Cleaning and Restoring a Historic Door Finish

Here's some detailed advice on gently and safely cleaning historic doors without damaging existing old finishes. July 2, 2008

I am helping to restore an old railroad station for our town, and we have some old veneered oak doors that are beautiful but badly crackled with a little delaminating at the bottom. I don't want to strip them (the committee feels the crackling is in keeping with the historic building). Does anyone have a suggestion as to the best way to clean the doors and re-coat? I was going to lightly wash with soap and water then spray with shellac.

Forum Responses
(Finishing Forum)
From contributor A:
Are you looking to design a treatment to refinish or conserve/preserve the existing coating? Do you know that the existing coating is shellac, and how have you determined that - through solvent tests, or...? What is the crackle pattern - is it finely fractured in a somewhat consistent crosshatch pattern, or is it more of a "curdled" pattern, sort of crocodile/alligator look? Are the doors interior on both sides or interior/exterior? Prior to all of this you will need to take care of the delamination areas, and I am assuming that you are referring to delamination of the veneer. Depending on the circa of the doors and whether they are interior and/or exterior doors will determine what type of adhesive they can/should be repaired with.

From contributor C:
Do not clean the doors with water or anything else till you've gotten back with more info!

From contributor R:
That sounds like a fun job. I helped out a friend who is into modeling railroad redo a station in San Leandro California. They have an unbelievable setup over there - it's like going back in time. This is an old time, but real, train station - not just a simple mockup. Everything in this station was 1/4 sawn oak, even the furniture.

If I was you I would clean the doors with paint thinner (not water) both inside and outside. Chances are they were originally finished with oil based varnish on either side. Once you have done that, I'd re-glue the veneers that were delaminating and then step back a moment (you say you don't want to replace missing veneer - that's up to you and the committee). If the decision is to leave well enough alone and you just want to re-coat the doors, you might consider an exterior grade oil based varnish. The reason I do suggest a varnish coating is because a shellac coating is pretty apt to wear itself down, be it an inside door or an outside door or even a 50-50 door.

From contributor C:
Contributor R, if I'm correct, the questioner is planning on washing the doors with soap and water and recoating with shellac. It sounds like it is an historic building, which I take to mean something they want to keep historically correct. If by chance the door is a shellac finish, and I'm not saying it is, then for historical sake it would only be right to have it prepped properly and the original type of material re-applied most correctly with a barrier isolation coat placed on it before the new shellac coating is applied. This is done so that in the future if someone wants to know what conservation was applied to it long after I and you are gone, they will have that information to go by if the committee plans on keeping those records, which would be the normal thing to do. It has nothing to do with your posting on what will work - I agree with you totally that wiping with mineral spirits and applying a new coat of oil varnish could work, on this or any old door - but when I see the word "historical" being used, I immediately think of preservation/conservation/restoration.

From contributor J:
I would clean everything with mineral spirits on a rag, or if you need something coarser, use 0000 steel wool soaked in mineral spirits.

From contributor A:
Mineral spirits alone is unlikely to clean this surface sufficiently to proceed to the next step. It is the first procedure I would do. Then there is, just about hands down, more to do to clean before going any further. Mineral spirits will remove any basic hand oils and wax but will not remove any drying oils or other concoctions, not later campaigns, nor any water soluble contaminants that have accumulated over the years and settled into the fractures and cracks/crevices. All of these foreign contaminants should be removed before you proceed to work on the remaining surface coating.

From contributor L:
I would get a natural bristle brush and cut the bristles about an inch or inch and a half from the ferule. Then get a squirt bottle filled with naphtha, squirt the naphtha on the surface and scrub the filth away with the brush. Put some rags or a towel at the bottom of the door to pick up the slop and dispose of it safely. This should clean the doors without lifting any of the coatings on there now.

From contributor C:
Contributor L, what you're stating is a good way for cleaning. I have used similar methods many times, but as contributor A states, this is only good to remove surface waxes and hand oils and the like that are soluble in aliphatic hydrocarbons such as MS and VMP naphtha or others. Many contaminants may still exist on the surface and in the cracks that are not solvent soluble but are water soluble. For this specialty, cleaners such as Vulpex soap - which is able to emulsify the water-soluble factors - is used in conservation along with Triton soaps X-100, X-100/14, etc. With these cleaners you can be sure that all possible contaminants are removed, no matter what base they are. And there is no harm done to the coatings. Again, if you're just doing an old door with no historical value in particular or no future significance, meaning just a plain door, one of thousands of commercial grade, then your or contributor R's way will work okay. No one is going to be concerned with what the original coating was 200 years from now.

From the original questioner:
Wow, lots of opinions out there! I have not determined that the finish is shellac but will do so. I guess it could be varnish. The doors are all interior, and not original to the building. However they were free and from the same period. We are looking to make the doors presentable, cleaned up, repaired and, I would guess, refinished with whatever would be appropriate to cover the original finish. The crackling aged look is fine - we are looking for the easy way out here. Maybe a good cleaning is all they need. Thanks for all the input!

From contributor Y:
This is an interesting discussion, but hasn't answered two questions that have bothered me. Is there a reason or advantage to use the solvent before the water? Do the contaminants mask each other... that is, do you need to go back and re-clean using the first method?

From contributor C:
There is no water involved. The Vulpex and Triton detergents are soluble in solvents or water. I use the spirit solvent for Vulpex, other for the Tritons, and only water if the finish is sound (no cracks or areas where the solvent would get into the wood). This is especially true if working on historical wood objects where hydrogen oxide could cause potential future adversities.

From contributor A:
"Vulpex soap, which is able to emulsify the water soluble factors, is used in conservation along with Triton soaps X-100, X-100/14, etc. With these cleaners you can be sure that all possible contaminants are removed no matter what base they are. And there is no harm done to the coatings."

Vulpex is a very effective/strong cleaner, but with a pH of 11.5 it can easily and quickly not only harm, but compromise and even remove a coating. It should only be used by someone familiar with the pH scale, how to adjust and buffer a formula for the desired pH, and the ramifications of pH levels on coatings.

When trying to clean a surface there are two things you first have to figure out.
1) What is the composition of what you are trying to get off?
2) What is the composition of what you are trying to get it (1) off of?

Lastly... water is a solvent... the most abundant one on this planet.

This is not remotely as difficult a project as it has begun to sound on this thread. Quite simple, actually. Once you have a better idea of what the existing coating is, simple answers can follow.

From contributor C:
Yes, it should be buffered with acid until neutral, usually with a weak acid addition - hydrochloric .01 - till it reaches a neutral PH of 7. This will require at least using PH indicating paper strips sold for this purpose or a PH meter.

From the original questioner:
I have finally been able to check the finish, and the members were right - it is varnish. My plan is to do a good cleaning with paint thinner and synthetic steel wool, glue up the de-laminations, faux in small damaged areas with something like acrylics(?), and then spray with a catalyzed varnish. Let me know what you think.

From contributor C:
Good plan, but I would stick with an oil varnish like Behlen's rock hard table top varnish. Cat varnish could give you problems over oil varnish. This way you will be safe in case there is any reaction problem or unseen contamination. If there is, you can remove the rock hard right away with mineral spirits. With cat varnish, not as easy.

From contributor T:
I think you're on the way. Bear in mind that you must remove both water soluble and solvent soluble grime. I go after the water soluble first with a mild Dawn/water solution used sparingly. Follow with solvent (I prefer VMP Naphtha) and an abrasive pad. When your rags come away clean you can in-fill and finish. You can use artist's acrylics to in-fill but a burn-in would probably be better.

I also would not select CV. The existing varnish is very hard and brittle so most any finish should work over it. But a thinned down varnish, wiped on, would be (IMO) a better solution. It will stabilize the existing finish and dress up the door without hiding the crackle.

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

Comment from contributor N:
I have done a lot of wood stripping and refinishing, when dealing with veneer you have an additional issue because of the adhesive bonding the veneers. Denatured alcohol and fine steel wool will soften the original finish while keeping its integrity. This is old fashioned elbow grease work - just do not overuse the product.