Preparation guide

Preparing the substrate: why prep matters for every finish

Every finish, from microcement and resin to lime plaster and paint, is only as good as what’s underneath. Each base needs its own preparation, and here’s what that looks like.

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The short answer

The substrate, or sub-base, is whatever you’re finishing over: concrete, screed, plaster, plasterboard, tiles, timber or old paint. Each one behaves differently, so each needs its own preparation system before the finish goes on.

Get the preparation right and the finish bonds properly, stays flat and lasts. Get it wrong and no finish, however good, will hide it. That’s why the ErreLAB and Rialto application manuals, and our own Politura guide, set out a separate preparation cycle for each base.

At a glance

Floors: Concrete, screed, tiles or timber
Walls: Plaster, plasterboard, tiles or paint
Check first: Rigid, dry, clean and sound
Unsure?: Call 01472 240 340

Why preparation matters

The finish is the part everyone sees, but the preparation decides how it looks and how long it lasts.

AdhesionA finish can only bond as well as the surface underneath. A weak, dusty or flaking surface lets it down.

MovementMicrocement and resin are only about 2–3 mm thick, so cracks or movement underneath can show through. The base has to be rigid, with no movement or flex.

DampMoisture coming up through a slab can push a coating off, however well it’s laid. Measure it, never guess.

FlatnessSmooth finishes show every dip and joint, so uneven walls need levelling first. Rialto recommends a levelling plaster under its finest lime finishes, such as Epoca Spatolato and Sinopia.

Every base is differentConcrete, plaster, plasterboard, tiles, timber and paint all absorb and move differently, so each has its own primer and base coats.

It costs less to get it rightA quick moisture reading or a small trial area costs far less than redoing a floor or a wall.

Before you start

Whatever the finish, check these first.

Rigid, with no movement or flexFix anything loose or flexing before you start. Anything that moves can show through the finish.

DryMeasure the moisture in floors and walls before you start.

Clean and soundFree of dust, grease and anything loose, flaking or chalky.

Cracks and jointsRepair cracks and stop any movement first. Tape over board joints, and on plasterboard seal and level the joints with mesh tape and filler.

Strong enoughFor Politura floors, concrete or screed of at least 35 N/mm², with new screed cured for 28 days.

Underfloor heatingRun new underfloor heating for at least 28 days, then switch it off before work begins.

Floors: preparing each base

These are ErreLAB’s preparation cycles for resin floors. Each one ends with a sound, even base, ready for the decorative coats.

Cement screed on a concrete slab

With no rising damp: Primer Cemento, then a coat of Malta, an epoxy base mortar, sanded once dry.

Screed on the ground, with rising damp

Primer Cemento, then Erre-Block One, which acts as a barrier against damp coming up from below.

Tiles on a concrete slab

Fondo Fibre, a reinforced layer that evens out the tiles and fills the joints, then Primer Cemento and Malta.

Tiles on the ground, with rising damp

Erre-Block One, then Malta.

Primers for Politura and ErreLAB floors

Base	Politura microcement	ErreLAB
Concrete, screed, metal or gypsum, dry	Politura Primer	Primer Cemento and Malta, as above
Damp or vapour pressure	EP72, in place of Politura Primer	Erre-Block One
Timber	EP80 epoxy primer, with kiln-dried sand scattered over it to rejection	An epoxy primer, with kiln-dried sand scattered over it to rejection
Tiles	We recommend removing them	Fondo Fibre, Primer Cemento and Malta, as above

Sand to rejection means scattering kiln-dried sand over the wet primer until the surface won’t take any more. Timber still has to be rigid, with no movement or flex.

Walls: preparing each base

ErreLAB’s wall cycles. For Politura microcement, plaster and gypsum take Politura Primer, and we recommend removing tiles first.

Cement-based plaster

Primer Cemento, then Fondo Vertical, an acrylic base coat, sanded once dry.

Tiles

Two coats of Riempitivo Fibrato to fill the joints and level the tiles, then Primer Cemento and Fondo Vertical.

Gypsum or plasterboard

Two coats of Primer GS, then Fondo Vertical.

Lime plasters and paints: preparing the wall

Rialto lime finishes depend on the wall underneath just as much. These are Rialto’s preparation cycles for the most common walls.

New plasterboard

Seal and level the joints with mesh tape and filler, then a basecoat such as Rialto Eco Fondo. Add a levelling plaster where the wall is uneven, or under the finest finishes.

Wall painted with ordinary paint

Remove anything loose, flaking or chalky and dull any glossy paint, then a basecoat such as Eco Fondo, with a levelling plaster if needed.

Wall painted with breathable paint

Remove anything loose, flaking or chalky, then a basecoat such as Eco Fondo before the finish.

Painted wall with mould

Treat the mould with a sanitising agent first and brush it clean once dry, then the basecoat and finish.

Questions about substrate preparation

What is a substrate or sub-base?

Both mean the surface you’re finishing over, such as concrete, screed, plaster, plasterboard, tiles, timber or old paint.

Do I always need a primer?

Yes. Every system starts with a primer made for that base, so the next coat bonds properly.

Can you go over tiles?

With ErreLAB, yes: the tiles are filled and levelled first, then primed. With Politura microcement we recommend removing them. See our over tiles guide.

How long should new screed cure?

For Politura, at least 28 days. Call us on 01472 240 340 for other systems.

What if the floor is damp?

Measure it first. Where there’s damp, ErreLAB uses Erre-Block One and Politura uses EP72 in place of its standard primer. For anything badly damp or water damaged, talk to our technical team before starting.

Can lime plaster go over a painted wall?

Yes, once anything loose, flaking or chalky is removed and glossy paint is dulled, with a basecoat such as Rialto Eco Fondo first.

Can you finish a timber floor?

Yes, if it’s rigid with no movement or flex. It takes an epoxy primer with kiln-dried sand scattered over it to rejection.

Do you supply the preparation products?

Yes. We supply the primers and base coats for our systems, and we’ll tell you exactly what your job needs.

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