David,
It looks like you are doing well so far. You have not filled the grain yet with the number of coats you have applied and that is what you are seeing in your picture of the sanded piece. Depending on the grain in the piece of material you are varnishing and your sanding technique it may take more coats. At the end of the day you are looking for protection not perfection. Anyone that has done much
varnish work will tell you there is no such thing a the final coat. That's just the way it is.
A few thoughts based on my
varnish experience:
You should be able to sand and recoat in less than the 48 hrs mentioned above. What does the manufacturer say on the can? What temperature is your workshop and how does that compare to the application guidelines on the can?
What are you using to thin your varnish if anything? You will get as many suggestions about that as there are people offering advice. What does the can say? Some varnishes are tempermental about what you thin them with.
I use the Interlux Schooner product and use their #210 and #333 thinners sparingly. I prefer to use Flood's Penetrol product to help with brushing and flowout but everyone has their own preferences. Here in NC in the summer it gets hot and humid and if one can't lay down varnish in high heat and humidity then you never get any varnish on. The Penetrol helps alot.
I use the #210 thinner when I am varnishing at temps between 55 and 65 degrees but only in small amounts as it cause the varnish to "kick" more quickly. I use the #333 thinner to wipe the surfaces to be varnished after I vacuum the surface. A soft cloth wetted with 333 is used to wipe the surface before using the tack rag. Then I tack the surface. Not the only technique for sure, just what I was taught as a young man working for a wooden boatbuilder in Florida. It works, so I use it to good result.
With respect to sanding , when starting from raw wood I use 2 coats of sanding sealer before I begin the varnish. If I am going to use a stain or paste filler, that gets done before you apply the sanding sealer. Once the sealer is hard, I use a foam sanding block with a half sheet of 220 grit paper wrapped around it and carefully block the flat surfaces being careful not to sand holes in the stain if used and to not burn through any edges, round or square.
Once that is done, a first flattening if you will, I begin to build the varnish coats and in doing so fill the grain. Depending on the graininess of the piece, I usually will apply 4-5 coats with just enough thinning to allow for good brushing and flowout. Between each of these coats I sand very lightly using one of the 1/4" foam sanding pads with a half sheet of 220 grit paper wrapped around it, This gives you a reasonably flat sanding pad and reduces the tendency to sand hollows with your fingers and just a folded piece of paper. I apply each coat and allow it to dry overnight then sand and recoat the next day.
After these build coats I do a second flattening sanding using the 1/4" foam pad and 220 grit paper. This sanding however is more aggressive but not so harsh that I burn away all of the previous 4-5 coats. This is where I am looking to remove most of the remaining effects of grain and brush marks. Once that is done, its back to build up coats. When sanding the sharp or rounded edges of the pieces be careful not to burn through the previous coats. The varnish there tends to be thinner and is usually the first to break down due to wear or UV exposure.
In my experience, 8-10 coats is necessary to achieve the UV protection and durability we need here in the south. Your needs my vary depending on your location so only time end experience will tell for your specific needs.
Respectfully, I disagree with one of the posters above who recommended a highly thinned coat as your final coat. In his experience that may have worked for him but it hasn't for me and is contra to most discussions and reading I have read about the topic. Only your trial and error will tell if it will work for you.
With respect to how to hold the pieces so you can varnish all sides, I drill a small hole on the edges of things like my drop boards and install a #6 screw leaving about an inch of the screw sticking out. These are used to hang the pieces from the overhead or tall sawhorse using safety wire or anything else you have to use for a hanger. Be sure to secure these well as there is nothing sadder than dropping a nearly finished piece and marring the finish or worse yet breaking the piece. (Don't ask me how I know
)
Hope this helps, best of luck with your project.
Best Regards, John