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What is a filler (in construction)?

The term filler is used to describe any material, usually in the form of powder, fibre, or a combination of the two, that is added to another material with the purpose of improving its quality and/or reducing the cost.

Contrary to the notion that fillers are used to cheapen products, the reality is using fillers improves chemical resistance and physical properties, resulting in efficient sealing devices.

Fillers help boost mix properties and decrease the amount of expensive binder needed, and is the reason these materials are gaining widespread popularity and importance. Every year, more than 53 million tons of fillers are used across different areas such as adhesives and sealants, coatings, paints, plastics, rubber and paper.

Fillers are usually semisolid compositions (e.g. paste) which harden upon dying and are commonly used to fill holes, pores or cracks in plaster, wood or other construction surfaces before finishing or painting. One instance where fillers are usually an easy fix is drafty doors and windows.

What types of fillers are there? / How to choose the right filler?

There is currently an abundance of different fillers available to those looking to repair surface damage (e.g. fill a hole) prior to redecorating. All broad filler types feature products specifically designed for either interior or exterior use, as well as fillers formulated to meet particular demands such as drying quickly, sanding easily, painting well or protecting from water.

Powder fillers, for instance, only need to add water, and are considerably cheaper than many other filler types. Ready-mixed micropolymer fillers, on the other hand, are especially convenient for small to medium sized holes and cracks. However, when it comes to the hardness of the finished surface, they often fall short in comparison to other fillers.

Ready mix fillers are an easy, quick solution, as they don’t require much effort to apply and spread. The main downside of this type of filler is its liability to shrink, which could make filling deep holes very time-consuming and result in cracks after setting.

Wood fillers come in a variety of colours for the sake of remaining inconspicuous and can provide a simple solution to degradation of wooden sections such as windowsills and frames by filling deep holes and restoring rotten wood to its former splendour. There are two main types – ready mix fillers and two-part epoxy fillers (also known as high performance wood fillers), a mix of chemical hardener and filler. The latter have a very short setting time and are much easier to sand than their ready-mixed counterpart, but they should always be used in ventilated area because of the strong odour they emanate.

What is decorator’s caulk?

Decorator’s caulk is a flexible filler used for filling gaps in the junction between walls and skirting boards, doorframes or the edges of shelves. Decorator’s caulking can also be used around windows, ceiling and corner lines, but isn’t suitable for filling holes in the wall, as it cannot be rubbed down the way powder filler can. Because caulk cannot be sanded, it is typically applied and smoothed once the rest of the preparations have already been completed.

Caulk is typically used to fill and/or conceal small gaps or cracks which might increase over time, or are prone to movement. This type of flexible filler is usually suitable for both indoor and outdoor use, and can be utilised in a number of repair jobs, including woodwork for filling the cracks around door panels and frames.

The range of flexible fillers available on the market also includes antibacterial caulk, which is a great solution for bathrooms and kitchens.

How to use decorator’s caulk?

Prior to applying your caulking, make sure you’ve cleaned out any dust and debris from the damaged area. It’s also advisable that you check whether the type of filler you are using requires the cracked area to be dry prior to application.

You might also need to acquire a cartridge gun if you are using a cartridge method of application. For the best results when using flexible filler, run a small amount of the decorators caulk along the crack and use a wet finger or rag to smooth it over.

Once the filler is dry and has been smoothed over, you can proceed with painting – if you find that emulsion causes the caulk to crack, go over it with an oil based undercoat before reapplying the paint.