Expert: Greg Scholl - 2/8/2010

Question
QUESTION: Hi Greg,
I'm building a figured cherry desk for a client and I am concerned that the top will darken unevenly over time as he will not be moving the items, keyboard, computer, speakers etc. placed on it. There is also a large window on the wall where the desk will be. I was planning on using a polymerized Tung oil for the top as he liked the idea of applying a coat once or twice a year to freshen it up.  Is there some UV stuff I can add to the Tung oil that may help this situation?  Or do you have some wildly creative solution to what may or may not be a problem?
Thanks,
Tim

ANSWER: Hi Tim, this is a valid concern with new, solid Cherry, and I'm not aware of a UV additive to add to a long oil finish like the one you want to use. Typically these sunscreens are only added to film type finishes like the ones used in Kitchen cabinet finishes.Because these Tung oil finishes are fairly dark amber in color, they do offer some moderate UV protection vs. a perfectly clear Lacquer type finish....but there's no way to predict how much change will occur due to the UV in the space. Veneers are also less prone to this color change by nature of their thickness( or thinness, actually), but it sounds like you're wanting to use solid, figured Cherry (which is a beautiful wood). The other option is to treat the window with a UV film, which many glass companies can do. This is a great choice because it will protect everything in the room, and also makes the glass more efficient as far as heating and radiative cooling of the space. The only caveat is that if there are other windows in the room, they'll likely need to be done as well to make them match, as the film does change the color/look of the glass slightly. Hope that helps a little, and don't forget to check into WaterLox, a modified Tung oil/varnish finish that excels at protection and making Cherry look awesome- regards- Greg


http://www.waterlox.com/desktopmodules/fathomecom/catalog/category.aspx?tabid=42

Hey Tim, just be advised that the Marine versions will be very Glossy, unlike the "original" product which yield a hand rubbed Satin finish....probably not too suitable for a piece of furniture...

---------- FOLLOW-UP ----------

QUESTION: Hi Greg,
Minor detail I forgot to mention--Initially I will apply a wash coat or two of 1 lb. cut (or thinner) de-waxed shellac in order to alleviate the figured cherry blotch problem.  Somewhere (probably Flexner) I read shellac itself has pretty good UV protection properties.  Anyway my plan for the top only (all else to be lacquered)is the shellac seal coat, thinned cherry stain to even things out a bit, then 4 or 5 coats of Waterlox --the glossy marine stuff.  Please know I will do a number of experiments on sample boards with different grades of Scotch Brite to hopefully tone down the gloss.  Sound reasonable?
The client liked your idea of the window film but I can't count on it actually happening.
Again thanks for your help on this.  What I enjoy/hate about custom stuff is each project tests my skill & knowledge & sometimes, miraculously I may even learn something new!!!
Tim

Answer
Hey Tim, a few thoughts. I would pick one finish and use it alone for the project. Lacquer will look quite different from a penetrating oil/varnish product like WaterLox on Cherry, and using a washcoat of shellac will prevent a penetrating finish from penetrating.....you can use the Waterlox as a washcoat for itself....a single coat wiped on and then wiped off well and allowed to dry for 24hrs. will give you the same affect as a sealer/conditioner that the shellac would, yet leaving the wood a bit more porous....stain and colorants can also be added to the Waterlox to augment it's natural color, (amber), carefully, during the initial coats.Transtints are great for this type of use... The Marine product is a high gloss and I don't think it's a good choice for a piece such as yours...4-6 coats of the "original" will produce a glossy enough finish, and the more you apply, the more "build" you will get, hence the more gloss level you will achieve. But too glossy a finish is a mistake on a solid Cherry piece such as this in my opinion.I hope you're considering a dye stain as well, as these can be controlled well by thinning and building up slowly to the final color in several coats minimizing blotching,and ther General waterborne dyes are an excellent product if you've never used them.... but also consider the Waterlox alone, as the natural color enhances Walnut, Mahoganies, and Cherry producing a beautiful "natural" color....Finally, don't overlook the General Gel stains and Gel Satin Urethane topcoat. This is a clear Satin Gel Urethane that has a "straw" like color very similar to solvent lacquer, yet is one of the easiest and most foolproof ways to apply a durable, satin finish. You just wipe it on the same way you would apply the Waterlox, and then wipe it off evenly, leaving behind a thin coat of the product.It dries smooth and levels out beautifully, and is very tolerant of manipulation and troublesome issues that affect other finishes. It dries very clear and has a pleasant, non sour odor, and it's a secret weapon that I use quite a bit.It does not look or feel like the conventional polyurethane finish, and resembles a fine rubbed lacquer when cured.The stains are the consistency of pudding, and blotch less than any other oil stains out there due to their thick nature and urethane carrier, and they can be used as shading stains, glaze, etc. with predictable results time after time. The color strength is also very good, and they can be intermixed and thinned with abandon...Hope that helps a little- best of luck and post back if need be- Greg

http://www.woodcraft.com/Family/2020491/General-Finishes-Water-Based-Dyes-.aspx

http://www.woodcraft.com/Family/2005555/GENERAL-Gel-Top-Coat-and-Stains.aspx