For seedlings, I like to use plain garden soil mixed 50-50 with fine gravel used in aquariums. Some vermiculite can be mixed in to lighten it up, since it is very dense and heavy. Please, DO NOT USE PEAT if you plan on keeping the seedlings in the same mix for more than 2-3 years. Smashing the leca may result in very fine clay particles, which may not work well, but I don't know for sure.

You've apparently thought this out, and you seem to know shower requirements. But just to clarify let me drone on a bit so I know we're on the same page so to speak: There are a few rules for shower construction, you're apparently aware of them but I'll repost for the heck of it: 1) When the shower is complete and with the drain plugged, the shower needs to be able to hold a 2" depth of water over the drain before water flows out of the shower. 2) The waterproof membrane in the shower must be pitched to the drain. 3) The shower floor should be pitched to the drain a minimum of 1/4" per foot and a maximum of 1/2" per foot. "Regardless of whether I use a preformed pan or build a mud bed, doesn't the fact that the entire pan will be lowered 2" below floor grade remove the need to slope the shower 1/2" per foot?" You want a "curbless shower", which means a non-vertical transition at the shower threshold. Meaning at the shower entry there is simply an "angled" transition from the flat bathroom floor to the sloped shower floor. With a 36" by 48" shower with a center drain, the drain will be 18" and 24" from the walls of the shower. To lose 2" of vertical over that short of a distance, you'd have to pitch the floor steeper than the 1/2" per foot maximum pitch allowed by code. That is for a shower with a sloped floor transition at the shower entry, what we refer to as "curbless". If you are willing to have a vertical drop at the shower entry, then you could use a premade pan like the laticrete pan. In general, the pans use a 1/4" per foot slope. The pans will also have a thickness of material at the drain. I don't have a schematic that shows the cross-section thickness of the hydroban pan, so I'll use the equivalent measurements from a Kerdi Tray for illustrative purposes only: Let's say you're going to use the hydroban pan, 36" by 48". The pan will have a thickness at the drain, let's say 1" thick. The longest dimension from the drain to the pan perimeter is 24"; half of the 48" dimension. The minimum shower slope is 1/4" pitch per foot, so the vertical drop over those 24" will be 1/2". Your pan will be 1-1/2" thick at the perimeter, the pan will have a vertical drop from the edge of the pan to the drain of 1/2", and at the drain the pan will be 1" thick. Getting back to the required 2" depth of water requirement: The pan only has a drop of 1/2". For code purposes, you need 2". So the edge of your pan will have to be 1-1/2" below the height of your bathroom subfloor. With the pan having a total thickness of 1-1/2", you'd need to cut down the joists in your shower enough so the top surface of the subfloor within the shower is 3" below the top surface of the subfloor in the bathroom. With the pan installed this way, you'll have a flat bathroom subfloor, then a 1-1/2" vertical drop down into the shower before you hit the edge of the pan, then the pan will slope another 1/2" to the drain. There's your 2" requirement. Made up of 1-1/2" of vertical drop at the shower entry, and 1/2" of pitch across the pan. So while there may be no traditional curb that you have to step up and over to get into the shower, there is a small step down. So by definition it's not what we call "curbless". I hope that makes sense. "With a 36" x 48" shower, I don't see there being the option of keeping a linear drain 48" from shower opening. [Drain placed on the back wall, is the 48" length, putting the drain less than 36" from the opening.] " With no drawing showing your door location, we're simply looking at this from different perspectives. You know your overall design. I don't. The description I wrote would require the entry to be on a 36" dimension of the shower and the linear drain to be 48" from the entry, on the other 36" wall. That 48" run will allow you to pitch the floor 1/2" per foot over a 4' distance for a total of a 2" vertical drop. That's simply one description of how you could get a true curbless shower (with a simple sloped floor transition) using the dimensions you gave. I hope all that helps, at least a little! lol

Hmm...well I never have managed to do things the easy way. So, basically it looks like if I can't get to the subfloor from underneath, I'll have to pull up a tile and figure it out from there. (Should be really interesting trying to keep Inspector Gadget and the Intrepid Explorer -- who's intrepid only when he's *behind* the Inspector -- from investigating the excavation.) Are there specs for minimum support requirements? And are there any considerations for tile choice? (I'm thinking clearance ceramic tile at Lowes.) With ceramic tile and epoxy grout what would be my best bets for subflooring? 3/4" plywood topped with cement backerboard? Thanks! Lorree

It depends on the plants you intend to use. For bog plants a mix of peat moss and perlite is often a good choice. For cacti, the cacti mixes sold in stores works well. For most house plants, standard potting mix may be used. Vermiculite, bark chips, coconut husk chips, and some orchid mixes are also suitable. Do your research and feel free to experiment. Of course please let us all know what you've found worked for you! : )