Refinishing old oak floor

Comparing methods and products for a reasonably priced, quality finish. January 28, 2002

A 50-year-old red oak floor, with lots of winter wood and dark grain, needs refinishing. I have received two very different proposals from subcontractors. The first to sand, stain and apply three coats of oil-based polyurethane and the second to sand, apply sodium dichcromate followed by a coat of "hard sealer", water soluble aniline dye, another coat of mahogany tinted PTO hard sealer followed by three coats of uralkyd. Can someone explain these two finishing techniques? I like the sample of the second proposal, but the price is much higher. How can I achieve the smoother, more natural finish of the second proposal more economically?

Forum Responses
From contributor B:
The first proposal is a standard procedure to a floor finish/refinish job. The second one is more complex and time-consuming, thus the difference in price. The "sodium dichromate" is a little different approach. Normally, potassium dichromate is used for a chemical change of color. The second step you mentioned is a hard sealer. This would seal in that color caused by the dichromate. What's confusing to me is the water-soluble aniline dye that is applied. I don't understand how this will work, but evidently it does. What that says is that a color dye is applied on top of the chemical dye color that has been sealed in with a "hard sealer". So this winds up with a different color from the chemical first color. Then a "toner" of mahogany made up of the hard sealer is applied--this adds more color in a small amount and evens out the overall color. Then all of this is topcoated with 3 coats of uralkyd (probably a polyurethane, either solvent or water base). I have some questions as to the dye stain application over a hard sealer, but if it works, it works. The second proposal involves more work and most likely looks the best because of the multi-layering process.

From the original questioner:
Does this second process take a great deal of expertise? Could another good floor refinisher handle this if they have the "recipe" and make some samples? Maybe we could save on labor rates?

From contributor B:
Yes. The person needs to know what he's working with and how it responds. It's a procedure that this particular finisher has evidently worked out. However, that is not to say another person with experience can't achieve almost the same look, without going through every step as described.

From the original questioner:

The process I described was $3.75 per square foot. This was the least expensive of four options he presented, the highest being $4.60 per square foot. Stairs ranged from $25-$45 per step (no risers or sides). I'm curious about your reaction to prices. He estimated it would take between 8 - 11 days to complete. Any suggestions on what to tell other floor refinishers to determine if they could do this job?

While $4.60 is definitely on the high side, $4 is an average price.

I understand the reason you want samples, but realize that the color/look you get from samples made with new red oak will not be the same as the look you get with 50-year-old floorboards, even with a multi-step stain/color process.

From the original questioner:
The difference in the samples (proposed) is in richness of color and depth of finish, the second being more of both. Is this only achieved through multiple layers of color and multiple sandings, conditionings and sealers?

From contributor B:
Let's see if I understand this pricing. Your standard finish of sand, stain, topcoat (3). This--the first option you described--was 3.75? And the one you like with all the steps was 4.60? Or are you saying that the same guy (the one with the finish you like) gave you a price with 4 options ranging from 3.75 to 4.60? If you are saying the first option was 3.75 and the best one (you liked) is 4.60, then you definitely are getting your money's worth with the last option. Basically, you are getting a "furniture" finish with the higher option. This is more than your average floor finisher would do.

There may be other ways to get the richness and depth of color than the sodium bicarbonate, but in order to get the look, multi-layering is necessary to some extent. Dyes are the most-used way of doing this. This guy is using dyes, and evidently he knows about chemical dyes and effects.

Did he do the sample on old flooring or new flooring? Will he get the same base from which to work if the floors are 50-100 years old? Even after sanding. Maybe that's the reason for the chemical dye change. I believe it's going to depend on what the floors look like after the initial sanding to remove existing finish.

The only problem with multi-layered furniture finishes on flooring is that you could wear through layers of color if the glaze coats are not "buried" deep enough in the finish. It sounds like he is doing this but I am always concerned about using glaze finishes on high-use areas.

From the original questioner:
Can the same colors be obtained using multi-layers or mixing two stains versus aniline dyes? And, can I have someone build up multi-layers using PTO and polyurethane? What is a "hard sealer"? Is screening needed between each finish coat?

1. Isn't the sodium dichromate used to match the patina of new wood to old wood?

2. Isn't this chemical quite hazardous to work with?

If both of my points are so, that would justify the high finishing cost.

From contributor B:
Coloring wood is an art and not a science. What works in one case might not work in another. Stains are both dye and pigment. Dye stains are more minute and penetrate deeper than pigment stains. Mixing dye stains will give you a color of choice and will be "clearer"--that is, the grain will show more than if you mix pigment stains that will cloud or cover over the grain of the wood. Both have advantages and disadvantages depending on the type of wood being colored. So if you want the wood grain to be pronounced, dye stains are usually used. Pigment stains cover more like paint would. There are some stains that are both dyes and pigments. It is up to the finisher to determine what is the best to use. Your guy uses chemical change to get a certain color, then seals it, then puts a dye on top of that, then seals it again and topcoats.

Chemical use can be dangerous. He is using chemicals when the floor has to be sanded and the existing finish has to be removed. This takes away the aged (patina) wood, so a newer look appears. If he is trying to match another patina, chemical change could be justified. But dyes can do that also, in most cases. So, getting your color with multi-layer dying will give you the depth that you want. Usually, multi-layer involves sealing each color, sanding or screening (as long as you don't remove the color) and then sealing as the last step before topcoat. All the sealers and topcoats need to be sanded and compatible. Your last topcoat, of course, does not need to be sanded if all other work is done satisfactorily.

What is hard sealer? I can only guess. I speculate that it means one with a high solids content. What is PTO?

From the original questioner:
PTO is polymerized tung oil. Can I get a floor that has the "depth" of a multi-layered process without all the harsh chemicals? (By the way, the finisher insists that there is no harm being around any of these chemicals. There are kids around that house - should the chemicals be avoided?) As far as texture, the owner likes the sample where the wood is smooth and the grain filled in.

Yes, you can get depth of color without using the dichromate (dichromate is primarily a problem to the user, not those in other rooms). Ask 10 people on this forum for a color formulation and you'll receive 10 different methods, all of which would probably work. It's a matter of time and cost.

The final finish needs to be very durable so as not to wear through a finish layer and begin wearing down a color layer. Polymerized or not, tung oil finishes are not as durable as other products on the market. I'd explore other options for the topcoat.

From contributor B:

I don't understand why your man has to use chemicals to change color. With children around, I would never use those potentially dangerous chemicals in living quarters.

Here's what I would do: get an old piece of oak flooring, sand it like the actual floor is going to be sanded. Put a stain on that is the general color you want. I might use dye stain or pigment stain or a combo (like Minwax). Minwax, though I normally don't use it, does a nice job on oak. I would seal this in with a wash coat or very light sealer coat. Then I would tint up my sealer with a color that would bring more clarity and depth. This also aids in making the overall look more even. (There might be some areas darker or lighter than others.) Then I would use a full sealer on top. This sealer can aid in the filling of the pores that oak has. Screen this well and vacuum dust up very well. Then lay down my topcoats (notice, more than one), smooth out between coats to knock down nibs and such.

Most floor finishers have solvent finishes. If the quarters are occupied, I would not hesitate to use a water borne product. Van Technologies has a wb product that I am sold on for flooring. The best part is, if in a few years it needs to be restored, all one has to do is sand out scratches and apply another topcoat without having to go to bare wood, unless of course the color is to be changed. It's a crosslinking urethane and when it's cured it's very hard. Several coats will fill in the pores to the smoothness that the owners are looking for. It has a high solids content.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor J:
Potassium Dichromate is toxic to the user. An alternative non-toxic solution to restoring patina to red oak is to pre-treat the red oak with tannic acid and apply a coat of iron acetate. Tannic acid is available in powder form from several internet sources, and can be dissolved in water to form different strengths. Iron acetate will react with the tannic acid to form iron tannate within the wood. Iron acetate can be made by taking 32oz household white vinegar 5% strength and adding 1 fluffed out 0000 steel wool pad in an uncovered plastic container. Let the mixture stand 24 hours, then remove steel wool and filter. Do not cover container because the resulting mixture gives off hydrogen gas. The iron acetate solution can be diluted with distilled water to yield desired look. When applied to tannic acid pretreated red oak, the iron acetate will yield a charcoal gray to ebony appearance, yet when sealed, it will yield warmer brownish/ebony tones. There is no need for the use of dyes with this process.

Pretreatment with tannic acid is not necessary for tannin rich white oak and other tannic acid rich wood species. Pricing sounds reasonable. Standard pricing is ~ $.50/sq ft/application + cost of materials + cost of sanding for finishes of this nature. Hard sealer is a mixture of polymerized tung oil, solvent, and uralkyd resin and is specifically designed for a uralky resin top coat or hybrid pto/uralkyd resin topcoat.