Filling cracks and holes
Pesky things. They spoil the look of your wall. Cracks, in particular, can be worrying because you’re always thinking that the side of your house might fall off. But be optimistic and take heart – cracks are most likely to be cosmetic rather than structural. I’ve certainly never come across a structural crack in someone’s house. Get the crack filled and sleep easily at night.
Click here for the quick card for this post
Materials and tools
- Old screwdriver
- Small brsuh for clearing dust
- Filler knife
- Filler
- Sandpaper
- Sanding block
Why do cracks occur?
If you live in a fairly new house
It’s likely that a crack is due to the house settling. If you pop your house on the bathroom scales, you’ll see that it weighs a couple of hundred tonnes. After a house is built, all this weight causes it to shift and sink just a smidgin. Different parts can sink at different rates, ending up in a tiny bit of twisting and bending of the whole building. This causes cracks. Also, there’s an awful lot of water involved in building a house: concrete, cement, plaster, new timber, etc. As a building dries out, things shrink, which can cause cracking.
In older houses
My house was built more than a hundred years ago. It’s inevitable that nails will come loose, timber will sag and twist, and frost damage will affect bits of the building. Things just aren’t quite so well held together as they were a few decades ago.
In any house
Differences in temperature cause walls and ceilings to expand and contract. The same thing happens with moisture changes in the air or the soil. Vibrations, perhaps due to traffic, can cause cracking, and so can leaks, flooding, tree roots, hot summers, and so on. The list of culprits goes on and on. Cracks are normal. If you don’t want cracks in your home, you probably need to invest in a decent tent.
Limitations of this post
Some cracks and holes are a bit more complicated than basic DIY, so let’s do a quick check.
Is your crack indoors or outdoors?
Does any of these describe your crack?
- wider than 5mm or so;
- in the same place on the inside and outside of a wall;
- travelling through a brick rather than around the outside of it;
- diagonal – which looks like a set of stairs;
- I can see daylight through it.
Does any of these describe your crack?
- my crack runs in a dead straight line;
- the crack is in an old ceiling;
- the crack runs from the corner of a door or a window;
- the crack is on an external wall which gets baked by the sun.
Would you describe the hole as worryingly deep or quite large – say, bigger than an orange (maybe a squashed, mashed-up orange)?
Can you see the bottom of the hole?
Let's get filling
Right then. If you’re still reading, you must have a bog standard hole or crack. It must be:
- indoors;
- not serious;
- doesn’t need strengthening;
- not huge;
- no need for a plasterboard repair.
Cracks might be offensive to look at, but they are quite easy to sort out with some basic kit. So let’s get the tools out and do a bit of work.
It’s best to fill most holes and cracks twice. The first time (first strike) should mostly fill the hole and the second strike will make it look neat. It’s normal to take two or three strikes.
Filling cracks
Rake the crack open
You need to get plenty of filler in there, so the crack has to be fairly open (2-5 mm or so). If it’s not wide enough, you’ll have to make it wider. Jam the corner of a flat screwdriver (an old one is best) into the start of the crack. Holding the screwdriver with both hands, rip it all the way along the crack. Be sure to use very firm pressure and travel in the direction of the red arrow. This will rake the crack open.
Clean it out
Once the crack is wide enough, give it a quick sweep with a dustpan and brush (or just your fingers) to make sure there are no gritty bits hanging about.
Fill the crack
Grab your filler and filler knife. (See blog post on A basic toolkit, if you need help with this bit.)
Pick up a bit of filler on the end of your filler knife, and smear it across the crack. Make sure to go in the direction of the green arrows in the picture.
Your aim should be to squeeze the filler against the side of the crack and make sure it sticks nicely.
Then smear some filler across the crack in the opposite direction (yellow arrows in the picture).
Finally, you can run your filler knife along the crack and smooth if off a bit.
Filling holes
Clean it out
Give the hole a quick sweep with a dustpan and brush (or just your fingers) to make sure there are no gritty bits hanging about.
Squeeze some filler in there
Grab your filler and filler knife. (See blog post on A basic toolkit, if you need help with this bit.)
- Pick up a bit of filler on the end of the filler knife.
- If the hole is small (an old drill-hole or something like that), just smear some filler into it. Try to make sure you press it up against the sides of the hole from both directions.
- If the hole is a bit bigger, start in the centre and smear some filler out to the edge (yellow arrow in the photo).
- Work your way around the hole, filling it from the centre towards the edges.
It doesn’t have to be neat but try to make sure the hole is completely filled up to the surface.
Don't worry about how it looks
It doesn’t have to be neat but try to make sure the hole is completely filled up to the surface.
It’ll probably end up quite messy but don’t worry about it.
The picture isn’t too clear, but it’s supposed to show you what it might look like after the first strike.
Sand it down and do it all again
Wait until the filler has completely dried, then sand it down. I recommend 60- or 80-grit sandpaper. It’s important to use a sanding block for this bit to make sure that you get it properly flat. (See blog post on A basic toolkit, if you need help with this bit.) When sanding, go past the edges of the hole by a few centimetres, onto the good bit of wall either side.
After sanding, just add a nice smooth layer of filler on top. But this time, your aim should be to get it fairly smoothish and ensure that it’s filled completely.
Finally, give it another sand and it should be done. If not, fill and sand for a third time.
Some things to know
Nail pops
Plasterboard walls and ceilings are built by screwing or nailing large sheets of board onto a framework. The whole lot is then plastered over. Sometimes, a little piece of plaster can pop out just over the nail / screw head. To fix this, you need to do the screw up tighter (it should be a Philips head – see post on Types of screw) or push the nail in further (with a hammer and old screwdriver).
Then you can fill the hole.
Old Rawl plugs / wall plugs
If you just try to fill over the top of a Rawl plug in the wall, it will end up looking a mess. You’ll need to remove the plug before filling (see post on Removing old Rawl plugs).
Takeaways
- Do your checks to make sure the crack / hole is a simple one.
- Widen the crack to ensure there’s enough room to get a decent amount of filler in there.
- It’s normal to fill holes and cracks in two or three goes.
- Don’t forget to sand it down when you’ve finished.
