There are acrylic, tile, and composite shower pans and each has its advantages and disadvantages. When installing, a shower pan mortar is the best material to put underneath. In this article, I will explain what kind of mortar to use for a shower pan.
As a general rule, you should use type N mortar or above. Type N mortar is around one part lime, one part Portland cement, and six parts sand. It’s strong enough but not too strong for a shower pan.
The main advantage of mortar is that unlike concrete it’s semi-porous, and allows water to pass through. However, shower pans have a bunch of different bottoms that have different designs. Below, I will explain whether you should use dry pack mortar, or wet pack mortar, and the key considerations for installing the mortar bed underneath your shower pan.
Why Type N Mortar Is the Best for a Shower Pan
There are 4 categories of mortar, and they are designed for different purposes. Each type of mortar has a different maximum weight it can hold before failing. Therefore, some types are used for building foundations, whereas, others are not load bearing and are used to repair existing mortar. Here’s how much load each of the different mortars can bear.
- Type M – 2,500 PSI – very heavy loads
- Type S – 1,800 PSI – medium loads
- Type N – 750 PSI – medium to light loads
- Type O – 350 PSI – very light non-load bearing
As mentioned Type N is the best to use for a shower pan. It’s designed specifically for the amount of weight a shower pan needs to hold. Here are the different uses for each of the different types of mortar:
|Type of Mortar||Used for|
|Type M||Very heavy loads such as building foundations, stone, and retaining walls|
|Type S||Shallow retaining walls, outdoor paving stones, outdoor patios|
|Type N||General purpose, indoor and exterior, most popular mortar for the interior of residential homes|
|Type O||Non-load bearing, repairing existing mortar.|
The difference between the different types of mortar is the relative amounts of lime, Portland cement, and sand. Here’s a table that shows how they differ.
|Type of Mortar||Composition|
|Type M||1 part lime, 1 part Portland cement, 12 parts sand|
|Type S||1 part lime, 2 parts Portland cement, 6 parts sand|
|Type N||1 part lime, 1 part Portland cement, 6 parts sand|
|Type O||2 parts lime, 1 part Portland cement, 9 parts sand|
As you may know, lime is made of limestone. Limestone is a sedimentary rock that forms from compacted sea shells, and over time turns into a hard stone that is typically white in color. Here’s a table that shows the relative percentage of the different materials used in each of the different types of mortar.
|Type of Mortar||Composition|
|Type M||7% lime, 7% part Portland cement, 86% sand|
|Type S||11% lime, 22% Portland cement, 67% sand|
|Type N||12.5% lime, 12.5% Portland cement, 75% sand|
|Type O||17% lime, 8% Portland cement, 75% sand|
Type N mortar has about a middle-of-the-road amount of each of the different materials used in mortar. A well-known brand of Type N mortar is Quikrete Deck Mud. The other main consideration is whether the mortar should be dry pack – where it’s made crumbly, or wet pack where it’s sloppy like mud.
Wet pack or dry pack mortar – which to use
Overall, dry pack mortar is better, it’s easier to shape than wet pack mortar. The reason is it holds its shape once you place it somewhere. Whereas, wet pack mortar will begin to run. Dry pack mortar is MUCH better for a tiled shower pan.
The reason is a tiled shower pan needs a slight angle to allow water to flow down and into the drain. With wet pack mortar, it’s more difficult to make this angle and smooth it out making it perfect.
How Thick the Layer of Mortar Should Be for a Shower Pan
There are various thicknesses that materials like mortar and grout should be to last for a very long time and to meet various building standards, especially for installing tiles. Here’s how thick the layer of mortar should be for a shower pan.
As a general rule, it should be thick enough to cover the entire underside of the shower pan and no more. The height of the mortar may need to be adjusted if the subfloor is not level. For example, if it’s raised on one side by a ¼ of an inch, you will need ¼ of an inch more mortar on that side.
There are many different styles of shower pans. Some can have grooves in the bottom that are a certain thickness. These grooves can, as an example, be half an inch deep. Therefore, you need to have a layer of mortar that is at least half an inch, and a bit more so that the mortar is underneath the entire shower pan.
Do You Have To Put Mortar Below a Shower Pan
Applying a layer of mortar is one extra thing that needs to be done when installing a shower pan. And the idea is to only do as much work as necessary and not more. So, here’s what the benefits of installing mortar under a shower pan are, and if it’s absolutely necessary.
Overall, you should put mortar below a shower pan. Avoid using concrete or plaster as these are not recommended. Mortar will provide increased stability, and will stop the shower pan from moving around. It will also be less likely to crack if the weight limit is exceeded.
An acrylic or fiberglass shower pan has a fixed weight capacity that is outlined in the specification. It’s typically around 300 lbs (136 kg). However, a tiled shower pan has virtually unlimited weight capacity. I explained this in more detail in this article about how much weight a shower base can hold.
A benefit of mortar is that it’s slightly cushy due to the sand content. When it’s put under a shower pan it disperses the weight. Rather than the weight being concentrated in a specific area of the shower pan, which can make it more likely to crack, especially when it’s getting close to the maximum weight capacity of a shower.
Amos Christen graduated with a bachelor’s degree in Interior Design from Drexel University — Philadelphia, PA. Since 2003, Amos has worked with top interior design professionals in this area, including architects and interior/graphic/lighting designers. As a skilled interior designer, Amos Christen is highly versed in fine arts and crafts and uses that to supplement his main area of expertise. He often publishes articles related to home décor on several websites, including Sprucetoilets.com, Sprucebathroom.com, and Mybesuitedhome.com. He also contributes to leading interior design magazines.