There are a number of issues that can cause your fiberglass shower floor to make an awful squeaking sound, but almost all of them are completely preventable with the proper installation and maintenance. Inspecting your floor and subfloor for damage and loose floorboards, choosing the correct flooring material, and making sure the floors are waterproofed and seals between the base and the wall are sealed go a long way to prevent the fiberglass squeak.

If your shower base is squeaking, especially if it’s a newer installation, you should contact the installer or contractor first. If it’s an older installation, assessing whether you have access from below will determine your most viable (and safest) repair options. It is also important to install shower pans properly at the original installation, preferably with thinset underneath. This article covers all the details for preventing that dreaded squeak.

1. Gaps Between the Pan and the Subfloor:
   • Improper Bedding: Many fiberglass shower pan manufacturers require the pan to be set into a bed of thinset during installation. If this step is skipped or if the mortar bed is insufficient, voids can form underneath leading to flexing and squeaking. This is the most frequent culprit.
   • Uneven Subfloor: If the plywood subfloor isn’t level or has high/low spots due to prior water damage, the pan won’t sit flat.  Thereby creating gaps that allow movement.
   • Loose Subfloor: The subfloor itself might be flexing on loose nails or screws. transmitting the squeak to the base of the pan.
2. Insufficient Internal Support: Some less expensive fiberglass pans may have insufficient internal ribbing or support structures formed into the unit itself. Oftentimes, the center of these drop if not well-supported.
3. Pans Screwed into Wall Studs (Improper Fastening): While it might seem like a good idea to secure the pan to wall studs, many manufacturers advise against it or have specific clip attachments. Screwing directly through the pan’s side into studs can create stress points that lead to squeaking or even cracking. Screws like these are better suited for pan liners that will be later tiled.
4. Heat Expansion: Less commonly, in areas with significant temperature fluctuations, expansion and contraction of materials can cause movement and squeaks.

1. • Resource: Houzz highlights the importance of a mortar bed: 7 Reasons Why Your Shower Floor Squeaks
   • Resource: Reddit’s r/Plumbing discussions frequently emphasize this as standard practice for new construction: new build shower pan creaks
     
   • Follow Manufacturer’s Instructions Precisely: Each shower pan manufacturer will have specific installation guidelines. These are non-negotiable. Some may have integrated leveling feet or specific adhesive recommendations instead of (or in addition to) a full mortar bed.

How to Fix an Existing Squeaky Shower Base (Challenging!)

Fixing an already installed squeaky shower base can be very challenging and often requires access from underneath or can be quite involved.

1. Access from Below (Best-Case Scenario):
   • If you have access to the underside of the shower pan from a basement or crawl space, you might be able to add support.
   • Low-Expansion Spray Foam: This is a common DIY attempt. Carefully inject low-expansion (window and door rated) spray foam into the voids between the pan and the subfloor. Use extreme caution not to over-inject, as too much expansion can distort or lift the pan. Apply weight to the pan beforehand.
     • Resource: The Money Pit discusses using foam sealant: Use Foam Sealant to Stop a Creaking Shower Floor
     • Resource: TrustedPros has a forum discussion with various experiences using spray foam: Squeaking Acrylic Shower Base
   • Mortar/Shims: In some cases, if access allows, small amounts of mortar or shims can be carefully placed to fill significant gaps.
2. Professional Job:
   • If there’s no access from underneath, fixing the squeak often involves removing the shower pan entirely and re-installing it correctly with a proper mortar bed. This is a significant undertaking, often requiring removal of surrounding tile and walls. It is time to get professional help and call CW Service Pros to replace this for you.