Paste wax offers minimal protection. While water beads up on it, that is a manifestation of surface tension. It provides nearly zero resistance to water passing through. Polyurethane does not stick well to things. I had to refinish a table like this a few years ago. The owner applied a coat of poly to make it shinier. (File this under: "It sounded like a good idea at the time.") Besides looking terrible, about 1/4 of the table top had poly peeling off. Teak typically has a low-build finish on it. While generally thought to be "oiled" finish, it is usually a low build, very low sheen lacquer. Teak also contains natural oils that inhibit a lot of finishes from curing or curing hard. It needs a little knowledge and extra care in finishing. As I see it, you have a couple of choices if you can't or won't cover it: - Discipline to treat it with more gentleness, use placemats, etc. No finish is immune from physical damage. It's all a matter of degree and type of damage. The strength of the wood and its substrates also becomes a limiting factor. I have seen where people scratch and chip even the "indestructible" finishes. - Take it out and have someone strip and refinish it with a different top coat. What top coat that might be will depend upon the "system" that the place that you go uses, or if you are doing it yourself, what you are able to do based on your skill level, equipment and working environment. Despite this advice, if you choose to apply poly over the top and it does not work, you still have the strip-and-refinish option, it's just that you might be forced into it. The biggest mistake you can make with poly is to apply it too thick and un-thinned. Thin it down up to 50:50 mineral spirits, so you can wipe on the finish with a rag. Very light coats. While you will need more coats to get the same dry thickness, each coat will go on faster and is more foolproof for a beginner than brushing a good finish.

I had this same problem a couple of weeks ago on a dining table we received from a relative. The top was partially discolored (it looked like the original protective covering had been partially worn away). I was hesitant about sanding it but I was refinishing a couple of smaller tables at the same time, so I figured what the heck. I got some fine grit sandpaper and lightly started sanding a small section, just to see what would happen. The old finish came off pretty easily and it was kind of gummy little balls (I had to change paper often). I went ahead and sanded the whole surface and then applied a polyurethane clear coat (3 coats). The table looks really good now. I think as long as there is no stain in your table, you should be able to sand it down no problem.

You could use a deck wash, but depending on what kind of wood the two pieces are made of and the time they have been weathered, the success of lightening them may not be good. It sounds as if you need to use paint---pick the color and use a good exterior paint. Linseed oil is not a viable finish for any wood, as it has just about zero moisture/water resistance. See the link. Here is a link that might be useful: Linseed oil

So I'm back where I started, with poly. That's what I'm going to do. But first I'll remove the old shellac with denatured alcohol then apply a thin coat of new shellac. A light sanding, then a few coats of poly. I'm guessing some of you will recommend against this. I've read in some places that poly won't adhere well to shellac, but I've read in enough other places that it works just fine. I love the look of the shellac so I'm willing to risk it. I just don't think I'll get that same look with poly alone. The problem with the glass idea is that I change the size of the table somewhat frequently. I have 12 leaves, so it can go from a small table for four to enough room to seat 14 adults comfortably. I really like being able to just pop in a couple of extra leaves if friends or family come for a meal, or take them all out if we need floor space. I can't thank you all enough for your help and advice. I've learned so much in this whole process! I'll post pictures when it's done. :)