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How Do You Fix A Leak In A Fiberglass Roof? 3 Simple Steps!

Fiberglass is a fantastic material used across many industries. It has multiple applications, including use as a roofing material. It is durable, easy to install, and forms around any shape. But how do you repair it when there is a leak?

The best way to repair a fiberglass roof is to clean the area thoroughly, mix resin with a suitable catalyst and apply the fiberglass mat in repeated layers until it forms a solid bond with the affected area. It is a simple process that almost anyone can do well.

Fixing a leaking fiberglass roof is a straightforward process. If the steps detailed below are rigidly followed, you will fix the roof satisfactorily, ensuring it continues to protect the house and occupants from the elements.

How Do You Repair A Fiberglass Roof?

Following the steps listed below will assist you in repairing the roof correctly:

Step #1: Find All Of The Damaged Parts

Look for the damaged areas on the roof, making sure you include the following:

Look On Top Of The Roof

Check the top of the roof for visible damage, chips, wearing, flaking, or other signs that the fiberglass has started to degrade.

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This job requires you to get on your hands and knees and carefully inspect the roof section by section, looking for any damage or cracks. It’s important to be thorough here, as you don’t want to go through the whole repair having missed out an area!

Look Below The Roof

Look inside the attic or loft and check for the following:

  1. Stains on the ceiling or walls which are caused by leaking water. If these are soft to the touch, they are recent, and therefore the roof has a current problem.
  2. Switch off the lights in the attic or loft and look for sunlight shining through. Every pinpoint, (or bigger), of sunlight is a hole that needs to be corrected. 

Step #2: Clean The Affected Areas

For any fiberglass repair to be effective, thoroughly clean the damaged area with soap and water. Using 80 grit sandpaper, sand down the area in and around the defect, leaving a slightly rough surface to which the fiberglass gel can attach.

Use acetone and a cloth to clean away all debris produced by sanding. Acetone removes all oils and resins from the area.

Step #3: Fill The Damaged Areas

Many products are advertised as being able to repair a damaged fiberglass roof. Whether these work or not or provide a durable enough result is unknown. However, if at all possible, it makes sense to repair any defect with the same material from which the roof is constructed.

There is a lot of fiction spoken about working with fiberglass and how difficult it is. It’s simply not true. And if you are prepared to spend some time doing the job properly, it is a straightforward process. Here are some instructions…

Prepare Your Tools And Materials

Source everything you need before you start the repair; this includes.

  1. A good pair of lightweight gloves.
  2. Sufficient quantities of fiberglass mat.
  3. A suitable resin and catalyst, (your local store will be able to advise you on this).
  4. A fiberglass paddle roller.

Put the gloves on, and don’t remove them until you have finished glassing the area. Cut fiberglass mat pieces to a shape that thoroughly covers the damage you want to correct.

Mix the new resin and catalyst. Depending on the product you use, the amount of catalyst you mix in, and the ambient temperatures you are working in, it is essential that you only mix as much as you can use in the time it takes for the mixture to “kick” start hardening.

Start Glassing The Area

Place the fiberglass mat in position and start working the resin into the mat using a paddle roller. You must work the resin into the fiberglass mat thoroughly, ensuring no spot is missed.

When the material has been correctly laid, it becomes almost indistinguishable from the surrounding area.

Repeat this process three times (in the same session) by placing an additional layer of fiberglass mat and working the resin in before the material hardens.

It will ensure that there are three good layers of fiberglass that have been laid down.

When the material starts curing, you will feel it heat up; this is perfectly normal and does not cause concern.

Finish Off The Fix

Fiberglass roofing sheet

Allow the resin and catalyst to cure for four hours (or less in warmer climates). When the fiberglass is cured and solid, sand it down again with 80 grit sandpaper.

Dust the area off and clean it with acetone. The fix should now be complete, and your fiberglass roof should be good for years.

The Types Of Damage Typically Found On A Fiberglass Roof

Fiberglass roofs are durable, but just like any other roofing material exposed to continually changing temperatures, moisture, and weather conditions, they become worn and brittle over time.

The deterioration initially seems minor, with microscopic cracks in the formed fiberglass fabric. Over time, these cracks widen, separating fibers and the resin that hold them together.

You will begin to see a range of issues with the roof, including cracks, splitting, and holes.

If the damage covers a vast area, it is recommended that you replace that portion of the roof entirely. However, if the damage is minor and each imperfection is slight, it is very viable for you to attempt the repair yourself.

Why Fiberglass Roof Begins To Crack

The only positive aspect of a fiberglass roof that has begun to crack is that the damage is easy to identify. The reasons for this may include the following:

The Installer Mixed The Resin Incorrectly

If the installers mixed the catalyst and resin incorrectly, it potentially leads to the roof beginning to crack. If this is the case, you may hold the installer liable for this.

If the cracking is limited to a small area, you can attempt to fix it yourself. However, you may need to contact a professional to resolve the issue if it is more generalized.

Temperature Changes Can Lead to Fiberglass Cracking

Due to years of natural wear and tear and changing temperatures which have caused the fiberglass to expand and contract for a more extended period, it starts to crack.

Installers should take this into account when the material is initially applied, by leaving a space at the edges for the material to expand and contract. If the gap sizes are insufficient, the fiberglass will ultimately begin to crack.

If the cracking is limited to a small area, you can attempt to fix it yourself. However, as mentioned earlier, if it is more generalized, you may need to hire a professional to resolve the issue.

When a Fiberglass Roof Leaks

Not only does a roof leak cause unsightly damage to the attic or loft area, including staining ceiling boards, but it may also point to a more significant problem that needs to be addressed.

Fixing a leak when it is first spotted is the best course of action as leaks which are left alone start spreading the damage to other areas of the home, and can also be responsible for mold or other health impacting conditions to form.

When a Fiberglass Roof Develops Little Pinholes

Pin holing of the resin layer is a common condition affecting fiberglass roofing and is generally caused by the resin being applied thinly.

It is the most straightforward issue to fix yourself by following the steps laid out earlier.

When a Fiberglass Roof Reaches Its End By Date

All good things come to an end, and the same is valid for fiberglass roofing. When the roofing material gets too old, it will shrivel and distort. It is clear that the roof has seen its best days, and it is time to look for a replacement.


Although fiberglass is a surprisingly sturdy and durable roofing material, it is subject to the ravages of father time. Eventually, like all materials, it will need some maintenance to keep it providing shelter for the home.

Unless the problems are caused by an incorrect installation method, the homeowner can complete most minor repairs if it has reached a point where it needs to be repaired.

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