Pool Construction with Wood?

Thanks in advance for feedback.

Perhaps logic is not relevant here, but in midst of a pool remodel that includes addition of 4' x 8' sun ledge with bubbler to replace old style steps. I was concerned to see the builder planned to use 2x4 and plywood decking to "form" the sunshelf and then rebar over top to strengthen the marcite structure. This leaves a void of underneath and means the wood stays in the pool??

Questions for the experts:
1. Why would you not fill the entire void with marcite to make solid?
2. Is a wood box really an acceptable frame for which to pour marcite and then diamond brite on top of?
3. My supposition is that wood will rot over time, am I missing something? They don't even use pressure treated wood.
4. This deck is likely to have 1000lb+ on it, is this really safe built this way?
5. Diamond Brite is brittle...........won't a tiny flex mean cracks?

Again. perhaps I am applying logic here, but marcite on wood to me means marcite cracks when wood flexes(or rots) AND marcite flex means diamond brite flexes and cracks and then water gets to wood and more issues.

Not sure I understand what you are describing.
1) No way anyone would leave wood underwater in a pool. It's obviously a temporary form. Can't leave untreated wood as it rots, can't leave treated wood as the treatment isn't safe in the water.
2) Forming with wood is normal. While it sounds like it's reinforced concrete, which can be used to cantilever over a space, the description is hard to picture.
3) Especially since it sounds like one can swim UNDER the ledge, possibly getting stuck there. Plus it's a GREAT home to grow algae in.
4) Filling a space with concrete can be very expensive...and heavy.

Thanks Carl-

Let me clarify:

1. Current entry to pool is three steps down to shallow end.
2. These 3 steps will be replaced with a sun ledge
3. What I am describing is how contractor has started to create the sun ledge
4. My expectation was they would form up the sun ledge and reinforce with rebar and then fill the area with concrete, remove the forms before shaping and applying bonding agent and Diamond Brite
5. Alternatively the have built a plywood and 2x4 frame that they are surrounding with rebar and connecting to existing pool walls to form the sun ledge-the void under this wood frame they are describing they are leaving empty. They describe that they are planning to leave the wood embedded in concrete(with nothing on the underside as this will be an empty void under the ledge.


My concern is that the ledge will be supported by wood 2x4 and plywood, with rebar over the top/embedded in concrete. And, won't the wood both flex and rot from the underside over time and eventually crack the concrete and Diamond Brite?