What Causes Hairline Cracks in Toilet Bowl?

Small cracks are common in toilet bowls which are invisible or hard to find. Hairline cracks can cause water leakage if it remains unchecked for longer.

What Causes Hairline Cracks in Toilet Bowl? Hairline cracks in toilet bowls are due to aging, overtightened bolts, heavy objects falling, wrong cleaning methods, poor handling in repairing procedures, accidental bumps, and defective materials.

It is necessary to inspect the toilets and their connecting parts during the cleaning procedure so you can see the hairline cracks on their internal and external surfaces.

Causes Solutions
Aging Use porcelain epoxy
Overtightened bolts Tighten the bolts carefully
Heavy objects falling Replace toilets
Wrong cleaning methods Do not use harsh cleaners and metal wire brush
Mishandling in repairing procedures Call a plumber for help
Temperature difference Avoid pouring hot water
Accidental bumps Use waterproof plumbing epoxy
Resistance or defective materials Select high-quality porcelain fixtures


The toilet bowls are mostly made up of porcelain material which is not highly durable. These can erode over time and develop cracks because they are not designed to last longer.

The glazing is the protective coating on the porcelain material to seal them. The glazing coat can get damaged when these become old and in frequent use.

You can see the line on their surface due to expansion and contraction of the glazed coating. Moreover, the problem comes from poor manufacturing and mishandling.

The unequal distribution of glazing material causes a problem when these become old. In addition, the problem is more persistent in older toilets because its priming material develops breakages.

The aging issue comes when they are made of a mixture of cement and other materials. The degradation of cement and other materials is common with their age.

In addition, you can see visible marks on cemented type because of the shrinkage process in these materials. Therefore, it is better to check regularly whether these are made up of porcelain or cemented material because both of them are less durable.

It is better to take measures when you see cracks because they can be dangerous. Use the porcelain epoxy if these are smaller and can fix easily.

Overtightened bolts

The bolts are used to tighten the toilet bolts from different sides. These bolts are made of plastic and metal material depending on the choice of the people and manufacturing brands.

The bolts become loose over time because of the weight of the people.

The screws become loose when you put excessive weight on them. In addition, corrosion on metal screws also makes them loose. You can tighten the screws with a wrench and pliers located on the bowl’s lower side.

Many people have minimal knowledge about them and overtighten their bolts. The overtightening causes shrinkage of the porcelain cemented and glazing layer.

These can shrink and develop creaks on their surfaces. You can call a plumbing expert if you are facing issues with loose screws and bolts.

Ensure you do not overtighten them by sitting on the seats because these produce creaking and squeaking noise.

Heavy objects falling

The hairline cracks come on the toilet bowls when something heavy falls. The bathroom contains various hanging materials mounted on the walls with screws and bolts.

The vase from the bathroom shelves can fall and cause this problem. The issue also comes when heavy key chains and multiple keys’ weight drop in them from your pocket.

The heavy tissue holders and boxes can also produce lines on the bowl surfaces when the lids are not closed.

Moreover, the shelves can also fall from the walls and damage the toilets. It is better to replace the toilets if these cracks are deep and more prominent because you cannot seal them with porcelain epoxy.

Wrong cleaning methods

The use of wrong cleaning methods and incorrect handling damage your toilets. Most people do not invest in separate cleaners for the fixtures according to their manufacturing materials.

Using bathroom cleaners on the bowl surfaces damages the glazing layer of the porcelain.

These hairline cracks range from mild to severe, depending on the harshness of the cleaners and the chemicals present in them. The ones that contain ammonia and bleach are more damaging because of their concentrated materials.

In addition, people use the metal wire brush to remove the stains from the bowl’s surfaces which can cause cracks. Avoid harsh cleaners and metal wires on their surfaces because they can damage the glazing layer.

Poor handling in repairing procedures

Most toilet fixes are easy, and people can do it alone without help from a second person or plumbers.

People try fixing minor cracks on the bowl’s surfaces using DIY procedures.

Using the wrong kits and tools during the repair procedure can damage them. In addition, people also put heavy objects on them during the repair procedure.

Sometimes you can leave unwanted damage on the other parts while fixing the affected ones. Avoid doing any procedures if you do not have minimum knowledge about them.

Call the plumbing expert because they know more about fixing procedures and preventive measures.

Temperature difference

The differences and fluctuations in temperatures damage the toilet bowl. These are made of porcelain material that is not resistant to temperature changes.

These expand or shrinks according to the changes in temperature. The problem comes in winter when the surfaces are extremely cold, and you use warm water for flushing.

In addition, many people intentionally pour hot water for flushing and unclogging purposes. The temperature differences cause the glazed material to shrink and develop crazing.

Avoid flushing boiling water from the bowls for unclogging. Using the plumbing equipment and plunger for these procedures is better because they are safe.

Accidental bumps

The accidental bumps damage the toilet bowl from the interior or exterior side. Hairline cracks on the exterior side come during the finishing of the bathroom floor, and heavy impacts from them.

The problem also comes when you sit hard on them, and these can shatter. In addition, the frequent slamming of seat covers produces heavy impacts on their surfaces.

The issue also comes when you dont handle these correctly while shifting from one place to another. Use the waterproof plumber epoxy to fix them if these are minor and less deep.

The epoxy is not the permanent solution if these are present inside the bowl because constant water pressure can make the deeper and leads to leakage.

Defective materials

Toilet bowl surfaces develop hairline cracks and lines due to manufacturing defects. Some of these are made of low-quality material and do not resist heavy impacts and objects.

These are made of resistant porcelain that can wear out early, and it is necessary to replace the toilets. In addition, the problem also comes when manufacturers use defective materials for their manufacturing.

The materials that have gone through several processes during manufacturing can also wear off early and is less durable.

It is better to check the material’s quality when selecting the toilets for your bathroom. Check the well-known brands and ratings from the online forums while selecting them.

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