Filling Cracks in Doors and Trims

How do you fill cracks in doors and trims, and which Selleys filler should you use?

A crack in a door, an architrave or a skirting board is almost always a cosmetic problem rather than a structural one, and it is well within reach of a first-time DIYer. The sequence is short: clean the surface, sand back any loose or chalky paint, press the filler firmly into the crack with a blade, scrape off the excess, let it dry, then sand lightly and paint. The product Selleys specifies for this job is Selleys No More Cracks Doors & Trims, a ready-to-use filler made specifically for doors, windows, architraves, trims and skirting boards.

The one thing worth knowing before you start is why that particular filler. No More Cracks Doors & Trims is formulated for use under gloss paints and its technical data sheet claims a mirror-like, durable finish with superior gloss retention. That matters on trim work, because gloss and semi-gloss paint are unforgiving: any filler that sinks, shrinks or sands unevenly shows up as a dull patch under a shiny coat. A general wall filler will fill the crack but will not necessarily hold the sheen.

What the technical figures mean for your job

Appearance	White paste
Sand / paint time	2–3 hours for 2–3 mm applications
Adhesion	Timber, plaster, concrete, mortar and primed metal
Use	Interior and exterior, under gloss paints

These are the manufacturer's indicative figures only, and are not intended for the preparation of specifications.

The figure that governs your afternoon is the 2–3 hour drying time, and the qualifier attached to it matters: that is the time for a 2–3 mm application. Fill deeper than that and you should expect longer. Humidity stretches it too. If you fill a set of door frames in a cold, damp room in July and sand at the three-hour mark because the sheet said three hours, you will drag soft filler out of the crack rather than levelling it.

The practical response is to fill thin and fill twice rather than fill deep once. Selleys' own direction for a perfect finish is to apply a second thin coat after the first has dried, then sand lightly with fine sandpaper. Two thin coats dry predictably, sand cleanly and give you a flatter result than one thick one.

What you need

• Selleys No More Cracks Doors & Trims
• A filling blade or scraper
• 240 grit sandpaper
• Selleys Sugar Soap and a damp cloth
• A dust mask, and gloves if you have sensitive skin
• Water-based undercoat and your topcoat

How to fill the crack

1. Clean the surface. Wipe the door or trim over with a damp cloth and a Selleys Sugar Soap solution so the surface is clean, dry and free from dust. Wear gloves for this if you have sensitive skin.
2. Sand off loose paint. Wearing a dust mask, sand away any loose or chalky paint with the sandpaper. Sanding painted surfaces generates fine particles, so ventilate the room and keep the mask on.
3. Prime first if the job is outside. Exterior surfaces should be primed before filling. Skip this on interior trim.
4. Apply the filler. Once the area is clean, apply No More Cracks Doors & Trims with the filling blade or scraper.
5. Press it in. Use the blade or scraper to firmly press the filler into each crack. Pressing matters more than covering — a filler that only bridges the top of a crack has almost nothing holding it.
6. Scrape off the excess. Take the surplus off now with the blade. Every gram you remove here is a gram you do not have to sand later.
7. Let it dry. Allow 2–3 hours. Longer in humid or cold conditions, and longer again for thicker fills.
8. Sand back. With the dust mask on, lightly sand away any leftover excess with the 240 grit paper.
9. Undercoat, then paint. For best results apply a water-based undercoat after sanding, then your topcoat.

Where this filler should not be used

Its technical data sheet gives two limitations, and both matter on trim work.

Where movement occurs, use a flexible gap filler instead. No More Cracks Doors & Trims is a rigid filler. If what you are looking at is not a crack in the timber but a gap that opens and closes — the line between a skirting board and the wall, or between an architrave and the plaster — a rigid filler will crack again within a season. Selleys directs you to No More Gaps for those joints, and there is a separate guide on filling gaps between skirting boards and walls.

Not suitable for exterior timber likely to absorb excessive amounts of water. Timber that soaks up water swells and shrinks, and the filler cannot follow it. Exterior applications also have to be protected from rain until they have been painted over.

Getting the paint finish right

Two details from the technical data sheet do most of the work here. The first is cleaning the surface with Selleys Sugar Soap before painting — a clean surface aids paint adhesion, and after sanding there is fine dust sitting in every corner of a moulding. The second is the undercoat: apply one before your topcoat. On a filled repair under gloss, an undercoat evens out the difference in porosity between the filler and the surrounding paint, which is what stops the repair reading as a flat patch in a shiny door.

Clean up and storage

Clean tools and hands with water before the filler dries. Once it has set, it has to come off by scraping or sanding. Close the lid tightly after use and store the tub in a cool, dry place.

Common questions about filling cracks in doors and trims

How long does No More Cracks Doors & Trims take to dry?

2–3 hours for a 2–3 mm application, depending on humidity. Deeper fills and cold or damp conditions take longer.

Can I use it outside?

Yes — it is rated for interior and exterior use. Prime exterior surfaces before filling, and protect the repair from rain until it has been painted over.

Will it work under gloss paint?

That is what it is made for. The technical data sheet describes it as being for use with gloss paints, giving a mirror-like finish with superior gloss retention.

What surfaces does it stick to?

It has excellent adhesion to timber, plaster, concrete, mortar and primed metal.

Do I need to overfill to allow for shrinkage?

Press the filler in firmly and scrape off the excess. For a perfect finish, apply a second thin coat once the first has dried and sand lightly with fine sandpaper — that is a better approach than laying one thick coat.

What sandpaper should I use?

240 grit for this job, used lightly. The aim is to take off the excess, not to cut back into the surrounding paint.

Do I have to undercoat before painting?

For best results, yes. Apply a water-based undercoat after sanding, then your topcoat.

The crack keeps coming back — what am I doing wrong?

Probably nothing about your technique. A crack that reopens is usually a moving joint rather than a split in the timber, and a rigid filler cannot follow movement. Selleys directs you to No More Gaps where movement occurs.

Can I use this on a skirting board gap?

Only if it is a crack in the board itself. The gap between the skirting and the wall moves, so use No More Gaps there instead.

How do I clean up?

Water, before the filler dries. Cured filler has to be scraped or sanded off.

Can I fill a deep hole in one go?

The stated drying time covers 2–3 mm applications. For anything deeper, expect a longer dry, and consider building up in thin coats. For genuinely large defects, No More Cracks Large Cracks & Holes is the product intended for the job.

Is there anything I should not fill with it?

Exterior timber that is likely to absorb a lot of water, and any joint that moves.