Mortar bed for whirlpool
How thick should I make the mortar under the support rails for a 6x3 whirlpool?
Will I still need leveling stringers if using mortar?
Which mortar should I use? I understand concrete and thinset are not acceptable.
My thinking is to sit the tub on (2) 4x4's, pour the mortar bed, then lower the tub.
Looking for recommendations, tips, and tricks to help this go smoothly.
The stringers hold the edges of the tub up so if someone sets or stands on it, it doesn't break off. If the tub was CI, they could hold the tub up, but it's still best to bed it into something in case the fastners rust or pull out.
Sand mix is a mix of mostly sand and portland cement. You can buy it premixed, or mix it up yourself with around a 4:1 ratio (sand to portland cement). It doesn't pour! You'll need to shovel it. Think wet beach sand. You mix it with enough water (you'll need something like a hoe to mix it) so it just holds together if you squeeze a ball in your hand. To help keep it from drying (it want to cure, not dry), put something on the wood subflooring - roofing felt or plastic, to keep the wood from sucking all of the water out before it can cure.
Stuctolite works as well, as can plaster of paris (but it sets up really quick).
You want it thick enough to hold together - that's nominally at least 1-1/4".
2 quick follow-up questions:
Should I also place the 6mil plastic under the tub, as well as, under the mortar (this would encapsulated the mortar completely)?
Should I place a full bed of mortar under the bottom of the tub completely, in addition to the support rails?
It somewhat depends on the design of the tub. Ideally, the entire bottom where you could step is supported. If the structure on the bottom of the tub is robust enough, the floor is flat, and the tub can sit on that structure, you may not need anything. The ledgers under the edges are to keep them from deflecting if you sit or step on the tub, not to support the major weight of the thing - that comes from what's underneath the tub. Most are better off with a full bed support. You need to keep the drain area clear so you can perform maintenance and install. A second layer of plastic under the tub won't hurt. The mortar will cure without exposure to air - it is a chemical reaction, not drying.