Waterproofing a window in a shower area can seem daunting, but is an achievable DIY project with the right materials and techniques. Properly waterproofing your shower window prevents leaks that can cause water damage and mold growth in walls and ceilings. We will walk you through the entire process step-by-step, from choosing the right products to properly applying waterproof membranes and sealants. With our expert tips, you can waterproof your shower window like a pro.

Assessing the Window and Surrounding Area

Before beginning any waterproofing project, it’s important to fully assess the window, its frame, and the surrounding shower walls.

  • Carefully inspect the window frame and any caulking for cracks, rot, or other damage that could allow water intrusion. A high quality caulk or sealant will be needed to seal any cracks or gaps.
  • Check that the window opens smoothly. Waterproofing may be difficult if the window sticks or does not have full range of motion.
  • Determine what materials the surrounding shower walls are made from. Tile, fiberglass surrounds, or other solid surfaces can be waterproofed differently than drywall.
  • Look for signs of current water damage like discoloration or bubbling from leaks. Any water damaged areas must be addressed.
  • Evaluate the slope of the window sill. A sloped sill will improve water runoff. If flat, adding a slope with mortar or foam can help prevent pooling water.

Thoroughly examining all potential trouble areas allows you to tailor the waterproofing project to the specific window and shower.

Choosing the Right Waterproofing Materials

There are several reliable waterproofing membrane and sealant options for shower windows. Choosing products designed for prolonged wet environments is key.

Waterproofing Membranes

Liquid-applied waterproofing membranes provide a continuous water barrier on shower walls, blocking moisture from seeping through. Common types include:

  • Urethane membranes – Flexible and long-lasting, these have excellent adhesion and are both water and chemical resistant. Urethanes can be rolled or brushed on.
  • Cementitious membranes – Made from acrylic latex mixes or mortar cement, these bond well to concrete, wood, and steel. They cure to form a waterproof barrier.
  • Epoxy coatings – Two-part epoxy resins create a glossy, durable coating that strongly adheres to shower surfaces. Prepare for chemical fumes during application.
  • Asphalt emulsions – Water-based asphalt blended with polymers bonds as a thick film for below-grade damp areas. Limited shower use.

Caulks and Sealants

Caulking fills gaps between window frames and shower walls, preventing moisture entry. Look for:

  • 100% silicone – Long-lasting flexibility and strong adhesion for any building material. Ideal for wet areas.
  • Polyurethane – Expands as it cures for a tight seal. Better longevity than latex acrylic caulk.
  • Latex acrylic – Water-based, paintable, and easy cleanup. Not as durable or flexible as silicone.


Flashing pieces made of waterproof materials like aluminum and galvanized steel are commonly used to divert water away from windows. Self-adhesive butyl rubber flashing tape can also be highly effective.

Prep Work for Waterproofing a Shower Window

Proper prep work ensures waterproofing materials bond well and provide maximum protection.

Clean and Dry the Area

  • Clean window frame, sill, walls, and surrounding areas with a wire brush to remove any dirt, efflorescence, oil, and soap film that could impede adhesion.
  • Wash all surfaces with an all-purpose cleaner or TSP substitute and rinse thoroughly. Vinegar washing helps neutralize any alkaline cleaner residue.
  • Allow all areas to completely dry for at least 24 hours before applying waterproofing materials.

Remove Window and Perform Maintenance

  • Carefully detach any interior window trim and remove the window from the frame if possible. This allows better access for repairs and waterproofing application.
  • Replace any cracked, missing, or loose caulking around the window frame. Consider adding backer rod for larger gaps.
  • Look for rotted, damaged, or warped wood on window sashes and sills and repair or replace as needed with wood filler, epoxy, or new wood.
  • Sand window components smooth, then apply primer and paint to protect any repaired areas from moisture damage.

Inspect and Repair Shower Surround Surfaces

  • Address any damaged, missing, or loose tile, fiberglass, or other surround materials to ensure a sound surface for waterproofing.
  • Use hydraulic cement to patch concrete or fill any cracks or holes in shower walls. Allow full curing before waterproofing.
  • Build up window sills with mortar for proper slope if needed. Allow full drying before waterproofing.

Thorough surface prep leads to effective waterproofing application and long-term performance.

Applying Waterproofing Membranes

With surfaces prepped, the shower window is ready for waterproofing. We’ll cover best practices for applying waterproofing membranes.

Liquid-Applied Membranes

Urethane, epoxy, and cementitious acrylic waterproofing membranes can all be applied in similar fashion:

  • Prepare the material according to manufacturer instructions, mixing multiple parts if required.
  • Apply an initial thin, smooth coat to act as a primer layer over the entire shower surround surface using a paint roller or brush.
  • Allow the recommended drying time before adding the second coat (often 2 hours minimum). Proper curing is vital.
  • Apply a second, thicker application to create a seamless waterproofing barrier. Use a brush to work the product into corners.
  • If recommended, add a reinforcement fabric or mesh between coats for increased strength and crack resistance. Smooth the fabric into the membrane.
  • Allow thorough drying and curing according to product guidelines before water exposure or adding tile or other finishes.

Proper application leaving no gaps, pinholes, or thin spots is crucial for waterproof membrane success. Carefully follow all manufacturer specifications.

Liquid Flashing Membranes

Flashing tapes and peel-and-stick membranes are also available. These create an impermeable seal around the window-wall transition:

  • Thoroughly clean and dry the area underneath where flashing will be applied.
  • Measure and cut flashing material to proper size and shape using utility knives, allowing an extra 1-2 inches for overlap.
  • Remove backing paper and firmly press flashing into place along window edges and 4-6 inches onto walls and sills.
  • Apply pressure with a hand roller to maximize adhesion. Avoid bubbles, kinks, or tears.
  • If needed, apply a bead of silicone caulk along flashing edges for extra leakage protection once cured.

Window Reinstallation

Once waterproofed, reinstall the shower window:

  • Apply a continuous bead of high quality silicone caulk around the interior side of the window frame before placing it into the opening.
  • Insert window and press firmly into place, sealing it into the caulk bead applied in the previous step.
  • Drill screws into the window frame at the appropriate points to secure in place. Avoid excess pressure that could warp the frame.
  • Finish by adding interior trim pieces, caulking trim edges, and sealing any remaining gaps. Allow full curing before water exposure.

Applying Caulks and Sealants

Caulking and sealing completes the waterproofing process and should be done with care:

  • Allow all waterproofing materials to fully dry and cure prior to caulking. Check manufacturer guidelines for proper cure times.
  • Ensure all surfaces are clean and dry before applying caulks or sealants.
  • Apply painter’s tape along each side of window frames and wall edges for neat caulk lines. Mask off 1/8″ from surfaces.
  • Load caulk gun and cut the tip at a 45 degree angle to the proper sized opening for the gaps being sealed.
  • Apply caulk in a continuous, smooth bead without gaps. Avoid air pockets.
  • Tool the caulk with a rounded spatula to create a concave shape that helps sheds water. Remove tape immediately after tooling caulk.
  • Seal all joints, seams, corners, and gaps around the full shower window perimeter plus any on window frames.
  • Allow caulk to fully cure based on product guidelines before exposing to water. Silicones may take up to 7 days.

Proper caulking technique prevents water wicking behind the waterproofed areas. Take your time for neat finished results.

Troubleshooting Waterproofing Issues

Even with proper installation, shower window waterproofing can sometimes fail. Here are common problems and their solutions:

Leaks at window edges – Gaps in caulking or membrane coverage allows water intrusion. Recaulk edges with quality silicone. Cover surrounding area with cementitious membrane.

Cracks or blisters in membranes – Improper surface prep or application can cause poor bonding. Repair cracks with sealant. Remove blistered areas and reapply membrane.

Peeling or detached flashing – Inadequate initial cleaning or surface moisture leads to poor adhesion. Allow to fully dry, clean with solvents and reattach securely.

Condensation or mold between window panes – Failing window seals indicates a need for total replacement. There are no quick fixes. Install a new insulated window.

Rotting window sill or frame – Chronic moisture exposure deteriorates wood over time. Replace damaged sections with new treated lumber before re-waterproofing.

Addressing issues at the first sign of leakage prevents more extensive damage. Seek professional assistance for major failures.

Maintaining Your Shower Window Waterproofing

Waterproofing shower windows provides long-lasting protection when properly maintained:

  • Inspect caulking every 6 months for gaps or cracks and recaulk as needed. Deteriorating caulk is the most common failure point.
  • Check for any wall or membrane cracking that could compromise waterproofing and make repairs immediately.
  • Repaint window frames regularly to avoid wood rot. Address any minor moisture issues right away.
  • Have windows professionally re-sealed or replaced once condensation or fogging occurs between panes. Don’t delay replacement.
  • Monitor closely for mold or mildew growth and remove immediately by scrubbing with bleach or vinegar solutions.
  • Limit window exposure to harsh cleaners, chemicals, razor scrapers or other damaging substances.
  • Reapply waterproofing membranes at least every 3-5 years or per manufacturer guidelines to maintain performance.

Proactive maintenance safeguards your newly waterproofed shower window for the long run.

Frequently Asked Questions About Waterproofing a Shower Window

Waterproofing a shower window brings up many common questions:

How do I know if my shower window needs to be waterproofed?

Signs like leaks, water stains on ceilings, deterioration of surrounding materials, mold growth, or high interior humidity indicate a need for waterproofing. If the window lacks proper sealing, flashing, or slope, preventative waterproofing is a good idea.

Does the window need to be replaced when waterproofing a shower?

Not necessarily. As long as the window frame is in good shape without rot or damage, it can be waterproofed successfully. But a window with failed seals or fogging between panes does need full replacement.

Can I use RedGard or a similar membrane on shower walls with a window?

Yes, RedGard and other liquid-applied membranes like AquaDefense can be great shower window waterproofing solutions. Ensure proper surface prep and application per the manufacturer.

What’s the best way to slope a shower window sill when waterproofing?

Building up the sill with mortar is an effective method. Install reinforcement mesh in the mortar for added strength. Keep the slope at 1/4 inch per foot minimum pitch.

Should I remove old caulking completely before re-caulking around a shower window?

It’s best to remove all old caulking to ensure good adhesion for new sealant. Carefully cut out the caulk without damaging surfaces. Ensure the area is clean and dry before applying fresh caulk.

Can I use silicone caulk over existing latex caulk around a shower window?

Yes, silicone will adhere to old latex caulk as long as the area is clean and dry. The flexibility of silicone makes it a good choice for sealing the shower window perimeter.

Properly waterproofing your shower window prevents damage, extends the window’s longevity, and provides lasting peace of mind. Carefully follow the techniques and advice above to keep moisture out and enjoy your shower. Let us know if you have any other shower window waterproofing questions!


Waterproofing a window in a shower area provides crucial protection against water damage, leaks, and mold growth. While it may seem intimidating, this detailed guide gives you all the information needed to properly waterproof a shower window like a professional. The key steps include:

  • Thoroughly examine the window, frame, and surrounding shower walls to assess condition and tailor the project.
  • Select high quality waterproofing membranes, caulks, and sealants designed for wet areas.
  • Prep all surfaces through cleaning, repairs, maintenance, and ensuring proper slope.
  • Correctly apply liquid membranes or flashing tapes around window and walls.
  • Caulk and seal with silicone for complete waterproofing.
  • Maintain the waterproofing through regular inspections and reapplication when needed.

Following proper techniques and using the right materials leads to effective, long-lasting shower window waterproofing. Don’t allow leaks and moisture damage to persist. With the help of this comprehensive guide, you can confidently waterproof your shower window like a professional.