Reasons for the destruction of slate and ways to eliminate it

Among all roofing materials, slate has always been regarded as one of the most popular coverings. This is understandable given that it is widely affordable, straightforward to install, requires little upkeep, and is remarkably durable. Thus, even though there are many more contemporary materials available, a slate roof is still found on the great majority of private homes.

Nevertheless, despite all of this material’s advantages, slate sheets cannot "boast" of high resistance to accentuated mechanical loads, and natural exposure gradually "ages" them. This is true even though the material’s constituent asbestos fibers are strong in combination with cement filling. As a result, the roof covering may eventually develop cracks or even large holes, which will cause the roof to leak. Many homeowners turn to renovation projects because replacing the entire roof covering is a costly and time-consuming task.

When there are visible indications of roof leakage, homeowners frequently inquire about how to fix holes and cracks in slate roofing. You need to take into account a number of the most widely used technological approaches in order to determine which one is best for a given situation and to organize the roof. This publication is devoted to this subject.

Slate is a desirable material due to its obvious benefits over other coatings. For instance, unlike steel roof coverings, such a roof is impervious to corrosion, has a high level of moisture resistance, can withstand temperature fluctuations with little to no linear expansion, and is essentially immune to the effects of UV radiation. You still have to resort to fixing it on occasion, though.

It is imperative to identify potential sources of defects in order to provide context for discussing technological approaches to repair work. Given this knowledge, it is very likely that damage of this kind can be avoided with careful attention to prevention and slate flooring maintenance.

Therefore, the slate may develop chips and cracks for the following reasons:

• Most often, these are some kind of shock loads, for example, large hail or large tree branches falling onto the roof surface. This also includes inaccurate, incorrect movement on the roof surface.

Protecting the slate with a deck of boards on top will lessen the pressure on the covering by increasing the supporting area and preventing damage during roofing or repair work.

A specialized mobile ladder, secured at the ridge with a unique fastener, is required to perform roofing or repair work on extremely steep slopes, exceeding 20 to 25 degrees. This is especially true in the vicinity of the ridge or the upper portion of a slate roof.

• The second reason is the appearance and development of colonies of simple plants on the surface of the slate, which attach themselves to it and slowly but steadily destroy the structure of the material. Lichens and mosses especially love the rough surface of the roof. Having established themselves in one place, they first grow in size and then reproduce by spores throughout the entire surface of the roof. Moss grows into the joints of slate sheets and thereby begins to lift them, which is why during rain water can freely get under the covering. If moss has chosen a place at the bottom of the wave, then it can delay the normal flow of water, which also leads to roof leaks.

These phenomena typically happen on the roof’s north side, where there is little sunlight, or on roofs with slight slopes, where moisture is retained and helps to support the growth of these plant colonies. The building’s overall appearance is messy and unappealing, in addition to the coating being destroyed and the roof starting to leak.

It is advised to apply specialized paint to prevent the growth of moss on the cipher. This will seal the material’s pores and prevent disagreements from taking root. Furthermore, as the roof’s surface becomes smoother, normal water outflow will be allowed, preventing the dirt clusters from becoming stagnant and frequently serving as a "starting point" for the growth of parasitic vegetation.

In the event that mossy colonies are already present on the roof and it is preferred to attempt roof preservation rather than roof replacement, the slate must be removed from this "garden." Three methods can be used to complete this process:

– mechanical, with a brush made of iron;

– applying strong pressure to water;

– chemical, employing specialized herbicidal compound spraying on the roof.

• The reason for the dilapidation of the slate may be quite a banal reason – a long service life. Unfortunately, not all slate produced today is of the proper quality, since often in its production, in order to reduce production costs, not only GOST standards, but even less “demanding” specifications are not fully observed. As a result, sheets of such slate covering turn out to be fragile, and, unable to withstand even minor impacts, they crack or even split along their entire length. Failure to comply with technological rules can occur at various stages of the slate production process, for example:

The ratios of the component ingredients were not followed when creating the slate solution, which was made against the recipe.

— Handmade machinery was used to produce roofing material.

— The reinforcement force was decreased by the manufacturer’s addition of short asbestos fibers to the mixture.

Slate sheets were not processed to a sufficient standard.

– Shortening the time needed for the material to fully mature; it should take at least 28 to 30 days after the date of manufacture.

Regretfully, it has been observed that modern slate frequently only lasts 12 to 15 years, whereas "old-school" products last for decades. In conclusion, you should consider the manufacturer’s reputation and the responsibilities it offers very carefully when buying material.

• Stagnation of water around chimney and ventilation pipes, as well as attic windows, can also cause cracking of sheets of material, especially with a sharp drop in temperature. Therefore, such problem areas require enhanced sealing and ensuring free flow of water.
• As mentioned above, a slight slope of the roof slope and stagnation of water on it can also contribute to cracking of the material. And stagnation of water very often becomes a consequence of a banal accumulation of dirt or fallen leaves, that is, a kind of damming of waves.
• The cause of damage may also be that the installation of slate sheets was carried out in violation of the established technology for this process, and as a result, the coating may experience excessive internal stress.
• To secure the material to the sheathing, ordinary nails were used or rubber gaskets were not used. In this case, cracks will certainly appear over time.
• The holes drilled for hammering in slate nails are too small, which, with temperature changes and expansion of the material, will also lead to damage to the roofing sheets. Therefore, when drilling holes, it is necessary to take into account that slate nails should enter them freely. But, at the same time, the holes should not be too large, otherwise leaks will occur.
• Snow also adds load to the roof, and not only with its considerable weight, but also with the formation of ice at the bottom of the slope, near the eaves. In spring days or during a thaw, the snow begins to melt, and water flows down to the bottom of the slope, and in the evening hours the air temperature drops, and ice forms on the edge of the slate, which leads to crumbling of the roofing material in this area.

In the event that the slate in this location is destroyed, water will seep through the cracks and onto the rafters, mauerlat, sheathing, and load-bearing walls. This will cause fungus to grow and the wood to gradually decompose. As a result, frugal homeowners frequently install cable heating in the drainage channels and lower portion of the slope to preserve all roof components and materials. This heating can be turned on in the winter to prevent the formation of ice.

Now that we have examined the primary causes of slate damage and the potential preventative measures, let us focus on determining the damage that has already occurred.

Since it is nearly impossible to see tiny chips or microscopic cracks on the rough slate surface laid on the rafter system, particular attention should be paid to some concerning signs indicating that the roof needs repair:

• If there is even a small leak, even imperceptible to the eye, it will soon manifest itself by the appearance of mold spots in the corners or at the joints of the ceiling and walls, and the appearance of an unpleasant smell of dampness.
• If thermal insulation material is not secured to the inside of the roof, then even the smallest crack can be easily detected by going up to the attic after rain. The leak will appear as a darker spot compared to the rest of the internal surface.

Now is the time to concentrate on the parts of the roof that require repairs the most frequently, as this knowledge will come in handy when looking for roof covering damage.

1. First of all, you need to monitor the edges of the slate facing the eaves. It is recommended to examine them every spring. If cracks have formed on the edges, then they will not be difficult to detect – sometimes you don’t even have to climb the stairs to do this, since they can be seen from below.
2. Moss may appear on a roof that does not have cracks or chips, but you should not wait for it to grow and occupy the entire surface of the slate. It is on a neglected roof that, after cleaning, a very sad picture with a lot of damage is often discovered. In addition, removing several islands of emerging moss is much easier and cheaper than subsequently cleaning the entire wavy surface.
3. Cracks can form at the crest of a wave or at its lowest point. It is more difficult to detect the latter, since they are invisible at first glance. How they can be identified was described above.
4. At the crest of a wave, cracks generally form along the line where the slate nails are driven in and are immediately visible to the naked eye. However, if these cracks have already appeared so much that they are visible visually, repairs should be started urgently.

After the roof has been inspected from every angle, a decision must be made regarding the most effective way to perform repairs.

• If significant chips are found along the edge of the lower sheets, then it may be necessary to replace one or all sheets of the first row, especially since the roof structure allows this to be done. However, it is necessary to take into account that the nails will have to be removed with great care so as not to damage the bottom edge of the next row, since it is this that overlaps from above onto the bottom.
• If it is not possible to replace the sheets, then the integrity of the edge can be achieved by placing a kind of patch on the inside of the sheet, but you cannot leave the coating in a damaged state, since in this case leaks cannot be avoided.
• If the crack goes along the crest of the slate wave, then it must be repaired using patches, applying them from the inside and outside. Usually, a piece of galvanized iron sheet, bent to the shape of a wave, is placed under such a crack from the inside, and a special roofing tape is applied on top of the damage.
• If the crack runs across the slate sheet, then there is no way to do without replacing it. You will have to carefully dismantle it and install a new one.

Therefore, it is essential to move forward with the consideration of repair work after fully understanding the subtleties of the occurrence of defects in this roofing material and the detection of damage on it.

Crack sealing can be done in a number of ways with both conventional and unique modern materials. In any event, all repairs have to be done on the roof’s surface, which needs to be thoroughly cleaned of any growths, dirt, debris, foreign objects, etc. P.

In the event that damage is discovered at a height rather than at the edge of the roof, cautious movement on slate should always be considered when choosing a repair strategy. On a gable roof, a ladder is used to prevent further damage to the slate, and on a single-pitch roof, a flooring consisting of boards is used to help distribute a person’s weight evenly across the surface.

The first method is using ordinary concrete mortar

Slate repair with cement and sand may seem like the easiest and most economical method—but that’s only if you don’t consider that working at a height will always make the task more difficult.

Sand and cement are combined in a 1:2 ratio to create the slate repair solution, and M-500 cement and fine-washed sand are the ingredients. Use high-quality tile adhesive (also known as complex bases) for external facade work is a viable alternative to this solution because it is more resistant to temperature fluctuations and high humidity. Because it is also based on cement, the glue has a fine consistency and good adhesion to the slate surface.

The mixture ought to cling to the surface with the same ease as soft dough. Slate in the repair area should be moistened to improve material adhesion. Should the damage be too severe, you should create a layer of galvanized roofing steel beneath it by bending a section of sheet into the shape of a wave and inserting it beneath the pothole or crack. This apparatus will offer an extra assurance of excellent solution adhesion to the asbestos concrete surface.

Using a spatula, the solution is applied to the surface. If the crack is at the wave’s base, there should be a thin layer of it on the surface that won’t retain water too much. The applied solution’s surface needs to be smooth; to achieve this, it is lightly moistened and worked with a hand that is covered in rubber gloves.

For outdoor use, the patch should be fully primed and then painted with waterproof slate paint after it has completely dried.

The second method is using butyl rubber sealing tape

In addition to being used for repairs, butyl rubber waterproof tape is also used for waterproofing the intersection of roofing coverings with chimneys and ventilation systems, as well as for sealing sheet joints.

Because the tape’s surface is composed of non-woven material, paint in the desired color can be applied to the applied patch. Such material is very easy to work with, and repairs are made in the following order:

• The area of ​​slate that requires repair must be cleaned and degreased. This can be done using white spirit, acetone or other organic solvents.
• Next, a piece of tape of the required length is cut from the roll (so that the entire crack is covered, plus the tape goes onto the undamaged area by another 50 mm along its edges).
• The adhesive layer of the tape is covered with a protective film. The tape is applied to the crack and as it is glued, this protective backing is removed from it sequentially, very carefully. There is no need to rush – you cannot allow the tape to wrinkle, wrinkle, or stick together.
• The tape is carefully pressed against the surface of the sheet, since it must fit as tightly as possible, without the slightest gaps, to the slate.
• To prevent the patches from standing out on the roof, the roof can be completely covered with paint or you can choose a shade for the patch to match the slate. But it is imperative to paint the patches on top with high-quality waterproof paint.

It should be mentioned that ready-made butyl rubber patches in a range of sizes are available for purchase instead of rolls.

Additionally, fiberglass mesh is advised for a more dependable method of repairing large slate cracks in addition to butyl patches. Fiberglass mesh serves as a reinforcing layer that strengthens the sealed seam.

If serpyanka is used for the work, you should use double-sided tape or a patch—that is, a coating with a protective backing on both sides—for the bottom layer that is glued to the damage. In this instance, the tasks are completed in the order listed below:

• First, butyl tape is glued to the degreased slate, in the same way as shown above – only the bottom backing is carefully removed. The tape is also carefully smoothed over the repaired area.
• Then the top protective coating is removed from it.
• After this, a cut piece of serpyanka tape is secured on top of the tape.
• Then, a tape with one-sided application of adhesive and a non-woven surface on the front side is attached to the serpyanka.
• The last step is coloring.

The third method is using bitumen mastics

There are two methods for applying bitumen repairs: hot and cold.

1. If repair work is carried out with hot bitumen, then it must first be prepared – this is done as follows:

• Bitumen is placed in an old bucket.
• A fire is lit and enclosed with bricks so that a bucket of bitumen can be placed on them.
• The contents of the bucket are stirred periodically so that it does not burn to the bottom or ignite. The composition must be heated to 160 degrees.
• If the work will be carried out at sub-zero temperatures outside, it is recommended to add about 10% of the total volume of waste oil to the bitumen. It will give the composition the missing elasticity, which will help avoid cracking of the patch. This is especially important if the edge of the roof is being repaired, since this area is considered the most problematic. In this case, it is best to additionally reinforce the patch with fiberglass mesh.

If you glue a TechnoNIKOL type (Euroruberoid) waterproofing material onto hot bitumen, typically used to cover flat roofs, you can skip the reinforcement.

The material will perfectly take on the shape of slate waves because of its elasticity. It will need to be heated with a torch or hair dryer if pressing it firmly against the applied mastic is not possible.

Using a brush or spatula, bitumen is applied to the roof’s degreased damaged area. The heated mass is then covered with reinforcement. On top of the serpyanka mesh, another layer of bitumen is applied once the first layer has solidified.

1. When using ready-made waterproofing bitumen mastic, it does not require heating.

Just thoroughly combine the ingredients and apply to a slate surface that has already been primed and cleaned of grease.

In order to further secure the two edges of the sheet that were separated by a crack, you can also place a sickle mesh on top of the first layer of mastic.

Any number of layers will do, but the longer the drying time, the thicker the layer. Thus, it is thought that the best option would be to lay two 1.5 mm thick layers of mastic between which reinforcing material will be placed.

The fourth method is using cement-asbestos mortar

Similar methods of slate repair involve the use of a cement mixture to which asbestos fibers and PVA glue are added. Crushing asbestos sheets, cords, or strips used for laying brick kilns can produce bulk asbestos. It is essential to wear goggles to protect your eyes and a respirator, or at the very least, a medical mask, when grinding this material.

The following proportions of materials are needed to make the mixture: PVA glue, water, and two parts cement are diluted one to three parts asbestos. The mixture is combined with all the ingredients until it has the consistency of thick sour cream. The composition is ready to use right away.

The slate needs to be thoroughly cleaned and dried before applying this composition. Following drying, the damaged section of the sheet is meticulously primed using a 1:3 solution of PVA and water. Two layers of this primer are applied, and they are both allowed to dry.

Next, the damaged slate area that has been primed is covered with the asbestos-cement mixture using a spatula. In the event that a fracture is fixed in the wave’s lower portion, the layer ought to be as thin as possible—roughly 1÷1.5 mm. The layer’s thickness is not crucial in the event that the defect is situated on the ridge. In the latter instance, it is crucial to fill the resulting crack all the way through the slate’s thickness. The material that has been applied needs to be smooth and well-leveled.

The fifth method is the use of polyurethane foam and epoxy resin

Given that polyurethane foam and epoxy resin are used in the repairs, we can conclude that this method was created by do-it-yourself artisans. You will need a container of polyurethane foam, sealant, and a two-component epoxy adhesive complex—the latter of which will act as the foam’s waterproofing—in order to carry out work with these materials. This technique is known as "three-layer," and the actual repair is done in multiple steps:

• The preparatory stage consists of cleaning and degreasing the area to be repaired. If the crack or break in the slate is large enough, you should clean and process the edges of the slate inside this hole, using, for example, a file.
• The next step is to fill the existing gap (hole) with polyurethane foam. After this, you should wait about a day for a pause necessary for expansion and polymerization of the foam. It should be noted here that if a very large flaw has formed in the slate, then it is recommended to place a piece of roofing felt or galvanized metal under it, but it must be well pressed from below to the slate, otherwise the foam, expanding, will push it away.
• After the foam has dried, its excess is cut off according to the shape of the wave.
• A thin layer of sealant is applied on top of the frozen and cut foam. It is necessary to ensure that it fills all the pores on the surface of the material. After this, the sealant is left until it dries completely. The time it takes for the sealant to harden and cure before proceeding to further operations is usually indicated on the packaging of the material.
• The third, final stage is covering the repaired surface with an epoxy composition, which will finally smooth the surface and it will merge into a single whole with the slate. The hardened epoxy will cover the repair patch with a reliable protective layer.

This repair process is highly intricate and costly. However, the repaired area gains high strength and is sure to solve the leak issue once it has fully hardened.

All you need is an epoxy composition to patch up a slate sheet that has split along its whole length in the middle of the slope. This will seal the crack completely. In this instance, a mounting waterproof tape is adhered to the crack on the bottom side of the sheet from the attic side first, and the gap is then filled with epoxy compound as tightly as possible.

Sixth method – chalk + drying oil

This mixture, also known as folk, is used to patch slate cracks. It is not recommended for filling in large holes, so if one has developed, it should be discarded right away.

In this instance, the repair mixture consists of drying oil and chalk. Eventually, the mixture should have the consistency of thick honey. Chalk is therefore added to the drying oil, so to speak, "by eye," in small amounts that are carefully combined. The solution is mixed continuously until the required density is reached.

After the prepared mixture has been applied, level the previously cleaned crack. The mixture is thickly covered with moisture-proof paint once it has dried. The process of fixing slate with this technique can now be deemed finished.

The seventh method is to use moisture-resistant nitro-based glue

This technique for fixing roofing material makes use of nitrocellulose glue that is resistant to moisture, like "Emalit." The following is how the flaw is fixed:

• The inner side of the slate sheet, facing the attic, is well cleaned with a wire brush and washed with water, then completely dried.
• Dry slate in places of damage is sealed with fabric. To do this, you can use regular thick fabric or fiberglass. The patch must have a size exceeding the size of the hole or crack by 40÷50 mm on each side.
• The fabric is impregnated with glue and applied to the damaged area, pressed well and smoothed out.
• After the materials have adhered and the glue has set, another layer of glue is applied on top of the patch.
• After the internal patch is completely ready, the hole or crack on the outside of the sheet is filled with concrete mortar or tile adhesive for facade work. The surface of the filled hole must be well leveled.
• If a crack is being sealed, then one hole is drilled at the beginning and end, which are filled with elastic sealant, and then self-tapping screws are screwed into them. This must be done to prevent the crack from developing further.

The eighth method is using special waterproofing coating compounds

Ready-made cement-polymer waterproofing coating compositions, available in buckets or as dry mixtures that need to be diluted, work great for fixing slate sheets. You can usually find preparation instructions on the packaging.

In any case, working with such compounds is quite simple because of their high adhesive properties and finely grained composition, which fits precisely onto the material to be repaired. The following order is followed when performing repairs:

• The surface around the damage, cleaned and degreased with one of the solvents, as well as the internal walls of the crack, is thoroughly dried.
• Then, the waterproofing mixture is diluted with water, and the surface that will be repaired is primed with it. The primer should also dry well.
• The next step is to apply a thick mixture prepared for repair using a spatula or gun.
• After six hours, the crack should be covered with fiberglass, and another layer of waterproofing compound should be applied on top of this patch and leveled well.

Inquiring about the weather forecast for the days the work is scheduled for would be reasonable if a specific repair method is selected. Since mixtures should dry at room temperature, roof repairs should be done in dry, calm weather—ideally not sunny, cloudy conditions. Consequently, the best time to do repairs will be at the end of the summer or the beginning of the fall, when it will be easy to select days based on the weather forecast.

Furthermore, keep in mind that even excellent and high-quality patches can only offer brief protection against roof leaks. The issue is that the density and coefficient of linear expansion of different repair compositions and roofing materials vary. Leaks will therefore reappear after repaired flaws can only withstand a few cycles of extreme temperature changes. These fixes are necessary to give homeowners enough time to decide on and buy a new roofing material. If the damage is severe enough to warrant covering the roof right away, you should address the issue head-on rather than trying to patch it up later.

Protecting slate from further damage

If cracks have developed over time on a roof that has been in use for a long time, sealing the damage or applying patches will not be sufficient because the damage will not stop. Here, there are a few other options to halt the accelerated aging of a slate roof in addition to replacing the coating entirely with a new one.

• First of all, the roof surface is well cleaned, washed and dried. If there are no moss growths on the slate, then the coating can simply be thoroughly cleaned with a broom. In any case, no matter what kind of cleaning is carried out, the respiratory tract of the master must be well protected during this operation – asbestos dust is extremely harmful.
• Next, it is recommended to prime the entire roof surface well and dry it.
• Next, the slate roof is completely covered with rubber paint, which creates an elastic waterproofing layer on the surface.
• Another way to save an aging slate roof is to cover it completely with Rizoline.

"Rizolin" is a foil-surfaced, self-adhesive, flexible material made of fiberglass that has been impregnated with bitumen-polymer compositions and specific additives to enhance the coating’s performance.

With its unique design, this material can be applied to roofing surfaces of any complexity and will consistently keep the roof waterproof. "Rizolin" clings tenaciously to any surface and is malleable enough to assume the form of slate waves.

Before the material is installed on the roof, its anti-adhesive backing is removed to protect the adhesive side. The sheets are pressed up against the slate surface and stick firmly to it after the protective layer is removed.

Another significant benefit of this material is that it shields the roof from direct UV light and prevents overheating because its outer layer is made of foil, or "rizolin." Because of this, the old slate is essentially "preserved," and a home with a "rizolin-covered" roof never gets too hot.

To sum up, let me remind you that the European Commission enacted a directive in 1999 that forbade the use of asbestos and products derived from it in EU member states as of 2005. Based on research and the finding that asbestos can seriously impair human health, this decision was made. So instead of sealing cracks and holes in a slate roof when it needs repair, might you consider this an opportunity to replace the covering entirely with a contemporary roofing material?

Despite their reputation for strength and beauty, slate roofs can sustain damage over time from a variety of sources, such as weathering, physical impact, and improper installation. Slate tiles are susceptible to chipping, cracking, and delamination due to moisture infiltration, freeze-thaw cycles, and the growth of moss or algae. Regular maintenance is essential to extending the life of a slate roof and preventing further damage. This include keeping the tiles clean, fixing or replacing any damaged ones, and making sure there is enough ventilation to prevent moisture buildup. Homeowners can maintain the integrity and aesthetic appeal of their slate roofs by taking quick action to resolve these problems.

Finally, enjoy this fascinating video story where the expert reveals how to make glue for repairing slate roofs.

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