: Like I said, I'll report my findings when I get around to sanding the hull.
: Regardless of how difficult it turns out to be in practice, I will not
: sand through the glass at the transition. Luckily, it's not a matter of
: guesswork, it's a matter of being careful. I may find out that it's more
: work than it's worth and I'll go back to placing the partial layer on top.
: Alternatively, I might find that it's not so difficult to sand at the
: transition. In which case, I've saved myself some aggravation during
: wet-out.

: I surprised that you've written-off this technique completely, having never
: tried it yourself and without any empirical or anecdotal evidence that
: it's responsible for failures.

: Upon further refection, I'm sure a case could be made for sand-through to be
: more likely with the partial layer on top. With that arrangement, you have
: to concentrate the sanding in that area to do the feathering. It's very
: likely that you'll hit some of the full layer of glass. Sounds like either
: method requires care not to damage the full layer of glass.

: Ross

I have sanded smaller areas of overlapping glass on parts of the kayak and found it more difficult to tell when I was and was not cutting through the layer.

I use the large layer over the smaller all the time on the inside of my hull for an expedition lay-up but I don’t sand it.

I don't know, perhaps I'm just such an outstanding sander and look at what I'm doing that no one else has ever noticed that;

When feathering the edge of a layer of glass on top of another, there is a very distinct edge I can see as I start sanding.

As I sand feathering the edge, I can see the whitish pattern of the cloth as I cut the edge of the top layer AND I can see the shiny surface of the untouched glass I'm feathering down to.

I don't touch the resin surface on the bottom layer of glass until I've broken the edge of the top layer. Once that happens I move on.

I have very clear visual cues every step of the way on my progress.

All this is happening while I am continuously moving my ROS back and forth along the cloth edge I'm feathering.

The times I have sanded a layer of glass over an underlying piece I found;

As I start to sand I see a matte surface where my sand paper it cutting and I see an untouched dip where the sandpaper has not cut below the step in the glass layers.

I can only guess at how long I can continue to sand before I will cut the glass of the top layer at the edge of the step. If I try to remove the dip I’m likely to cut the glass.

This takes a lot more effort and attention to know when to stop. The only visual cue I have here is when I see I’m cutting the tops of the cloth weave. It's too late!

I have done a LOT of sanding. I will match anyone for sanding skill. I have sanded all the glass off boats and not broken the resin soaked wood layer.

I’m not trying to bust your balls on this Ross, I know you’re already committed.

I truly believe is that it’s easier to screw up, ESPECIALLY FOR A NOVICE.