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  • Writer's pictureAndrew Putilin

How to Repair a Flat Roof Blister: A Step-by-Step DIY Guide

some tools that a flat roof commercial building manager or a property owner will use to do a DIY repair of their flat roof blister in portland oregon

Flat roofs are a popular choice for many commercial and residential buildings, but like any other roofing system, they require regular maintenance to ensure their longevity and performance. One common issue that may arise with flat roofs is the formation of blisters. A blister is a raised area on the roof's surface caused by trapped air, moisture, or both, between the layers of roofing material. If not addressed promptly, these blisters can lead to more significant problems, including leaks and structural damage.

In this blog post, we'll guide you through the process of repairing a flat roof blister by providing step-by-step instructions. However, it's essential to keep in mind that some repairs may be beyond the scope of a DIY enthusiast, and in such cases, professional help should be sought. To help you determine whether your flat roof requires expert attention, we at Flat Roof Pros in Portland Oregon offer a free inspection.

a hardhat that DIY owners and managers should use if they plan on DIY fixing their flat roof in PDX

Identifying the Cause of a Flat Roof Blister

Before attempting any repair, it's crucial to understand the root cause of the blister, as this can help prevent future issues. Here are some possible causes of flat roof blisters:

A. Trapped moisture: Moisture can become trapped beneath the roofing materials during installation or over time as a result of leaks. When exposed to sunlight, the trapped moisture heats up and expands, forming a blister.

B. Poor adhesion: Insufficient adhesion between roofing layers can lead to the formation of blisters. Adhesion issues may occur due to improper installation, use of incompatible materials, or application in cold weather.

C. Inadequate installation: Blisters can also develop as a result of errors during the installation process, such as failure to remove dirt or debris from the substrate, inadequate sealing of seams, or not allowing enough time for adhesives to cure.

Identifying the cause of the blister can help determine the appropriate repair method and prevent the issue from recurring. If you're unsure about the cause of the blister on your flat roof, we recommend scheduling a free inspection from Flat Roof Pros in Portland Oregon. Our team of experts can assess your roof and provide recommendations based on their findings.

Preparing the Surface for Repair

Before you begin repairing a flat roof blister, preparing the surface is essential to ensure a long-lasting and effective repair. Follow these steps to get your roof ready for the repair process:

A. Safety precautions: Working on a roof can be dangerous, so always take necessary safety precautions. Wear non-slip shoes, use a safety harness, and have someone assist you or be aware of your activities in case of an emergency.

B. Cleaning the affected area: Remove any dirt, debris, and loose roofing material from the area surrounding the blister. Use a broom or a soft-bristle brush to clean the surface gently. This step ensures that the patching materials adhere properly and that you have a clean surface to work on.

C. Cutting open the blister: Use a sharp roofing knife to carefully cut open the blister. Be sure to cut only through the top layer of roofing material and avoid cutting into the underlying layers or insulation. Make an X-shaped cut to expose the area beneath the blister.

D. Drying the area: After cutting open the blister, thoroughly dry the area underneath using a clean, absorbent cloth or a heat gun set on low heat. Be cautious not to damage the roofing material with excessive heat. Removing any trapped moisture is crucial for a successful repair.

At any point during the preparation process, if you feel unsure or encounter complications, don't hesitate to seek professional help. Flat Roof Pros in Portland Oregon offers a free inspection to assess your roof's condition and recommend the best course of action.

an image of a whole bunch of flat roofs in downtown portland oregon that Flat Roof Pros has helped keep leak free

Applying Patching Materials

Once the surface has been prepared, you can move on to applying the patching materials. Choosing the right materials compatible with your existing roofing system is essential to ensure a long-lasting repair. Here's a step-by-step guide on patching a flat roof blister:

A. Choosing the right materials: Consult your roofing system's manufacturer guidelines to determine the appropriate patching materials for your roof. You may need roofing cement, reinforcing fabric, and a top coating compatible with your roof's membrane.

B. Step-by-step patching process:

  1. Applying roofing cement: Use a trowel or a putty knife to apply a layer of roofing cement to the area beneath the blister, covering an additional couple of inches around the edges. Ensure that the cement is applied evenly and fills any voids in the roofing material.

  2. Installing a reinforcing fabric: Cut a piece of reinforcing fabric large enough to cover the blister area and extend at least 2 inches beyond its edges. Press the fabric into the wet roofing cement, making sure there are no wrinkles or air bubbles.

  3. Adding another layer of cement: Apply another layer of roofing cement over the reinforcing fabric, covering it entirely and extending slightly beyond its edges. This layer should be approximately 1/8-inch thick to ensure a proper seal.

  4. Applying a top coating: Once the roofing cement has cured according to the manufacturer's instructions, apply a top coating compatible with your roofing system. This coating will protect the patch from UV damage and help it blend in with the rest of the roof.

Remember, it's always best to consult with professionals if you feel uncertain about any part of the repair process. Flat Roof Pros in Portland Oregon provides free inspections to help you determine the right course of action for your flat roof repairs.

Preventative Measures and Regular Maintenance

After successfully repairing a flat roof blister, it's essential to take preventative measures and establish a routine maintenance plan to keep your roof in top condition. Regular maintenance can help prevent future issues, extend the life of your roof, and save you money in the long run.

A. Importance of flat roof maintenance: Regular inspections and maintenance can help identify potential issues before they become significant problems, reducing the chances of costly repairs or premature roof replacement.

B. Benefits of Regular Maintenance: For a more in-depth look at the benefits of regular maintenance, check out our blog article called "The Benefits of Regular Maintenance on Your Flat Roof".

C. Professional maintenance services offered by Flat Roof Pros: While some maintenance tasks can be performed by DIY enthusiasts, it's crucial to have your roof inspected by professionals periodically. At Flat Roof Pros, we offer comprehensive maintenance services tailored to your specific roofing system and its unique needs.

Don't wait until problems arise to take care of your flat roof. Schedule a free inspection from Flat Roof Pros in Portland Oregon today, and let our team of experts help you keep your roof in top shape.

an inspection from Flat Roof Pros preforming an inspection on a flat roof building in the neighboring cities of portland oregon

When to Seek Professional Help

While some flat roof repairs can be tackled by DIY enthusiasts, certain situations call for professional expertise. Knowing when to seek professional help can save you time, and money, and ensure the longevity of your roof. Here are some signs that indicate a need for professional assistance:

A. Signs that indicate a need for professional assistance:

  1. Extensive damage: If your roof has multiple blisters or other widespread issues, it's best to consult with professionals to address the underlying causes and perform repairs.

  2. Recurring blisters: If blisters keep forming despite your repair attempts, there may be an underlying issue that requires professional attention.

  3. Structural damage: In cases where the blister has led to structural damage, such as sagging or waterlogged insulation, it's crucial to involve professionals to assess and repair the damage.

B. Flat Roof Repair: DIY vs. Professional: For more information on when to choose between DIY and professional roof repair, read our blog article "Flat Roof Repair: DIY vs. Professional Services".

C. Flat Roof Pros' expertise and pricing: Our team at Flat Roof Pros has the knowledge and experience to address various flat roof issues, from minor repairs to complete roof replacements. Visit our pricing page for more information.

If you suspect that your flat roof requires professional attention, don't hesitate to reach out to Flat Roof Pros in Portland Oregon. Schedule a free inspection today, and let our team of experts assess your roof and recommend the best course of action.


Addressing flat roof blisters in a timely manner is crucial to maintaining the integrity and performance of your roofing system. By following this step-by-step guide, DIY enthusiasts can tackle minor blister repairs and keep their roofs in top condition. However, it's essential to recognize when professional assistance is needed, as some issues may require expert intervention.

Regular maintenance is key to preventing future problems and extending the life of your flat roof. At Flat Roof Pros, we are committed to helping you maintain your roof and address any issues that may arise. Our team of experts in Portland Oregon offers free inspections to assess the condition of your flat roof and provide guidance on the best course of action.

Don't wait for problems to escalate; take proactive steps to care for your flat roof today. Schedule a free inspection from Flat Roof Pros in Portland Oregon and let our professionals help you maintain your roof's integrity and performance.

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