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All You Need to Know About Flat Roof Repairs


This is a comprehensive guide on flat roof repairs. It will discuss typical roofing systems as well as how to effectively repair them (both permanent and temporary). If you want to know how to repair common roofing systems, from professional quality to DIY type, you have come to the right place.

To give you a brief overview of the types of flat roof repairs:

  1. Temporary repair: This is a cost-effective, as well as a quick and easy way to repair a flat roof. Temporary flat roof repairs will prevent the small leaks from destroying your precious belongings while allowing you to wait for professional roof repair quotes. It can buy you time while you are still saving for the expenses of roof repair or deciding which professional roof repair service provider to choose.
  2. Permanent repair: A permanent repair for flat roofs are more costly than temporary repairs but it extends the life of your flat roof until the time comes when you need to replace it completely. Permanent flat roof repairs are performed by trained professionals so you can be sure it will last longer than a temporary flat roof repair. Professional tradesmen will repair the flat roof with patches or install another layer on top of the damaged roof.

Between the two types of flat roof repairs lies the useless type of roof repair that should never even be considered as an option. Why is it a waste of time? If the condition of the roof is very poor, repairing it will only make your repairman miserable, as well as make you spend money on a roof that is no longer worth repairing.

Now we go to the comprehensive discussion of flat roof repairs.

Temporary Flat Roof Repairs

If you have always wanted to DIY repair your flat roof, here’s your chance. One of the main requirements of DIY repairing your roof is that your knees with the thought of heights. Another main consideration for DIY temporary roof repairs is utilizing the proper material for the specific type of roof. The trick to a temporary flat roof repair is to use only the right amount of product so that it will not be too difficult for a professional repair or replace it eventually.

Here are the common types of roofs and the comprehensive guide for repairing each type:

Felt Roof Repair (may be grit placed on top of the roof, or a reflective silver coating/mineral finish)

Whether your felt roof is the traditional (read: old) pour and roll kind or the modern Torch-on felt roofs, these are the problems that you will likely encounter:

  • Puncture holes from impact, cracks, and splits
  • The roof’s surface has a significant hollow or dip
  • Stuck or lifting joints in the felt roof
  • Corroded flashings cause leaks in the walls

There are various types of felt roofs, such as those with a mineral finish with purple or brown colors. Felt roofs with grit finish used to be common but rarely used nowadays.

Splits on felt roofs may be caused by sunlight exposure. For temporary repair of felt roof splits, a waterproofing paint may keep you worry-free for a few weeks – or if you are lucky, a month up to two years.

Dry joints or leaking joints in felt roofs can be caused by age, substandard materials, bad workmanship – or all of the above. Troublesome lifts due to stuck or dry joints can be temporarily resolved by using a paint-on waterproofer.

Leak on flashings can occur in areas where the flat roof meets the wall. Water flowing down the leaks can cause damage to the property. This can be resolved by removing the old mortar and replace with a new one – using the right mix, of course.

The most common DIY repair for most felt roofs is applying paint like the ones you see on YouTube repair videos.

There are different ways to permanently fix a felt roof. You could choose between applying a “layer on top”, patches, or liquid systems. It is important to assess whether the damaged roof is still fit to be repaired. Sometimes, if the felt roof is too worn our, it may be more expensive t repair it than getting a new roof.

Speaking of no longer worth fixing – it is best to assess the real condition of the roof before attempting to fix it or spend money to call a professional roof repairman.

Asphalt Roof Repair (may look like a stone because of the grey hue; also referred to as bitumen-based waterproofing)

An asphalt roof is very sturdy and will last even longer when proper maintenance and repair is done.

However, due to age and exposure to the elements, asphalt roofs can still have damage such as:

  • Blisters on the asphalt itself
  • Wrinkles, splits, and cracks
  • Asphalt may sag or shrink on flashings and roof upstands

Asphalts roofs get cracks due to heat as well as age. Although these cracks will normally not cause any problems until the cracks expand because of water freezing during winter.

Another problem that you may encounter with asphalt roofs is bumps or blisters. These happen when moisture is trapped below the surface of the roof. Similar to cracks on asphalt roofs, blister or bumps are usually nothing to worry about until the blisters burst and create a hole.

To repair asphalt roof temporarily, you can apply flashing tape with heat or simply fix it with paint that can repair lead.

If you are looking to repair an asphalt roof permanently, you can apply a torched-on patch roofing felt, or maybe put another layer on top. Some professional liquid systems are used in repairing asphalt roofs, such as Kemper systems, Gacoroof, or 3M. There are worthwhile roof repair systems but can sometimes turn out more expensive than installing a new roof for your home.

Sometimes, damages in asphalt roofs are not worth repairing at all. In case you do find irreparable damage on your asphalt roof, you can place a tarpaulin on top or better yet, invest in a new flat roof.

Ready to get a quote from local tradespeople?

Concrete Roof Repair (regular concrete appearance, if not coated)

Concrete flat roofs are not very popular nowadays due to condensation and insulation issues, but still considered a long-lasting type of roof. The description “built like a brick outhouse” perfectly describes a concrete roof. One of the advantages of installing a concrete roof is that it can be repaired quite well, if necessary.

But just like any type of roof, concrete roofs are still susceptible to damage such as:

  • Splits and cracks
  • Wearing of the surface

A concrete roof with cracks or splits can leak, and the problem is that it can be challenging to find the troublesome area. If the surface of the roof has signs of wearing, it will not immediately cause a leak. However, surface wear makes it more difficult to repair the concrete roof when the top part of the concrete roof is starting to break away.

To DIY repair a concrete roof temporarily, you can apply a bitumen-based paint like the one shown on DIY repair videos. The process usually involves applying a thin primer of bitumen-based paint. It must be allowed to dry well for better results. Waterproofer is then applied, but it is a must to remove all dirt and moss before application.

Repairing a concrete roof permanently can be done by putting a torch-on roofing felt patch. Placing a layer on top is a cheap but effective way to repair a concrete roof.

When is it not worthwhile to repair a concrete roof? When the original concrete roof was done with very little cement, the roof is susceptible to dampness since it is porous and rough. Putting a new concrete layer on top is not a smart solution. Instead, a new roof should be installed of screwing or bonding a timber deck to give way to the new roof.

Fibreglass Roof Repair (also referred to as GRP)

One great advantage of fibreglass roofs is that they are usually easy to fix when there’s damage. When the time comes that your fibreglass roof needs repair, remember to utilize products that are designed for fibreglass to prevent further damage and ease in fixing.

You may encounter such problems with fibreglass roofs:

  • Leaks on flashings
  • Splits and cracks near the board joints, trims, and upstands

When a fibreglass roof starts holding water, some people think that it is what causes the leak and breaks in fibreglass roofs. The common cause of leaks in the fibreglass roof is missing or cracked mortars.

If you are thinking about repairing fibreglass roofing on your own, make sure to check the flashings against abutting walls. There are times when the root cause of problematic GRP wall flashing is poorly applied sealant.

Cracks on fibreglass roofs are usually caused by contraction/expansion and fatigue. These can be caused by improper planning of expansion, or the lack of trims and joints for reinforcement. An ideal (temporary) solution for impact holes or cracks is to apply acrylic sealant on the affected area. It can also be reinforced by putting some plasterers scrim. Before applying anything, make sure the surface is free from dirt. Fibreglass roofs can be cleaned with warm soapy water so the repairing materials can apply well. If you need to perform a permanent repair in the future, use acetone to scrape off and clean the old acrylic sealant.

If you want to permanently repair a fibreglass roof, you need to make sure that the surface is totally clean. Clean the surface of the fibreglass roof with acetone and then sand the area (at least 3 inches or 7mm around) with grit paper (60 grade). The next step is to laminate a 600g CSM (chopped strand mat) in the following procedure: clean/sand area, laminate the chopped strand mat, apply resin on top, remove all bubbles. The are should be cured well before applying a topcoat with a matching color.

To make sure you won’t be wasting your time repairing your fibreglass roof, consult a GRP roofer to ensure that there is no major issue with the fibreglass’ lamination (which may be because of contamination, decontamination, resin starvation, and more).

EPDM Roof Repair (also referred to as a rubber roof, EPDM is short for ethylene propylene diene terpolymer)

EPDM roofs are known to be extremely durable. It is also quite easy to fix DIY or with the help of a professional. If the rubber roof has a cut, hole, or small tear, the best way to deal with it is by using a suitable product for repairing rubber roofs. Using other repair materials can lead to further damage.

Despite a rubber roof lasting many, many years, it is still possible to still experience:

  • Shrinking due to insufficient support in upstands or edges
  • Unprofessional detailing of the rubber roof at the joints or flashings
  • Cuts and holes resulting from impact from an object with sharp edges

The most common manifestations of rubber roofs that were unprofessionally installed are rubber membrane contracting, wrinkling, and ponding. Poor detailing can result in an aesthetically poor rubber roof. Cuts and impact holes, on the other hand, can be fixed by a professional and even a competent DIY’er.

Looking to DIY repair your property’s rubber roof? Temporary repairs are great for buying time and if the tear or hole is still small. The best possible option at this point is to purchase a tube of sealant and apply it on the affected area, but very sparingly. Remember to avoid going crazy when applying sealant since it will be removed later on if you are having your roof repaired professionally. Also, too much sealant means more work for the tradesmen which means bigger expenses for you.

Permanent repairing an EPDM roof is relatively easy – all you need is a simple patch. First, you should buy self-adhesive flashing. These self-adhesive patches are available in two different types:

Rubber flashing tape – you can form different shapes with this highly-malleable tape. This is especially useful for bends and areas with round corners. Self-adhesive flashing tape – is usually thicker, although it is not as malleable as the first type of tape. Unlike the first one, however, the self-adhesive flashing tape is stronger and more durable.

Whether you choose the first one or the latter, you should choose one with at least 3 inches (75mm) coverage for both sides of the affected area. The EPDM roof must be cleaned thoroughly and dry before applying anything else. The EPDM primer is then applied to the area by placing it firmly around the hole or tear. It is best to use a hard roller to press around the edges. If the roof is always subjected to water, you should consider applying a lap sealant to ensure that the patches are firmly attached.

If a rubber roof was poorly laid, it may be better to install a new roof than repair it. Since rubber roofs are very easy to install, many folks attempt to do it themselves, resulting in improper layout. The most common issues of DIY rubber roofs are poor flashing that results in leaks, poor joints, stretching or contraction due to age, and lack of mechanical fixings around the edges.

Oftentimes, small problems repaired by professional tradesmen are usually cheaper. DIY repairs may end up more expensive since you have to buy different components and tools on your own.

Choosing a Paint-On Waterproofing Solution: Convenient Roof Repair for Emergencies

Temporary repairs to a lead roof or a bitumen-based roof are usually resolved with a paint-on waterproofer. These are available on tin cans for DIY repairs and are usually very effective. If the repairs required are small and only in one area, you may give the DIY repair a whirl.

Paint-on waterproofers are usually acrylic or bitumen-based. Too much paint-on waterproofing solution, however, may make it difficult for a professional to remove in the future. Too much solution applied will make it challenging to perform professional repair solutions, whether a patch, a hot flame solution, a layer on top, or a liquid roof permanent repair.

What is the Best Waterproof Paint?

For DIY repairs, there are three viable options: rubber type, acrylic-based, and bitumen-based. Most professionals, however, prefer acrylic-based waterproof paint.

There are several acrylic-based paint-on waterproofers out there bit one of the best is Cromapol. Professional roofers usually have these on hand which comes in handy when small repairs are needed because first, it’s not messy to work with; second, it’s effective. Plus points for looking good and staying put quite well.

Other companies have produced similar products such as Acrypol, Evercryl, and Roofacryl. It is not dirt cheap, either, but you can buy small amounts for small repairs.

Another benefit of using an acrylic waterproofing paint is that it can be applied on a wet surface. However, it is best not to use it when the roof’s surface has algae, dirt, grease, or moss. Applying it on dry roofs will, of course, produce the best results.

Is it Okay to Paint the Entire (Asphalt, Concrete, Felt) Roof with a Waterproof Paint/Sealer?

Well, this is not to play safe, but the answer is both yes and no.

To put it in perspective, let’s say you have a roof that measures 4×4 meters. The roof has holes and splits so you obtain a big can of bitumen-based paint and apply it over the surface. The problem is that even with a nice and even coat, the bitumen-based paint will dry out eventually, producing cracks. So it’s always a god idea to assess the condition of the roof before slathering the entire thing with waterproofing paint since poor roof conditions will make the waterproofing sealer unreliable.

Given another scenario – let’s assume that you bought a professional-quality sealant such as a polymer-based, rubber-based, or acrylic-based paint. These compounds are known to last longer than a bitumen-based repair. The goal here, of course, is to coat the roof evenly throughout.

Even professionals find it challenging to guarantee a nice and even application with a paint-on system. So the best answer to the question it is okay to paint an entire roof with a waterproofing paint-on solution, it depends on the size of the area. Otherwise, you may be just wasting your time and money on something that will not be completely effective.

Permanent Repair for Asphalt, Concrete, and Felt Flat Roofs

Permanent roof repair has been mentioned throughout this guide, but what exactly is it? The truth is, permanent roof repair is not permanent at all. If repairs were permanent, there will be many professionals without jobs to do.A permanent roof repair is one that prolongs the life of the current roofing system – about 10 years or more.

An asphalt roof repair, for example, will deal with blisters and cracks first before another layer of felt is applied. A permanent roof repair will produce results that boast of value for money. This kind of repairs will also work for concrete and felt.

These three permanent repairs are the most promising options:

Professional patch: A professional patch repair works in the same ways as a Torch-on felt. A liquid repair system may also be applied.

Professional liquid-based repair: One of the disadvantages here is the cost: the repair may cost as much as a new roof installed. Why would customers choose a professional repair as expensive as a new roof that may come with a guarantee for several years?

A layer on top: An asphalt roof or a felt roof that is about to expire may still be a candidate for a well-placed patch repair. The main consideration to push through with the repair is that the structure and roof underneath are still in a worthwhile state. If the old roof is in a reasonable condition, a Torch-on felt may be laid on top. The process involves putting one layer of polyester felt with a blowlamp. The roof must be free from dirt and grit. The process ends by applying new flashings or edge details. Although this may not be a popular suggestion from some roofing professionals, these low-cost repairs may last more than 20 years if done well. There may be challenges in removing them later on, but that’s another problem.

How Do You Know If It Is Not Worthwhile to Repair a Flat Roof?

This can be a tricky question as there are several factors worth considering. There are different roofing systems and each comes with a variety of repair options.

The first factor to consider is the condition of the current roof. Most professional roofers will assess the situation by looking at the roof’s surface and how the timber under the roof cover looks like.

If the roof deck is weak because of internal condensation or leaks, the type of roof cover will not matter too much anymore. The joints will be damaged and they are visible dips on the roof deck. This happens to different kinds of roof covers and decks such as Plywood or OSB3 but is more common with bitumen felt roofing systems. If the flat roof joists have visible humps or ridges, it simply means that the damage is significant, and not just because of aging. Professional roofers will assess the roof by walking over it very carefully.

There are two possible reasons why flat roofs have visible humps and ridges:

The roof deck has significant deterioration: If the deck of the roof has rotten, it means the roof’s support is no longer sufficient. Unless the damage is a crack or visible hole in a specific area, repairing the roof is going to be a waste of resources. If the hole or leak is very obvious, a temporary repair may be viable. It is alright to temporarily repair the flat roof if the process will not damage the roof further, or it won’t cause you to fall off the roof and cause personal or physical damage.

If the bitumen felt has been exposed to the elements for quite some time, it has likely lost elasticity over several years of contraction and expansion. Although the roofing system may still expand with heat and contract with the cold, the felt itself may have become brittle and hard. A roof repair at this point will be a waste of time.

A walk test is usually performed to assess the condition of the roof’s support. If the flat roof has obvious dips and hollows between the joists, the roof deck likely has rotten badly, thus, extreme caution must be observed when planning to walk over the roof to inspect it. The professional roofer may try standing on the raised joists to assess the roof’s condition. The weight of one foot is used to press a little on the dips or hollows without fully stepping on it to establish its firmness or lack thereof. If the roof looks visibly worn, it may be unsafe to do this test.

If the roof, however, seems sturdy enough for a walk test, the substrate condition can be assessed up to a certain degree. The roof should feel nice and firm in a walk test, and at least built on torch-on felt, felt roof, or asphalt roof. This is an indication that a flat roof is worth repairing and may be fixed using a liquid roof repair system, or a layer on top.