA. I happened to be visiting in the off season and got to wander around a bit more than most visitors. I climbed a staircase and encountered the curatorial staff working on an as-yet-unopened-to-the-public room. They were busily at work washing the floor of the room, with you guessed it: Murphy's and water. So if it's good enough for such an important and professionally cared-for house, it's probably good enough for mine. Otherwise I use Organic Linseed Oil Soap - imported from Sweden, doncha know. I got it from the site that sells the Silent Paint Remover. I find it's an excellent cleaner, smells nice and wasn't particularly expensive since I only use a little at a time. In olden days the floors were sometimes washed with lye, leached out of wood ashes, so I imagine a little Murphy's or Method won't hurt. Floors were also strewn with sand which was then swept up. (That's why you'll likely encounter sand in the cracks even if you're far from the beach.) Don't try washing unless you have a huge pile of rags on had to handdry the floor off at once. Yes, hand sanding or scraping is a one-room-at-a-time type project. More so than renting a drum sander. The only catch is how to meld the meeting point of applied finishes at the threshold when the adjacent rooms are not done all at once, if you don't have a raised threshold. One of the beauties of shellac is that it can be patched up or touched up, or joined together seamlessly anywhere, even in the middle of board in the middle of a room. It's not without its detractions however, the primary one being that it is not bulletproof the way modern poly is. OTOH, should trouble ensue you just clean the surface where the problem is of any wax and dirt and get out a brush and touch it up. It redissolves the old shellac, mixing it with the newly applied stuff and dries so the patch is invisible. Can't say that about any poly finish. You can get it completely off with rags and alcohol and start the whole thing anew if you want. The fix-ability and the reverse-ability have much to recommend it. It is also pretty easily DIY-ish, and cheap. You can search for more info using Google and here on thsi site. But be forewarned there is a LOT of anti-shellac prejudice out there by floor pros, and some people who are just repeating what someone else said. There are also some excellent reports by people who took the chance on it and are very happy. It is relatively slower to apply and more hands and kness sort of work. Don't try it unless you are in a warm-ish, but mostly unhumid time of year. You need to ventilate the room. It is not the worst stuff for breathing, but not benign either. Shellac itself (though not the carrier) is an organic product made from exudations of a beetle in India. I'm imagining you might be interested in seeing what can be learned from your floors. Here are two things to look for (get down on your knees with a good flashlight.) Look for little rows of holes running along the floor. The holes will probably close be together but the rows separated by about 21-27 inches apart. This is evidence of an early floor covering called ingrain carpet held down by tacks. Another thing to look for is evidence how the floor was finished originally (and to know if it has ever been sanded by modern methods). Drum and orbital sanders didn't exist, even sand paper as we know it didn't, so very sharp broadknives were used to scrape the floor flat and ready for finishing. If you hold a light at a raking angle in a place where the wouldn't have been much foot traffic, you may be able to see shallow 1/16th to 3/16 ths inch wide grooves on the surface. This are the still-remaining toolmarks of the original floor's finishing, you are looking at the hand-made work of the floor installer. If you can see the undersides of the boads, say y looking up at the first floor from the cellar, you may be able to see the saw pattern, which can tell you if it was made from logs using a hand-powered pit saw, circular saw, etc. This helps nail down the age of the building because of technology of locally available materials is often known pretty accurately. Have you sorted out which floors are the splintery-est? I have some fir and it has narrow, sharp, fierce splinters. The flat-sawn wide-board pine pretty mellow. Quarter-sawn oak strip is rarely that way. It's not uncommon to find many types of wood in a single house. It's worth learning the correct indentifications of both species and board type (flat, quarter, radial, T&G, butted, lapped, etc.) as sometimes choices of floor finishing techniques are limited by type of wood. Oh, I forgot to add: the reason I use old credit cards (and similar plastic things) to clean out cracks is that the edges and rounded corners are less damaging to the board sides within the groove than metal implements. Plus all the credit cards that are expired get another round of use if recycled into my floor tool box. Card companies used to send out plastic versions of fake ones they use to try and get you to apply for them. I was in plastic tool heaven, but, alas now the facsimiles are just cardboard. Another solvent to try is Soygel. It is particularly, though slowly, useful on floors. Leave it covered with plastic wrap for days, if necessary. Let time do the work, rather scraping it yourself. It also cleans up nicely which is something you can't say about most chemical strippers. All these solvents and the rags used to apply and clean off have the potential for spontaneous combustion. Either air them out on a line for days or dispose of them in a metal, closed container filled with water, and kept outside away from the house. HTH(elps) more than just adding to the overload. L. Here is a link that might be useful: source of Excellent Technical on Info on Care of Old Buildings (NPS Preserv. Briefs)

I might have set the face nails deeper and used filler in the nail holes and staple holes but definitely not between the boards. It is just going to pop out and floors look awful when the filler starts falling out. I also might have tried to bleach some of the stains to see if they would become less noticeable. Unless the filler is well matched and applied sparingly, the filler may just highlight the flaws. However, those are issues that a knowledgeable DIY or flooring person can address when they are working on their own house. As a remodeling contractor or a floor refinisher, those tasks require a fair amount of time and effort for unknown results that likely don't justify the expenditure. When working in an old house, the goal should be an appropriate appearance, not new. Old houses dont look right filled with plastic finishes and vinyl windows and acrylic tub surrounds.