# Wood expert



## Superpack (Oct 28, 2009)

Is anyone a wood expert enough to know what kind of wood to look for in creating one's own dance space, or in apartment/house shopping?

Regards,


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## Nestor_Kelebay (Oct 29, 2009)

The way I'm interpreting your question is that you want to know what kind of wood to use for a dance floor (that may be a selling feature to someone wanting to buy a house with a room for dancing.

In my opinion, ANY and EVERY one of the hardwoods used for flooring would be fine to use on a dance floor.  What's more important than the wood you use is the hardness and durability of the FINISH you put on top of that hardwood to protect the wood.  The harder and more durable that finish, the longer the floor will look good, and the less often it will be necessary to replace that finish to keep the floor looking good.

The hardest hardwood floor finishes I'm aware of are "Traffic" by Bona and "Street Shoe" by Basic Coatings.  Both of which are waterborne catalyzed polyurethanes.  When you hear that word "waterborne", don't think it means "latex", it doesn't.  It means that the product comes as a prepolymer of solid particles of urethane plastic suspended in water.  You add a small bottle of catalyst to the jug of waterborne prepolymer, shake, and spread that solution on your floor.  As the water evaporates, the concentration of the catalyst increases, and it then promotes the crosslinking of the urethane particles together to form a film of pure urethane plastic over the floor.  That film of urethane plastic will typically be about 3 times as hard and durable as the alkyd or "oil based" polyurethanes that have been used on residential hardwood floors since the mid-1950's.

Really, the "polyurethanes" that we use as "varnish" and that we have put on our hardwood floors since the 1950's are nothing more than modified alkyd paints.  They don't have any pigments in them to give the film colour and opacity, of course, but the fundamental difference between an alkyd resin in a modern "oil based" paint and a "urethane modified alkyd" resin in an "oil based" hardwood floor finish is that the urethane modified alkyd resins in the polyurethane will each be harder and stronger than the alkyd resins in the oil based paint.  That's because each of the urethane modified alkyd resins have urethane linkages inside them which make them harder and stronger than normal alkyd resins.

An alkyd paint resin is made primarily of three things;
1.  something called "phthalic anhydride"
2.  glycerine (which really should be called "glycerol" cuz it's an alcohol), and
3.  souped up fatty acids with lots and lots of unsaturated sites.

When you cook those three together, you get "clumps" of those souped up fatty acids, and each of those fatty acids  has lots and lots of unsaturated sites along it's length.

Wherever you have two unsaturated sites in close proximity on the same or different fatty acids, then O2 molecules from the air that pass between those two unsaturated sites will react and form a pair of C-O-C cross links that connect the former unsaturated sites together.  That process is called "auto-oxidation", and it's the reason why linseed oil will gradually dry from a liquid oil into a solid.  It's those C-O-C crosslinks that form to connect linseed oil molecules together that make the oil progressively more and more viscous until it's effectively a single huge molecule, and behaves like a solid.

Because the fatty acids used to make alkyd resin have many more of those unsaturated sites on them than the fatty acids in linseed oil, modern "alkyd" paints dry to a harder film in a few hours than the old linseed oil based paints did in a few days.  That's because the fatty acids in the alkyd resins have many more of those unsaturated sites, so there's very many more of those C-O-C cross links formed in an alkyd paint film than in a linseed oil paint film, and that results in a harder and stronger paint film than linseed oil can form.

To make the kind of "polyurethane" we use as varnish or hardwood floor finish, they add something called a di-isocyanate or a tri-isocyanate to the pot when making alkyd resins.  Remember that glycerine was an alcohol.  An "alcohol" is anything with a hydroxyl group (-OH) bonded to a carbon atom.  Glycerine has three such hydroxyl groups and each one is bonded to a carbon atom.  So, glycerine is an alcohol three times over, or a "triol".

Now, an isocyanate is anything with an isocyanate group (-N=C=O) group in it.

When you mix an isocyanate with an alcohol you produce a urethane linkage:

R1-N=C=O  +  HO-R2  =  R1-(NH)-(C=O)-O-R2

and that ugly thing between Reactant #1 and Reactant #2 is a "urethane linkage".

If the computer didn't automatically eliminate unnecessary spaces, it wouldn't have been hard to type the above chemical reaction more explicitly as:







And, when you add a di-isocyanate when making alkyd resins, the di-isocyanate reacts with the -OH groups on the glycerines inside the alkyd resins, and you get:

R1-OH  + O=C=N-R2-N=C=O  + HO-R3   =   R1-O-(O=C)-(HN)-R2-(NH)-(C=O)-O-R3

and so two isocyanate linkages connect the -OH groups of different glycerine molecules inside the alkyd resin.

Similarily, a tri-isocyanate would simultaneously connect three glycerine -OH groups inside the alkyd resin simultaneously, and would provide even greater strength and hardness to the alkyd resin.

So, if you add di-and tri- isocyanates to the pot when making alkyd resins, the clumps of fatty acids you get have urethane linkages inside them connecting various glycerine molecules together within that clump.  Urethane linkages are very strong, and they act very much like the roll cage inside a race car, making the alkyd resin much harder if you were able to squeeze one, and much stronger if you were able to stretch one.  As a result, alkyd based "polyurethane" forms a film that's much harder and stronger than one made from the ordinary alkyd resins in modern "oil based" paint.  That's because each resin in that polyurethane film has that urethane linkage roll cage inside it that makes it much harder and stronger than an alkyd resin without a urethane roll cage.

To make Traffic or Street Shoe, they leave out everything but the glycerine and isocyanates.  They just mix glycerine and di- and tri- isocyanates to get a solid clump of urethane linkages connecting glycerine molecules and the cores of the isocyanate molecules together.  These clumps are suspended in water, and when a catalyst is added, and the water evaporates, the clumps of urethane linkages find themselves in a bath of catalyst at an ever increasing concentration.  Those clumps of urethane linkages then form urethane linkages with each of their neighbors, and you get a film of solid urethane linkages on your floor, or a coating of nearly pure urethane plastic.

Since it was the urethane linkages that made alkyd based "polyurethane" harder and stronger than alkyd paint, pure urethane is much harder and stronger still than alkyd based "polyurethane".  Typically, Traffic or Street Shoe will be 3 times as hard and durable as any of the oil based polyurethanes you can buy in hardware stores to apply over a hardwood floor.

Bona Traffic - Bona

STREETSHOE® 275 Waterbased Wood Floor Finish The fastest-curing finish on the market, StreetShoe® is the industry benchmark for waterbased finishes. Available in four sheens. Ideal for all commercial, sports and residential applications.

Hope this explanation was clear enough for you to follow.  It's not really the wood you use that will make for a durable dance floor, it's the protective finish you use over that wood that makes for a durable dance floor.  Shoe leather should never touch wood.  You just replace the finish when it eventually wears off to restore the floor to it's original as-built condition, and whatever wood you use will last forever as long as you keep replacing the finish every few decades.  It's like asking how long a floor will last if you keep replacing the carpeting on it.


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