There are two basic kinds of mud used in tile work.

1) Deck mud. aka dry pack. This is used on floors. In showers it is used for the pre-slope under the liner and the final deck above the liner.

2) Fat mud. aka wall mud. This is used to float mud walls, and to float shower curbs.

**Deck Mud**
Deck mud is used on floors, and is made of portland cement and sand. The ratio of sand to cement is anywhere from 4:1 to 6:1, every mud man has his own preference. John B. likes 5:1. That's by volume by the way, so it's 5 shovels full of sand for every 1 shovel of portland.

It's mixed with a minimal amount of water to the consistency of sand castle sand. It should just barely hold together if you make a ball in your hand.

It is possible to buy pre-bagged deck mud at tile stores. It's a "just add water" product, but can be difficult to obtain for diy'ers.

Another option is to use Quikrete "Sand Topping Mix" and sand. This works well for diy'ers, because it can be found at home centers. The mix is already about 3:1 sand to portland, so to get deck mud we just need to add some sand. If you buy a 60 lb sack of "Sand Topping Mix", add about 15 to 30 lbs of sand to it to get to 4:1 or 5:1. For an 80 lb sack of "Sand Topping Mix", add about 20 to 40 lbs of sand to get to 4:1 or 5:1. Here is a graphic that describes how to make Deck Mud with a 60 lb sack.

**Fat Mud**
Fat mud is different than deck mud because it has lime in it, plus it's mixed with more water. The lime and extra water help it cling to vertical surfaces. This is easier than deck mud, just buy one of the following and mix it up.

Edit by Mike2:

Here's a great Mud Calculator DaveM put together. A real handy tool for calculating how much mix/sand to buy.

Mud Calculator