How to clean mortar from brick, stone, and patios
One of the jobs that I like to do is repointing brickwork but it is not a job I do often so that I can get it perfect every time and there are always a few mortar stains left behind. But repointing is one of those jobs that need to have a good finish to look right.
Cleaning off the brick or stone after laying bricks or repointing can help clean up any unsightly mortar stains caused by slips or overuse when applying the new mortar.
Here are a few tips I have found for cleaning the old mortar from brick, stone, and patios:
Give yourself space to work, remove large lumps of mortar with a hammer and chisel, use a wire brush on harder mortar stains, and wash off with water. For really stubborn mortar stains use diluted Phosphoric or Muriatic Acid, apply with an old brush leave for a few minutes and then wash off with clean water.
Following these simple steps will clean off most mortar stains, for all my tips and the tools you need to get a really professional finish keep reading the post below.
Prepare your work space
Prepare the area you are going to work in, clear some space to allow easy movement with as few restrictions as possible, if you are going to work at height on ladders or scaffolding make sure you can access it easily and the ground is firm and level.
Make sure you follow best practices to work safely and whenever possible always work with someone else to avoid working alone.
Cover the ground below where you are working with a drop cloth or plastic sheeting, this makes clearing up much quicker as you can catch any falling mortar and prevent any accidental spills from damaging the ground.
If you are working near cars or expensive furniture move them to a safe distance so they are not likely to be covered in dust or flying debris.
Check and set out your tools, here’s a list of the tools I typically use for cleaning mortar from brick:
- A small club or lump hammer
- A cold chisel or bolster
- Wire brush
- Cordless drill
- Wire wheel
- Builders bucket
- Stiff bristle hand brush
- Hosepipe connected to the cold water tap
- Dropcloth or plastic sheet
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The hammer and cold chisel are used to knock off any large lumps of mortar, and the rest of the tools help to remove the more stubborn mortar stains.
Cleaning off the larger lumps of mortar
Now that your workspace is prepared it is time to prepare yourself by wearing the appropriate safety equipment. As a minimum, I away put on a pair of safety goggles, a good quality dust mask, and wear work gloves
Using the lump hammer and cold chisel check for any large lumps of mortar and carefully remove them.
Hold the cold chisel at a shallow angle against the brick or mortar and tap it with the lump hammer, you can adjust the angle until the chisel bites into the mortar but does not cut into the brick or stone.
Always try to work towards the center of the brick or stone, rather than towards the edges, this will help avoid chipping the edges of the brick which can potentially leave you with a bigger mess that will need repairing.
I recommend doing this part by hand, it may take longer than if you used a power tool like an SDS drill for example but it means you will be much less likely to damage, chip, or break a brick or stone.
Brushing away small mortar stains
Once the large bits of mortar have been cleaned away with a hammer and chisel, assess the surface to look for local staining which is often left behind after repointing or mortar repairs.
The first step is to wash down the brick with clean water, Use a hose to lightly spray the area and wet it down, this helps to reduce dust.
Using a wire brush, rub the mortar stained area, working in different directions to make sure the bristles get into all the crevices, you can use a cordless power drill with either a wire brush or abrasive wheel fitted for larger stains,
Running the drill at high speeds to brush off the staining works really well, you can find out how fast the market-leading cordless drills are in our recent post:
Make sure you wear an appropriate dust mask as brick and stone dust contains silica which can be harmful to your lungs.
Occasionally spray the area with clean water to wash away any dust or debris, this helps you see how much mortar you have removed.
Repeat the brushing until you have removed as much of the mortar stain as possible.
For Stubborn Mortar stains use Phosphoric and Muriatic Acid
For really stubborn mortar stains, using chemicals to clean the area may be the only way to refurbish your brickwork, but these should really only be used as a last resort.
One of the most popular chemicals for cleaning brick and stone is Phosphoric Acid, this liquid is also commonly used to clean grout from tiles as well as mortar stains from brick and stone.
Phosphoric acid is a relatively weak colorless and odorless liquid with the chemical formula (H₃ PO₄)
When using any chemicals make sure you are wearing the appropriate safety clothing, acid-resistant gloves, goggles, and a respirator or face mask, keep your arms and legs covered by wearing long sleeves and trousers rather than shorts.
Always test a small area of brick or stone before you apply any chemicals to a surface and the same rule should be followed when cleaning mortar from brick masonry, stone walls, or patios.
To test the acid and make sure it won’t cause any unwanted damage, dampen a small area of brickwork to work on with clean water, then using an old brush carefully apply the acid and leave for a few minutes before washing it off with more clean water.
If the mortar is cleaned away without any other problems then you should be able to brush the formula over the whole area and clean the wall or surface.
Always work in small sections about 3 ft/Sq (1mSq) this prevents the acid from drying out on the brick, which can then weaken the mortar and means you can keep watching for other unwanted effects.
Before using acid on walls or patios, wash down the brickwork or stone with clean water, this helps to prevent high concentrations of acid from attacking the brick or stone. I find using a hose with a spray nozzle works well to cover large and small areas.
Brush the area over with a stiff hand brush, to prevent splashes wear a face mask or visor over the top of your goggles and dust mask.
What is Muriatic or Hydrochloric Acid?
The most effective chemical for cleaning really stubborn mortar stains from brickwork is Muriatic acid also known as Hydrochloric acid.
This chemical is a solution of hydrogen chloride and water, the liquid is colorless but has a pungent acidic odor and has the chemical formula (HCI), and is very similar to the components of gastric acid found in the stomach.
Muriatic acid is available in diluted form for household use and is often called Brick, cement, or patio cleaner.
This type of acid is very reactive, it will attack most substances including skin and must be used with caution, work in a well-ventilated area, and always read the label and follow the manufacturer’s guidelines.
How to dilute the Muriatic Acid
To clean mortar or cement stains from brickwork always dilute Muriatic acid by mixing it with clean water, never mix acid with anything other than water, otherwise, you can create unwanted and potentially violent chemical reactions.
Always pour the water into the container first and then add the acid second, never pour acid into an empty container as this can cause splashing.
Always wear appropriate protective equipment such as acid-resistant gloves, safety goggles, respirator, and long sleeve clothes, before you handle mix muriatic acid,
Using a suitable plastic container carefully mix the Muriatic acid with water, for most mortar stains a ratio of 1 part acid to 5 parts water will work well but for really tough or old mortar try using 1 part acid to 2 parts water by equal volume.
How to test a small area first
Before applying the Muriatic acid cleaning mixture to your brick or stone, try testing it first on a small area that won’t be too obvious.
Use an old paintbrush and gently brush the acid onto the stained brickwork, leave it for a few minutes. The acid will dissolve the cement and there should be some fizzing as the acid reacts to the mortar.
After a few minutes, I would recommend leaving the Muriatic acid on the brickwork for no more than five minutes the first time, wash off the area with lots of clean water, this way you can make sure the acid will not cause any unwanted damage.
Brush over the mortar stained area
Once you are happy the acidic mixture is not going to cause any issues, gently apply it to the stained area with an old paintbrush and work it into the mortar.
I tend to work in manageable areas of no more than 3 ft/Sq (1mSq) this means that the acid won’t dry out and can be washed off before it eats into the brick or stone.
I find this size of area good to work on because you can work quickly across it and keep an eye out for any issues and deal with them quickly and they won’t be too big to sort out.
Leave the acidic mixture to work on the mortar stain for a few minutes keeping an eye on the area, it may fizz as the acid dissolves the cement stain.
After no more than five minutes rinse the area with clean water, you can reapply the acid as needed until the mortar stain has been removed.
Once the mortar stains are gone and you are happy with the refurbished and cleaned brickwork, give it another rinse off with clean water.
If you have been using stronger Muraitic mixtures then washing the surface with a neutralizing solution is a good idea.
A simple and effective neutralizing liquid can be made from one cup of household ammonia mixed with 1 gallon of water and then give the brickwork a final rinse with clean water.
How to dispose of Muriatic Acid
Muriatic or Hydrochloric acid needs to be disposed of properly and responsibly, any unused mixture should be placed into a plastic or glass container that can be fully sealed and then safely taken to your local recycling centre, check your local authorities website for your nearest centre.
You can also neutralize the acid by mixing it with an alkali substance such as lime, add 3 or 4 cups full of lime into a large bucket, at least 5 gallons, and then fill the bucket with a gallon of clean water.
Mix the lime and water together using an old piece of wood. Then slowly pour in the acidic mixture, the lime and acid will react to each other, so keep your face away from the bucket and make sure you are wearing a respirator.
Once the fizzing chemical reactions have stopped the mixture should be neutralized and can be poured away, however, I would still recommend you take this to your local recycling centre.
Clean up and admire your work
Once you have properly disposed of the chemicals, clear away any leftover dust and lumps of mortar, and clean off any tools. Wash out any brushes, they can then be put safely away ready for the next DIY project.
Now you can admire your clean refurbished wall or patio and plan the next DIY job on your list, for inspiration on what to tackle next why not read about easy DIY jobs you can do in our posts:
This article was written by: Richard Quinton – The DIY Help Desk Owner, Engineer & technical specialist.
Richard is one of the key partners in The DIY Help Desk team. He is a qualified Engineer, writer, and publisher, educated to Master’s level. He is a keen advocate of DIY and home improvements.
Richard enjoys helping others to learn new skills and reach their goals and believes that passing his knowledge and experience on through his writing is an effective way to positively impact the lifestyles and well-being of others on a larger scale.