Page 68 - CFJ_Apr26

ADVICE & INFORMATION

David Powell

Smoothing compounds - why are there different types?

With so many smoothing compounds available, understanding their differences is key to
selecting the right product for each project, says David

HERE’s a wide range of smoothing needed to make an informed decision. remains critical to achieving a successful
Tcompounds because no one product They outline compressive and flexural finish.
fits every situation. Choosing the right strength, coverage at various thicknesses, Priming subfloor surfaces helps
compound helps create a durable, long- and recommended application methods. control absorption, reduces the risk of
lasting floor finish and reduces the risk Application thickness can range from a pin holing and improves overall finish
of failure. thin scratch coat up to 50mm, depending quality. Dilution ratios will vary. For
Some projects require fast installation on the product. example, one part primer to two parts
to keep on schedule, while others Working and drying times depend on cold, clean water.
demand stronger compounds for heavy how absorbent the substrate is, plus Highly absorbent surfaces may require
traffic, better flow for large areas, greater the site’s temperature and humidity. a second coat.
depth build-up, or improved smoothness On fast-track jobs, picking the wrong Most smoothing compounds are
for resilient floorcoverings. Often, these product can cause delays, but in other compatible with warm water and
factors combine. Different compounds cases, longer working times might electric radiant underfloor heating
are designed to address these site and actually help. systems, provided the recommended
performance requirements. surface temperature limits are observed.
There is an abundance of information Application methods and coverage
available to help narrow the selection, Always apply smoothing compounds
including manufacturer websites and to a clean, uncontaminated, and
mobile apps, as well as the option to well-prepared subfloor. Whether
speak directly with technical support. you use hand trowels, cam rakes, or
Many manufacturers also offer hands- pumped application, proper placement
on training so you can see the options is important. A spiked roller can
and application methods in action. help release trapped air from wet
Assessing the substrate first compounds.
Assessing the substrate is always the Some compounds allow the addition
starting point. It will determine the of aggregate to support thicker
product requirements and the preparation applications where required.
methods, ensuring subfloor contaminants Online tools and mobile apps like the
and imperfections do not transfer through Bostik Pro App often have coverage
to the finished installation. calculators. By entering the product
Some compounds work well on name, area size, and thickness, you can
common substrates like concrete, Advanced specialist compounds estimate how many units you’ll need.
sand and cement screeds, stone, and feature enhanced flow characteristics For example, a 100sq m area at 3mm
calcium sulphate screeds, firmly bonded and can be applied directly to many depth might require about 20 units,
unglazed ceramic, terrazzo, quarry tiles, common substrates without priming, depending on the floor’s smoothness
and can even help form slopes and thanks to their high adhesion and low and absorbency.
ramps when needed. shrinkage. This may include surfaces Closing thought
Using a compound that doesn’t match with minimal old adhesive residues, The reason there are different types
the substrate can lead to debonding, ceramic tiles and flooring-grade plywood. of smoothing compounds is simple.
cracking, or excessive movement. So, Some products are moisture tolerant, Substrates, site conditions, and
it’s important to know exactly what meaning they can be used over damp performance needs all vary. Matching
surface you’re working on. subfloors prior to the application of a the compound to the environment and
Understanding compound types damp proof membrane, provided this the floorcovering is what ensures a
Smoothing compounds usually come is permitted by the manufacturer’s reliable, long-lasting installation. When
in two types: ones mixed with clean guidance. unsure, check the technical data sheet
water and others that include a bottled Preparation and priming or speak to technical support before
liquid component. The bottled type is Technical data sheets also provide application. 
especially handy on sites where access guidance on preparation and david.powell@bostik.com
to clean water is limited. recommended materials. Proper www.bostik-profloor.co.uk
Technical data sheets provide the details physical preparation of the substrate David Powell is technical consultant, Bostik UK

68 CFJ April 2026 www.contractflooringjournal.co.uk
@CFJMagazine