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Preparing the substrate well before levelling
The smoothing compound is a fluid mortar poured onto a new or existing surface to create a smooth or level surface. This precedes the application of a floor covering, such as LVT, PVC, linoleum, rubber, carpet, timber or tiles.
The choice of smoothing compound will depend upon the nature and prior state of the substrate.In all cases it is necessary to apply it on a sound, dust-free and clean substrate. Substrates differ in properties and may need different preparations. They vary from one site to another, depending on whether the smoothing has to take place over a concrete screed, old tiling, an old timber floor, a damaged surface following the removal of a previous coating, a surface covered with scattered greasy stains, or any other type of floor. For example, smoothing on tiles will require a preparation different from smoothing on timber flooring. It is usually advised to apply a primer before smoothing is carried out, whatever the substrate.
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Six tips for preparing to apply a smoothing compound
Testing the dampness of the substrate
The floor to be coated with the smoothing compound must be tested for dampness. If not thoroughly dry, it will need to be treated with a moisture control system.
Test the dampness of your substrate and check to see if a moisture control system needs to be applied
Assessing the porosity of the substrate
Selection of the primer will depend on the porosity of the substrate as impervious substrates require different primers compared to porous substrates.
You must test the porosity of your substrate and use a suitable primer
Applying the compound to a screed or a slab with adhesive residue
You are applying a smoothing compound to a refurbished subfloor with an old adhesive residue.
You must use a primer to deal with old adhesive residue
Smoothing on a tiled surface
Before any smoothing operation on impervious surfaces, such as tiles, you will need to use a primer specifically for impervious surfaces.
Use a primer that is suitable for smoothing on tiles
Smoothing a flooring grade timber floor
To level a timber floor, prepare your surface with a primer designed for wooden substrates.
Apply a special parquet primer
Smoothing a painted floor
Painted surfaces will require a bonding primer.
Apply a primer before smoothing a painted floor
Check the condition of your substrate
Before any operation begins, test the condition of your substrate. It must be clean and sound with no laitance or flaky substances. Check the hardness and strength of the floor using a sharp tool. If it readily chips away or easily scratches then it is best to mechanically prepare the floor to return to a sound, strong surface. Ensure it is dust free before proceeding.
- Clean and remove all wax, paint and grease stain residue by using a suitable degreasing agent or by stripping.
- Remove the wax from old waxed floors and sandpaper any varnish.
- Any remaining adhesive residue must be strongly bonded and non-water soluble.
- Remove as much adhesive residue as possible, ensuring only a thin and firmly bonded film remains. This can be done mechanically or with a suitable construction standard scraper.
- If there is old tiling, inspect the bond integrity of the tiles by tapping with a hammer. Remove any that sound hollow or are cracked or partially unsealed.
- In the case of an old parquet floor, remove any damaged or loose wooden blocks.
After each of these operations, remove any dust and clean the substrate thoroughly.
Everything you need to know about preparing the substrate well before levelling
Wondering which products you need to use to prepare the substrate? Below you can find all the information you need for every unique solution.
Testing the dampness of the substrate
Introducing the ideal adhesive for preparing the substrate
The floor must be evaluated to ascertain whether it is prone to water seepage or rising damp. If you have concerns, contact our technical department. Diagnose with an electrical moisture metre. In uncertain cases, always use a surface hydrometer. Refer to the table below indicating the permissible dampness limits according to the substrate and selected floor covering.
What should I do if there is dampness or I suspect there may be dampness?
Use a moisture barrier. A suitable two-component epoxy resin enables a substrate that is damp or prone to rising damp to be prepared before smoothing. Water-based single component moisture suppressants are recommended for residual moisture only.
Screedmaster One Coat Membrane
Screedmaster One Coat Membrane is a two part, solvent-free, epoxy surface damp proof membrane (DPM).
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Screedmaster Rapid DPM
Screedmaster Rapid DPM is a ready to use, one part, water-based damp proof membrane developed to suppress residual construction moisture in cementitious subfloors and sand/cement screeds. Water-based moisture suppressant with a fast drying time.
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Do you want to put a new coating on old tiling?
Prepare a tiled surface
A smoothing compound can be applied to tiling. The tiles and grout lines must be degreased, abraded and cleaned before applying the right bonding primer.
BOSTIK GRIP A936 XPRESS
Dual-function high-performance bonding interface. A water-based primer and adhesion promoter with high grip and a fast drying time. High-performance primer for non-absorbent subfloors.
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Screedmaster Universal Primer
Water-based, solvent-free acrylic primer for use with most common substrates. Bostik Cempolay Universal Primer is a water-based, solvent-free acrylic dispersion floor primer and bonding agent that’s suitable for use prior to the application of any Bostik levelling compound.
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Screedmaster Epoxy Primer
Two-component water dispersible primer, ready for mixing. Bostik Screedmaster Epoxy Primer is a non-flammable, two component, water dispersible primer containing exact quantities of resin and hardener, ready for mixing together.
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GRIP A500 MULTI
High-performance primer for indoor and outdoor flooring. Indoors/outdoors. Blue-coloured. High-performance dual-function bonding interface.
Do you need to apply a smoothing compound to wooden panels - flooring grade boarded floors, such as P5 chipboard and SP101 plywood?
Do you want to carry out a levelling operation on timber flooring?
Smoothing may be carried out on timber, such as parquet flooring, if a special wood-bonding primer is applied.
GRIP X910 FILL & WOOD
Special bonding paste for parquet floors and panels before applying fibre coating.
Is your substrate covered with adhesive residue from an old flooring installation?
Old adhesive residue
Old tile or flexible floor adhesives are particularly difficult to remove. Sometimes this cannot be done without seriously damaging the substrate. The best solution to prepare a suitable surface before laying a new covering is to carry out smoothing. Ensuring the appropriate primer is used prior to smoothing is essential.
GRIP A500 MULTI
High-performance primer for indoor and outdoor flooring. Blue-coloured.
Screedmaster Universal Primer
Water-based, solvent-free acrylic primer for use with most common substrates. Bostik Cempolay Universal Primer is a water-based, solvent-free acrylic dispersion floor primer and bonding agent that’s suitable for use prior to the application of any Bostik levelling compound.
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Carrying out levelling on old painted floors
Levelling painted floors
Make sure any painted surfaces are sound and firmly bonded before smoothing begins. For a paint-covered substrate, use a primer suited to the nature of the coating. Refer to the instructions to ensure compatibility between the old paint, the primer and the future smoothing compound.
BOSTIK GRIP A936 XPRESS
High-performance primer for non-absorbent subfloors. Dual-function high-performance bonding interface. A water-based primer and adhesion promoter with high grip and a fast drying time.
Discover more
Screedmaster Universal Primer
Water-based, solvent-free acrylic primer for use with most common substrates. Bostik Cempolay Universal Primer is a water-based, solvent-free acrylic dispersion floor primer and bonding agent that’s suitable for use prior to the application of any Bostik levelling compound.
Discover more
Screedmaster Epoxy Primer
Two-component water dispersible primer, ready for mixing. Bostik Screedmaster Epoxy Primer is a non-flammable, two component, water dispersible primer containing exact quantities of resin and hardener, ready for mixing together.
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Before any levelling operation, test the substrate's porosity
Testing the porosity
Diagnose the porosity of the substrate with the water-drop test
Carry out a water-drop test to check the porosity.Pour a small amount of water onto the flooring. The longer it takes for the floor to absorb the water droplet, the less porous the floor. The level of absorbency will determine the nature of the primer to be used.
Controlling subfloor porosity with a suitable primer
A primer will address any shortcoming in the substrate's porosity, enabling smoothing compounds to flow and cure correctly, and minimising the formation of pin holes. For best results, apply a smoothing compound to a subfloor that has been appropriately primed to control subfloor absorbency.
GRIP A500 MULTI
High-performance primer for indoor and outdoor flooring. Blue-coloured.
Screedmaster Universal Primer
Water-based, solvent-free acrylic primer for use with most common substrates. Bostik Cempolay Universal Primer is a water-based, solvent-free acrylic dispersion floor primer and bonding agent that’s suitable for use prior to the application of any Bostik levelling compound.
Discover more
Screedmaster Epoxy Primer
Two-component water dispersible primer, ready for mixing. Bostik Screedmaster Epoxy Primer is a non-flammable, two component, water dispersible primer containing exact quantities of resin and hardener, ready for mixing together.
Discover more
BOSTIK GRIP A766 ECO+
Multi-purpose primer for absorbent subfloors. A concentrated primer for use on absorbent cementitious subfloors and as a barrier primer on dry calcium sulphate (anhydrite) screeds prior to the application of cementitious materials.
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