Painting rooms in your home: How to prep for the perfect finish

Kya deLongchamps shows how to fill in cracks like a pro before painting your interior walls

Wed, 19 Jun, 2024 - 11:23

Prepping is the essence of a great final finish when painting your walls, including the challenge of woodwork.

First of all, not all dings and holes need more than a paint fill. What we’re going to do is fill those really tiny imperfections with an extra coat of paint. Take for example, those tiny indents from those oval nails holding on your new or old skirting. If these are almost flush with the timber, it’s going to take very little to disguise their presence.

Prime your woodwork as usual and then take some of the top coat (for instance, a water-based satin wood) and give the small indentations a small spot application. When you put on the next two coats, chances are you will not see those holes on show.

Always start on woodwork or walls with a light clean with a sugar soap solution to lift any dust, debris, and grease.

Moving up to small cracks. First of all, it’s important to ensure any actual cracks, as opposed to dings, are not wide enough to indicate any structural trouble. If the walls appear to be heavily damaged with extensive holes and deep continuous cracks, it’s worth considering having an engineer take a look.

Cracks larger than 5mm or cracks “stepped” up the wall could be concerning. Once you have the all-clear, a professional plastering will bring those crazed walls back to sleek perfection. Plastering is a highly skilled job — don’t trust yourself after a bit of YouTube inspiration — trust me.

Any crack over 5mm wide or a wide, suspicious, stepped hairline cracking should be examined by an engineer. File picture

Otherwise, most small indentations and simple hair-line cracks under 5mm can be addressed with a little deft DIY, filled with dabs from a ready-mixed tub or squeeze tube of lightweight or classic flexible filler, scraped flat. Polyfilla even offers a Quick Dry Spray for hairline cracks, 300ml for €15. Other popular brands of creams, caulks and powders include Ronseal and Unibond. With a buttery texture and smooth finish, a typical tube of ready-mix comes in around €8-€10, with versatile products that can handle plaster, stone, concrete and wood.

Cracks in old and even new plaster are not unusual and are largely the result of the plaster-coat or skim-coat (on plasterboard) just drying out. No biggie and easily solved.

Tube products are handy for fine detail, and used carefully can release a continuous bead, handy for both wall-plug holes and gaps left at the edges of door frames for example.

Before we start, if the crack is a bit ragged with crusty edges, score it just lightly along its direction with a Stanley knife or the end of a putty knife. We need a clean, stable surface for the filler to bond to. Then brush away any loose material, swipe it over with a barely damp sponge to pick up any finer dust, allow to dry and only then apply your filling product.

If you don’t have a putty/filler knife with a flat edge, invest in one. These tools have some give when you apply pressure and are perfect for pushing filler into tiny gaps and smoothing the filler out before drying and sanding. Squeeze a blob of filler out onto something like a clean tile, lifting some onto your filler knife and swoop it across the dent or crack with the edge. Go from various directions to coax if fully into the gap. The edge will lift most of the excess, and don’t worry if the filler covers a wider area in a thin coat, it will easily sand back and going beyond the edges of the cracks seals it all nicely. Expect the product to shrink back as it dries.

Every product has a drying time, but the lighter and airier it is the quicker it will set. Some are very light — with the texture of a mousse, setting up and ready to paint in about an hour. The appropriate grade of sandpaper will be recommended on the packaging. For nail holes, I like the wooden edge of a match-stick — perfect for poking a tiny spec of filler. Resist licking your fingers as you will get a taste of filler once you do it twice. Use a small sponge, well squeezed out, to lick the applied filler neatly into corners and more complex gaps.

Every product has a drying time, but the lighter and airier it is the quicker it will set. File picture

It’s worth popping on a paper face mask during the following sanding process as the fine dust that will wing out on the air can be an irritant. Why take a chance? To lift any fine dust left on the wall or woodwork before painting just wipe over with a well wrung out small sponge and let the area dry out. A sanding pad or block is easier to work with than a handheld sandpaper sheet, as it will direct the paper cleanly across the wall.

Professional plasterers use self-adhesive joint tape or scrim (there are tapes for both plaster-board and plaster on block) over significant cracks and joints in plasterboard to reinforce areas that might flex and open.

After the imperfections or joints are filled to give it a nice smooth surface, the filler is spread over the top far beyond the edges of the tape. You are unlikely to need to go this far with standard hairline cracks and small holes. Sanding has to be done over a wide area to hide tape, and in any case if the cracks are reappearing, you should ask yourself “why” before cheerfully taping them over! If the crack or hole has any depth to it, we need to build up the filler in the hole, allowing it to dry between applications, until we have a dry, filled hole with the filler sitting just very slightly proud of the hole.

Now, we sand it flat, and you know you’re getting there when you can close your eyes and run your hand over the hole or crack without detecting its presence. Patience is key. If the holes you fill sink below the surface of the surrounding wall, apply more filler, leave it a little proud, stick to those drying times and sand again.

When buying your filler, keep in mind that caulk is a slightly different product with a bit more elasticity. It’s used when filling gaps between skirting boards, door-frames or the edges of shelves and the join of the ceiling and wall. In a gun it takes some practice to shoot straight, but this is a great skill to practise at as sealant is all over your house and it needs occasional replacement, for example around your shower and bath. Elsewhere use dedicated acrylic polymer-based wood filler or multipurpose filler to build up any holes caused by empty knot holes. Knotting agent painted onto any existing knots in bare wood will prevent sap bleeding through your paintwork.