The size and closeness of the annual growth rings to the left is a great indicator that you might have a variety of redwood heartwood from the center of the tree. Since heartwood is very rarely cut and sold nowadays, it can give you an indication of the woods age. From a pinkish hue to a deeper red color, redwood can vary in color but some boards will also contain 'whitewood' as they were most probably curt from the outer part of the tree or a different species of redwood.
Wood can also wear unevenly on its surface from wind or water erosion. The raised parts of the board are actually a little tougher than the weaker parts that are usually between the annual growth rings. This phenomenon can also accidentally occur when folks use a pressure washer too close to the surface of the deck or project trying to remove old stain or paint. The weaker parts of the board will wear away faster and easier than other parts thus leading to a need to sand it smooth again. It is okay to use a pressure washer in a deck or wood project, you just have to be aware of how close is TOO close. It will vary so start out with the wand of the washer at a distance and then move closer and closer you notice it starting to do a little damage and then back off a bit. Easy does it in the beginning is good advice.
Using a board from the project as a sample board can give you a good indication of what the combination of stain and finishes you choose will look like on the actual wood after it has dried and cured.
Growth rings for each year the tree was living can be as wide apart as 3/8" depending on how the wood was cut all the way down to 1/16" wide or less for every year of growth. This 1 1/2" wide joist took 44 years of growth to produce just these rings. Redwood can grow to more than 15 feet in diameter!
In the old days before we had such access to a wide variety of screws for decks and outdoor projects the only thing available were nails. Although redwood is a very stable wood in dealing with expansion and contraction for wind and cold it must be sealed properly. Once a protective layers integrity is breached, any wood exposed to the elements, including UV light from the sun, wind, rain, heat or and cold temperatures, will decline much more rapidly. This loss of protective layer and expansion from heat and cold can expand and shrink much like a sponge will absorb water and then dry out again over time. This action will eventually, over time, move back and forth forcing the nails up and out of the wood that it was meant to hold down or fasten together. This picture is a good representation of that very movement over time. Untouched and left alone, you can see how far these nails moved up and out of the wood.
Sand until you remove all remnants of the old stain or paint. Remember, "paint peals and stain fades" is the main difference now that stain has come so far with technology pushing forward greatly over the last 20 years. Nails will have to be driven down again prior to the resealing or pulled and replaced with screws. Since redwood is a rather soft wood, pulling the nails can be problematic as you can damage the surface around it as you apply pressure to it. the need for a 'helper' board to spread out the pressure can help and save you from a further sanding.
Sometimes you have to be inventive in the moment to get the desired result.
Once the sanding is done you can begin to apply the stain. Remember, with stain, you get what you pay for. There is a time and place to cut costs and trim the budget of an overall project but for me, the choice of stain is not one of those places. You might regret choosing to pinch pennies on the stain. Choosing a very good quality stain like Cabot can save you alot of headaches in the future let alone alot of work in the future. The trick is to know where to cut cost. I have used Cabot brand stains for over 20 years and they have never let me down in quality. I am not endorsed by the stain company, I just like to make my work look as good as possible and yet stand the test of time. As I say to my customers, "My finished project IS my business card" as all of their relatives, friends, family and coworkers will be seeing it for the next 30 years. It is up to you to decide what your budget is and what you can afford. The money saved over replacing the deck with new wood will more than cover the upgrade to a good quality stain and Cabot stains are at the top of the heap.
And now, the majestic Redwood can live on and last for many more years to come.