Is "optional mortar bed" necessary?

YES !!! it will help to set in mortar .

Cal

jammin said:

I am using a Sterling Acclaim unit with webbed bottom. The floor is pretty level. Is setting in mortar not recommended? Will it help to set in mortar?

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I, personally, would not. If the webbed bottom is flush with the bottom of the threshold, then you would have to squeeze the mortar out from under the webs, (which would be almost impossible), or the base will be above the floor and/or uneven.

jammin said:

I am using a Sterling Acclaim unit with webbed bottom. The floor is pretty level. Is setting in mortar not recommended? Will it help to set in mortar?

Click to expand...

either way it should be installed level. i've seen guys stick wooden shims in. it works but for how long. flip a coin its your house! my house all pans and tubs are set in mud. its an easy way to get it level and have support under most of it.
install it already so we can move on to your shower valve.