Hi,

I just bought a 1960s era house which has shellacked birch floors that are pretty beat (original finish, maybe?). I am planning to sand and refinish myself (with dewaxed shellac topped with water-based poly). I know that shellac can be hard to sand off and may potentially melt and clog if the sander isn't kept moving. However, I am concerned that there is something else (dah-dah-DAH!!!) on the floor, on top of the shellac, that might interfere with the whole process. In places, there appears to have been another substance put on top of the shellac. It is dark, dull, greyish, and seems to have only stayed in places, in a patchy way. It is pretty hard (I tried to scrape it off with my fingernail, gently, and could not). What could this be and should I worry about it for sanding, should I clean the floor first, or what?

Thanks for your help.

Mary

Do you have a picture of it ? It might be old urethane that never stuck properly to the shellac / varnish that was already on the floor. Hard to say without seeing it. Either way, you will have to sand it off. Cleaning probably wont have any effect on it but you can try using some mineral spirits/paint thinner and something like a 3M scotchbrite pad.

Thank you! I will post a photo.

I am actually experimenting with shellac topped with water-based polyurethane (to compare satin, semi-gloss, and glossy) on scrap wood, and I have to say that I like the shellac by itself much better (looks better, feels better). Part of the problem is that I somehow introduced microbubbles into all 3 layers of poly. Questions:

1) I know shellac is an old finish and has a reputation for not being an acceptable floor finish, but it is really lovely (even the old finish looks nice in the less worn areas). Am I crazy to consider just doing my floors with a few coats of homemade, dewaxed shellac? FYI: I have pets (who don't pee on the floors unless they are ill); would they tear it to pieces? I wouldn't want to be patching it every other month, but I could probably do a scan and touch up once a year or so.
2) If I do cover it with something more durable, is poly best?
3) If I use poly, are there brands that are least likely to discolour, form bubbles, etc.?

Mary

To start with, modern shellacs are decent products but are not nearly as durable as good urethanes.You can do multiple coats of shellac but you can expect it to wear much more quickly than urethane.Among contractors, shellacs are considered suitable only for priming / sealing the wood.And frankly, I have issues with shellacs and tend not to use them

As a sealer, shellac does seal the wood and does allow for good bonding of urethane top coats. The problem I have with it is that when I buff it, the shellac melts and sticks to my buffer screen.This is a hair pulling process as the shellac raises the wood grain and the raised grain makes the floor feel rough.And getting your top coats to lay out smooth is a priority so the sealer coat needs to be something that buffs out well and shellacs really don't. Some contractors just coat right over the shellac without buffing and I consider that to be a bad move.

Moving along to your other questions, poly is a great wood floor coating.There are other light oil finishes that can be used but none that will approach the durability of polyurethane.

What's best ? That depends on your needs. The clearest and hardest are the 2 part water based urethanes like Bonakemi Traffic and Basic Coating's Street Shoe .That being said, they take a lot of skill and precision to apply compared to the more forgiving oil urethanes.

Oil urethanes are easy to work with and are reasonably durable.Far more durable than shellacs. But on a durability scale of 1 to 10 , with oil based urethane being a 5, the two part catalyzed water based urethanes would easily be an 8 or a 9.Cosmetically, oil based urethanes will yellow/amber over time. Some water based finishes can yellow as well such as Bonakemi's Pacific Strong.Pacific Strong is probably best described as a urine yellow color and not very appealing to look at.

So.....to re cap

Shellac Easy to use, dries fast. Not very durable and does not buff out well

Water poly Cheap water based poly is not any harder than oil based poly but 2 part catalyzed water can be nearly twice as durable as oil if applied properly.Water poly also dries quickly and has low odor.Downside is that they are much more expensive than oil products

Oil PolyEasy to use, readily available and not very expensive.But odor can be strong.YOu can also expect yellowing/ambering over time

As far as bubbles , you might be getting those due to too thin of a coat or too cold of a temperature. When applying poly ,there's always some air bubbles getting trapped no matter what you do. IF temperature is at least 70 degrees, humidity is not too high and there's no air blowing across the finish, the air bubbles should pop out on their own.

Hi,

Thanks again for the detailed response. Here are some photos of the surface stuff:





Mary

In the first photo looks like your down to bare wood in spots. You need a complete sand and finish

Yes, that photo doesn't show anything like the worst of it; heavy use areas like doorways have no finish, just grey. Is the superficial stuff anything to be concerned about? How should I remove the old finish, just sand (renting a drum and edger), or something else (e.g., scrape, try to dissolve the shellac and remove it, other prior to sanding)?

Should I do any special cleaning or wax stripping before sanding the floor?

Thanks again!

Mary

I'd say you need a professional finish guy. Rental machines are notorious for not being maintained properly and you could ruin the whole floor. And by the looks of it it could be a beautiful floor if finished properly. Finishing wood floors is not for the novice.

Hi,

While I respect your opinion and superior level of knowledge and experience, and I appreciate your recommendation, I have given this a lot of thought and had already made a deposit on rental equipment, and bought supplies for the refinishing. I am motivated, physically fit, and also have a meticulous personality. I anticipate spending several days working on this, and have actually rented the sanders for a week so that I shouldn't feel rushed.

I understand that there are risks of damaging the floor with sanders, and I certainly want to minimize that risk. Can you help me to know how to evaluate the equipment I rent to determine its condition? I was considering trying it out on a sheet of plywood or particle board (will that work) to test it out, first. I also wondered whether it would be best to use just the drum and edger for the whole sanding job, or to use an orbital buffer-sander for the last cut. Finally, I wonder if I should do more than sweep and vacuum the floor to get it clean before sanding (should I wash it).

Thanks again,

Mary

A good drum sander will take all the crud off the floor easily enough so no need to pre scrape it off or anything like that. But keep in mind that drum sanders can do a ton of damage to your floor if you aren't familiar with how to control them.

If you plan on using a multi disc sander like a U-Sand , you will have a lot more control but it will also be a lot slower than a drum sander.As for the quality of rental sanders, it usually is average to poor.

Thanks!

I have a drum and edger rented. I have a large sheet of particle board and a thin sheet of plywood in my shed. Should I do a practice run on them?

Mary

Probably.The drum sander can leave big drum marks so maybe practice your take offs and landings until you get the feel memorized.

Great. Thank you.

What about cable holes (present in a few spots)? I presume it is best o replace the boards, which might be overly ambitious for me. Should I patch (how - filler, wood plug, etc.), or ignore them? My friend is in construction and can help with a strip of wood for one large gap in the boards. I don't know how easy it would be for him to make plugs for the cable holes, if that is necessary.

Mary

Hi again,

New question: the store I rented the equipment from gave me a Clarke American OB 18 Sander rather than a drum sander, and said that they "had decided it would be better". My understanding is that this machine isn't for sanding off a finish, but for lighter sanding at the end of a job. That being said, this floor does not have cupped boards or any major unevenness (just the finish worn off and some scratches, with a rare gouge (I found one so far) to about 3/8" deep maximum. Should I just go with the OB 18, or get the drum elsewhere? I understand that I can do less damage with the OB, but is it up to the task of sanding off the shellac and down to healthy looking wood?

Thanks yet again.

Mary

You want the drum sander, unless you would like to spend many day's behind the square buff.
Or better, hire a Pro and come back to a really nice floor.