Paint is the visible part of a job. Everything underneath it — filler, primer, sealer, caulk — is what decides whether the job lasts. Most failures that get blamed on paint started with a missing preparation product.
This page covers each one, what it is for, and the order to use them in.
Fillers
Filler makes a surface flat. It fills cracks, holes, old fixing points and shallow hollows so the wall reads smooth under a topcoat.
Interior filler is for plaster and plasterboard — cracks, dents, chased cable routes. Prestige Super Filler is the general-purpose option.
Joint compound is a different product: softer, sanded more easily, used for taping and finishing joints in plasterboard and for skim-coating large areas. It is not a substitute for a structural filler in a crack that moves.
Exterior filler needs to take weather and movement. Standard interior filler will shrink and crack outside; deep or wide cracks need cutting back and repairing with mortar before any filler goes near them.
Whatever the product: fill slightly proud, let it dry fully, then sand flush. A filled patch that is not sanded shows through even a good topcoat.
Primers
Primer is the bridge between the substrate and the paint. It seals, it provides a key for the topcoat, and it blocks stains. It is the most commonly skipped product on a painting job and the one that causes the most failures.
Masonry primer goes on new plaster, render and concrete. Bare plaster absorbs paint unevenly; a primer evens out the absorption so the topcoats dry to a consistent colour.
Wood primer seals the grain and stops the topcoat sinking in. Bare timber painted without primer shows every grain line and dries patchy.
Metal primer provides adhesion and, on steel, corrosion inhibition. This is the product that decides whether a gate lasts five years or fifteen. There are different metal primers for ferrous and non-ferrous metals.
Stain-blocking primer seals water stains, nicotine, grease and ink so they do not bleed through the new coat. Paint alone does not block a stain, whatever the coverage claims.
Sealers
A sealer is closely related to a primer, and the terms are often used interchangeably. The distinction that matters in practice is what it is doing: a sealer is closing a porous surface, a primer is providing a key.
New plaster needs sealing. Fresh plaster is highly absorbent and alkaline; painting it too early, or without sealing, gives a patchy finish and can cause the paint to fail as the plaster continues to cure.
New POP needs sealing before painting, or the first coat dries with lighter and darker areas that a second coat does not fully even out.
Chalky or dusty old surfaces need a penetrating sealer after washing, to bind the surface so the new paint has something to hold.
Caulks and sealants
Flexible sealant goes where two surfaces meet and move: around window frames, door frames, skirting, and any joint between materials. Paint is rigid and joints are not, so without sealant a hairline gap opens and the paint cracks along it.
Interior caulk is paintable and sandable. Exterior sealant needs to take weather and ultraviolet light, and often has a longer curing time. Silicone is not paintable; use an acrylic or hybrid sealant where the joint will be painted.
The order of work
- Wash the surface and let it dry completely
- Scrape back anything loose, and sand to a key where the surface is glossy
- Seal joints with caulk or sealant, and let it cure
- Fill cracks, holes and hollows, then sand flush
- Dust off — filler dust stops paint bonding
- Prime bare areas, repairs and stains
- Paint two coats
Doing these out of order is how a good paint job fails. Filler over paint does not bond; primer over filler dust does not bond; paint over caulk that has not cured wrinkles.
The mistakes that matter
- Skipping primer to save money. Primer is cheaper per litre than topcoat and it is what makes the topcoat work. This is a false economy in the strictest sense
- Filling over a crack that moves. It reopens. The crack needs to be assessed, not just filled
- Painting over damp filler. It traps moisture and blisters
- Using interior filler outside. It fails within a season
- Caulking with silicone then painting. The paint will not stick to silicone
- Not dusting off after sanding. The most common single cause of a coat that peels
What to buy for a typical repaint
- One interior filler for cracks and fixing holes
- One masonry primer for bare patches and repairs
- One stain-blocking primer if there are water marks or nicotine
- One paintable acrylic caulk for joints around frames and skirting
- Sandpaper in two grades — coarse for shaping filler, fine for finishing
That list is small and it is the difference between a job that lasts and one that does not.
Getting the right products
Tell us the surface, what is on it now, and what you are trying to achieve, and we will tell you what preparation the job needs. Call +234 802 562 5333, message WhatsApp, or send your project details.