Here's a link to where the layout saga starts: Putting the top on the GRJ Layout. I've posted a few shots from the build below, but you can check that thread for the whole tale.
The basic steps were to install the plywood and join all the sheets and secure it to the benchwork framework. As you can see, I used 5x5 Baltic Birch sheets and they were joined between the beams into one continuous large surface.
Once all the plywood was in place and secured, then the edge profile was cut, that's where the curves were initially determined. The pegs were to keep all the sheets exactly aligned before they were stapled down with several thousand power staples.
Next came the support blocks for the first layer of fascia. The blocks butt against the benchwork supports and are cut to conform to the curved shape. They're screwed, glued, and clamped into place using construction adhesive. When that dries, they're permanent.
The blocks are then covered with 3/8" 3-ply Lauan plywood, the really bendable stuff, Tom calls it "wiggle wood". It's formed to the curved shape desired, and any bumps in the curves are smoothed by simply pulling the Lauan into the "perfect" curve. The adhesive used allows really large gaps and it dries into an immovable object! The first fascia layer is the top piece in the shot below.
The support blocks are generously covered with the Loctite PL3 adhesive, and the first layer of fascia is applied. Hopefully, the canvas catches any drips of adhesive, once it dries, it's a permanent part of anything it's attached to.
Here you see the gaps I spoke of, this varied as adjustments were made to get a smooth curve on this layer of fascia. Since this will determine the flow of the curves on the finished product, any adjustments need to be made now.
Next is the Homasote, any straight cuts were done with a utility knife to minimize the mess.
Curves were cut with a jigsaw with a metal cutting blade, and the vacuum was always nearby to get most of the dust. The Homasote was secured using 1" coarse drywall screws.
Once the first layer of fascia is on, the Homasote is laid, and the edges are routed to exactly match the curves of the fascia layer.
Final shaping and clean-up of the first fascia layer with the Homasote surface.
Homasote installed, screw heads covered, and sanded out. Well, mostly covered still have to get to a few of them.
Homasote filled, painted to seal it, ready for the next step.
Second layer of fascia getting adhesive to secure it to the bottom layer.
A flexible board is placed on top of the second Fascia layer to keep it firmly in contact with the bottom layer and it's all clamped with spring clamps.
A LOT of spring clamps!
That's all it took to end up with this.