Replies

1. 
   Danford_C_ | Jul 24, 2002 05:31pm | #1

   Charles,

   The following takes you to a post I did back in April of last year on this subject that should be of some help:  http://forums.taunton.com/n/find/findRedir.asp?webtag=tp-knots&mg=534639A6-A147-42C0-AD53-E0D7F3E92C91

   Dano

   "Form and Function are One" - Frank L. Wright
1. 
   CHohenberg | Jul 25, 2002 04:43pm | #3

   Thanks Dano,

   What I don't know is whether a stain was used on the mahogany before shellac or laquer was used, or whether an oil finish was applied, then laquered.  Once I get the old surface sealing coat off, I want to match the rest of the piece. 

    Thanks for interest, and the reference.

   Charles 

1. 
   Danford_C_ | Jul 25, 2002 05:29pm | #5

   Charles,

   You're welcome.  Typically, a grain filler would be used on Mahogany and staining would be an exception rather than the rule.  Strippers, rarely will lift a stain but can lift a filler.  At this point, I can only recommend that you determine the type of final finish as previously referenced to, proceed with caution in your stripping operation, then determine what should be done next, it's very likely that you will have to apply a Mahogany grain filler.  Keep us informed and someone will help.

   Dano"Form and Function are One" - Frank L. Wright

2. 
   goldhiller | Jul 25, 2002 03:56am | #2

   Charles,

   I think I understand just what it is that you want to accomplish and why. So, here’s how I would approach this particular situation: Determine via a solvent test whether this is lacquer, shellac, or varnish. (See previous posted link) You will want to perform this test on an inconspicuous area, say the bottom of the piece. It is doubtful that this piece has a different finish on its’ top than on its’ bottom, so it should be safe to conclude that they are the same.

   If it is shellac or nitrocellulose lacquer, you should have no problem renewing this finish with a minimum of effort. Since both of these are evaporative finishes, the next coat of either will “melt” into and fully adhere to the previous coat of the same. All you need to do is prepare the surface for the additional coatings. Sand the entire surface until it appears that the problems have been removed with 320, to both scuff it and to hopefully remove any contaminants that are on its’ surface. Wipe the surface off well with a soft cloth and mineral spirits to remove any traces of paste wax, or the like, that may be present. Allow any mineral spirit residues to evaporate entirely. Next, remove all dust and debris via shop vac and/or tack cloth. Then apply your new additional coatings. To be safe, apply shellac over shellac or lacquer over lacquer.

   If your solvent test leads you to believe that this may be varnish, the same procedure may be followed, but the results are not as predictable in terms of longevity. Most of the commonly available oil-based varnishes are reactive finishes and the bonding characteristics of these finishes to coatings of the same or similar material made years ago may prove to be insufficient. Since it is something that you are doing for yourself, I’d give it a shot anyway. You don’t have much to lose, and if nothing else, you will gain experience. If the finish “gives way” after a time, you will simply be faced with stripping the top and applying the finish of your choice at that time.

   We’ll hope that you don’t encounter any silicone contamination problems from the prior use of silicone bearing furniture polishes, such as Pledge. If you know that these products have been used on the table, then you are forearmed. If you are applying shellac, it will be of no consequence to you. However, it will cause problems with the application of either the nitro lacquer or the varnish. I know of no pretest for the presence of silicone. You will find out at the moment of truth, as you will see the dreaded “fish-eye” for yourself. The finish will form small to large craters on the surface that will defy smoothing out and remaining there, but will return to the typical fish-eye appearance.

   Remedies include silicone cleaners that are used to remove silicone from the surface or the use of products such as Sil-Flo, which are added to the finish in order to reduce the surface tension of the finish until it comes into alignment with that present on the surface of the piece.

   If you encounter this problem and have no remedy on hand, remove the finish from the surface with its’ solvent on a cloth until such time as you are prepared to deal with it.

   Rub out the final coat of finish when cured via whichever of the numerous proven techniques will best suit your intentions for appearance.

1. 
   CHohenberg | Jul 25, 2002 04:48pm | #4

   Thanks Goldhiller,

   I know that Pledge has been used (I used it myself), so I will first try to remove the silicone before I do anything else.  I will then sand down the old finish with 320, followed by another applicatio8n of the silicone remover.  What I don't know is if a stain was used prior to the sealer.  What do you think about using Tung oil, or something similar, riguit after the surface is prepared, then a shellac sealer?  I am a novice at these finishes so any advice will be appreciated (before I screw it up).

   Thanks,

   Charles

1. 
   goldhiller | Jul 26, 2002 09:55pm | #6

   Charles,

   The use of silicone bearing products on furniture usually, IME, isn't a big problem at refinishing time unless it has been able to penetrate thru the original finish and into the wood via cracks in the finish or worn- thru areas. Bear this in mind as you assess the likely course of action for your piece.

   Perhaps, I misinterpreted your description of the piece and it's condition. I imagined a piece that wouldn't require sanding down far enough to reach the coloring of the piece, but rather a piece whose flaws lie entirely in the finish itself. If this is the case, how the piece was initially colored is inconsequential to your efforts, as you wouldn't be altering it.

   However, if there is color in the original finish coats ( toning lacquers, or the like) then you would begin to alter the color of the piece to some degree with your sanding of the finish. I doubt somehow that this is the case, but it's possible.

   If it's necessary for you to remove all of the finish, ascertain first whether or not the top of this piece is veneered. If it is, you'll have to use the greatest of care, especially near the edges of the tabletop to ensure that you don't sand through that veneer or you're not going to be very happy.

   I'd hate to surmise if any artificial colorant was used on your piece or not without seeing it firsthand. My guess would be that there has. If you need to sand all of the finish off of the piece in order to rid yourself of the problem areas, I'd suggest that once the sanding is complete, you should, in a controlled fashion, (don't let it get on the rest of the table parts) apply some lacquer thinner to the surface in order to see just what color you have if you were to apply nothing but a clear coat. If you don't like what you see at this point of the procedure, you'll have to take steps to alter that color to better suit your aims.

   The reason that I suggest using lacquer thinner is that it will evaporate quickly and you can resume work. If you use mineral sprits for this, you'd have to wait much longer for it to evaporate before you could continue with any sanding and such.

   There are numerous coloring techniques and products that could be used and numerous variations on those techniques. For your purposes and level of experience, you'll likely get along best by using an oil based stain to alter or enhance the color. You'll have to make certain that all of the finish is removed equally on all areas of the surface or the stain is guaranteed to take unevenly. Remember….don't sand through if it's veneer. Unfortunately, there's no way for me to suggest which product or color of that product you should use. Every manufacturer's color is different from the next. You'd simply have to choose one that looks like it will likely produce what you're after and then try it. Remember that there is no way that you can make the color lighter than the color you observed when you had the top wet with lacquer thinner. You must use a color that is as dark or darker. If its unsuitable for some reason, remove it the best that you can with some mineral spirits on a rag as soon as you can & and try again.

   Once you've achieved an acceptable color (be certain that the stain is dry before proceeding), you can apply most any finish that you like if you've removed all of the previous finish with your sanding. Various finishes offer various looks and resistance to wear, alcohol spills, water, etc. One of the most practical finishes for a coffee table, and your level of experience, if you want to use it without having to be anal about its' care, is oil-based polyurethane ( two or more coats). No coasters needed (even for alcohol) and you can wipe up spills or food goo with dish detergent and a rag, if necessary. While it's not considered to be a "premier" furniture finish, it is very practical. I usually use satin poly when I use it, but you could use one of the other sheens if you want or need more gloss. One potential downside to the use of oil-based poly is that it will yellow some over time. If this is unacceptable to you, you might consider using a water- borne poly which won't yellow, but IME, tends to scratch a bit easier ( two coats- no more). If you decide to go with a lacquer finish, you might consider using Deft as it can be brushed on, so should work well for you all things considered (two or more coats). (I'm imaging that you don't have access to spray equipment).

   You've made some mention of combining various types of finish on this tabletop.

   The fact of the matter is that these various types of finish cannot simply be layered willy-nilly. Not all of them are compatible with the others, and even if they are, the order of layering is highly important. If you'd like to know all the particulars of this, I'd recommend that you buy Bob Flexner's "Understanding Wood Finishing". Therein you will find everything that you'll likely ever need to know. I recommend this book so often that you'd think I was getting a kickback.

   Good luck to you and your project.

1. 
   CHohenberg | Jul 26, 2002 10:11pm | #7

   Thanks Goldhiller for all of these suggestions.  Following your recommendation, I just ordered a copy Fexner's "Understanding Wood Finishes".  I will take all of your advice to heart and I particularly like your suggestion of using lacquer thinner or minearl spirits to see how the even surface and color are after fine sanding.  You suggested an oil-based poly.  What do you think about  wipe-ons?  They might allow me to better approach the glass-smooth effect that the original (probably lacquer) finsh had.

   Thanks again,

   Charles

1. 
   goldhiller | Jul 27, 2002 12:38am | #8

   Charles,

   The basic secret to getting a glass smooth finish is…………….to get a glass smooth finish. That mahogany of yours has open pores in the surface. They may or may have been originally filled with a grain filler. They may simply have been filled with multiple coats of lacquer or shellac. The smoothest effect would be achieved, in this regard, by doing a bit of sanding, with some 320, in between coats to re-smooth the surface between the coats. Each successive coat leaves the surface closer and closer to imperfection free. This approach would leave the surface pores filled with the clear finish and the entire surface "dead flat". The result is a surface with no little dimples from the pores of the wood revealed and hence the glassier or glassy surface. That's the basics. This can be done with any clear finish as well as a grain filler. There will be some visual sheen and clarity differences in the end result depending upon which clear finish you should choose to use, but the procedure is basically the same for all of them. And, of course, there's the ever-important final rubout of the last coat.

   One of the advantages to using an evaporative finish such lacquer or shellac is that each subsequent coat dissolves into the previous coats and they become one thicker layer. When the final rubout is done, there is, therefore, less danger that one rubs thru and exposes underlying coats, with the telltale halo that would accompany such an event. However, lacquer and shellac do not have the everyday durability that most of us ( at least those that occupy our home) need for casual use of a coffee table.

   Reactive finishes, such as oil-based poly, or coalescing finishes, such as water-borne poly, do not melt into one another but rather bond to one another. Therefore it is possible during the final coat wet sanding and rubout to "go thru" and be left with a sadden heart, a halo around the area of transgression revealing the underlying coat, and the job of trying again with a successive coat. If you apply the final coat full strength from the can and see to it that you don't apply it too thinly, the odds are greatly reduced that this will happen. Nonetheless, one must be careful whilst wet sanding, especially near the edges. Experience will teach you how much is permissible. It will also teach you how much is not permissible. Don't bother whining (swearing is permissible) if this should happen to you. Remember, 90% of learning is a negative experience.

   If you use poly, I'd restrain myself from rubbing it out for a minimum of 5 days. More won't hurt. It takes oil-based poly about 4-6 weeks to cure out and reach a final hardness, but it should be safe to rubout in 5-7 days.

   Anyway, you can see how the glassiest of surfaces requires the absence of even tiny little "flaws" in the surface, which brings us back around to your question about using a wipe on varnish, or the like. You can do this, if you so choose, but…………..you're going to be at it quite a while. A wiping varnish or oil finish is thinned down, if you will, and this thinning is what gives you the ability to wipe it on. Consequently, the build up of a sufficiently thick result is going to require the application of many more coats. If you want the light to reflect across that table as if it were a piece of glass, get ready to append a lot of time applying all those coats.

2. 
   gerry001 | Jul 27, 2002 06:13am | #9

   A few minor comments here. First, I wouldn't suggest lacquer thinner to check the appearance, especially as it may be veneer and we don't know how it's sealed. A safer course would be naphta as an alternative to mineral spirits.

   About the wipe on finish, I've heard of people having to apply 30-40 coats to obtain enough film thickness to rub out the surface. Not very much fun there.

   Comparing poly to laquer and shellac, you would find that it takes more effort to achieve the same sheen when rubbing out the surface, as the material does not fracture as sharply. Still, it can be done.

   Achieving a high sheen surface takes a bit of planning , with careful surface preparation and film leveling. I would suggest you try this first on a relatively small scrap piece to develop your technique. That could save you a great deal of effort and frustration.

   On halo effects with poly, as Flexner notes, adjusting the time between coats will improve the adhesion as you then obtain more than just a physical bond. With this I would follow Goldhiller's advice, but especially make sure that your surface is fully leveled to a fairly high grit before applying the final thick coat. That can be done within the recoat time (before fully cured) and will reduce the amount of sanding needed on the final coat. I would also wait a bit longer before rubbing out water-borne poly, as opposed to oil-based, as it cures somewhat slower.

   The final variable that cannot be easily explained here, for any finish you choose, is the coat thickness. For instance, in one day I could apply heavy coats of shellac where it would not fully cure for several weeks. Alternatively, I could apply the same thickness over several days, and have it cure much faster. This is not often mentioned, since it is more difficult to measure. Yet another reason for practice on scrap wood.

   Gerry

3. 
   goldhiller | Jul 27, 2002 07:00am | #10

   Gerry001,

   Relevant points you make. I would concur with the most of what you've said. I didn't want to mention the extra effort (sweat) involved in rubbing out the poly or the "window of opportunity" concerning bonding and merging of successive coats of poly as our poster is a novice and I guess I felt that too much info at one time could be overwhelming and confusing. And yes, I failed to mention the shelf life of shellac in the event that he should be using some. I intentionally try to gear my responses to my perceived notion of the expertise of the poster (it's the only perception that I have) and the facilities at their disposal. Now that we know he will be helped by Mr. Flexner, it will be easier for him to pre-plan his approach and final rubout, but as you well know, there's no substitute for hands- on experience. Tis apparent that you are no novice at this.

4. 
   gerry001 | Jul 28, 2002 04:00am | #12

   Goldhiller,

   Agreed. It's always difficult to decide how much to say, short of writing several books. On that note, I'll also recommend several of Jeff Jewitt's books as a follow-on to Flexner. He adds quite a bit more practical experience.

   A curious question, though (since you mentioned it), on the shelf life of shellac. I know all that's been said in the literature, but I keep several bottles of different types. While some are used more often and freshly mixed from refrigerated flakes, a few have sat for several years. I have yet to find any going "bad" on me. Curious if you've actually seen this. These are all dewaxed.

   Gerry

5. 
   goldhiller | Jul 28, 2002 05:25am | #13

   Yes, I've had shellac that simply wouldn't dry properly on several occasions over the years. Shelf age ranged, to the best of my memory, from about 8 months on the shortest life to one batch that didn't go bad until it was nearly two years old. I've never had any shellac sitting around unused longer than that. Needless to say, after my first experience of this, I took to doing a test prior to usage.

6. 
   gerry001 | Jul 28, 2002 06:02am | #14

   Hmmm...thinking about that, I realized my basement shop isn't heated. It stays comfortable most of the summer, and winters get too cold for some finishes. Probably the same reason why Jeff Jewitt suggested keeping shellac flakes in the refrigerator. So it seems that shivering can be an advantage:-)

   Thanks, I'll keep that in mind

   Gerry

7. 
   goldhiller | Jul 28, 2002 07:06am | #15

   My shop is not air-conditioned, so things get pretty warm in there during the summer and the relative humidity becomes high, also. In the winter, it's heated to approx. 72F or so during the day, but I turn it down overnight to approx. 50F unless I have need to maintain higher temps for finishes or adhesives drying/curing. I'd be pretty sure, also, that this has an effect on the shelf life of that shellac. Good assumption on your part. Perhaps I should store my shellac over at your shop.

3. 
   BG | Jul 28, 2002 02:53am | #11

   I've refinished lot of mahogany for the 30's and 40's.  The first thing to determine is if the piece is a veneer or solid, and are the rings you speak of white or black.  White rings can be removed with potash (ashes form fire place) and vegatable oil and a little elbow grease, black means it's been absorbed into the wood.  Most if not all the pieces I have worked with have some stain on them.  Personally, I'd keep any and all sand paper away from the piece until I knew it's value..and the depth of the problem.  The most beautiful finish is a french polish.  There was an article on this technique in a recent issue of FWW.  Good luck