When it comes to the installation of your shower floor, there are some issues to consider. If you do not have anything over-top of your plywood when you apply mortar to create your pre-slope; you will compromise your plywood floor as illustrated in the photo below. Your mortar bed will evaporate into your plywood, eventually rotting your floor. It’s important to take the right steps to prevent any damage to your shower floor.
There is a solution to this: Use the Mortar Reinforcement Kit that is installed directly on your floor. This kit enables you to have full protection of your plywood. It includes a Synthetic Lath and Tar Paper.
This is recommended to be used when putting mortar on any wooden sub-floor in order to reduce cracking of your mortar bed from moisture being drawn into the wooden sub floor. You can use the 16 Sq/Ft or the 11 Sq/Ft size