Cvendet1:
You should be aware that there are much better choices for finishing your hardwood nowadays than there was only a decade ago. Nowadays, there's a newer technology that's replacing the "oil based polyurethanes" with a completely different kind of polyurethane that's very much harder and more durable.
There are two such products on the market that I know of now, and there may be others that I don't know about. In both cases, they're water based, and in both cases you add a small bottle of catalyst to a gallon jug of the "prepolymer", and then spread the stuff on your floor. The resulting coating is about 3 times as hard and durable as the "oil based polyurethane" we've been using since the 1960's.
Bona's "Traffic" is one of these new catalyzed waterborne polyurethane, and Basic Coatings' "Street Shoe" is the other:
Bona Traffic - Bona
Basic Coatings - Waterbased Topcoats
The only problem for you is that these finishes aren't as user friendly as the old oil based polyurethanes. If you discovered a problem with the old oil based polyurethanes, you could put the lid back on the gallon, and stop to rectify the problem. Not so easy with these new polyurethanes. Once you pour that catalyst in the jug of prepolymer, it's gonna start curing, inside the jug if it ain't on the floor. So, if you're thinking of hiring someone to apply the finish to your floor, make sure it's someone with experience applying these kinds of finishes. You don't want your floor to be a new learning experience for them.
Probably 10 years from now, it'll be these catalyzed waterborne urethanes will be the standard, and "oil based polyurethanes" will be extinct.
You don't need to know the rest:
Since 1956, when the Bayer Company (who also make Aspirin) patented the first "urethane modified alkyd", "polyurethane" has replaced Carnauba wax as the finish of choice over hardwood floors. Carnauba wax was soft by today's standards, and so it was normal for everyone with a hardwood floor to have a Hoover floor polisher to polish the wax on their hardwood floors. A coating has to be very soft to respond to polishing with a machine that weighs all of 10 pounds and draws about the same amperage as a clock radio.
The polyurethane that replaced Carnauba wax is really the cousin of the oil based or "alkyd" paint we use nowadays. Bayer modified the alkyd resin by adding something called di- and tri-isocyanates to the pot when cooking glycerine with something called "phthalic anhydride" (or, quite literally, what you have to add water to to make naphthalic acid. KoolAid crystals are "Koolaid Anhydride") When Bayer did that, the isocyanates reacted with the glycerine and they got urethane groups forming right inside the alkyd resins. Urethane groups are very strong, and they acted very much like the roll cage inside a race car, making that alkyd resin much harder if you tried to squeeze it, and much stronger if you tried to stretch it. The result was a "urethane modified alkyd" coating that dried to a considerably harder and stronger film than regular alkyd paint would dry to. So, polyurethane is kinda like alkyds on steroids.
Here, this drawing from this web page shows the basic components of alkyd resins:
Chem 381- CHAPTER THREE- Third Part
The things that look like crabs are phthalic anhydride molecules, the [CH2]n is supposed to be a fatty acid from a plant oil molecule (typically chemically modified soy bean oils) and the C-C-C where they all meet is a glycerine molecule. Now, imagine about 10 to 20 of those things shown in the picture all in a clump, and that's what an alkyd resin would look like.
Now, an "isocyanate" is anything with an -N=C=O group in it and a di- or tri- isocyanate will have two or three of them. An alcohol is anything with an -OH group bonded to a carbon atom, and a diol or triol will have two or three of them. Glycerine is a triol since it has three of those -OH groups all bonded to different carbon atoms. When you mix isocyanates with alcohols, you make urethane groups. Like this:
A-N=C=O plus HO-B gives you A-(NH)-(C=O)-O-B
and that ugly thing between at A and B is a urethane group or "urethane linkage".
Chem 381- CHAPTER THREE- part 4
So, by adding those isocyanates to the pot when cooking alkyd resins, then the isocyanates would react with the glycerine to form urethane groups right inside the alkyd resin, and it's those urethane groups that make "urethane modified alkyd" resins or "polyurethane" resins form significantly harder and stronger films than ordinary alkyd paints.
What companies that make catalyzed waterborne polyurethanes sell you is a jug and a catalyst. That jug contains tiny particles of glycerine already reacted with isocyanates to form little pieces of pure urethane plastic. Those tiny pieces are suspended in a solution of water, glycerine and a di- or tri- isocyanate that's soluble in water. You add the catalyst to the jug, and shake it up to ensure that the catalyst is fully dispersed in the jug, and immediately start spreading that solution on your hardwood. The solid plastic particles find themselves suspended in a glycerine and isocyanate soup with the concentration of the catalyst steadily increasing as the water evaporates. As the catalyst promotes the formation of urethane linkages between the glycerine and isocyanates, those solid particles of urethane plastic all get cemented together with more pure urethane plastic to form a solid sheet of pure urethane plastic over your hardwood.
Thus, your floor finish is made of the very stuff (urethane) that makes oil based "polyurethane" stronger and mure durable than oil based "alkyd" paint. The result is that the pure urethane coating on your floor is several times harder and more durable than traditional oil based polyurethane hardwood floor finishes.
(Some people think that this product is like a "latex" coating since it comes in the jug as a milky white liquid and dries clear. That similarity is only because the tiny particles of urethane plastic in the jug are clear in colour. So they reflect and refract light just like the water droplets in a clowd. Once the liquid dries on your hardwood to form a solid film, you no longer have those liquid/solid phase boundaries to reflect and refract light, and so the white colour disappears and you're left with a clear colourless solid film.)
