Concrete Mud Pan: Reinforcement Needed?

When it comes to concrete mud pans, such as those used in showers, reinforcement is not always necessary. The size and scale of the project, as well as local building requirements, will determine whether reinforcement is needed. For example, a small residential project like a pathway or shed floor likely won't require reinforcement, whereas a carport or garage floor should have reinforcement due to the weight and traffic they will bear.

If reinforcement is required or desired, there are two main options: rebar (steel rods) and wired mesh (a flat sheet of melded wires). Neither will rust inside the concrete due to the lack of oxygen, and thicker slabs are better for steel reinforcement.

Rebar and mesh reinforcement options

Concrete is a brittle material that performs well under compression but is less effective under tension. Reinforcement is used to absorb tensile forces, preventing cracking and extending the life of the concrete. Steel reinforcement in the form of bars (rebar) or mesh has been used for many years. More recently, concrete technology has included reinforcement in the form of fibres, such as polypropylene, glass or steel.

Rebar

Rebar, or reinforcing bar, is made from steel and is used to prevent cracks from forming in concrete slabs. The steel bars are hot-rolled and come in various sizes, grades and finishes. Most rebar features heavy ridges to assist in attaching the reinforcement to the concrete. Rebar is a versatile option, which is why it is widely used in the construction industry.

Rebar is beneficial as a tensioning device to support structures and hold the concrete in a compressed state. It is a good option for larger projects, providing considerable strength to any structure. Rebar can be arranged to meet the specifications of each job, but the length of the bars usually matches the concrete slab, and the weight depends on the thickness.

One downside of rebar is the weight and size of the bars. Rebar often requires more space in the concrete than mesh, and the concrete needs to be thicker to prevent the steel bars from being flush or above the surface. Rebar requires precise placement and securing of the steel bars, making it a more labour-intensive process. It takes longer to install than mesh, and it may end up being more expensive overall.

Mesh

Wire mesh is made from steel and is widely used in construction projects. It is manufactured from steel and sold in large sheets, which are cut to size on the construction site. It is available in stainless steel and polymer varieties, although these are often more expensive. The mesh is inserted into the concrete mixture to provide support and prevent chips, cracks and crevices from forming. Like rebar, wire mesh can significantly prolong the life of the concrete slab.

The mesh provides added strength that can prevent cracking caused by fluctuating temperatures. It flexes as the concrete expands and contracts, helping to prevent damage. Wire mesh is generally cheaper to use than rebar since it utilises only thin steel bars. It is also easier to work with, making it a good choice for DIY projects and residential applications.

However, wire mesh requires considerable space on a construction site since the sheets are delivered and cut on-site. It must be placed carefully and maintained in position to ensure adequate reinforcement. If the wire mesh moves during the pour, the concrete will not be reinforced in the position where it needs it, potentially diminishing the useful lifespan of the structure. Wire mesh is also prone to corrosion unless the polymer or stainless steel variety is used.

When to use reinforcement

Reinforcement is necessary for concrete mud pans in some cases, depending on the scale of the project and the requirements of the building plans.

For smaller-scale projects, such as residential pathways, shed floors, or even some driveways, reinforcement may not be required. However, for larger projects or slabs that need to withstand heavy loads or high foot traffic, reinforcement is often essential. This includes projects like carports, garage floors, or public buildings.

The ground underneath the concrete mud pan should also be considered. Softer or spongy ground may benefit from extra reinforcement to ensure the slabs on top remain stable.

Additionally, certain locations and building codes may mandate reinforcement, regardless of the size or nature of the project. It is crucial to consult local building codes and guidelines, such as the Tile Council of North America (TCNA) Handbook and ANSI108.1, to determine if reinforcement is necessary for your specific project.

When reinforcement is required, there are two main options: rebar (steel rods with ribs for better grip) and wired mesh (steel wires melded into a flat sheet). These options can be used individually or in combination to strengthen the concrete and prevent cracking.

Waterproofing membranes

Types of Waterproofing Membranes

• Liquid Membranes: These are ready-to-use liquid coatings that can be applied with a roller, brush, or airless sprayer. They cure to form a flexible, waterproof barrier and are suitable for both indoor and outdoor use. Liquid membranes can be used on a variety of surfaces, including concrete, wood, stone, tiles, and metal. They are also safe for use in fish ponds and other areas where they may come into contact with saltwater or plant life.
• Fabric-Reinforced Membranes: Fabric-reinforced waterproofing membranes are used to bridge and reinforce cracks in surfaces. They are applied in conjunction with a liquid membrane, providing additional strength and ensuring a continuous waterproof barrier.
• Pre-formed Sheet Membranes: These are sheets of waterproof material that can be unrolled and applied to surfaces. They are often used in conjunction with a liquid membrane and serve as an additional waterproof barrier.

Considerations When Using Waterproofing Membranes

• Surface Preparation: It is important to properly prepare the surface before applying a waterproofing membrane. This includes cleaning the surface, filling any cracks or holes, and ensuring that the surface is dry and free of any existing coatings or treatments that may affect adhesion.
• Number of Coats: Most waterproofing membranes require two coats for effective waterproofing. However, for fully submerged applications or below-grade applications, three coats are usually recommended.
• Drying and Curing: Adequate drying and curing times must be allowed for waterproofing membranes to achieve proper adhesion and waterproofing capabilities. Avoid applying membranes in direct sunlight or high temperatures, as this can cause the product to dry too quickly and affect its performance.
• Compatibility with Other Materials: Ensure that the waterproofing membrane is compatible with the surface to which it is being applied. Some membranes may not adhere properly to certain types of surfaces or coatings.
• Ventilation: Proper ventilation is essential when working with waterproofing membranes to avoid inhaling fumes.

Building a pre-slope mortar bed

Step 1: Prepare the Substrate

Before starting the pre-slope, ensure that the substrate is properly prepared. For a wooden floor, use kiln-dried lumber to create the curb, as this has a lower moisture content and is less likely to warp or twist. Avoid using pressure-treated lumber. For a concrete floor, use grey concrete bricks stacked two or three high and adhered with regular thinset.

Step 2: Install a Cleavage Membrane and Metal Lath

Install a cleavage membrane, such as a sheet of plastic or tar paper, on the substrate. This will prevent the wooden floor from absorbing moisture from the pre-slope. Staple metal lath or reinforcement over the cleavage membrane to provide a base for the mortar bed.

Step 3: Calculate the Slope

Determine the slope of the pre-slope by measuring the distance from the drain to the farthest wall. The target slope is 1/4" per foot from the wall to the drain. Multiply this distance by 0.25, then add 1/2" to find the high point of your mortar bed in inches. Mark this point and extend it around the entire perimeter of the shower.

Step 4: Mix the Mortar

Mix a batch of deck mud or sand mix to create the pre-slope mortar bed. The mixture should be on the drier side to ensure it packs well.

Step 5: Pack the Mortar Bed

Start by packing the mortar bed in the corners and along the perimeter of the shower, using a rubber or wooden float to tamp down the material. Use a hand level to ensure that the perimeter is level both side-to-side and edge-to-edge. Once the perimeter is level, fill in the centre of the shower pan, establishing a rough slope from the edges to the drain. Pack down the material as you progress.

Step 6: Smooth the Surface

Use a straight edge to confirm that you have a smooth slope from the edges to the drain in all directions. Add more material where necessary and continue packing it down. You can also use a steel finish trowel to create a smooth finish surface, although this is not mandatory.

Step 7: Let it Cure

Allow the pre-slope mortar bed to cure for at least 24 hours before moving on to the next phase, which is installing the waterproofing membrane.

Tiling on a mortar bed

Preparing the Substrate:

Before starting, ensure the concrete slab is fully cured and free from any cracks or surface contaminants. For softer or spongy ground, consider adding extra reinforcement to the slabs. If your project is residential, like a pathway or shed floor, reinforcement may not be necessary. However, for heavier traffic areas or walls, reinforcement is recommended.

Creating the Mortar Bed:

The mortar bed can be created by mixing one part Portland cement with five parts damp sand. Optionally, you can add 1/10 part hydrated lime to the mixture. When mixing, use limited water to prevent excessive shrinkage. The mortar bed should be at least 1-1/4" thick for light commercial installations and can go up to 2" thick for greater strength.

Reinforcing the Mortar Bed:

Reinforcement of the mortar bed is essential, especially if it is not bonded directly to the concrete slab. Wire mesh or rebar can be used for reinforcement and should be placed in the centre of the mortar bed. This adds strength and helps resist cracking.

Setting the Tiles:

Once the mortar bed is prepared, you can set the tiles. Soak the tiles in water for at least half an hour before setting them. There should be no standing water on the back of the tiles. Apply a pure coat of Portland cement and water to form a rowelable paste and then lay the tiles.

Curing Time:

Allow the mortar bed to cure for at least 24 hours before grouting and finalising the installation.

Frequently asked questions