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Sealant 101 – When, where and how, your one stop sealant guide

For the DIY crowd, sealants are a bit of a step up from your screwdrivers, hammers, and spanners, but that doesn’t mean that you can’t learn to differentiate between them and apply them yourself with relative ease and confidence. For the tradesman, they’re just another tool in the handyman arsenal and one that can be used in a vast array of ways.

Sealants can be quite weak or remarkably strong, but it’s important to remember that sealants and adhesives are two very different beasts. Sealants may have adhesive qualities, but they are used to create seals – hence the name – that restrict the flow of air or water. Secondary properties include insulation against noise and protection against fire – in fact, most sealants perform several different tasks at once, though the basic process remains the same throughout most applications.


  • The sealant fills a gap between two surfaces.
  • It hardens to form a physical barrier by adhering to those surfaces.

The concept has matured from mud and grass in ancient times through to wattle and daub in the Middle Ages to the advanced modern polymers of the 21st century. Nowadays, you can find a sealant to handle just about everything, which is both a blessing and a curse for the uninitiated.

Luckily enough, we’re about to cover:

Types of Sealant

Sealants are used across numerous different industries for numerous different purposes; in short, there’s no such thing as your typical sealant. The upshot is that you’ll need to put some time into deciding on the right sealant to meet your own specific needs, and the silver lining is that you should be able to find one that seems tailormade from such a diverse array of options.

To get yourself started, here are the most common sealants you’ll encounter during DIY projects or professional construction jobs.

Acoustic Sealants

Looking to soundproof? Acoustic sealants are going to help hold your efforts together. Used to prevent noise filtering through any gaps and disturbing people in other rooms or outside your property, they also create an effective barrier against moisture and vapours. Acoustic sealants are easy enough to use, usually requiring nothing more than a caulking gun. They should stay relatively soft after application to help reduce sound transmission, so you’ll find it easy to trim away any excess sealant and create a smooth finish.

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Adhesive Sealants

Wait, didn’t we just go over the differences between adhesives and sealants? Yes, but sometimes the two come together as adhesive sealants. These possess inferior holding strength compared to traditional adhesives thanks to the inert material that makes up the sealant, but they’re still ideal for holding lighter items that require fixing and sealing at the same time. Lighter windows and skirting boards are a good example. An example of Adhesive Sealant is CT1 Sealant.

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Elastic Sealants

Sometimes referred to as elastomeric, elastic sealants became popular after the rise in use of curtain wall construction. A rubbery liquid often applied in relatively thick layers, it’s used to fill and seal up larger spaces. It dries hard but remains flexible, expanding to fit between two surfaces to create a watertight barrier.

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Floor Sealants

Not a thick foam or paste, but rather a thin, transparent protective layer that can be applied to a variety of flooring surfaces. Essentially, if your flooring is porous, you need a layer or two of floor sealant to create a barrier against stains, bacteria, moisture, and various signs of wear. But with candidates as diverse as solid hardwood and granite, you’ll need to make sure you pick up the right one. This is definitely a case of ‘always check the label’.

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Foam Sealants

Often used in older homes that have developed significant gaps and cracks, foam sealant is employed to create a barrier against escaping air. Application is relatively easy; you’ll layer it on thickly through a spray can. Foam sealants expand after application to cover a wider area, with expansion rates varying significantly, and they require plenty of time to dry before trimming.

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Latex Sealants

These water-based sealants are the DIYer’s best friend. They produce very little odour, very few volatile organic compounds, and can be painted with ease. They won’t fade under UV light, and they’re surprisingly simple to apply, work, and clean up after. As an added plus, latex sealants are less expensive than most other types. For interior finish applications, you’ll usually end up using a basic latex sealant.

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Metal Sealants

Metal demands a little more attention due to its weight and the fact that it contracts and expands. Silicon is a popular option when dealing with metal – you’ll find it used across plenty of metal roofs and window structures thanks to its firm hold and wonderful resistance against water penetration. Polyurethane is another option, coming in semi-solid form for joints or liquid form for large surfaces of metal.

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Patio Sealants

Patio sealant is floor sealant taken up a notch. Designed to cope with those harsher outdoor conditions, it will penetrate deep into the surface to reduce bacterial growth and prevent moisture from penetrating and causing damage during freeze/thaw cycles. It can be applied by the enthusiastic and experienced DIYer, but inexperienced hands would do well to contact a professional.

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Polysulfide Sealants

Polysulfide sealants are more likely to be used by a specialist. They boast the ability to withstand prolonged immersion in liquids, phenomenal chemical resistance, exceptional strength, and resistance to most fuels.

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Polyurethane Sealants

Polyurethane sealants are some of the toughest around, and they’re particularly valued for their abrasion resistance. Once dried, they produce an extremely tough elastic seal that can be used for masonry, plastic, rubber, wood, and various metals. However, this high-performance number can be difficult to apply and relatively expensive to buy.

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Rubber Sealants

When people speak about rubber sealants, they mean butyl sealants nine times out of ten. It holds a strong grip against a variety of materials and possesses sought-after weathering characteristics. However, it’s not particularly easy to apply and doesn’t allow for much movement. As such, butyl sealant tends to be used by construction professionals more than the DIY set.

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Silicone Sealants

Silicone sealants have a lot going for them. As well as resisting temperature changes, UV fading, and remaining flexible over long periods, they also have a very high movement capability and are completely waterproof. In homes, they’ll usually be utilized around sinks, tubs, shower stalls, and window frames; in commercial projects, they’re often used to bond glass panels to skyscrapers. That performance comes at a cost, both literally and figuratively. You can expect to pay top dollar for a silicon sealant, and they have a strong odour that makes them hard to work with. They’re also not paintable.

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Stone and Tile Sealants

If you’re using a natural stone, such as granite or marble, the surface is going to be porous thanks to hundreds of mineral micro-channels. That makes staining a possibility and gives bacteria an area in which to thrive. Enter the stone sealant – it forms an invaluable protective layer. The same is true of most types of tile, particularly ceramics. In either case, you’ll want an appropriate sealer.

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Urethane Sealants

Urethane sealants exhibit some of the strengths of silicon, but they can also be painted. Ideal where strong tear resistance and low shrinkage is required, their main drawbacks are that they require plenty of curing time, won’t wash out very quickly when they get on your skin, and, most importantly, cannot be used with any polycarbonate plastics. Additionally, painting is mandatory rather than optional since urethane sealants significantly degrade under UV light.

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Acrylic Sealants

Urethane sealants exhibit some of the strengths of silicon, but they can also be painted. Ideal where strong tear resistance and low shrinkage is required, their main drawbacks are that they require plenty of curing time, won’t wash out very quickly when they get on your skin, and, most importantly, cannot be used with any polycarbonate plastics. Additionally, painting is mandatory rather than optional since urethane sealants significantly degrade under UV light.

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Where should I use Sealant?

Sealant is used just as readily for simple home improvements as for complex works of engineering – it’s a truly many-headed beast.

For your basic DIY needs, you’ll generally find yourself using a latex sealant to patch up any joins that have developed gaps. If you’re particularly handy, you can go over the fixtures in the bathroom with some silicon sealant to ensure a total seal against water penetration. If extruded sealant ever needs to be applied from scratch, you might want to contact a professional instead.

Typical applications include:

  • Window & Glass: Flexible and non-staining sealant is used for light fittings, windows, doors, and other such applications.
  • Bathroom & Tile Sealant: From toilets to shower cubicles, you’ll find silicon sealants used extensively across the bathroom.
  • Roof & Gutter Sealant: Exterior sealant application should be left to the pros. Get it wrong and water could easily penetrate to wreck considerable damage. Guttering, downpipes, sheet metal, and other such surfaces require sealant that won’t corrode.
  • Brick & Concrete Sealant: Working with stone or concrete demands a sealant at once strong and flexible. It isn’t necessarily hard to apply, but working time can be extensive.

You should also use sealant to protect surfaces as well as form stable bonds between them. Across flooring, tiles, or paintwork, sealant essentially forms a shield against stains and bacteria by filling the pores of a porous surface. From metal garden sheds to ceramic kitchen tile backsplashes, most applications are straightforward enough to take care of all on your lonesome, but patios and other outdoor areas that require more intensive protection should be tackled by a contractor.

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When should I use Sealant?

Knowing what type of sealant you need to use is only half the battle. Equally important is coming to grips with when you should use it yourself, when you should call a professional, and when a caulking gun should be considered necessary.

DIY or Professional?

If you’re in the construction trade, you’ll probably be certified to use most sealants and familiar with the proper procedures. If you’re tackling your own property, you need to be realistic about your own skills and make sure a proper tradesman is employed for trickier jobs.

The first thing you’ll need to consider is what type of sealant is being used. As detailed above, latex is ideal for amateur use. In contrast, silicon, polyurethane, and rubber sealants are often best left to the experts since they can be hard to work and will often produce toxic fumes when not mixed correctly.

Secondly, consider how visible the final result will be and how easy it will be to do it again if you make an error. Sealant applied along the bottom of a window is going to be reasonably visible whereas sealant applied between toilet and floor won’t be.

Next, remember that some sealing projects are more important than others. By more important, we mean that the results of a poor job will be more serious. Take the sealant around your shower cubicle – if it isn’t applied properly, you’ll have leaks that could add up to thousands of pounds worth of damage.

For flooring and tiles, sealant is generally quite easy to apply and will not require the assistance of a professional; for outside paving and patios, heavy-duty sealants demand the skills and experience of a professional.

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Caulking Gun?

Sealant and caulking guns go together like peas and carrots; in fact, most people assume they are entirely dependent on each other.

Here are three main signs you need to use one:

  • Precision: Plenty of projects require precision. If you’re applying sealant along a shower door or a window, for example, there’s little room for error, and you’ll want the line of sealant to appear roughly equal across its length. When you don’t use a gun, it’s common to end up with a slightly uneven appearance.
  • Labour-Saving: Okay, squeezing out sealant is never going to get your heart pumping too hard, but it can become tedious when you need to apply quite a lot, and your fingers and wrists will bear strain during larger projects. A caulk gun works against such issues.
  • Versatility: Guns come with various tips, so you’ll be able to move from thick, heavy application to thin, intricate application

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How do I Apply Sealant?

1. Prepare the Area

Applying new sealant over old sealant might be tempting, but the result will likely be a seal that is both untidy and ineffective, so make sure you remove any existing sealant from the area before you get started. A utility knife can be used to cut it away and shave it off. Next up, clean the area to remove any dirt, oil, or grease – all will interfere with the bonding process.

If you happen to be applying sealant around a bath, you might want to fill it with some water before starting – this will replicate the actual weight your sealant will be expected to hold.

2. Apply Tape

The secret to a professional finish? Nothing more than a few strips of masking tape. Apply to both edges of the joint you’re working with to ensure a consistent width.

3. Prepare the Tube

Whip out your utility knife again to cut open the end of the sealant tube at a 45⁰ angle. The blade needs to be sharp to avoid any snags. Keep it reasonably small to maintain a controlled flow – remember that it’s far easier to make that hole bigger than it is to make it smaller.

Before you begin with the actual application process, test the pressure and flow using an old piece of cardboard. It should flow out evenly without dripping or squirting.

4. Start Applying

Now for the fun part. Apply sealant steadily, holding the end of the tube at a 45⁰ angle just above the surface you need to cover. Move along the edge slowly and steadily, avoiding the temptation to stop until you reach the end. It’s going to help if you position yourself so you can make full runs without pausing, so clear an area and take some practice paces. When you do get to the end, it’s vital that you stop the flow of sealant quickly and swiftly pull the tube away. Fail to do this and a thin string will be left.

One of the most common rookie errors is applying too much sealant. Keep in mind that you’re going to smooth it out, so you’ll probably need to use a little less than you think.

5. Tool to Smooth

Tooling is basically a fancy word for smoothing, and that typically involves nothing more than running your finger along the sealant to create a stronger bond and more pleasing appearance. Try dipping your finger into some warm soapy water to reduce friction, and make sure you only press down lightly as you go. Some people simply wet their fingertip in their mouth. Don’t be one of them; bacteria can be transferred from your mouth, eventually leading to mould growth beneath the sealant.

6. Remove the Tape

Content with your smooth sealant? Make sure you peel away the tape before everything sets to avoid making any rips in the sealant itself. Conduct some further finger-smoothing along the edges that were covered by tape to make sure dirt and moisture isn’t able to penetrate.

7. Let it Set

Last but not least, allow adequate setting time. The exact timeframe is going to differ between sealants, but you’ll generally be looking at around 24 hours.

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