On Sunday, October 22, 2017 at 2:50:48 AM UTC-4, wrote:
Rob:

My hunch is that DadiOh is on the right track-- especially if this is in full sun, the Sun's UV will break down that wood with a reasonable amount of speed... But a week's a little quick.

However, just to check-- you said "cloth." How often did this cloth get wet? Did the cloth retain any moisture? Moisture, in the form of water, oil, (or the protectant that you're intending to apply, for that matter) will darken wood.

I would recommend first, get the cloth off the table; second, make sure the teak is completely dry. Completely. Use a hair dryer (or heat gun on LOW and pulled WAY back from the surface-- about 2 feet+ if you use the gun) to see if that darkness disappears with heat. If so, do not coat the surface until that moisture is gone.

Regardless, yes, you should sand the surface prior to coating. Often things called "bare wood" coming out of furniture plants are still coated with.... something to help protect them while in the company's possession. It could be a waxy or quick oil coat. I've even seen thin plastic-y veneers used for this purpose. if you don't scruff that stuff off, you'll get an uneven, blotchy finish-- if your finish sticks at all. In addition, if DadiOh is right, and the surrounding lighter tone is from UV breakdown, then you need to get through that graying dead-wood fiber to get your coat down to the good lumber you're intending to coat.

For an outdoor teak table, no need to go any further than 120 or 150 grit paper WITH the grain (goes w/o saying) and I wouldn't go to a power sander of any variety fr this. Just scruff the surface until you see color get reasonable consistent throughout (with tolerances for grain and different boards of course.) If you run into plastic or wax, keep going until that's gone-- plastic you'll see pieces peeling upward from abrasion and heat; wax will clog your paper with sticky residue pretty quickly. Get all that dust off of there, and then coat it with a quality oil--

The object is teak; I'm assuming that you'll have it in sun or water per the above comments and from your original post-- the word is QUALITY oil. Don't go to Thompson's for this.

You'll need to recoat this item fairly often in the outdoor environment, assuming full/partial sun and moisture. Tung Oil and Boiled linseed oil (AVOID the RAW Linseed Oil at all costs for this project) are both traditional teak finishes but you need to make sure that the one you grab is rated for outdoor/exterior use. Additionally they often need to be recoated more often. Anything that calls itself "X Oil FINISH" has other ingredients in it; it may add a sheen. If that's what you want, then that's fine, again, just assure yourself you can use the stuff outside.

Avoid "teak oil" 'cause you can't tell what it's really made with from manufacturer to manufacturer, and it's usually marketed at a higher price point to "teak consumers" even though it's little more than a combo of the above two.

I've had good success with General Finishes Outdoor Oil for teak & cedar-- decent UV and great water protection. Cabot Australian Timber Oil's line is good as well. For my money and time, I'd go General for this project-- it lasts longer than the traditional products and is a little more viscous than the Aussie.

There are also a bunch of other "Just fine" products on the market for what you're doing-- there's honestly not a lot of precision required on this project. But there's even more junk, and the junk is usually the first thing that someone can put their hands on at a big box store. If you've already picked something up, post it here, and someone will definitely get back to you with a metric from 'quality to junk.' If you don't have anything yet, head to your nearest Rockler, Woodcraft or other local quality woodworking shop.

Finally, I've seen a lot of slatted teak tables recently-- not 6" x 2" boards you'd see on a traditional picnic table, but instead about 3/4" x 2" slats with another 3/8" to 1/2" of space between them. If your table looks like this, don't forget to do the sides of these slats. Saturate a rag in your finish, floss it through the slats, and make sure you get those sides. (...then dry/dispose of the rag according to our knowledge of finish disposal-- any of these products has the potential of spontaneous combustion.)

Good luck-- Hope that helps.

S