Soap: Making a Clean Finish
by Christopher Schwarz
from the October 2016 PWM
When I tell fellow woodworkers and customers that I use soap as a finish on some of my tables and chairs, they think I’m joking. Then, when I pull out a Mason jar filled with soap finish to show them how it works, they laugh because it looks a lot like, well, snot.
After seeing the results on finished pieces, however, they know it’s no joke.
Using soap as a finish on furniture and floors is common in Denmark and other northern European countries. It produces a low-sheen finish that is remarkably soft to the touch. It looks best on light-colored woods – from white maple to woods about as dark as white oak.
And, as you can imagine, it is a safe finish. It might be the only finish where your hands and clothes are cleaner after using it. It is best used on bare wood or wood that has a soap finish on it already. It doesn’t do much over an existing film finish.
There are downsides to the finish – it’s not durable and requires regular but simple maintenance.
For the last year, I have been experimenting with different recipes for soap finish made using a variety of products you can get through the mail, at health food stores and at your grocery. After finishing, and living with, about a dozen pieces using soap, I am a convert. It might not the best finish for every situation, but if you are curious it is definitely easy to try and master.
The Right Soap
You can’t just rub a bar of Irish Spring on a chair and call it done. (Wait, maybe you can. Try it for yourself.)
A Danish soap finish uses natural soap flakes that are mixed with hot water. Soap flakes are a pure form of soap that doesn’t include additional detergents, fragrances or other modern chemicals. It is simply an oil that has been mixed with an alkali solution to create a salt of a fatty acid. Our ancestors made soap by pouring tallow (animal fat) onto the ashes from a fire.
You can still buy this important and elemental soap from a variety of sources all over the world. Look for companies that specialize in “natural soap flakes.” You’ll find a bunch.
The flakes are white and soft to the touch. They don’t have much of a smell until you mix them with water. Then they will smell just a wee bit. Your nose will register the smell as “clean.”
The other option is to make your own soap flakes from “Castile soap.” Castile soap is a simple soap made from a vegetable oil, such as olive oil. You can find bars of this soap at many health food stores. I can get it from my corner grocery. Shred the Castile soap like you would a hard cheese to make your soap flakes.
If you mix these flakes with hot water you will produce a solution that is somewhere between whipping cream and a soft wax in consistency. The trick is deciding how much water to add to how much soap.
When I first started to dig into the recipes for a soap finish, I found two types. One used a lot of water and a little soap – a couple spoonfuls of soap and a liter of water was a typical recipe. Then there were recipes that used equal parts soap and water. I tried both.
When you mix equal parts soap and boiling water you quickly end up with a waxy solution that gives furniture a semi-gloss sheen and mild protection.
When you mix a little soap and a lot of water you make a mayonnaise-like solution that’s easy to apply and imparts a matte finish with mild protection.
Neither soap finish is bullet-, baby- or waterproof. But both are easily applied, repaired and renewed.
To mix up a watery solution – what I call “soap soup” – boil four cups of water and pour that into one cup of soap flakes. Stir vigorously. The result looks like bathwater after a long soak. Don’t throw it out in frustration (like I did the first time I made it).
To mix a hard solution, begin with a cup of boiling water and a cup of soap flakes. Pour about half of the boiling water on the flakes and mix. Add water bit by bit until you get a stiff whipped-cream-like solution. Let that cool and set up. After about an hour, it will be waxy and ready to use.
Put the solution in a jar to let it cool and set up. After a few hours, the liquid will turn an opaque white and become a bit stiff like shaving cream or mayonnaise. After 24 hours, the stuff is ready to use on furniture.
Applying the soap soup is easy. Rag it on so that the wood is wetted and a bit foamy. Let it stand for a couple minutes. Then take a clean rag and wipe off the excess. Let it dry for an hour then sand the surface – I use a #320-grit sanding sponge – and repeat.
After four coats you will start to see some sheen build up. Stop whenever you like the way it looks. Two coats is reasonable – so is 10.
To renew the finish, apply more soap solution to clean it and create the original soft sheen. How often you need to apply soap depends on how much you use the piece. I have a soaped worktable that sees daily use and needs a new coat every six months.
The waxy solution is applied more like a wax. Get a clean, cotton cloth and scoop a single dip-sized dollop into the middle. Wrap up the soap and twist the cloth around it to create a ball of rag and soap.
Squeeze the rag and the soap will begin to leach out of the rag. Rub the rag on your work and a small amount of the waxy soap will flow onto the wood. After you finish a leg or seat or door of your project, come back with a clean rag and buff out the soap solution. It will polish up to a semigloss sheen like any wax polish.
Repeat the process a couple times until you get the look you want.
This soap polish can be renewed at any time. You can use either solution at any point – use the watery solution over the waxy solution if you want to experiment with a flat look. Or vice versa.
It’s a great finish, but it requires upkeep. If you are happy with the ease of melamine or the durability of bar top, you probably won’t like a soap finish.
What Happens if…
Many people wonder if water, stains, heat or nasty solvents can hurt a soap finish. Yes, but the finish can be easily renewed with more soap. So don’t worry about it.
Can you use it over other finishes? Sure, but it’s best on raw wood. I’ve applied it over milk paint, cured oil, varnish and other finishes with varying results. If you aren’t sure (or don’t trust my advice) then try it on a sample board. You’ll get your answer.
No finish is perfect. But when it comes to a finish that is safe, easy to apply and easy to repair, soap is hard to beat. PWM
Christopher is the editor at Lost Art Press, a contributing editor to this magazine and the author of “The Anarchist’s Design Book.”
From the October 2016 issue: