Coat Gravel Roofs

Gravel covered home roofs are popular in some areas. Customers have requested information to help guide them in converting these roofs to “cool roofs” using reflective coatings. Not all gravel roofs are suitable for conversion, so please read this bulletin carefully before proceeding.

Gravel Roofs

Our experience is that most gravel roofs are 3-ply hot-mopped asphalt built-up, with a gravel finish applied. Pea gravel, crushed rock, and decorative rock (white quartz) are often dispersed into a flood coat of hot asphalt and applied over the top of the roof membrane. This acts as an adhesive when it cools.

(NOTE: Some commercial single-ply roofs are ballasted with gravel—this report does not apply to these)

Gravel Roof Advantages
Most gravel roofs are inexpensive to build, offer some protection to vulnerable asphalt against UV damage, and the stones are very durable.

Gravel Roof Disadvantages
On the other hand, gravel roofs are hot, energy inefficient, heavy, moisture trapping, and unstable. They are typically more difficult to service, as the owner can’t see problems developing and must clear the surface entirely to repair. Unprotected asphalt has very poor resistance to weathering.

Gravel becomes very hot in the sun and holds heat (poor emissivity) long after the sun sets. This keeps the roof hot and promotes the loss of the natural asphaltic oils that are intended to keep the roof pliable. As a result, roof life is reduced.

Loose gravel is washed down the roof’s slope during rainstorms, leaving some areas unprotected and subject to UV exposure.

Gravel collects along gravel stops (drip edges) causing more heat and moisture to be directed against the roof surface causing damage over time.

Gravel is heavy and concentrations of gravel can contribute to roof deck deflection (low areas).

As the roof ages, more gravel is released, increasing the displacement effect.

Advantages to White Coating
Coating the roof white reduces rooftop temperatures and prolongs roof life through lower temperatures and protective coating.

Cooling costs will decline and roof servicing is much easier.

The overall weight on the roof is reduced, and roof protection can be renewed repeatedly.

What to Avoid

• Do not apply coating directly over gravel; this is costly and guaranteed to fail.
• Do not apply fabric membrane to a gravel roof; this is costly and guaranteed to fail unless surface has been filled and smoothed.
• Do not apply coating to a badly worn or dried-out roof.
• Avoid applying coating to roofs that need repairs (fix these first).
• Avoid applying coating to roofs with serious standing water problems.

STEPS

1. Determine if the roof is a good candidate for coating. Trying to save a bad roof is expensive and frustrating.

• Is the roof under 10 years old? Older roofs may be too fragile to survive.
• Is the ply sheet still flexible? Locate ply sheet edges at seams and around penetrations; bend side to side to determine flexibility. Roofers may choose to take a core sample. Don’t coat roofs with dried out, inflexible ply material.
• Consider the condition of the roof, drainage, cooler or AC leaks, and repairs that may be needed. Avoid coating problem roofs.

2. Decide in advance how to dispose of the gravel removed.

• Can it be spread around the property or must it be hauled away?
• What will disposal cost?
• Where will gravel be taken off roof and what ground preparations need to be made (i.e., tarp, containers, truck bed)?

3. Carefully remove all loose gravel without damaging the roof membrane.

• Use a push broom and coal shovel to remove free gravel.
• Clots of asphalt and gravel are common. Remove as much these as possible without damaging the roof ply. Clots can be coated over later.
• Gravel roofs will always have some pits and clots that are visible.

4. Pressure wash the roof membrane and repair any problems.

• Check all lap seams and repair as necessary. Use Elastek Crack & Joint Sealant (not plastic roof cement) and fabric to reinforce as necessary.
• Caulk all roof penetrations with Crack & Joint Sealant (not plastic roof cement). Use fabric to reinforce as necessary.
• Replace gravel-stop drip edge with conventional material or gently flatten enough of the high-lip to promote good drainage.

5. Apply two (2) thick coats of asphalt emulsion and allow a week or more to cure.

• Emulsion is an inexpensive way to fill in the many stone pits on the roof’s surface while also resealing the membrane. It is cheaper to use than white elastomeric coating.
• Use a quality emulsion like Elastek Sealer Emulsion.
• Apply per emulsion manufacturer’s instructions. This is best done in warm weather.

6. Apply at least two coats of appropriate Elastek coating.

• Use either Elastek Solar Mastic™ or Solar Tek Extreme™ for durability and long life.
• Use Solar Tek Extreme™ as a first coat where drainage is marginal.
• Coat all asphalt surfaces, parapet flashing to above roof attachment or counter flashing, and penetrations to above the sealant line.
• Renew coating periodically.

Warranty Coverage
Due to the variables involved in converting a gravel roof to a reflective roof, only the Elastek Defect in Manufacture Warranty is available.

Repair Blisters

Blisters can frustrate anyone who works with roofs. Their arrival is usually a surprise, their cause is often unknown, and their removal is a lot of work. In this bulletin, we offer some ideas that may be helpful in dealing with blisters. What causes blisters? Blisters represent a localized loss of adhesion and the lifting of roof ply or roof coating film from the underlying surface. The most common cause is water or moisture vapor migrating through from below or above the roof surface. If the volume of trapped moisture exceeds the permeability (breathability) of a roof ply or coating film, pressure caused by rising temperatures on a warm day expands the moisture below the ply or coating film, and separates it at its weakest point, forming a blister. Blisters may occur below or between ply sheets in a built-up roof system, at the roof coating interface with the roof surface, or between coating layers when multiple coats have been applied to the roof. It is important to recognize the difference before proceeding. Blisters may be filled with water or air. Osmotic blisters can occur when moisture permeates the coating film from the outside due to continuous or frequent contact with water (i.e. ponding water). Moisture collects at the interface between roof ply, or the coating film and the ply, eventually causing a loss of adhesion and a blister. Osmotic blisters are not likely in areas where drainage is good. Moisture can come from below the roof and through the ply system to cause blisters. Some roofing experts maintain it is impossible to build an absolutely moisture tight BUR membrane. The nature of the process always creates tiny voids. If the area beneath the roof can’t breathe, then moisture may be drawn to the roof deck. Buildings can be too air tight to breathe adequately. Surface blisters in coating can sometimes be caused by the actual moisture in the liquid coating at the time of application. Small blisters can form when the coating dries so rapidly some of the water can’t evaporate completely before the coating surface cures. What to do about blisters If blistering is evident; try to determine the source of the moisture. Likely possibilities:

• Coating blisters confined to standing water areas are osmotic blisters.
• Coating blisters over asphalt emulsion or 505 Puddle Plaster™ often mean these were coated before fully cured.
• Blisters between layers of coating (as opposed to blisters originating between the coating and the ply) are often caused by:
  • Thick roof coating applied over a hot surface (flash-drying that traps moisture)
  • Applying a second coat before the first coat is dry
  • Poor coating adhesion, either due to coating over a dirty/chalky surface (lack of proper cleaning) or not fully rinsing away cleaning agents such as TSP, causing areas of chemical interference
• Blisters originating at the coating/substrate interface, indicating moisture coming up from below:
  • Moisture trapped in roofing plys, insulation, or wood decking due to past or current roof leaks
  • Moisture trapped in roofing plys, insulation, or wood decking — caused by moisture from the living area being lifted by warm air that ultimately condenses on cold roof and deck surfaces — migrates through tiny passages in the ply layers.
  • Moisture trapped in voids during construction of BUR roofs where ply sheets are not fully sealed by hot mop asphalt can cause blisters between ply sheets.
  • Moisture trapped in spray-down foam due to deterioration or loss of protective coating.

What to watch for Roof coating blisters in ponding water areas are due to moisture permeation from above. Roof coating blisters in areas of adequate drainage are usually coming from below. Consider venting. Watch out for roofs with coatings that have blistered before. Try to determine why the blistering occurred before recoating, as the blisters may return. Roofs over cathedral ceilings often blister because they are likely poorly vented and collect moisture from the interior. Coatings on older foam roofs that have not been well-maintained will result in blistering (water intrudes into the foam and can’t be seen when recoating). Look for water squishing out of small openings as you walk the roof. Water can permeate foam, asphalt, and decking and is very hard to dry out. Coating roofs in extremely hot weather results in flash drying. The coating may separate from the substrate even before it dries but not be visible as a blister immediately. By examining the underside of a coating blister, look for numerous tiny tendrils indicating the film pulled away from the surface at application. Recoating tinted roofs (coated with a dark color) or asphalt emulsion on a hot day also can result in flash drying and blistering. Coating roofs too soon after heavy rains or washing leaves roofs vulnerable to blistering, as does coating roofs with frost or condensation present. Coating roofs just before it rains is poor timing. Water in the coating that has not had time to evaporate provides an avenue for rainwater to penetrate and damage the coating. “My old coating never blistered until I put on your coating!” This can happen. If the roof membrane is allowing moisture to enter from below and the original coating was thin and permeable enough to allow moisture to escape, no blisters formed. A new coating reduces permeability by adding to total coating thickness and moisture is now trapped causing blisters. Our 120 Solar Tek Extreme™ and 121 High-Tek Basecoat™ are unlikely to blister because of their exceptional adhesion. Special Blister Issues Tinted Roofs: We have spent an entire day cutting hundreds of small blisters off a desert tan-colored roof with shop knives. What a job! After smoothing them over with 103 Crack & Joint Sealant™, with the owner’s permission, we recoated the roof with white. There was never another blister on the roof. We surmised that the excess heat on the roof promotes blistering, and the original coating itself may not have been well-adhered to begin with. Water Blisters: We have seen cases where larger water-filled blisters form in surfaces that drain well. These blisters form even when there has been no rain for months. Cutting into the blister releases a gush of water. The source is below the coating and inadequate venting may be the cause. Water passing through the roof system can apply pressure over a wide area and not cause a blister until it finds a weak point.

Repair Ponding Problems

Some Suggestions

Customers with flat (low-slope) roofs often have questions about standing water. Premium Elastek elastomeric roof coatings are highly resistant to all but the most prolonged standing water situations. Over time, water standing on a roof surface will damage roof coatings and roofing materials. Standing or “ponding” water eventually leads to roof leaks, damage to roof and deck materials, and damage inside the structure.

By definition, all properly designed and constructed roofs should have adequate and proper drainage. This means at least 0.25 inch per foot roof slope with proper grading and placement of drains or outlets. Roofing practice forbids and roofing material manufacturers usually will not guarantee, any roof subject to prolonged ponding water.

Ponding water is often defined as water that will not drain or dissipate from the roof surface within 48 hours after precipitation. Ponding water may also result from other water sources such as leaking cooler lines and pans, AC-condensate lines and pans, and similar sources. Water condensation, a cool weather problem, can also occur frequently in winter weather.

Recommended Solutions

Eliminate any water leaks coming from AC units, coolers, or drain lines. Check around drain areas for roof debris or roof patching materials that may be blocking drain exits and remove them. On granulated roofs, remove all loose mineral granules as they trap moisture.

Refer all other ponding problems that you wish permanently fixed to a qualified roofing contractor. The contractor may suggest repitching the roof, installing crickets to redirect water, additional drains, the opening of existing drains, or other procedures. Professional solutions are always best.

Other Ponding Control Strategies

If you are unwilling or unable to get professional roofing assistance, we offer several less permanent strategies to help control the leakage that can result from ponding water.

Reduce the depth of ponding areas with Elastek 505 Puddle Plaster. This material is used in smaller areas to reduce pond depth up to 1-to-2 inches, helping the water to move to a drain or helping to reduce the time necessary for water to evaporate.

Increase the water resistance of the roof within the ponding area by applying two liberal coats of Elastek 120 Solar Tek Extreme™. These coatings may be used on top of the cured 505 Puddle Plaster.

Laminate a single-ply of our polyester roof fabric to the ponding area with a thick coat of 120 Solar Tek Extreme™ (at 100 sq.ft. per gallon) under and over the fabric. Apply two finish coats of 120 Solar Tek Extreme™  over the treated area.

See specific Elastek Product Sheets for further details.

Note: The suggestions offered here are not roofing specifications. Roofers should follow accepted roofing practices.

Apply in Cool Weather

“Ninety percent of all roof coating failures occur during winter months when coatings, not fully cured, are subjected to condensation and standing water.”

Background Information

This bulletin offers suggestions for minimizing application problems in cool weather (Southwest desert area).

All latex-emulsion-based products use water as a diluting agent. When applied to a roof, coatings will dry or cure by evaporation, bringing latex particles into direct contact with each other to form a solid film. Once cured, Elastek coatings form a tough, weather-resistant barrier that is highly resistant to water.

It is critical that the initial drying phase of each coating application be complete BEFORE additional moisture is introduced to the coating surface! Damaged coating often appears wrinkled, loose, and lifeless. Coatings can fail from moisture above or below if present before curing is complete.

• Water still in the coating provides a pathway for surface moisture to penetrate the coating and break the new coating’s adhesion with the roof.
• If moisture from rain, condensation, or any source reaches the new coating before water within the coating has evaporated, adhesion to the roof surface can be affected.
• Problems also occur when a damp roof surface traps moisture below the coating surface. This can be caused by dew, standing water.

Weather

Drying time increases as temperatures fall and humidity rises. Coatings dry much more slowly at 60º than at 90º, and humidity is often higher in cooler weather. Direct sun is very helpful in drying. Overcast skies dramatically slow drying. Days are shorter in winter, allowing fewer hours of drying heat. Temperatures often drop rapidly when the sun sets.

Condensation on roofs at night is common in cooler weather. This moisture must cause a delay in the application of coatings until the roof is dry. This may be 10 AM or later in some areas. Higher altitudes or proximity to washes may cause increased roof frost, longer periods of moisture on the roof during the day, and longer drying times. If conditions on a roof are unfavorable, wait for better weather!

If water is present on a roof in the morning, it is likely to form there again the next night unless the weather warms. So, coatings must be given adequate drying time before sundown to prevent the uncured coating from being damaged overnight.

Multiple Coats

Multiple coats cause longer drying times and can lead to moisture damage. Second coats should not be applied the same day when temperatures are below 80 degrees. Remember, liquid applied fabric membranes represent two coats and should only be installed when weather is favorable. Primers dry more quickly than topcoats. Thick coatings, such as Elastek 103 Crack & Joint Sealant and coatings in PolyTek Fabric will take much longer to dry. Primer alone does not have as much water resistance as primer plus topcoats (thicker is better but it takes more drying time).

Never dilute coatings with water…this extends drying time.

Shaded areas and low areas on a roof present the greatest danger for moisture damage. The water in coatings and moisture in the roof migrates to low areas, such as around scuppers and drains. These areas may remain un-cured long after the balance of the roof is dry. At night, condensation also follows gravity and collects in the same low areas. Standing water in areas of uncured coating can lead to failure.

Tinted coatings can speed drying by absorbing more of the sun. Energy is heat. Elastek can tint primers and sealants a light gray in winter.

To Minimize Cool Weather Application Problems

• Coat only when the temperatures are above 60º and unlikely to fall below 50º during drying time, a minimum of 4 hours after application.
• When temperatures are below 70º, coat only on sunny days when no moisture is predicted for 24 hours. In cool weather, stop coating early in the afternoon (2 PM) to allow for drying.
• Coat only over a dry roof and don’t dilute coatings. Apply only one coat per day.
• Delay coating over recently applied asphalt emulsion until daytime temperatures exceed 75º (asphalt emulsion often holds moisture and has a slick surface which may cause adhesion problems for coatings when cold).
• DO NOT apply thick layers of Elastek 103 Crack & Joint Sealant in ponding areas during cool weather. It may not cure in time.
• Use Elastek 500 Puddle Plaster as an alternative to 103 Crack & Joint Sealant.
• Allow extra drying time for shaded and low areas on the roof. Apply to these areas first if practical or wait for better weather.
• When roofs are wet overnight, do not coat ponding areas.
• Wait for dry weather forecast. Consider the likelihood of rain, day and night temperatures, and the dew point prediction.

When in doubt, WAIT FOR BETTER WEATHER!

Apply Cool Roof Coating

If you are a contractor or an aggressive do-it-yourselfer, applying elastomeric cool roof coatings can be an easy job. Good results require care, attention to detail, but few special skills. This bulletin takes you through many of the basics of coating a typical roof.

Sprayed polyurethane foam, gravel, roofs over cathedral ceilings, as well as roofs with severe ponding problems are higher risk applications and should be discussed with us before proceeding. Product warranties may be limited or voided in these situations.

Please consider that a quality coating application will take time, often working in a very warm environment. Protect your eyes and skin from excessive exposure. In very warm weather, work early in the day. See our Cool Weather Application bulletin when applying coating from November through February (desert Southwest).

Pails of material weigh over 60 pounds each and must be lifted to the roof. This requires strength and safe equipment. Consider pouring the coating into a smaller container to make lifting easier.

A strong ladder and someone to help with the project are desirable.

Getting Started

Carefully examine the roof membrane (surface material) for cracks, tears, blisters, evidence of ponding, exposed foam, and open seams. If already coated, evaluate the condition of the coating. Pay particular attention to areas around roof penetrations (vents, skylights, pipes, etc), ponding areas, cracks in parapet walls, and the attachment of roof membranes to parapet walls. Roofs should be in good condition to warrant coating.

Serious roofing problems should always be referred to a qualified roofer for repair before attempting any coating. Coatings cannot save worn-out, dried-out, or structurally weak roofs.
Measure the length and width of the roof to determine the size in square feet. Be sure to allow for parapet walls, garage and porch roofs to be covered. (NOTE: The roof size is not the same as the living space.)

Purchase all necessary materials and tools in advance. Nothing is more frustrating than climbing off a roof in the middle of a job to buy more material.

A coating job can often be completed over a two-day weekend in warm weather. Dry, sunny weather over 70° is ideal. Avoid periods of very cold nights when dew and frost can be a problem. See for our Cool Weather Application post.

Do not coat roofs that may have moisture trapped below the surface. Always allow each coat to cure before applying the next coat.

In extremely hot weather, start as early as possible and get off the roof before temperatures become too high. On extremely hot surfaces (dark roofs or very hot days), apply top coatings before roof temperatures are too high (causing drying on contact).

Applying the Coatings

There are three simple steps for applying cool roof coatings:

• Thoroughly clean the roof surface. Roofs collect oils from asphalt, chimneys, and cars plus lots of dirt and dust. Coatings don’t stick well to any of these. We recommend cleaning with an inexpensive solution of TSP or TSP Substitute in a bucket of water (follow label instructions). Use a broom to scrub ponding areas and areas of peeling coatings. Work a section at a time and hose off the dirty water. Sweep away puddles to promote drying. Do not allow wash water to dry on walls, furniture, windows, and visible surfaces. 
• Repair and seal roof penetrations, tears, open seams, etc. using Elastek 103 Crack & Joint Sealant and reinforce with polyester roof fabric as necessary. In larger or deep ponding areas, apply Elastek 500 Puddle Plaster to fill in areas that hold water. Avoid using plastic roof cement. Serious ponding should be referred to a roofing contractor. Blisters in previous coatings may be opened but these areas must be allowed to dry-out completely. Blisters in the roofing ply should be left alone unless likely to break. Caulk and reinforce open seams, roof penetrations, cracks, and tears. These are potential leak points so work carefully and thoroughly. Use fabric to build flashings around roof edges or roof penetrations, and to reinforce various coating repairs. A polyester fabric is used because it will stretch with the coatings. (Fiberglas fabric is not recommended.) Fabric is normally cut to extend three inches beyond the repaired area in all directions. The coating is applied to the roof surface and the fabric is immediately pushed into the wet surface. An additional coat is applied over the fabric and the patch is allowed to dry. If your roof has stucco parapets, examine them for cracks along the sides and top. These areas often permit water to enter the wall and can cause blisters and wrinkles in the roof surface. Repair with Elastek 103 Crack & Joint Sealant. If you do not have parapets, examine the metal drip edge for a tight seal with the roof membrane. Use 4″ or 6″ roofing fabric covered under and over with Crack & Joint Sealant to seal cracks along drip edges, penetrations, and open seams.
• Apply coating when the roof is dry and the sealant has set. You will be using a 9-inch heavy-duty frame, ½-inch paint roller for spreading coating on roof or 1-1/4-inch roller for dipping in pail, and a 5–to-6-foot extension pole. Use a 3/4-inch roller with basecoats and emulsions. Map out your roof and make each pail fill that area. See Elastek Product Sheets for recommended coverage. An inexpensive 3-inch or 4-inch brush should be used to reach areas not possible with a roller. Use a stiff paintbrush for applying 103 Crack & Joint Sealant.

Topcoat should always be applied in a very thick coat, to achieve a rate of 100 sq. ft. per gallon, and a dry coating thickness of 10 mils. Two thin coats or one heavier coat may be used to achieve this result.

Do Not Over-Roll Coatings

Coatings are applied with a minimum of working the product for a maximum thickness. Work right from the pail, dipping the roller or pour on roof and spread.

Give scupper and ponding areas several additional coats for added protection. Allow each coat to dry before recoating. In cool weather, one coat a day is the maximum; two may be possible in the summer. Watch the weather!

For maximum durability and leak resistance, we recommend that two coats of topcoat be applied at 100 sq. ft. per gallon, or a minimum of 20 mils dry coating. If two complete topcoats are not applied, always apply two thick coats to problem areas such as scuppers, drain areas, ponding areas, seams, and repaired areas. Avoid using Elastek Solar Magic™ or The Shield™ on ponding roofs. Clean skin and tools promptly with water.

Be sure to inspect the roof to note changes several times per year. Much of the reflectivity of a coating can be preserved if the surface is washed occasionally.

Save any unused coating for minor repairs that may be required later.

How Much to Buy

Before you go to the store to purchase roof coating, you will need to measure your roof. Knowing the square footage of your roof helps determine how many pails of Elastek coating you will need. Measure the length and width of the roof to determine the size in square feet by using the following formula:

Length x Width = Square Feet

A good rule of thumb is that every 100 square feet of roof equals one gallon of coating. Be sure to allow for roofing on parapet walls, garages, and porches. Take a simple sketch of your roof with dimensions to your coating dealer for help. Here’s an example roof:

Calculate the square footage of each area and then add them together:

Now, take the total Sq Ft, 2670, and divide it by 100 which equals: 26.7. This means you would need approximately 27 gallons to make one coat of the example roof shown or six 5 Gallon pails (27 divided by 5).

Below is a table with some example square footages to further help you determine how much coating material you’ll need for one coat:

How many coats do you need?

A single, thick application of Elastek roof coating may be adequate if you have a coated roof in good condition. Two coats should be used on new roofs or roofs in worn condition.