I would have sanded sooner than the last coat but I thought I'd check to see what CLC says in their boatbuilding tips, and they recommend doing exactly what you've been doing.

https://www.clcboats.com/shoptips/finishing-tips/varnished_kayak.html

"24 hours between coats is a typical drying time.  You need a light sanding between coats, at minimum to give the first coat some "tooth" to stick to.  We use 3M Scotch-Brite pads between the first few coats. Before the final coat, I always wetsand with 400 grit. (Wetsanding, which requires special paper sold at any paint or hardware store, permits sanding with grits finer than 220.) The kayak will require a minimum of three coats for protection of the epoxy. It will start to look really glossy at five coats. More than that is probably overkill."

   Thanks for the reply Bob..... That's the thread I used and have a nice finish.  I was curious on what others may have done.  Regards......

   Thanks for the reply Bob..... That's the thread I used and have a nice finish.  I was curious on what others may have done.  Regards......

I did the opposite.  I sanded eary coats, thinking that the sanding helped establish a smooth surface as well as provide scuffing for adhesion of the next coat. Of couse the base was already well sanded, but there is something about laying down varnish that has a way of showing imperfections that you didn't see or feel previously.  So sanding early coats is a way to refine the surface to varnish quality.

Once I had a few sanded coats and the surface is smooth, the final coats only need to be scuffed.  So that's when I switched to abrasive pads.

Probably the lesson here is that both ways work.  You just don't want to be so agressive with your sanding that you impede the build up of the varnish.

i think bob santore got to the key point.  you don't want to sand so much that you prevent the build up of varnish coats.

i end up usually doing about 5 coats.  my approach is scuff it up to ensure the next coat adheres.  i also use the scuffing to identify drips and sags which i then take down with 400 wet sanding.  400 wet sanding is actually pretty agressive which is why i leave it primarily to take down imperfections that i detected.   

you can use 400 wet sanding, with a light hand, to scuff up the surface absent a scotch brite pad ...but i would simply say 400 wet can also take a lot of varnish off pretty easily.

ultimately, the final coat requires a lot of care if you are looking for perfection....unless you want to do a 'polished varnish' finish where you are actually creating, through polishing, the final surface.

i would also say that, just taking a couple steps back, signficantly improves, what on close inspection, is sloppy varnish work.  frankly, from a couple steps back, it is almost impossible to notice anything other than the most egregious mistake in varnish work.

h