Caulk & Sealant Explained

The Difference Between Caulk and Sealant

To begin with, it helps to understand how caulk and sealant differ from each other. The simplest explanation is that caulk is generally used for decorative purposes within dry indoor areas. For instance, this could be filling in cracks and gaps such as on a skirting board. Silicone sealant, on the other hand, has special properties to seal off areas from water and damp. Thanks to their chemical-resistant nature and waterproof properties, sealants are particularly useful in kitchens and bathrooms. However, the rubber-like nature of the chemical is very difficult to paint over.

So, how do you choose between caulk and sealant? It depends on the project you’re working on. Decorators’ caulk does not offer a reliable seal from water or other chemicals, but it does fill gaps and can be painted over, allowing for a clean and tidy look. Silicone sealant can be used as a seal but may not leave such a refined finish.

The quick and simple explanation is that caulk is generally used for decorative purposes inside (in dry areas) to fill in cracks and gaps (such as on skirting board) whereas silicone sealant has special properties to seal off areas from water and damp. Sealants are used in kitchens and bathrooms because of their chemical resistant nature and waterproof properties, however, this means that the rubber like nature of the chemical is very difficult to paint over. Decorators caulk does not offer a reliable seal from water or other chemicals, but it does fill gaps and can be painted over- allowing for a clean and tidy look.

What about “Mastic”?

It is quite common for builders to refer to sealants as mastic. However, mastic refers to an older material that was processed from the resins of mastic trees. Modern sealants no longer use mastic but the name has stuck for many in the trade. As such, when you hear someone mention mastic, the chances are they’re still talking about sealants.

Types of Sealant

Low Modulus Sealants

One of the main ways to classify silicone sealant is by flexibility. On the tube or in the product description, the sealant’s flexibility will be referred to in terms of its ‘modulus’. This is just another term for stiffness. Sealants that are ‘low-modulus’ have high flexibility, making them better in applications that tend to experience movement such as windows on windy days. Standard general purpose sealants still have a fair amount of flexibility and are suitable for most applications. High-modulus sealants, however, have very low movement and are not sold as sealants but as adhesives instead.

Sanitary Sealants

One of the most popular types of sealant is sanitary sealant. Certain rooms, such as bathrooms and kitchens, can be much damper than others. This makes the sealant more susceptible to rot and discolouring. Sanitary sealants, however, feature fungicidal properties that offer longer lasting seals to kitchen counter tops, shower basins, sinks, and so on. Sanitary sealants can be varied in their qualities and application, such as the Everbuild Forever White or the best-in-class all-rounder CT1 Sealant and Adhesive.

Fire Rated Sealants

In industrial settings where fire rated standards need to be met, fire rated sealants must be applied. Due to this sealant’s unique ability to slow down the spread of a fire for up to five hours – as specified in the BS EN1366-3 & 4, UL 2079, and BS476-20 standards – fire sealant is commonly specified for use around fire doors and windows. Generally speaking, these also tend to be used alongside B1 Fire Rated Expanding Foams. Our bestselling fire sealant at Tradefix Direct is the Fischer Intumescent FireStop Sealant. Like most fire sealants, this features excellent acoustic properties and can also be painted over.

Hybrid Polymer Sealants and Adhesives

At the cutting edge of building chemical technology are hybrid polymers. These ingeniously merge characteristics from various polymer families, such as silicone, polyurethane, and acrylics. For the most part, these hybrids include silane-modified polymers (SMPs) and MS polymers (modified-silane polymers). They are skilfully designed to amalgamate the superior qualities of each individual component. This means they combine the elasticity and heat resistance found in silicones with the strong adhesion capabilities and ease of painting associated with polyurethanes.

For tradesmen, hybrid polymer sealants and adhesives can be highly cost-effective. After all, you don’t need to buy two separate products for sealing and fixing. They can also be painted over, meaning they could be used as decorators’ caulk. That said, decorators’ caulk tends to be much cheaper and so this would be quite an expensive solution. Still, if you need to caulk a small area, you could use a hybrid polymer instead of going to buy a new tube of caulk.

The most popular hybrid polymer sealants on the market, such as the Everbuild Stixall, have extremely strong adhesive properties and can stick to pretty much any material. Not only can a product like Stixall be used in wet and damp conditions, but they can also be applied effectively while under water! On the higher end of the market, hybrid polymers can be used for pretty much any sealant, adhesive, or caulk application. The CT1 range is well known for being the best of the best for tackling almost every sealant application to a very high standard. Read the product description to see how much it can do!

Other Properties of Sealants

When reading the gripping and exciting product descriptions of silicone sealants (you’re as thrilled as us, right?), you will find that most mention acoustic and VOC properties.

Acoustic properties refer to the sealant’s ability to reduce noise. Noise reduction tends to be more common in lower modulus sealants as their higher elasticity means they can absorb the sound vibrations. However, acoustic properties are also found in higher grade premium sealants.

VOC, or ‘volatile organic compounds’, refers to chemical compounds polluting the environment. Again, most higher quality sealants feature a low VOC, making them better for the environment and safer to work with.

For more information about the technical details, we recommend visiting the Soudal website’s FAQ page.

Types of Caulk

While there are several different types of sealant, there is only one type of caulk: the water-based acrylic caulk. This is mainly used for decorating, hence the common name of decorators’ caulk. Premium versions tend to be odourless and have better colour properties, such as the Soudal Acryrub Extra White Superior Decorators Caulk. The cheaper alternatives tend to satisfy most requirement and are very popular.

If you’re looking for caulk or sealant for your own project, why not browse our full range online? If you’re unsure which product you need, or simply want advice on choosing the best sealant for each task, you can also get in touch! We’ll be happy to talk through your options and make sure you’re coming away with the right equipment for the job. For more guides and resources, check out our other blogs.