Why sand pack for showers?

[Stephen Tashiro]

From the internet, I gather that the floors of showers are generally constructed over a base of "sand pack". Why is this material used instead of an ordinary concrete mix?

(Of course, from the perspective of tearing out old showers, I greatly appreciate the sand pack.)

[roger wiegand]

These days shower floors are almost invariably made with either a pre-fab base or an impermeable membrane topped with thinset and tile. In past times a " mub job" involved using a very stiff mortar (what I assume you mean by sand pack) that was compacted into place and served as the substrate for the tile. The dense sand/cement mixture could be shaped and sloped to provide drainage; a more conventional concrete mix would tend to level out and be harder to maintain a uniform slope to the drain. It was also applied in a relatively thin layer over a wire mesh and waterproofing material, concrete with aggregate would tend to break up in such a situation. The "mud" was also used on the walls of the shower, it would be difficult to get concrete to hang on in that orientation but the mortar will stick just fine.

[Stephen Tashiro]

These days shower floors are almost invariably made with either a pre-fab base or an impermeable membrane topped with thinset and tile.

Is the membrane usually set on "sand pack". These videos show the membrane set on sand pack.

https://www.youtube.com/watch?v=1vNapRUC5Sw
https://www.youtube.com/watch?v=9vBwwsSTCXM

[Jim Andrew]

These plastic shower units do not have a solid floor, in most cases, and to keep the floor from moving up and down, creating a plumbing leak, found you have to throw some sack crete under the floor of the tub or shower unit. I always mixed it up wet, but barely. Whirlpool tubs always were recommended to set in some kind of mortar base, you can use a type of plaster or sack crete.

[Ken Fitzgerald]

I am a big guy. You only have to step into one those plastic showers or tubs where they haven't put mortar or sand to figure out why they recommend it.

[Ron Citerone]

These days shower floors are almost invariably made with either a pre-fab base or an impermeable membrane topped with thinset and tile. In past times a " mub job" involved using a very stiff mortar (what I assume you mean by sand pack) that was compacted into place and served as the substrate for the tile. The dense sand/cement mixture could be shaped and sloped to provide drainage; a more conventional concrete mix would tend to level out and be harder to maintain a uniform slope to the drain. It was also applied in a relatively thin layer over a wire mesh and waterproofing material, concrete with aggregate would tend to break up in such a situation. The "mud" was also used on the walls of the shower, it would be difficult to get concrete to hang on in that orientation but the mortar will stick just fine.

I learned something today, and you explained that perfectly! Even though I did not ask the question, I appreciate the nice answer!

[Wade Lippman]

I am a big guy. You only have to step into one those plastic showers or tubs where they haven't put mortar or sand to figure out why they recommend it.

The shower in my cottage didn't have anything under it; it was just a matter of time until it broke. I put down some fiberglass. Looked horrible, but much easier than repairing it properly.

[Peter Christensen]

We had a rat bag of a builder and I bought the plumbing fixtures. Told him the instructions for the shower pan called for setting the base in mortar. He told me nobody does that and to go get one that didn’t need mortar. I went back to the plumbing showroom and they couldn’t find one in any of the 3 or 4 lines they sold. Builder finally said it would be installed with mortar. When it was installed I couldn’t see any signs of mortar or the empty bags. So I drilled a hole underneath from the basement and poked around with a coat hangar. No mortar. When confronted he said the installer screwed up and he would fix it. Second time they got it right.

Had to check everything to make sure they didn’t cut corners.

[Peter Rawlings]

From the internet, I gather that the floors of showers are generally constructed over a base of "sand pack". Why is this material used instead of an ordinary concrete mix?

(Of course, from the perspective of tearing out old showers, I greatly appreciate the sand pack.)

In the world of shower waterproofing, there are essentially two methods, with some tangential variants. Either is viable if done correctly. Way too much info on YouTube and elsewhere which would lead one down a path to failure. Best to understand how systems work to assess whether what you're reading/seeing is BS.

Briefly and over-simplified:

1. Conventional liners with weeping drain. This consists of two layers of drypack mortar. The first is a preslope on top of which the PVC liner is installed. The liner directs water that moves through the upper drypack layer(and it will) to the weep holes in the drain body. On top of liner is another layer of drypack. Drypack is porous to allow migration of moisture to liner. Thus the primary water drainage is on top of floor tile to drain grate. The secondary plane of drainage (and you want one) is the sloping liner directing moisture to the weep holes. Walls are typically tile backer such as Durock or HardieBacker with moisture barrier behind or on top, but never both. This method has been around for decades and works, but is frequently compromised by improper installation.

2.Surface applied membranes are designed to put waterproof layer directly under tile on entire installation. More recent to the game, but just as viable, if not more so, IMHO. These are typically semi-liquid such as Laticrete Hydroban or Custom RedGard or sheet membranes such as Schluter Kerdi or USG Durock Membrane. They use specific drains that have large bonding flanges. Many badly thought-out home-brew variants that I'd steer you away from, but generally I like these a lot. It's all I install for clients. More expensive, but worth it as it takes the potentially moist upper drypack layer out of the equation. In my experience the quicker a shower dries out after use, the less chance for mildew. I'd use it for my own, and that's saying something, because I analyze things ad nauseum.

For the best info I've found on the web for tile and waterproofing in general, I recommend John Bridge Forum.

https://www.johnbridge.com/vbulletin...splay.php?f=11