Gypsum? On subfloor

[46&TOOL]

Replacing shower and decided to redo bathroom flooring at same time. Got the tile up and there is something that appears to be thin Gypsum or drywall (1/4 in.) Is this normal? Just a different underlayment? I only ask because the previous owner tried flipping this house and messed up several things before giving up and selling it to us at a loss. I've replaced several types of flooring over years and never came across this before....

 

[46&TOOL]

Replacing shower and decided to redo bathroom flooring at same time. Got the tile up and there is something that appears to be thin Gypsum or drywall (1/4 in.) Is this normal? Just a different underlayment? I only ask because the previous owner tried flipping this house and messed up several things before giving up and selling it to us at a loss. I've replaced several types of flooring over years and never came across this before....

 

[highup]

If it's actually gypsum and it gets wet it will fall apart and get moldy. I don't recall quarter inch gypsum. If he was cheating using regular drywall there would be paper on top of the gypsum. That should be very easy to identify as it will crumble just using a screwdriver.
There are a lot of different quarter inch underlayments for ceramic tile that might resemble gypsum. Most have a pattern empressed into them. These types don't look like cement board which used to be a more common underlayment for tile.

 

[highup]

There's no reason for a survey. Gypsum or sheetrock is made for walls ceilings and nothing else.
There are many newer underlayments for tile including foam and fiberglass and even plastic grid materials that resemble a waffle iron configuration.

 

[highup]

You posted twice. I just now looked at the image. If that is gypsum sheetrock that was just plain stupid. If it is Sheetrock that also looks what might be on the walls of the shower. If that's the case it needs to be stripped down repair any rotted wood and use the proper backer board for your tile installation. I don't do tile but I know that showers are extremely difficult and must be done correctly. You do not ever skimp on proper procedure when doing a shower.
Don't use gypsum on the walls or the ceiling when installing tile.