Dance Floor Refinishing

Update 2017-11-05: Don Veino tells me the Scout House has switched finishes: "We've been using Bona Traffic for several years now with great success and at a significantly lower cost due to much less prep and finishing labor plus extended durability. ... I'm not the expert, Jack O'Connor typically manages the work for us with the floor refinisher. My understanding is that it is a minimal typical screening (sanding with a mesh) and roller application (i.e.: per the mfgr. data sheet). It has worked out so well for us we went from a twice-yearly, out of commission for nearly a week process (which sometimes had to be redone due to curing problems) with the old finish to a once per year 1 day process. In fact, we recently decided to put off the annual refresh because the finish was still in good shape."

Mark Jones, who deals with the scout house floor, wrote the following on a mailing list I'm on in July 2010:

Here is the varnish that the Concord Scout Uses:

Type MC2
Urethane - Clear Gloss

Manufactured by:
Absolute Coatings
28 Portman Road
New Rochelle NY

It is a varnish that has high percentage of volatile organic compounds (VOC), and takes a week to cure properly when two coats are laid down. There is a potential that some day the Environmental Protection Agency will ban the manufacture of the varnish. It is the hardest varnish that the refinisher for the Scout House knows of. This varnish cures via a process that requires water to be in the air, and if applied in winter, industrial humidifiers should be rented to maintain humidity for sufficient water vapor to be present for the varnish to absorb. Otherwise the varnish will not cure and adhere properly.

The Scout House puts down varnish twice a year in a heavy-use envirionment, with at least two coats each time. The hall is put out of use for a week while the varnish cures.

Useful to know, when one changes varnish, one should sand a floor down to bare wood, so that the new varnish adheres properly to the floor. From a hall owner's perspective, sanding down to bare wood is EXTREMELY undesirable, since you get to do this only about four to six times over the entire life of a floor. Ideally, the only time a floor is sanded is immediately after installation of the floor.

What should be done ALWAYS for a public hall, if the varnish type is not changed, is to "buff" meaning scratch (not "buff" in the polishing sense) the previous varnish, without taking the floor down to bare wood (if there is any varnish left on the floor, after the neglect of failing to varnish the floor regularly), so that
  1. the wood is not touched and
  2. there's an opportunity to lay a coat on the prior existing varnish of the same manufacture.
All bets are off when changing varnish because of issues of adhesion of different varnish products.

In general, the individuals that damage a floor the the most over the lifetime of a floor are uninformed hall owners that don't know that one should NEVER SAND a floor down to bare wood without a very good reason, and floor refinishing companies that mostly sand floors of houses and do not care about the cost of replacing a floor. Such refinishing companies out of ignorance always take a floor down to bare wood, taking a lot of wood off the floor, and don't pay proper attention to avoiding gouges and uneven floor-sanding over a big area. The result of this combination is an impaired floor that eventually splits at the tongue and groove, when several tenths of an inch of wood is turned to dust over the course of five or six sandings.

The ultimate consequence of such floor maintenance is the installation of a floor at the cost of somewhere around $12 to $15 a square foot, which for a medium size hall might amount to around $20,000-plus dollars, and the shock and dismay that the improperly "well maintained" floor needs to be replaced.
I think, the ideal floor finish is something similar to an unfinished hardwood, like maple, with an attached large and carpeted lobby to remove grit, sand, water, and salt from shoes, but suitable only for a hall that does not have public meetings, or food or drink in the hall.

With public meetings and food, then it becomes more necessary to protect the wood from the visitors and food accidents, which leads to the whole varnish question, which is a big topic, and I admit I don't know much about what is available and possible, in my limited experience.
When I asked him more, he followed up with a "mini essay" about floor refinishing:
Floor Refinishing: A Primer

This lacks details about various varnishes itself a separate and substantial question.

Intended as a guide for how to think about the long-term value of the precious public hall floor, and on how to deal with refinishing companies. You get what you pay for from refinishing companies.

Fundamental: The hall owner's aim is to protect the capital investment in the floor from the people most able and likely to severely abuse the floor: the floor refinishers.

  1. Don't sand the floor!

    The correct technique is to "buff" the floor, to merely scratch (what is left of) the previous layer of varnish, to accept the next coat of varnish. Not intentionally sanding down to bare wood.

    Most hall administrators and maintainers are uninformed about the shortness of the life of a floor when sanded repeatedly. There are only five, or so, sandings that can be done to a floor.

    Sanding destroys the longevity of the floor, by needlessly removing as much as one-tenth of an inch of precious wood, and more where the machines gouge the wood.

    Five sandings times 1/10 of an inch each time equals half of an inch of wood turned into dust. Eventually the tongue and groove joints that fit each floor board to each other become so thin that the boards to split there, and the splinters caused by splitting boards mandate the installation of an entirely new wood floor.

    The cost of a new floor after the fifth or sixth sanding: at current prices, to buy floor boards, install, sand and varnish, about $12 to $15 a square foot, more or less. A small hall of 40 by 40 feet is 1,600 Square feet , and probably about US$ 20,000 to re-floor.

    Floor sanding companies will not advise to people to avoid sanding: they are in the business of sanding, and it's a bigger job and more money for them than buffing, and "sanding" keeps their labor force and equipment going. Most of those companies sand house- floors, which are sanded once or twice in their 100 year lifetime, and they are often unaware of the issues for a constantly-used and often-refinished floor.

  2. In general, use the same varnish, as previously was used, so that it adheres well to the previous layer of the same material, unless there are good reasons to abandon the previous varnish or it has mostly worn off. Changing varnishes _might_ cause pealing floor-varnish, if the new coating does not adhere well to the old varnish. Type of varnish to use its own separate question. Only sand the floor if it is necessary to change vanishes, and extremely minimally at that.
  3. Use, if possible, the hardest varnish available. There are a number of directions to go on the varnish front.
  4. Refinish regularly, so the underlying wood does not wear from abrasion, or exposure to food, water, salt, and ordinary use while unprotected. Annually or every two years is reasonable and desirable for a well-used hall and floor. Don't wait until most of the floor is down to bare wood. Once again, refinish without sanding, but rather by "buffing" (meaning scratching) the previous layer of varnish.
  5. Refinish with several coats of varnish: at least two, and better three, or four, or more layers if the hall owner intends NOT to refinish the floor for more than two years. Most commercial firms wish to get into a hall, and out, as soon as possible, and have no commitment to the long-term life of the hall, only to their fee and their next job. Here you get what you pay for. Most refinishers are on a tight margin, and closely scheduled. They are impatient to wait for a hall floor to dry for the vitally important two-plus days between each coat of varnish. (Some water-based varnishes do dry in less than a day and can be applied again within 24 hours or less).

    Beware of firms that proposed to "seal" a floor, then varnish on top of the sealer. The sealer dries quickly, allowing an immediate varnish coat, but the sealer does not allow the varnish to penetrate into the wood itself to protect the wood for the long-term uses of the floor and hall, and sometimes there are issues about the varnish adhering to the quick-drying sealer. The refinisher's hope is to apply one coat of sealer, and one coat of varnish, which is not even close to suitable for a public hall.

  6. Schedule the hall to be unavailable for at least a week, more is better, in case the curing process does not go as planned. The aim is for multiple layers of varnish to individually and completely dry before the next later is put down. Otherwise an uncured layer, buried under a dry layer of varnish will never dry, and cause trouble to users and the owner of the hall.
  7. Ultimately, doing this correctly, time after time, permits the hall-owner to have the valuable floor last another fifty-plus years, and avoid installing an expensive new wood floor.

Last modified by Jeff Kaufman: Sat Sep 15, 2012