You can never just assume that a wall or household fitting is straight and true. Structures move over time, and both DIYers and tradespeople can make mistakes.
One thing you can trust is that gravity will always pull a suspended object towards the centre of the planet. There’s a cheap, simple, traditional tool that uses this natural law to establish a true vertical reference: a plumb bob and line. This type of tool has been used since antiquity, and it’s still popular in the present day.
Whether you buy a plumb bob and line from a hardware retailer, or make your own using household items, it should help you to establish exactly which way is up. This can ensure neat, straight edges in DIY projects, which makes using a plumb bob one of the most effective wallpaper hacks you can learn.
What is a plumb bob and line?
A plumb bob is a weighty object, typically made of metal and featuring a pointed tip. The line is simply a piece of string, cord or another flexible material which the plumb bob can dangle from. Together, they’re a highly effective tool for plotting a perfectly vertical reference line onto a wall.
When the end of the line is tied to a fixed point such as a nail or hook, the bob should dangle exactly vertically, as it is pulled towards earth’s centre of gravity. This holds the line taut, straight down the wall.
“A plumb bob and line is one of the oldest and most dependable tools in DIY and despite the growing popularity of laser levels, it’s still an excellent way to establish a true vertical reference line,” says Laura Nicholson, head of buying at B&Q.
“The tool relies on gravity rather than batteries and calibration, so it’s highly accurate when used correctly. It’s especially handy for everyday DIY jobs where a straight vertical guide is needed, from hanging wallpaper and aligning shelving to checking door frames, fitting wall panelling or making sure posts and stud walls are upright.
“It’s also particularly useful when tiling, helping to establish a true vertical starting line, especially as walls, corners and bathtubs aren’t always perfectly level or square,” she says.
An affordable, effective plumb bob and line:
I’ve used this B&Q plumb bob and line set, costing £5.49, in the photography throughout this article. Straightforward and highly effective, it is made up of a steel plumb bob and an 18m nylon line.
As Head of Buying at B&Q, Laura Nicholson has an encyclopedic knowledge of tools and DIY materials – from tiny plumb bobs to contractor-grade power tools. She has over 25 years of retail experience.
How to use a plumb bob and line
1. Tie the line to a fixed point
“Securely attach the line to a fixed point above the area you’re working on, and allow the weighted bob to hang freely,” says Laura Nicholson.
In most cases, you will need to install a small fixing into the wall in order to suspend the plumb bob. I drilled a hole and installed a small hook into a suitably sized Rawlplug.
Choose the place from which you hang your plumb bob carefully. If you’re tiling the wall or wallpapering it, then it would make sense to use the horizontal centre of the area being decorated, so that the reference line can line up with where your laying or papering pattern starts.
Do not allow the plumb bob to dangle down past a skirting board or similar obstacle, as this can disrupt its accuracy. “Make sure the line can hang freely without touching the wall or anything else,” Laura advises.
2. Be patient
A plumb bob will inevitably swing or spin for a while after you’ve hung it up. It will stop moving after a minute or two (unless there’s a disruption such as excessive airflow through the space).
“It’s important to wait until the bob has completely stopped moving before taking your measurements, because even the slightest swing can affect the accuracy,” says Laura Nicholson.
“Once completely still, the string will provide a true vertical line that you can use as a guide for marking, aligning or checking surfaces.”
3. Mark along the line
You’re now ready to make your perfectly vertical reference marks, but, "rather than measuring against the bob itself, mark alongside the string once it has settled,” says Laura Nicholson.
“If you’re marking a finished wall, applying a strip of masking tape first allows you to make pencil marks without marking the surface directly,” she suggests. This Status IONOS Masking Tape from Amazon is light in colour, making it easy to see any marks that you make.
Try not to knock the line while making your pencil marks, as this can cause the bob to start swinging or spinning again.
4. Align your project materials
Use a ruler or straight-edge tool to join up the pencil marks you’ve made using the plumb bob and line. Try this White Aluminium Cutting Ruler from Amazon to create a straight line between your pencil marks.
You can now use this pencil line as a reference point for your project. If applicable, place your materials (such as tiles or a section of wallpaper) along the line, and work outwards across the wall.
If your materials are perfectly square, then the accurate verticality should carry through across the laying pattern. However, you will often benefit from drawing multiple vertical references across the wall so that you can keep checking your pattern as you work, especially if you are decorating a wide area, as no material or DIYer is perfectly accurate.
FAQs
Can you make your own plumb bob and line?
Plumb bobs can be one of those makeshift tools that you cobble together at home from commonplace items (such as a washer and a piece of string), although it won’t cost you much to get a good, purpose-made plumb bob and line set from a DIY retailer.
For most people, the maximum length of line you could need will be the height of the highest-ceilinged room in your home (or the stairwell). Cut your line to suit and tie it securely to an object that is heavy enough to pull the line taut.
What does ‘plumb bob’ mean?
The term ‘plumb bob’ refers to the material that was historically used to make these tools: lead (which is called plumbum in Latin and also gives us the word ‘plumbing’). Plumb bobs are also sometimes called ‘plummets’.
The same type of tool and the same principles have been used in construction and decorating since antiquity.
What has replaced traditional plumb bob and lines?
The plumb bob and line hasn’t been replaced, but other, more modern measurement tools have been designed to do similar or slightly different tasks – in some contexts more effectively than a plumb bob and line.
“Modern laser levels such as the selection we have at B&Q are ideal for larger projects, but a plumb bob remains an affordable and dependable addition to your DIY toolkit,” says Laura Nicholson.
“Plumb bobs are simple to use and can provide excellent accuracy for everyday home improvement tasks, making them a reliable alternative when a laser level isn’t needed.”
Nowadays, you can also get relatively sophisticated plumb bobs, including models with pins and/or magnets that can be attached rapidly to walls or steels for quick, convenient measurement.
This premium plumb bob and line is quick and easy to use. It can attach into a wall using its retractable pin, or attract to steels via an in-built magnet.
What are the drawbacks to a plumb bob and line?
A plumb bob and line is by no means perfect. It can only show you a vertical line (unless used with a tape measure and multiple lines of reference), whereas a good laser level will provide both vertical and horizontal references.
Another downside to this tool that we’ve already touched upon is that a plumb bob and line can be rendered inaccurate by disruptions (such as breezes) or obstacles (such as skirting boards or dado rails).
Yair Meshoulam, founder of Wallpaper Hangers, avoids using a plumb bob and line, although he does find the tools interesting. “A spirit level is more accurate,” he says. “The longer it is, the more accurate it is, and the more truly straight the line will be. You don’t have to wait for it to stop swinging before you make your line, and you can draw your line along its straight edge, which is much easier.
“I do have a plumb bob and level from about 40 years ago, but I haven’t used it in years,” he adds. If you would prefer to use a spirit level in the way Yair describes, you will need one that has a plumb vial for vertical measurement.
Royal College of Art graduate, Yair Meshoulam, founded the specialist firm, Wallpaper Hangers in 1988. The company provides wallpaper hanging services in London and beyond, with clients including The Wolseley Restaurant in Piccadilly, Madame Jo Jo's in Soho, and the Yoga Centre in Muir Beach, San Francisco.
Small and cheap tools like plumb bob and line sets are sometimes overlooked, but they can make a dramatic difference to your DIY projects. For more toolbox inspiration, read our guides to tile spacers and masking tape vs painter’s tape.
