Why Does a Shower Pan Flex or Move?

A shower pan that flexes or moves when standing on it is a common issue that can occur for several reasons:

Improper Installation: The most common cause of a flexing or moving shower pan is that it was not properly installed and supported. Shower pans need to be fully supported underneath by a mortar bed or other substrate. If the pan is just sitting on the subfloor, it will flex when weight is applied.
Rotten Subfloor: Over time, moisture can cause the subfloor under the shower pan to rot away. This leaves the pan without proper support, allowing it to flex and move. Checking for soft, spongy areas in the subfloor is important.
Not Level: If the mortar bed or substrate under the shower pan was not properly leveled during installation, it can cause the pan to rock and flex when standing on it. There should be no dips, hills or uneven areas under the pan.
Improper Materials: Using the wrong materials can also lead to a shower pan that moves and flexes. For example, foam board should not be used under a pan as it will compress when weight is applied. The correct solid mortar materials provide unmoving support.
Loose Surround Materials: If tiles or shower surround walls are moving or loose, this can allow the shower pan to shift and flex along with them. The pan depends on the walls being completely solid and immobile.

Knowing the potential reasons why a shower pan may flex or move is helpful when it comes to diagnosing the problem and choosing the right repair method.

Dangers of a Flexing or Moving Shower Pan

A shower pan that flexes up and down when standing on it or feels loose and rocky is more than just an annoyance—it’s also a safety hazard and needs to be fixed. Here are some of the dangers of having a shower pan that moves:

Slip and Fall Risk: The flexing motion when standing on a loose pan can cause you to easily lose your footing and slip. This leads to an increased risk of falling and injuries in the shower.
Underlying Damage: As mentioned previously, a moving pan often means there are subfloor problems or damage under the pan. This damage will only get worse over time if not addressed.
Leaking and Water Damage: With all the movement and flexing, re-applying new caulk and grout can only temporarily hold back leaks. The flexing will repeatedly break the seals leading to water damage under and around the shower.
Insect/Pest Infestation: Any moisture getting under the shower pan can attract termites, ants, roaches and other pests. These insects will damage the subfloor and can spread to other areas.
Unable to Support Weight: In worse case scenarios, a severely compromised shower pan may suddenly crack under weight or even partially collapse. This leads to a very dangerous situation for anyone showering.

The severity of the flexing and movement will determine how soon repairs need to be made. But in general, this is not an issue to put off, as conditions will worsen over time.

Inspecting Under the Shower Pan

Before determining how to fix a flexing or moving shower pan, it’s important to fully inspect under the pan to identify the cause. Here are the steps:

Materials Needed

Flat pry bar
Hammer
Tape measure
Flashlight

Steps to Inspect Under the Pan

Turn off the water supply to the shower and drain any standing water under the pan. Have towels ready to absorb any remaining water.
Carefully pry up the edges of the trim or surround around the shower pan. In fiberglass or acrylic showers, remove caulk to free the trim.
Once you can get underneath the trim, use the pry bar and hammer to gently free the shower pan from the mortar below. Lift up on one entire side of the pan.
Thoroughly inspect the shower floor area under the pan. Check for levelness, soft/damaged subfloor areas, proper substrate like mortar, and sources of moisture.
Use the tape measure to check for dips and unevenness in the subfloor that could make the pan rock. Mark any problem areas.
Reposition the shower pan back into place temporarily and repeat process on other sides to fully inspect underneath.

This inspection will help you get to the root of the problem and assess if repairs or replacement are needed. Certain issues like significant rot may require replacing sections of the subfloor.

Fixing a Flexing Fiberglass or Acrylic Shower Pan

For molded fiberglass or acrylic shower pans, there are a few ways to repair flexing or movement:

Shimming the Pan

Inspect under the pan to find any dips or uneven areas in the substrate.
Cut shims from wood blocks to fit into the dips and level the pan. Wedge shims under the pan until it sits flat.
Check for any wobbling or rocking motion. Add additional shims where needed to fully stabilize.
Use a flexible sealant to hold the shims in place permanently.

Reinforcing with Mortar

Completely clear out any loose material under the shower pan.
Mix non-shrinking waterproof mortar and apply it under the pan to create an even base.
Build up the mortar to fill any thin spots and create a robust reinforced area.
Allow the mortar to fully cure and harden before using the shower.

Attaching to Studs

Locate the studs around the perimeter of the shower pan and mark them.
Using long screws, drill up from inside the pan into the studs to attach the pan securely.
The screws should penetrate at least 1 inch into the studs. Space screws evenly for stability.
Seal screw heads with waterproof silicone.

Attaching the pan to the solid framing helps limit shifting and flexing motions. This works best for fiberglass and acrylic pans.

Fixing a Flexing Tile Shower Pan

Tile shower pans can also develop movement over time as grout and substrates weaken. Here are some repair strategies:

Regrouting the Pan

Completely remove all existing grout from the shower pan tiles.
Thoroughly clean and prepare the tile surfaces for regrouting.
Use a flexible, waterproof grout designed for shower pans.
Pack grout tightly into joints according to product instructions.
Seal grout with a penetrating grout sealer to protect from moisture.

Reinforcing Mortar Bed

Chip out existing mortar under the tile pan using a hammer and chisel.
Vacuum and clean the area thoroughly to create a fresh base.
Reapply a new mortar bed, building up any thin spots.
Allow mortar to fully cure before regrouting tiles.

Filling Cracks in Pan

Use a rotary tool to open any thin cracks wider and clean out debris.
Fill cracks with a flexible polyurethane sealant or epoxy filler.
Smooth and tool sealant with wet finger for a seamless finish.
Clamp heavy objects over cracks as they cure to prevent shifting.

Replacing Damaged Tiles

Use a chisel to carefully pry up any broken or damaged tiles.
Set new tiles into place, making sure surfaces are clean.
Use tile spacers to get consistent grout lines between tiles.
Apply flexible grout between new tiles and surrounding ones.

When to Consider Replacing the Shower Pan

In some cases, attempting to repair a flexing or moving shower pan is only a temporary fix. Extensive damage, improper installation issues, or severe weakness in the pan itself may mean a full shower pan replacement is required. Consider a complete new pan under these circumstances:

The pan has areas of severe cracking or structural damage.
Makeshift repairs have failed shortly after completing them.
There are large sections of rotted or damaged subfloor that cannot support the pan.
The pan is not properly draining or has drainage problems.
You discover improper substrates like foam or cardboard were used under the pan.
The pan is over 10-15 years old and well past its normal life expectancy.
You want to change the size, shape, or type of shower pan installed.
Water damage from the leaky pan is too extensive.
The pan does not feel solid at all when standing in the shower.

Replacing an old failing pan with a new properly installed and supported pan is sometimes the best permanent solution. This avoids having to continually struggle with repairs.

How to Replace a Shower Pan

If replacing a faulty shower pan, follow these key steps:

Materials Needed

New shower pan kit
Mortar mix
Concrete backer board
Drain assembly
PVC pipe & fittings
Tile edging
Silicone caulk

Steps to Replace a Shower Pan

Turn off water supply and prepare the shower area by removing surround material, plumbing, etc.
Cut the shower pan away using a reciprocating saw. Scrape and clean mortar beds.
Make plumbing drain alterations as needed to fit new pan drain. Add access for PVC trap.
Install new drain assembly tightened and sealed to the shower pan.
Test fit pan and use concrete backer board to strengthen subfloor as needed.
Create perfectly level mortar base for pan to sit in. Compact very firmly.
Carefully lower and set new pan into mortar base. Check for level.
Connect drain plumbing. Build up pan mortar supports on all sides.
Add thin final mortar layer over lip of pan and tile edging.
Allow mortar to fully cure before applying tile, grout and sealing materials.

Taking the time to properly replace the shower pan will help provide many more years of dependable shower performance. Be sure to thoroughly research pan installation before beginning.

Preventing Future Shower Pan Movement

To avoid issues with a flexing, rocking shower pan in the future, focus on proper installation and support:

Mortar Reinforcement: Use a thick mortar bed reinforced with gravel to fully support the shower pan.
Level Surface: Make sure subfloor and mortar are perfectly level with no dips before setting the pan.
Solid Pan: Only use enamel coated steel, molded acrylic, or fiberglass material for the shower pan.
Surround Attachment: Securely connect the walls and surround materials directly to the pan.
Proper Drainage: Use the correct shower pan slope and drain style to allow for drainage.
Waterproofing: Coat subfloor and under pan with waterproofing compounds to limit moisture damage.
Professional Install: Hire an experienced contractor for shower pan installation and avoid DIY mistakes.

Putting in the effort during initial installation to sturdily support and reinforce the shower pan will help it last for many years without flexing or moving out of place.

Frequently Asked Questions About Fixing Shower Pans

What if my shower pan is slightly out of level?

A shower pan being slightly unlevel can contribute to flexing and instability. Try using a self-leveling compound to fill low spots and even out the surface under the pan.

Why is my fiberglass pan make cracking noises?

Fiberglass and acrylic can shrink over time, causing cracking sounds which allow pan flexing. Use flexible sealants on cracks and reinforce pan supports.

Should I use cement board instead of drywall around the shower?

Yes, cement backer board is more water-resistant and will provide stronger support for the shower pan perimeter.

How can I find and fix leaks under my shower pan?

Dig out old caulk and grout to locate leaks. Seal cracks or gaps with hydraulic cement. Waterproof the subfloor for a lasting fix.

My mortar bed crumbled – what should I replace it with?

Replace crumbled or hollow mortar with a fresh mortar mix. Add latex additive or gravel to strengthen it and prevent future cracking.

Can I use self-leveling compound under the shower pan instead of mortar?

No, self-leveling compound does not provide enough durability and support. Use a reinforced mortar specially designed for shower pans.

How thick should the mortar bed be under the shower pan?

Aim for a mortar bed around 2″ thick. It should be thicker in any dip or void areas to create a perfectly smooth and level surface.

What slope should my shower pan have?

Shower pans should slope 1/4″ per foot towards the drain. This provides adequate drainage while still meeting ADA standards.

Can I install my own acrylic or fiberglass shower pan?

It’s best to hire a plumbing professional, as shower pan installation requires specialized skills to support, level and waterproof it properly.

Conclusion

Fixing a shower pan that flexes, shifts or moves while standing on it is an important repair that should be addressed right away. Identifying the root cause by inspecting under the pan and making structural reinforcements or replacing faulty support materials can help resolve the issue. For severe cases, a full shower pan replacement may be required. Be sure to always use solid mortar beds, proper slopes, and waterproofing when installing a new pan. Addressing problems early on and preventing future movement or flexing will help extend the life of your shower. With the right repairs, you can feel confident standing firmly on a solid, stable shower floor.

How to Fix a Shower Pan That Flexes or Moves