Being a remodeling contractor, I do my best to have a firm grasp on all types of construction trades. When I began working in the industry, I believed that certain traditional methods were to only be executed by aged craftsmen with years of experience under their tool belts’. One of my biggest anxieties when I started tiling was teaching myself how to work with dry-pack mortar. Whether it was to flatten a floor or to pitch a shower pan, it seemed to be very complicated. From the way you had to mix it, to forming the screeds, to pulling the mortar, to ensuring a consistent pitch or perfectly flat substrate. Long story short, with proper knowledge and patience it is a great technique to add to your arsenal, and it is actually somewhat fun.
Add the proper reinforcement to the shower pan. I used an unbounded mortar bed, so I have a tar paper slip sheet on the subfloor with wire mesh stapled to the top of it.
Determine the drain height, and the height of your perimeter screeds relative to the drain (in my case with the drain system I used dictated the drain height above the subfloor). Generally you want 1/4″ of pitch per linear foot for the water to drain. I measure the furthest point in the pan from the drain and calculate the 1/4″ of pitch per linear foot. The furthest corner was 36″ from the drain, so I make the pitch 3/4″ above the top of the drain for the entire pan. This means some areas of the pan, will have a pitch greater than 1/4″ per linear foot, but that is okay.
The flange of the drain with loose mortar. Loose mortar is essentially the same thing as dry-pack just with more water. Once that is jammed under the flange, and the flange is level, the 4th step is to mix the dry-pack mortar. As a side note, 3/4″ would be the thinnest I would ever install dry-pack, I usually aim for the thinnest areas to be roughly 1 1/4″ thick and try not to go greater 2″ thick.
Step-4: I have always mixed my own dry-pack mortar with sand and cement. Many other guys use premixed mortar with the proportions already sorted out, but it has been just as easy for me to make my own, and I like the way that it pulls, so why change now?
The ratio that I prefer is 5:1, sand to cement. You want to add all of the dry ingredients to the mixing container and dry mix them prior to adding any water. Once they are consistently blended you can start adding in sponges full of water. You will not add a lot of water at all, honestly there is no exact amount that can be specified as sometimes the sand is wetter than other times when purchased. You basically want to wet the cement particles and activate the cement, but not make the mix too wet that it shrinks once the water evaporates. Even a little bit too much water makes the mix stick to itself and this makes it much more difficult to float and get smooth.
Essentially you want your dry-pack to be the same consistency as sandcastle sand. Not too wet, not too dry. If you put some in you hand and squeeze it into a ball in your fist, you should be able to throw it up in the air and catch it without it breaking.
If you poke the same “sand ball” with your finger it should break apart.
Once you drop the mortar out of your hand, your hand should be relatively clean and not wet. The pictures should help you gauge the consistency.
I then form screeds with the dry-pack around the perimeter of the pan. I start my screeds at the initial mark I made that was 3/4″ above the drain. I then build the screeds with the dry-pack, compacting it by slapping it with my steel float. I next use a straight board or screed to make them level. I generally start against the wall with the screed, put the level on top of the screed, and bang it into the dry-pack so that I have a perfectly level depression. I then pull the rest of the excess mortar on the screed to the same height as my depression.
By continuing the same process as mentioned above, you can complete all of your perimeter screeds. By the time you finish your last wall, the screeds should all connect, be perfectly flat, and perfectly level.
In the process is to fill in the inside of your screeds. Start shoveling in your dry-pack, spreading it out to get a general sense of how much more or less you need in the different areas. You want to leave the dry-pack high at this point to ensure that once you compact it with your steel trowel, it is not below the height of your perimeter screeds. Once you have the proper amount necessary, start beating it down and compressing all of the sand particles with your steel trowel. Any low spots should be raked out and more mortar should be thrown into it to ensure it bonds to the existing dry-pack. You should then compact it again.
Once you have the correct amount of dry-pack you can start screeding the inside area of the pan using your perimeter screeds and the drain as a gauge to how much mortar needs to be removed. I usually have a few different size screeds cut at this point so you can constantly switch to the correct size without banging into walls, being too short, or being too long.
Once you are all screeded, the seventh step is to take a wood float and rub the top of the dry-pack to smooth out any imperfections and flatten out the mortar so that there are no high spots. After rubbing it with a wood float remove any excess mortar that is on top of the pan and slick it down with a steel trowel. This will bring up a tiny bit of water (unnoticeable) and seal the sand and cement to make a very thin smooth “crust” on the top layer of the dry-pack. It embeds any loose sand/cement particles. Now it is time to clean up and admire your work of art.