i would go with a super dense foam…maybe something equivalent to the clarkfoam classic. then glass it with 10oz volan all around(10 bottom, 2 10 top) + gloss and polish. you can even do the cooperfish 4oz glass cap top and bottom, but imo the 10 oz with a super dense foam is plenty. how old is your dano?
Have you ever actually weighed the board with an accurate scale? 40 sounds ridiculously heavy. Also, I often see or hear people speak of a waterlogged board and claim that as the cause of a significant weight gain. In my experience of doing ding repair for over 40 years, i’ve never come across a board that could truly be descrobed as ‘waterlogged’.
As far as intentionally added weight. Consider this… In the mid 60s, a stock board was glassed with dbl 10 oz, top and bottom. Rails fully lapped, hot coat and gloss. The average weight of a 9’6" was 25 to 28 lbs.
I agree with SammyA. I’d be surprised if the board is really 40 lbs. You would have to have over a gallon of water in there to get it even close to that. (A pint’s a pound the world around)
Most of the solid balsa boards I make wind up around 30 lbs for a 10’ board. Occasionally they’ll get up to 34-36 lbs.
One thing you could do to add weight is do a heavy pigment color design.
Classic foam. Double 10 top and bottom. Lots of pigment. Multiple stringers. You could get over thirty pounds pretty easily with all of that.
Three fours on the deck and two fours on the bottom is I want to try for my next longboard. Four ounce lays flatter and requires less resin to fill coat it. Add to the fact that fibreglass adds the most of the strength, there becomes less reason to use 6oz (more resin in between the weaves).