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12-15-2009 04:45 PM
I plan to use Watko Danish oil on a cherry project and would like to apply polyurathane as a protective top coat. How long should I wait for the oil to dry completely enough before using the poly? Bob D.
12-15-2009 04:56 PM
If your finishing space is approximately 70° warm, and assuming that you did a good thorough job in wiping off all the excess oil/varnish mix from the surface, then you should be able to overcoat with oil based varnish after a good overnight drying period. Oil based polyurethane isn't a very good choice. A traditional resin varnish--such a Pratt & Lambert 38 would be a relatively light colored choice, though if you want a darker varnish, that is also a bit tougher, then a phenolic resin varnish such as Behlen Rockhard, or Waterlox would be excellent choices.
If by some chance you have adopted calling a water borne product "polyurethane", as led on by label, then I would have several more days of cure before overcoating the Watco. That product won't over nearly as much extra protection as any of the oil based varnishes would.
12-15-2009 05:43 PM
...to reconsider your finishing schedule. First, there is absolutely no benefit in applying an oil/varnish blend and then toping with varnish, whether polyoneverythane or one of the varnish products mentioned by Amateur60. If you are looking to "pop" the grain/figure on your cherry and topcoat with varnish for increased durability you will be better served by applying simple BLO (Boiled Linseed Oil) in place of the Watco "Danish Oil" (an oil/varnish blend). Apply a liberal coat of BLO, allow it to soak into the grain for 25 to 30-minutes, wipe off the excess, "buff" the surface dry, and apply your varnish after a cure period of 8-hours or so.
If you are absolutely determined to use the Watco than consider the fact that the "oil" you will be applying is over 70% mineral spirits. If you really believe your cherry will benefit from the initial application of an oil/varnish blend (that is what Watco is) then you can make your own for less and obtain a better product in the process. Here is a link to making and applying a home brew oil/varnish blend that you may find helpful.
Finally, while you don't identify your "cherry project", I suspect there are any number of finish options that will be superior to poly (and I too would be interested to know if the "poly" is actually oil-based varnish, or a water-borne acrylic finish deceptively identified as "poly" by the manufacturer...
12-23-2009 07:35 PM
Steve, I purchased the Watko Danish Oil (Cherry) because it was recommended by a friend that uses it to deepen the color of the cherry, and then I wanted a little more durable top coat so I planned to use Defthane Polyurathane. Someone, it may well have been you Steve, recommended using a phenolic resin varnish rather than a polyurathane on a previous project. The reason given that it would produce a more professional quality finish. I had some trouble finding someone who knew what a phenolic resin varnish was at first, but at a local woodworking shop I was given McCloskey Man o' War Marine Spar Varnish. The can says it is a phenolic resin varnish. Is Spar Varnish another name for Phenolic Resin?? Anyway I had a one foot slab of walnut that was a cutoff from a table I made, and I used the Spar (phenolic resin) varnish on one side and polyurathane on the other. I asked several woodworker friends to tell me if they could tell any difference in the appearance or clarity of the two sides, with no stain on the wood, just the varnish. I couldn't tell any difference myself, but then my vision Isn't what it used to be. Only one of the six men could see any difference in the top coats. Did I purchase the wrong varnish or is spar varnish ok as a phenolic resin? As a closing note I would like to thank you very much for sharing what is obviously your very in depth knowledge of the mysterious (to me) world of finishing. I enjoy reading your response to the varied questions. Finishing seems to be one of the "arts" where there can be many satisfactory outcomes using a variety of methods, as the one offered by amateur 60, who also offers many helpful suggestions. I always enjoy learning how to move from just satisfactory to professional. Thanks again, Bob.
12-25-2009 10:40 AM - edited 12-25-2009 10:51 AM
Watco is intended to be a complete in-the-wood finish. It is not intended to be over coated with a film finish. It is mostly linseed oil which is the component that "pops" the grain and figure. But I see that you are using it as stain colorant. Using it as you intend will not be a problem if you want the resulting color to your cherry.
The "phrenolic resin" varnishes being referred to are Waterlox Original Gloss or Satin or Behlen Rockhard. Both are hard, durable finishes that impart an amber coloring that is very effective in bringing out the inherent grain patterns in cherry.
I am not aware that Man-0-War Spar varnish is a phrenolic resin varnish. Even if it is, I would not recommend using a spar varnrish. Spar varnish is formulated to be soft and flexible so it remains attached in extreme outdoor environments. Spar varnrish is not particularly durable in interior applications.
12-26-2009 03:22 AM - edited 12-26-2009 03:25 AM
...to cover in your reply so I will try to take them in order. Also, it would still be helpful to know what you are finishing before making an alternative recommendation. I may very well have recommended a phenolic resin varnish (Waterlox) for a previous project; but, I may or may not recommend it for your current project. It may be that the oil/varnish blend will do just fine with no added topcoat. If a topcoat is indicated then the oil/varnish blend ("Danish Oil") would not be the place to begin. Further, if an oil/varnish blend is appropriate I encourage you to make your own (see my previous reply). You will pay (or have paid) about $16/quart for Watco. A quart of BLO would be yours for about $10/quart. Applied beneath a varnish topcoat they will do (visually) the same thing. But more to the point, for your $16 you are getting a can filled mostly with thinner. Follow this link to the MSDS for Watco and note Section 2 (Composition/Information on Ingredients) and Section 15 (Regulatory Information). In Sec. 2 we are provided with a laundry list of "hazardous ingredients"; the stuff the feds require the Rust-Oleum Corp. to tell us is in Watco. When we total the contents of these ingredients (by weight) we see that listed thinners can comprise as much as 75% of what is in the can. Moving on down to Sec. 15 we get to the disclosure requirements imposed by Pennsylvania and New Jersey in which the prominent non-hazardous content must also be disclosed. Thanks to these two states we are able to get a grasp of what is actually in some of these finishes. In both lists we see Raw Linseed Oil, Alkyd Resin, an unidentified resin, and Gilsonite. The first two, Raw Linseed Oil and Alkyd Resin (and the mystery resin) are the components use to make the varnish in an oil/varnish blend. The linseed oil is also the oil component in the blend. Gilsonite is basically the colorant that will "deepen the color" of your cherry. It is derived from asphalt, the same petroleum derivative use to pave the street in front of your house. The bottom line is that for your money you have purchased a can largely filled with thinner with as little as 30% (by weight) actual finish.
McCloskey Man O' War Spar Varnish is indeed a phenolic resin varnish; but, it would not be an appropriate finish (in all likelihood) for your project. Spar varnishes are what we call "long-oil varnish"; they are manufactured with a higher oil content. As a result they are more flexible that regular or short-oil varnishes. They are also much less "durable"; they are softer, less resistant to abrasion, less resistant to moisture and liquid water, and less resistant to household chemicals. Here is a link to an article on Marine Varnish that you may find helpful in understanding the differences in these varnish types.
It is also important to understand that detecting differences in varnishes visually, especially soon after the varnish has been applied is virtually impossible. The differences in varnish formulations have to do with the properties imparted by the components used in their manufacturer; for example, the oil, the resin, and the proportions of each. These differences show up in how those properties will serve the finish in different environments. These have to do with moisture resistance, abrasion resistance, hardness, color stability, the ability of the varnish finish to be repaired, etc. This brings us back to the missing information in your question. What are you finishing and what look & feel do you want to achieve? An oil/varnish blend (homemade, I hope) may serve you quite well. So might BLO followed by varnish; but, which varnish? It all begins with what you are finishing, how you want the finish to look, and how the item being finish is to be used...
12-26-2009 12:42 PM
Howard & Steve, Thank you both for your reply's. I really appreciate the education, because as previoulsy mentioned the world of finishing can be confusing to say the least. Steve, sorry I didn't mention my project previously but it is a little out of the ordinary. A family member coaches soccer for Father Judge High School and they recently won the city and state championships. I was asked if I could make some type of stand (2 of them) to hold a soccer ball that would be signed by all the members of the team. The stands, with the ball on top, would be presented to the coach and assistant coach as a trophy for the successful season. I designed a stand consisting of a base (10"x12"), center post, and top platform (6"x6") to hold the ball. The assistant coach has three small kids under four years old, that are likely to be handling the stand (probably with sticky fingers), so I thought it would be good to have a protective clearcoat on the piece. It is not something that would normally need a protective clearcoat but under the circumstances I thought it would be good if it could be wiped off if it gets soiled by the kids. I'm using a nice 5/4 piece of cherry for the project. Now that I know BLO makes a better finish how would you recommend I darken the cherry in the future (I already put the Watko cherry on this project)? I also plan to get some of the phenoli resin varnish you recommended and stay away from the spar varnish. Thanks again, bob.
12-26-2009 01:31 PM
...than that offered by a good oil/varnish blend. Lose the Watco and apply two more coats of home-brew oil/varnish blend as described in the article to which I linked in my first reply. Apply the o/v blend as instructed in the article. A phenolic resin varnish in this application (even with two uncivilized children) is overkill in the extreme. The varnish content in the o/v blend is more than adequate to ward off the kit's finger prints.
As an aside, before you get rid of your cherry scraps from this project I would encourage you to apply the o/v blend finish to them and just set them aside. See how quickly they oxidize naturally to give you a deep, warm "cherry finish" with no added stain. Applying stain to cherry should really be against some sort of law...