Knowledge Builders

should a chimney be sealed

by Dr. Casimir Schuster III Published 10 months ago Updated 2 months ago

Sealing a Chimney Causes More Problems Than it Solves.
Plain and simple, DO NOT seal off a chimney or fireplace because you will get a flue full of condensation problems! Even when your fireplace is blocked off airtight you'll still end up with “hidden” water issues. But these problems are only hidden for so long!
Nov 26, 2019

Full Answer

What does sealing a chimney do?

As chimneys heat up and cool down, moisture is created inside the chimney; this moisture normally escapes through the brick and mortar joints, but if a sealer is used, the moisture will remain trapped, and this trapped moisture will freeze and then thaw as it warms up.

Do I need to water seal my chimney?

As a result, chimney masonry should be protected from exposure to water. That's why many chimney professionals recommend homeowners apply a waterproof sealer to protect the chimney from water damage. It's important to bear in mind that the waterproof coating will wear over time and gradually lose its effectiveness.

How often do you need to seal a chimney?

Ideally, when done properly, and when applied in the right amount, this chimney sealant should last roughly 15 to 20 years. On the other hand, there are some professionals who say that waterproofing should never be done.

How much does it cost to seal off a chimney?

Sealing your chimney with HeatShield is typically between $2,500 and $3,500. Price estimates vary based on location and how extensive the project is.

Do brick chimneys need to be sealed?

A well-built chimney can last for many years, but you need to put the work into maintaining your chimney for a long life. Waterproofing your chimney can keep it functioning smoothly for years. Most masonry chimneys are designed with bricks or stone with mortar or cement to bond the materials.

What should I use to seal my chimney?

Polyurethane is often used as a chimney sealant as it has remarkable toughness and flexibility. This type of polymer has a remarkably low cost because of its plentiful source of basic chemicals that make it up along with relatively low manufacturing cost.

Can You Use Flex Seal on a chimney?

What Does Flex Seal Spray Work On? Flex Seal will work on roofs, gutters, skylights, windowsills, flashings, downspouts, foundations, awnings, chimneys, vent pipes, RV's, campers, trailers. It can be applied to wood, copper and other metals, concrete, masonry, glass, fabric, plastics and much more.

How do you reseal a brick chimney?

0:154:00Waterproof Chimney Sealer - YouTubeYouTubeStart of suggested clipEnd of suggested clipAnd all of the bricks you can see all these bricks are still really bad chipped out and this isn'tMoreAnd all of the bricks you can see all these bricks are still really bad chipped out and this isn't going to fix any of that obviously but it's gonna hopefully prolong the life of this chimney.

How long does a brick chimney last?

All in all, a well built chimney should last decades and if you keep up on the maintenance along the way you could have your chimney for 50+ years!

How do I stop cold air coming down my chimney?

Keep cold air out Along with the common throat damper located just above the firebox, some homeowners add a top-sealing damper at the top of the chimney to double their protection. Another great way to block cold air is with a chimney balloon or plug.

How long do chimney crowns last?

50-75 yearsHigh-quality chimney crowns are able to last anywhere from 50-75 years. However, a poorly constructed crown could break down in less than 20 years and will cost far more to rebuild than a correctly constructed crown.

How much heat is lost up a chimney?

Putting a Damper on Your Energy Bills What's more, between 80 and 90 percent of the heat produced by wood burned in an open fireplace is lost up the chimney. This means that for every $100 you spend on firewood, you get only $10 to $20 worth of heat.

How do you waterproof a chimney stack?

One way to deal with a non-vertical surface is to waterproof it over and over and over. Another is to use a solvent-based material, still with polysiloxanes, because it soaks deeper into the substrate. For a chimney with a breast below, opt for the more expensive solvent-based waterproofing.

How do you waterproof a chimney cap?

0:161:52CrownSeal Flexible Waterproof Coating - YouTubeYouTubeStart of suggested clipEnd of suggested clipTape. Can also be applied to the flue tile about one inch from the vase of the tile to produce aMoreTape. Can also be applied to the flue tile about one inch from the vase of the tile to produce a clean edge on the tile as well brush.

How do you seal a chimney stack?

0:362:32How to Use FlashSeal Chimney Flashing Repair - YouTubeYouTubeStart of suggested clipEnd of suggested clipApply a heavy base coat of about 1/8 inch flash seal between the mask areas embed fabric into theMoreApply a heavy base coat of about 1/8 inch flash seal between the mask areas embed fabric into the base coat of flash shield. And apply a liberal top coat. Making sure to completely cover the fabric.

Can Drylok be used on chimneys?

DRYLOK® Masonry Crack Filler seals, waterproofs and repairs cracks and mortar joints in concrete sidewalks, walls, steps, chimney crowns and floors.

How Does Sealant Protect Masonry Chimneys?

Sealing your chimney is one of the simplest, most affordable ways to prevent water from penetrating the bricks. Here’s why this form of chimney maintenance is so worthwhile:

How long does a chimney sealer last?

The proper chimney sealant can protect against moisture intrusion for up to 15 to 20 years. The trick is to waterproof your chimney with vapor-permeable chimney sealant. This product protects the brick exterior from moisture while still allowing the pores to “breathe.”

Is cracking a chimney a sign of a bad chimney?

Cracks: Cracked chi mney bricks are never a good sign. The damage may be evidence that the bricks are deteriorating due to water intrusion.

Can water damage chimney bricks?

Damaged mortar joints: Water doesn’t just damage chimney bricks—it can also deteriorate the mortar between them. Flaky mortar exposes more of the brick to water intrusion, accelerating the wear and tear.

Why does a chimney rust?

Also, water in the chimney can cause rust on the steel and cast iron. Rust weakens or destroys the metal parts.

What is a prefab chimney?

Prefabricated chimneys are built prior to installment or the development of the home. These are becoming to be the most common method of adding a fireplace into a home. Prefab chimneys function similar to masonry chimney, but cost much cheaper. There is a major design difference between the two. There is an offer the ability to vent a wood-burning fire from the fireplace and are built from sheet metal rather than the pounds of masonry. They do require similar maintenance requirements and have some drawbacks.

What is the roof cap on a chimney called?

Resting at the top of the chimney is a chimney cap, or also called a rain cover . This is the most inexpensive preventive measure that a homeowner can employ to prevent water penetrating or damaging the chimney. Chimney caps are recognized as an important chimney safety and damage prevention component. According to Underwriters Laboratories (UL) specific that a chimney lining system must include a chimney cap.

Reasons for Sealing A Chimney And Fireplace

Before deciding on whether your chimney needs to be sealed temporarily or permanently, there have to be real reasons. Such reasons may differ from one person to the other.

How To Temporarily Block An Unused Chimney

If you wish to temporarily seal up an unused chimney, there are effective ways to go about it.

How To Permanently Block An Unused Chimney

Not everyone wants to temporarily seal their unused chimney and fireplace.

Getting the Right Chimney Technician For The Seal

Who you call for the job determines how well your unused chimney and fireplace are sealed or blocked. It is important to be extra careful in scouting for the right professionals.

Why are chimney crowns important?

Chimney crowns are an important part of the chimney, however they are also the most susceptible to the elements of the winter weather due to their location above the roofline. Next to flue tiles being installed incorrectly, chimney crowns are the second biggest defect we see.

How many crowns do you need for a chimney?

Either as part of a complete chimney rebuild or as a stand alone chimney replacement, we pour 150 to 225 chimney crowns annually.

Why does my fireplace smell so bad?

Another sign that there might be a problem is that you have some unpleasant odors coming from your chimney during air conditioning season .

How much does it cost to repair a chimney crown?

If we were to estimate the cost of a chimney crown repair, we might estimate between $500 and $2000 as a general range, however each project really needs to be assessed individually before a price is discussed. The best person to give you a fair estimate of the repairs is your chimney sweep. Your Certified Chimney Sweep® will be able to assess accessibility to the roof, pitch of the roof and the necessary scaffolding to get the job done and safely.

Who is the longest certified chimney sweep?

Terry Dearborn of Valley Chimney Sweep is the longest continually Certified Chimney Sweep® in the United States. Derek Dearborn has been sweeping and repairing chimneys since his parents started Valley Chimney Sweep in 1978.

Can you replace a chimney crown?

The least expensive option in repairing your chimney crown is sealing your chimney crown. This is not a good solution if the damage is more than surface area cracks. However, this might be a good temporary solution if you have discovered your problem during a time in the year that it is often below freezing and not possible to do a crown replacement.

Can a chimney crown be rebuilt?

If the chimney crown has missing pieces or lacks structural integrity, it might require some rebuilding. At this time, you should be sure to have an experienced chimney masonry person do the repairs to ensure that they will last through the Illinois winters for many years to come. It is important that the new replacement chimney crown overhangs the outside vertical dimensions of the chimney structure and has expansion joints.

What to do if you have cracks in your chimney?

If there are a few small cracks in the chimney crown but it is otherwise intact then sealing the crown is a viable repair option. Sealing the cracks will prevent any more moisture from leaking between the walls and flue inside the chimney. The chimney mason will use a specially formulated waterproof sealant ...

Why do you need a chimney cap?

Installing a chimney cap will help protect the chimney and the crown. The cap is attached to the crown and acts like an umbrella keeping the surface underneath dry. A wire mesh surrounds the cap allowing smoke and contaminants to ventilate while preventing small animals, pests, and debris from obstructing the flue.

What is the best way to repair a chimney crown?

Repairing the Chimney Crown. Rather than sealing, repairing the chimney crown is a better option when there are more significant, hairline cracks in the surface. When repairing the crown, a skilled mason carefully fills the cracks with a patch cement material. The entire chimney crown is then sealed with a waterproof sealant to protect the surface.

What is the purpose of a chimney crown?

The chimney crown is the upper-most portion of the chimney. Its purpose is to allow smoke and fume to vent through the flue to prevent moisture from getting inside. It is built using cement reinforced with a wire mesh for stability and durability. The lip of the crown is sloped to direct moisture away from the chimney.

Why is the crown of a chimney sloped?

The lip of the crown is sloped to direct moisture away from the chimney. While concrete is extremely durable, it isn’t impenetrable. And without annual chimney inspections by a certified professional chimney sweep, homeowners have no way of knowing that they may have a problem with the chimney crown until they notice water inside the chimney.

Why does my chimney crown crack?

The exposure to pounding rain, sleet, and snow can eventually cause the crown to crack under the pressure of Mother Nature. When these cracks begin to surface on the crown, it exposes the interior of the chimney to moisture. Without repairs, the crown will continue to deteriorate.

Can a chimney crown be repaired?

Depending on the extent of the damage, your chimney mason may recommend sealing or repairing the chimney crown.

How long does a chimney sealer last?

If you live close to the ocean, which means the saline content in the air will be significantly higher and the surface of the chimney will also be exposed to sand blown in by the sea breeze, even then, a good quality sealer will last over 10 years.

What is the best sealer for a chimney?

Chimneys are exposed to the elements, including rain and snow. Ideally, you should pick a chimney sealer that is made of silane and/or siloxane. This holds true not just for brick chimneys but all masonry-based chimneys.

What is the best chimney cap?

A stainless steel chimney cap is the best option as it will last longer, but it costs more as well. Alternatively, you can get a galvanized chimney cap, which will cost a little less but does not last for a long time. Place the chimney cap over the flue liner and with the screwdriver, fasten it securely.

Why do chimneys have crowns?

All masonry-based chimneys, including brick chimneys, have a crown on top that is usually made of mortar, which sits like a cap in order to prevent water or moisture from entering the bricks and eventually, into the house itself. It should not be made of mortar, but in most cases, it is.

Why is my chimney so hard to reach?

One of the reasons is simply that the chimney is hard to reach and something that we do not lay our eyes on a regular basis. While that is true, it does not take much of an effort to check up on the state ...

How much does it cost to repair a brick chimney?

If you spot them early, the repairs may cost you anywhere from $500 to $1000. But the longer the delay, the higher the cost of repairs.

Does siloxane sealer work?

Siloxane-based sealers are particularly good as they form a protective barrier around the surface of the chimney and prevent damage due to moisture. In addition, it does not change the appearance of the chimney in any way, such as making it look shiny or glossy, because of its clean and natural finish. The protection from moisture also means that mold and mildew will not form and settle in the chimney.

What does sealing a chimney do?

Robert Linder / The Associated Press Capping or sealing an unused chimney will prevent air intrusion and stop pests from entering the home.

Why should I cap off an old chimney?

Answer: It is true that myself and others have recommended capping off an older, unused chimney to prevent moisture and air-leakage issues, but we have been vague about specific methods. I will try to highlight the key considerations when doing this task, whether by yourself or with professional help.

Why do you need a chimney cap?

The key to capping the top of the chimney is to install a barrier that will be moisture and tamper resistant and will not be affected by environmental factors such as snow, wind and sunlight. Squirrels and raccoons have been known to invade poorly sealed chimneys. The cap must be durable enough to keep these nuisances out. For that reason, installing a galvanized or painted-steel chimney cap is the most common option.

Why is my chimney leaking air?

Air leakage may occur from warm house air leaking into the bottom of the chimney, rising inside due to the stack effect. Preventing this will be of primary importance, but cold air intrusion from the top of the chimney must also be eliminated.

What is the chimney used for in an oil furnace?

The oil furnace used the chimney to exhaust its combustion gases. It is obviously not in use anymore, as my new high- efficiency furnace uses PVC piping for intake and exhaust through the side wall of my house. The chimney is brick with two clay tile liners running through it. The chimney runs up along the exterior wall.

Where is the flue cap on a chimney?

At the bottom of the chimney, a tighter fitting flue cap may be installed if you have a standard round metal clean-out protruding from the chimney. These caps can be easily found and should be secured only with short sheet metal screws, to allow for future removal.

Do chimney contractors have scaffolding?

Many masonry contractors or chimney experts already have their own scaffolding and safety equipment to minimize these costs. It would definitely be a good idea to call for a couple of estimates, even if you were thinking of doing the exterior sealing yourself.

Why do you need a waterproof sealer on a chimney?

That’s why many chimney professionals recommend homeowners apply a waterproof sealer to protect the chimney from water damage. It’s important to bear in mind that the waterproof coating will wear over time and gradually lose its effectiveness.

How long does a chimney last?

With its sheer strength and tenacity, a well-built brick masonry chimney can last nearly a century leaving many homeowners to wonder, “Why should I waterproof my chimney?”

What material is used to build a chimney?

The majority of masonry chimneys are built with bricks or stone bonded with mortar, a cement material, to form a sturdy and practically impenetrable structure. But like most structures, water is a mortal enemy that can bring down a chimney like a falling deck of cards.

Why does my chimney lean?

The chimney may also begin to lean as the foundation shifts due to its weight. This can also damage the structure of the home as the chimney pulls apart from the flashing material attached to the roof. As a result, chimney masonry should be protected from exposure to water.

Can a chimney be waterproofed?

Without waterproofing the chimney tiny holes will begin to form in the brick surface like a sponge that will gradually grow larger allowing water to penetrate the flue and damage other chimney components. In addition, excessive exposure to moisture will also soften the mortar.

Do you need to waterproof a chimney before you waterproof it?

However, it is highly recommended homeowners have a chimney inspection before waterproofing a chimney to determine the extent of repairs, if necessary, to spalling or missing bricks. Chimney deterioration may require tuck pointing work to replace missing mortar and will need to be completed before waterproofing.

What is a chimney sealant?

Sealants are a type of substance used to block fluids from penetrating the material it is on. In terms of chimneys, these sealants are typically organized into one of two camps – that of polyurethane or silicone. Not all sealants are made the same and in order to determine which is the best for your chimney, we first need to go over the two substances in detail.

What is the best tool to seal a chimney?

When sealing a chimney, the best tool to use is a sprayer. On vertical sections, which should be the majority of your chimney, this waterproofing should be applied from bottom to top – the reason for this is that sealers have a tendency to run.

Why is polyurethane used in chimney sealants?

This type of polymer has a remarkably low cost because of its plentiful source of basic chemicals that make it up along with relatively low manufacturing cost.

How long does silicone last?

This results in polyurethane having a lifespan upwards to 10 years, while silicone can easily double this or more.

Which is cheaper, silicone or polyurethane?

That being said, while labor comes out to about the same, polyurethane will need to be replaced more often than silicone – this means that while in the short term polyurethane is cheaper, silicone wins out in the end.

Can silicone be used as a sealer?

Certain spots like mortar joints, flashing, and the crown should all have a particular focus on them. The hardiness of silicone means that many people want to use it as a sealer but already have polyurethane on the original structure.

Do children have chimneys?

Chimneys are instantly recognizable – even from a young age, many children incorporate these structures into their drawings even if they don’t have a chimney on their own home. While they can be remarkably beautiful, chimney’s do require a great deal of upkeep.

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