How to Reseal Lifted or Unsealed Shingles With Roofing Cement
Small dabs, in the right places, in mild weather. Why shingles lift, and when resealing is the wrong fix.
- Advanced
- 1 to 3 hours
- Updated
The short answer
To reseal lifted asphalt shingles, work on a dry day above about 10 degrees Celsius, lift each loose tab gently, put a dab of asphalt roofing cement about the size of a quarter under each lower corner, and press the tab down. Use small amounts, since too much blisters the shingle. If shingles are cracked, curling or brittle, repair or replacement is better than resealing.
Asphalt shingles are held down by a strip of factory sealant that activates with the sun's heat. When the sealant bonds, the shingle lies flat and resists wind. When it does not, the tab lifts, flaps in wind and finally creases or blows off. Lifted shingles are one of the most common storm repairs in the Fraser Valley after a strong windstorm.
Shingles fail to seal for several reasons. Some were installed in cold weather and never had enough heat to activate the strip. Others collected dust and debris on the strip before being laid. Older shingles lose sealant strength with age, and shingles laid on a dirty or wet surface may not bond. In some cases, wind breaks a bond that was already weak.
Hand sealing is a small fix that works well on shingles that are otherwise sound. It does not repair a cracked or curled shingle, see how to replace a damaged shingle for those. To find out how much damage a storm caused, start with how to check your roof after a windstorm.
Tools
- Caulking gun
- Putty knife
- Flat bar
- Binoculars
- Extension ladder with stabilizer
- Roofing harness and anchor (for steep or high roofs)
Materials
- Asphalt roofing cement in cartridges (plastic roof cement)
- Galvanized roofing nails, 1-1/4 inch, for nailing where needed
- Rags and mineral spirits for cleanup
Safety first
- Go up only on a dry day, and never on a wet, frosty or mossy roof.
- WorkSafeBC requires fall protection where a fall could be 3 metres (about 10 feet) or more. On a steep or high roof, this job is one for a roofer with proper equipment.
- Roofing cement is sticky and flammable. Keep it off your hands and boots, since tracked cement makes the ladder slippery, and keep it away from open flames.
Step by Step
Step 1: Find the lifted shingles from the ground
Lifted tabs throw a shadow along their lower edge, especially in low sun. Look on the windward slopes and near the eaves, rakes and ridge, where wind pressure is highest. Mark where they are so you can go straight to them.
Note whether the shingles are merely unsealed or also damaged. A crease across the tab means the shingle is broken and will not lie flat.
Step 2: Choose dry, warm weather and set up safely
In cold weather, shingles are stiff and crack when lifted, and cement does not stick well. Ideal weather is mild, dry and with the roof surface dry. Avoid the heat of a summer afternoon when the shingles scuff easily under your boots.
Watch out: If the roof is steep or above the first storey, hire a roofer. A fall is a far bigger cost than the repair.
Step 3: Clean the contact surfaces
Cement sticks to clean asphalt and fails on dust. Use a dry brush or a cloth. If the surface is wet or has moss on it, wait for a drier day or have it cleaned first.
Do not bend the tab far. If it is stiff, let it warm in the sun or move on to another tab and return.
Step 4: Apply small dabs of roofing cement
Most manufacturers recommend spots of cement about 1 inch in diameter, placed near the corners, with two to four dabs per shingle depending on the product. More is not better. A big smear squeezes out, traps dirt and moisture, and can cause blisters in the shingle above and below.
Use a putty knife or the tip of the caulking gun nozzle to place the dab. Check the cement manufacturer's instructions and the shingle bundle wrapper for the spacing they call for.
Step 5: Press the tab down and hold it
Press for several seconds so the cement bonds and spreads slightly under the tab. On a windy day, you may need to hold it a little longer. Wipe away any cement that oozes out, using a dry rag, before it collects dirt.
Step 6: Check for nail problems under the lifted shingle
A popped nail props up the shingle above it. See how to fix exposed and popped nails. Sealing a shingle over a raised nail head will not hold, and the nail will wear through the tab.
Step 7: Recheck after wind and sun
Repairs that hold lie flat with no shadow along the bottom edge. Any shingle that lifts again is usually old, brittle or has a bigger problem. If many shingles across a slope will not stay sealed, the roof may be reaching the end of its life.
Why Shingles Fail to Seal
The factory sealant strip needs warm sun to soften and bond to the shingle below. Shingles laid late in the year in cool, damp weather may never seal, and in the Fraser Valley many roofs are installed in autumn. Dust and debris on the strip from storage or a dirty roof stop it bonding. As roofs age the sealant loses strength, and heat and cold cycles slowly work the bond loose.
When Resealing Is Not Enough
If the shingle is cracked, torn, curled or has lost most of its granules, resealing just holds a failed shingle in place. Widespread lifting across slopes points to old age or poor installation. A roofer can tell whether the roof can be repaired or is better replaced, and will check the nailing pattern, which may be too high or too few, see shingle nailing placement, count and depth.
Common Mistakes
- Using too much cement. Big smears trap moisture and blister shingles. Quarter-sized dabs are enough.
- Working in the cold. Stiff shingles crack when lifted and cement does not bond.
- Sealing over a raised nail. The nail keeps the tab up and will wear through it.
- Using the wrong product. Use asphalt roofing cement made for shingles, not general caulking or silicone, which may not stick to asphalt.
- Gluing a broken shingle. A creased or torn tab will not hold, and needs replacing.
- Not cleaning the surfaces. Cement does not stick to dust, moss or wet asphalt.
When to Call a Professional
Call a roofer if the lifted shingles are on a steep or high roof, if the shingles are brittle and crack when touched, if lifting is widespread across slopes, or if you can see missing shingles or exposed underlayment.
A roofer can also judge whether the roof has enough life to justify repairs, and will check the nailing, flashing and ventilation, which are often the real causes of shingles that will not stay down.
Fraser Roofing does free roof inspections across the Fraser Valley, from Hope to Abbotsford. See our Emergency Roof Repair service or the towns we cover.
How to Reseal Lifted or Unsealed Shingles: Questions
Why are my shingles not sealing down?
The factory sealant strip needs warm sun to bond. Shingles installed in cold weather may never seal, dust on the strip prevents bonding, and sealant weakens as a roof ages. Wind can also break an existing bond. In the Fraser Valley, roofs laid in late autumn are common cases of shingles that do not seal until the next warm spell.
How much roofing cement should I use under a shingle?
A dab about the size of a quarter, roughly 1 inch across, under each lower corner, with two to four dabs per shingle depending on the product. Check the manufacturer's instructions. More cement does not hold better. Large smears trap moisture and dirt, and can blister the shingles above and below.
Can I use caulking or silicone to seal shingles?
It is better to use asphalt roofing cement, often sold as plastic roof cement, which bonds to asphalt shingles and stays flexible. General-purpose caulks and silicone may not stick to asphalt and can stain the surface. Always follow the shingle and cement manufacturers' instructions for the product you are using.
Will lifted shingles reseal on their own?
Sometimes. If the strip is clean and the shingle lies flat, a warm sunny spell can reactivate the sealant. If dust, age or a raised nail is the problem, it will not. A shingle that keeps lifting needs hand sealing, and one that is cracked or curled needs replacing.
What temperature do shingles seal at?
Most asphalt shingle sealant strips activate from sun and surface heat, and the usual guidance is that mild, sunny weather, often above about 10 degrees Celsius, is needed. The exact figure varies by product, so confirm it on the bundle wrapper. In winter, hand sealing with roofing cement gives wind protection that the strips cannot.
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This guide is general education. Always follow the product manufacturer's installation instructions, the BC Building Code and WorkSafeBC requirements, which take priority over anything written here.
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