13 Flat Roof Repair Tips and Ideas Shared by Professionals and DIY Lovers

It can happen, you know:

Annoying flat roof problems like leaks, cracks, buckle in membrane, gaps between the wall edge and roof material, alligatoring, and more.

When these problems surface – approved filling materials, smooth cement paste, and flat roof leak repair by hot tar are just some of the many ways to fix such defects and extend the lifespan of your roof.

To help inspire you, here are 13 case studies and problem solving ideas on how to repair flat roofs, shared by professionals and DIY lovers:

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#1: Flat Roof Leak Repair with Liquid Waterproofer

Flat roof leaks due to cracks can also be stopped by using a fiber-reinforced acrylic sealant. It is made of a mixture of fiber and bitumen.

When you apply this sealant over the cracked ridges of the flat roof, then you will realize several fibers holding the cracked surface together.

You can then paint that patch area as shown in this video:

#2: Easy DIY Way to Patch a Flat Roof

Flat roofs made of rolling granular materials are known to fold and then start to crack along these folded lines just like a paper.

When those ridges start to crack, one of the easy remedy option is Henry Wet Patching.

Wear gloves to avoid contact between your hand and the wet patch, and use a flat-headed chisel to smear or apply over the cracked ridges and you are good to go.

This approach has been demonstrated by Mr Hunter through the excellent video below:


#3: Rockwool Flat Roof Overlay Board

Other modern technologies have been introduced, such as Rockwool Flat Roof Overlay Board. This is unique, new and technologically modified way of repairing flat roofs.

With this repair technique, you need new high-density stone wool. They are waterproof and resistant to cracks caused by alternating heat and cold.

Also, you don’t need to remove any of your roof patches or the original flat roof material.

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#4: Consider Liquid Rubber Flat Roofing System

The other option for your flat roof is the application of liquid rubber.

When repairing your flat roof, you could consider pouring liquid rubber over the cracks and lines of weakness. They are fume-free and odorless since heat and solvents are needed.

To do this, you just need to pour your liquid rubber over the identified area and then cool it with water for it to solidify hence forming a patch over that area.

Steve Roofer shares more on this topic here:

#5: Flat Rubber Roof Repair Secret

Some of the experts have advised the need to coat your rubber flat roof with a silicone seal.

Considering that flat rubber roofs tend to be hot during the day, there are high chances that they will weaken over time.

Black means heat is absorbed during the day and you need a whitish silicone to reflect heat away. That will lengthen the life of your EPDM flat roof.

Watch the following video on a secret roofing contractors won’t tell you:


#6: DIY Large Area Flat Roof Repair

Your leaky flat roof can also be fixed using low-cost paint. Here, you need a bitumen primer and to make things easy and efficient, you also need a 9-inch roller.

Your first pass paint should be thicker but you need to reduce the thickness during the subsequent applications.

As soon as you are done, don’t let any primer go to waste. Consider applying a thicker patch of pain on the mineral edge – as shown in the video below with more detailed information:

#7: Repair Leaks on Flat Roofs with Flashing Cement

For those whose flat roofs are made of asphalt, there is a solution for you by Karnak.

To repair leaks and forget about it, you simply need to consider Karnak 19 professional-grade flashing cement. To repair your roof, you need a trowel, a fiberglass membrane, protective glasses, and gloves.

Apply your Karnak 19 cement on the damages are, then mount the fiber membrane on top. Cover the membrane with a final topcoat. Your roof will be done and free from leaks.

#8: Tips to Repair Flat Roof Leak Underwater

It is also possible to repair flat roof even with stagnant water on it. To do this, you can use Karnak 19 Ultra Rubberized flashing cement. This is a water-resistant material that repels water.

The first step is to apply this material on the surface under the water, then go ahead and mount your fiberglass before applying a final coat on top of the glass.

The good thing is that you don’t need to dry your roof surface.

#9: How to Remove, Repair and Install a Flat Roof

Some of the flat roofs are made of different layers of material. The first layer is wood, then the tar paper and the last one could be a rubber sealant.

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In some flat roofs, flat metals sheets are also used. To repair such a roof, you need to tear away the old materials completely. You may leave those that look fine. Clean the wood layer before mounting the tar paper using an adhesive.

Tom Leeman shares his tips in the video below:

#10: Stripping a Flat Felt Roof

If you have an old mineral finished the flat roof, you can strip it away before replacing it with a new. To do this, you need a flat-like spade/chisel (the size of a hand pam).

Use the sharp corner of the rectangular flat spade/chisel to tear a starting point. Then you will continue with the entire section of the spade to peel the entire material. Check the viability of the woods below and then plan for a replacement.

#11: Low Slope Roofing Repairs – Sealing a Flat Roof

Another easy way to repair your low slope roof is by suing non-fiber asphalt emulsion.

Here you need a polyester fabric and a roller. Apply your emulsion to the damaged area. This will be the first coat before laying the fabric on top of it.

The last step is putting the last layer of asphalt emulsion to cover the fabric. This will make a durable patch that will last for a year or so.


#12: How to Find and Fix Water Leaks on Flat Roof

Finding water leaks on a huge commercial building flat roof is sometimes hectic.

However, you can do that by checking signs of leaks from the interior and measuring the surface area from which the leaks are coming from. Those same measurements should be transferred to the top section of the flat roof.

As soon as you have an approx. area, you can then go ahead to remove all the roof material and then lay new ones.

The video below covers related tips by Eric Garcia:

#13: Water Damage Repair on a Flat Roof

For total water damaged flat roofs, you can consider removing all the roofing materials all down to the roofing woods.

Here you need to start with the removal of mineral granules, then proceed and remover the tar membrane. This can be done by cutting a section that will act as the start of your peeling point. Check the woods if they are free from rot.

From here, you may clear away the old material then decide on the right type of flat roofing.