Re-varnishing

Once you've done the prep work sanding, it's exactly like varnishing the first time.

1. how many coats does it need? - 3 to 5 coats minimum, depending on how thick the coats are

2. do I need to sand with 400 between coats? - only to remove surface irregularities like brush marks and drips. I like to use the technique where you don't start sanding until the first few coats are thick enough that you don't just sand them all off again, then only sanding when there are drips and brush marks.

3. do I need more than a quart of varnish? - depends on how big the boat is

Laszlo   

if its a normal size kayak, one quart will get you through a refinishing easily...and depending on your technique will probably get you something like 3 to 5 coats with some varnish to spare for little touch-ups.

i only sand between coats to deal with a drip or run and to slightly abraid the surface so the next coat will attach properly.   for the abraiding i just go over it lightly with a scotchbrite pad and 400 wets sand to deal with a drip or sag.  if i am careful, no sanding occurs.

the most important thing is to then wash the boat after any sanding/abraiding and to work in as dust free an environment as possible.  the CLC tips for varnishing and refinishing is a great little resource if you did not see them and can be found here:  https://www.clcboats.com/shoptips/finishing-tips/ 

Two suggestiins. 

First, are you re-varnishing with the same varnish that was originally used?  If not, you should call the tech support for varnish you plan to use this time to make sure that there are no compatability issues.

Secondly, follow the manufacturer's directions for application.  If they say that you should sand between coats, then do it.  

   Thanks ,yeah I'm using same varnish as before. That's pretty much what I'd planned on doing but came across some conflicting info .

 "......  if its a normal size kayak,...."

Not sure that that is. But for most of mine I start with a quart.......or whatever was left from the last one....and go on untill I need another quart and go to the local marine store for a replacement.