Sentinel cement foam board for floor

[Scottoz1]

Hey all, Newbie here. 1st post. Getting ready to document a 13'9" V-hull build with my 14 year old son. Has any one used Floor and Decor's Sentinel cement foam board for flooring? 4x8x1/2" is 70 bucks and seems like is super strong and really light for the price. I can not find any weight specs. I will weigh the sheet if/and when I buy. I have read many readers builds and looking forward to use some and show you some of my own twists.
Tight Lines

 

[MrGiggles]

Hey all, Newbie here. 1st post. Getting ready to document a 13'9" V-hull build with my 14 year old son. Has any one used Floor and Decor's Sentinel cement foam board for flooring? 4x8x1/2" is 70 bucks and seems like is super strong and really light for the price. I can not find any weight specs. I will weigh the sheet if/and when I buy. I have read many readers builds and looking forward to use some and show you some of my own twists.
Tight Lines

The stuff they put under tile? It's heavy, and not all that rigid. A 3x5x1/2 sheet is 36lbs. I think the concrete would break if it was only supported by stringers, as most boat floors are. Concrete is not very strong under flexure, but is very good at resisting compression.

Hard to beat a well sealed high quality sheet of exterior ply IMO. Cheap, light, lasts for a long time.

 

[Scottoz1]

This seemed really light. Yes for tile backer but nothing like dura rock or hardi backer. this looked like fiberglass mesh concrete with a foam core. Seemed pretty stiff in store and durable. I might have to just buy the 5x3 for 35 bucks to test it.

 

[LDUBS]

If a 3x5 sheet weighs 36 lbs then it is a lot heavier than 1/2" exterior plywood. So, I guess the question is what is the benefit? There are too many "ifs" for my comfort. If you test it out come back and let us know how it worked.

 

[MrGiggles]

I have never seen it with a foam core. Would save on weight for sure.

I would still worry about the cement breaking. Guess the only to find out is to try it.

 

[Scottoz1]

Ok, Went at lunch. Bought a 3x5 piece. Weighed on ups scale at work. 11.4lbs. So it .76 asf. Coosa 15 is .625 asf and 1/2" plywood is 1.50# asf.
Next step to see what kind of weight and what spacing it can handle. Coosa is 200 bucks a sheet this 70 bucks. I will let you all know.

 

[MrGiggles]

Interesting, if it holds up you may be on to something.

 

[lckstckn2smknbrls]

If you put foam in between the ribs so the cement board does not flex that would help.
My question is how do you plan to secure the cement board down? Rivets will probable pull through as you set them, screws might fracture the cement board leading to mounting failure. Also if you have foam under the cement board and the boat takes on water is it going to be strong enough to resist the under floor foam trying to float to the surface?