Flat Roof Repair Guide

If you are experiencing problems with your flat roof and are looking for ways to fix them then this handy troubleshooting guide is for you. Our guide covers a range of different flat roof complications such as water ponding, roof blistering, leaking flashing, roof alligatoring and more. We discuss how to repair these troublesome issues and fix signs of deterioration without having to replace and re-roof the entire area. In general, a roof repair is recommended only if the roof damage is situated within a small portion of the roof. The topics we cover in this repair guide are as follows:

The most important thing to remember when repairing a roof is your own safety. Be sure to follow all local regulations and use the correct personal protective equipment to ensure you remain safe and secure when working on your roof.

Fixing Cracks and Splits

If your roof is leaking and you identify the source, you may only need to do a quick repair job. Once you have identified the offending split or tear that is causing the leak you can use a sealant or waterproofing paint to temporarily fix this problem.

Ensure the area where you will be applying the sealant is dry, clean and free of debris. Then proceed to apply two to three layers and wait for them to cure. Remember, this is only a temporary fix and you may need to do a whole roof repair for a long-lasting solution.

Fixing Ponding in Flat Roofs

Ponding Water

Water ponding is one of the most common flat roof problems you may encounter. If the excess water accumulating on your roof doesn't dissipate, this can lead to leaks and property damage. If your roof is sagging, has an insufficient slope or has drainage issues, the water will eventually degrade roofing materials and add extra stress and damage to the load-bearing structure of your flat roof.

The LRS RapidRoof Ponding Filler Kit is a two-part pourable rapid cure system that is a simple solution for the problem of ponding. Designed to seal uneven areas, large gaps, and cracks, this Ponding Filler Kit is quick and easy to apply if you follow these steps:

  1. Prepare your surface by removing all laitance, grease, oil, dust and other contaminants to provide a sound, clean substrate.
  2. Prime the prepared surface with LRS RapidRoof Primer. The mixed primer should be applied by brush or roller at a nominal rate of 1kg per 3-4m², depending upon surface profile. Allow the primer to cure for a minimum of 60 minutes.
  3. Thoroughly mix the ponding kits resin component and aggregate component using a low-speed drill stirrer.
  4. Once mixed, the ponding filler should be applied by trowelling to ensure good compaction and a tight finish. The material should not be feather edged.
  5. Allow a minimum cure time of 1 hour at 20°C.

Flat Roof Blister Repair

Blistering of flat roof membranes usually occurs because of excessive heat or poor ventilation. Any air pockets in your flat roof should be fixed as they may eventually rupture or tear and allow water to ingress into your property. Below we detail a simple fix that will enable you to repair a small section of your roof that has blistered.

  1. Clean and prepare the affected area. Use a utility knife to cut an X pattern into the blister. This will create flaps that can be folded back.
  2. Fold the flaps back and ensure the sublayer of roofing is clean and dry. Using a round-nosed trowel, apply a generous layer of an adhesive sealant to the subsurface under the blister.
  3. Fold the flaps back into place and press them into the adhesive sealant. If extra sealant oozes out this will help to seal the seams.
  4. Apply more sealant to cover the entire area and its surroundings. You can then lay a piece of reinforcing fabric or matting that has been cut to the desired size. Press this into place to form a smooth layer that is free of air pockets and buckles. Finally, apply a second coat of sealant on top of the reinforcing material.

Roof Alligatoring

Roof alligatoring is usually a sign that your roof is ageing and gets its name from the fact that it looks a lot like alligator skin. Primarily caused by the sun’s UV rays, if you spot the signs early enough you can do some patch repair work. However, if you notice the alligatoring across your entire flat roof, it’s time for a replacement.

To fix a roof that shows signs of alligatoring, you’ll need to apply a new coating to the area. Clean the repair site thoroughly, making sure that all dust and debris are removed. Then apply a primer that is compatible with the roof’s original surface, and once dry, apply the coating itself. You may also want to apply a UV top coat for protection against UV rays.

Flat Roof Flashing Repair

Leaking flashings can occur to any flat roof where it joins with a wall. If there are splits and cracks in the material used to adhere the flashing to your wall then any time it rains, water will drip behind the flashing and cause water damage. Once you identify the problem area, remove any old tar or caulking and paint. Use sandpaper to roughen up any smooth surface. Apply a coating of a polyurethane sealant using a brush in a layer thickness of 1.5 mm. For extra reinforcement, you can apply a piece of mesh scrim onto the area. Apply a final coat of sealant over the scrim making sure it is completely covered. Once dry, the area should be fully waterproof. Depending on your roof materials, you may also find a lead sealant useful.

EPDM Roof Patch Repair

Flat Roof EPDM

If there is a small area of your EPDM roof that needs to be fixed, including any small holes, tears and rips that are causing leaks, then you can apply some lap sealant to the areas. Surfaces on which lap sealant is to be applied must be clean, dry, and free from loose and foreign materials, oil and grease.

For a more long-lasting fix, you can do a simple patch repair. Clean and prep the repair site and surrounding area to ensure it is free of dust and dirt. Once the area is dry, apply a suitable primer with a brush. While you are waiting for this to dry you can cut your patch material.

You will want to use an EPDM Seal Repair Tape that is robust, rubberised and waterproof against water, air and moisture. This will create a flexible and secure barrier. They are specially formulated with a thick, flexible, rubberised backing that conforms and flows to any shape or application and due to the high levels of adhesive on the seal repair tape, it creates an instant super-strong bond.

Cut your patch with a sharp straight blade and once the repair site is primed and dry, apply the repair tape. For a seamless finish, you can use a professional seam roller to ensure you remove any air pockets and achieve a tight bond between the patch and the existing roof material. To finish off your repair job, apply a bead of sealant around the edges of the patch.

GRP Fibreglass Roof Repair

If you notice that the laminate on your fibreglass roof is damaged after installation, this can usually be repaired very easily. First, you will need to prep your surface by sanding the affected area. Then you will need to clean the area using an acetone cleaner, making sure all debris is removed so that the wind does not blow any foreign particles into the area.

Once the site is clean, apply GRP Roofing Resin to the affected area and lay a piece of reinforcement matting onto the resin. Using a paint roller to apply more resin over the matting and then use a paddle roller to consolidate the area. A brush can be used to blend the edges for a neat and professional finish. Next, apply a wash coat of resin and once consolidated, sand the area and its surrounding edges. Wipe with acetone and apply a top coat to fully repair the damaged area.

To keep your flat roof in the best condition possible, regular checks and maintenance are the best course of action. Check your flat roof at least twice a year for any cracks, rips or other issues. Make sure to clear any debris off the roof and check that all guttering is clear to make sure water is being effectively drained.