Problems that can occur when resurfacing over an old finish:
I see quite a few blog posts about refurbishing/restoring old finishes. I have never seen one blog that dealt with any of the potential problems that can arise from choosing this process. I’m going to give you a list of issues and possible solutions if you decide to recoat a piece of furniture over the old finish.
1. Adhesion Issues with the old and new finish.
Problem: Silicone, dirt, wax, oils etc. will almost always be a problem with the new finish adhering well to the old finish. The process of resurfacing makes for great “Before and After” photos but the concern of being able to use the furniture without flaking or peeling will almost always be an issue if it is something like a dining table or chair that receives a lot of contact with people in any way.
Solution: Cleaning the surface well is a MUST but even then the surface needs to be lightly sanded so that the new finish has something to “BITE” into for some type of a physical bond.
2. Compatibility of finishes
Problems: Oils based finishes like urethanes can be put over lacquers (solvent based) but lacquer cannot be put over oil finishes as they can wrinkle he oil finishes. There will be no chemical bond between the coats of finish between urethanes and lacquers.
Solution: Sanding with the 220 to 400 grit sand paper is a must to give the finish is something to bite into. The coarser the better but if your top coat is not thick enough the sanding marks will show up in the top coat.
3. Deterioration of the original finish.
Problem: Some finishes have so deteriorated that they are too soft to work with. It is possible that the finish may even be wax so be careful! If this is the case the piece is not a good candidate for the purpose of resurfacing. On a deteriorated finish you can take your fingernail and scape it off just like was wax. The deterioration aways happens where hands or body parts come in constant contact with the finish such as the arms or backs of a chair or the edges of a table. Do not even try to resurface furniture that has this damage.
Solution: If you can find a stain that will match the surrounding areas the old finish can be removed with the solvent such as Naptha or even a water-based product such as TSP and try to blend the color to the surrounding area. Then you can apply your finish coat.
4. Resurfacing will not work over all types of finishes
Problem: These days there are more types of finishes then one can imagine. The finish that works best for resurfacing is a good “old-fashioned” nitrocellulose lacquer. Normally it will have a “sprayed-out” look to the finish. Unfortunately, unless you’re professional you will probably never know if this is the case. Nitrocellulose lacquer was the standard finish in furniture manufacturing for 75 years. The reason that it works well for resurfacing is because it can be amalgamated, which means that you can take a lacquer thinner and melt the finish back to its original liquid state. On the other hand, urethanes chemically changed as they dry and do not allow for much of the damage to disappear just by wiping another finish over it.
Solution: There is no solution to this problem that I would recommend to the home user.
5. You can water damaging the original finish while cleaning with water-based products.
Problem: If you use any type of water-based product such as TSP (tri- sodium phosphate) it is great for cleaning wax buildup but in many cases you can and will water damage the finish as water will instantly seep in to small cracks in the deteriorated finish or into any open grain wood such as walnut, mahogany or oak. It will lift the finish from underneath just like a water ring left by condensation from a cold glass.
Solution: If you have a finish like this, you will need to clean it with a product such as naphtha or turpentine. Work in a well ventilated area. These products can be purchased at any paint or hardware store.
6. Silicone build up from products like Pledge or Favor
Problem: Most of the products used for polishing such as Favor and Lemon Pledge are silicone based products. Silicon and ANY type of finish are not compatible. Silicon will reject finish in the same way that water rolls off of a duck’s back. If when you apply your new finish in it begins to push away and leave craters (fisheyes) you will know that there is still silicone on the surface. Even if you clean the surface the silicone will be hidden in the bottom of a pore and you will notice the finish being rejected forming a crater around each pore.
Solution: Using naphtha, turpentine or mineral spirits is one way to clean the finish without worrying about the problems of water damage. You will need to work in a ventilated area or open a window. I use TSP to clean furniture if possible but try not to saturate the finish as to cause water damage.