How To Clean Mortar Off Concrete Blocks

If you have ever built a garden wall or an outdoor fireplace, you will know that mortar splatters during construction are something you can’t avoid. For those who aren’t aware of the meaning of mortar, we can explain it to you in simple terms. Mortar is a building material composed of cement and sand. It’s used in masonry work to bind together building blocks, bricks and stones, fill the grout, seal the gaps between them first or add decorative colour or patterns to brick walls

Building a wall with concrete blocks and mortar

Cleaning the mortar off bricks and blocks is something you need to do while installing brickwork. However, if you don’t do it right away and the mortar has dried, there are a couple of ways to remove it. Ready to find out how to clean mortar off concrete blocks? 

How to clean mortar off concrete blocks

Mortar is a necessary building material. Whether you want to build a brick BBQ or garden steps, mortar is what will bind together the blocks, stones or bricks. And in the end, you’ll have to clean off your work. There are two ways to clean mortar off the blocks, either using chemicals or not. We are about to share with you details for both ways.


Preparation is a necessary part of this cleaning process to have the desired results. Here are the materials you are going to need and the steps to follow.

Needed materials:

  • A trowel
  • A medium-soft bristle brush
  • Plastic sheeting
  • Scaffolding
  • A bucket
  • A sponge
  • A light bristle brush
  • Rags

Steps to follow:

1. Even the mortar

Prior to everything, you need first to even out the mortar with the face of the block, using forward lifting and rolling motion with the short edge of the trowel. In case you don’t have a trowel, you can do the same with a sponge.

2. Scrub the blocks

Get the medium-soft bristle brush and rub off any mortar dust left on the block, using back and forth motion. Keep wiping until all the dust is being removed from the face of the blocks.

Cleaning a floor with a brush

3. Install the scaffold

Now, it’s time to set up a scaffold to prevent mortar splatter. Set it up about 5cm from the wall. The closest to the wall scaffold boards should be angled away and down from the wall.

4. Lay plastic sheet

Lay on the base of the wall, plastic sheet. Instead, you can lay straw or fabric drop cloths. You should do this to prevent mortar from staining the base of your wall. Lay these protective sheets about 90 cm from the wall. They will also protect your landscaping and vegetation, especially if you’re planning to use acid. 

5. Let the mortar dry

Before you begin cleaning up the mortar from your block wall, you should let it dry. Then you can choose to remove it either with an edge tool or the acid method.

Cleaning dried mortar with a chisel and a hammer

If you don’t want to use any chemicals, you can try to clean mortar residue with two tools that you probably have at home, especially if you like DIY projects. Chisel and hammer are the two main tools that will help you remove them from your blocks.

Cleaning mortar off concrete blocks with a chisel and hammer

Needed materials:

Steps to follow:

1. Wet the blocks

The mortar should have stayed at least seven days to dry completely before you begin the DIY clean up. Using a hose, wet the blocks with water (trying not to jet directly onto the mortar joints). It will be much easier to remove mortar residue with your edge tool, plus it will protect your blocks from being damaged. If you don’t have a hose, you can just use buckets filled with water.

2. Chiselling

Hold the tool at 20 to 30 degrees angle over the area where there’s mortar build-up. Start tapping the tool over the wall to break up as mortar as possible. You better start the process from the top and move to the bottom. Use a hammer to tap on the edge tool and keep tapping until you remove most of the mortar.  

3. Wipe with the brush

Once you have removed the largest pieces of smears, grab your brush and move it in a back and forth motion to wipe the blocks and remove mortar dust. If there are any mortar pieces on the wall you couldn’t remove with the scraper, you can try to do it with the scrub brush. Apply heavy pressure while brushing until you clean bricks or blocks completely.

Cleaning dried mortar with a muriatic acid solution

Muriatic acid is a colourless solution also known as spirits of salt or acidum salis. It’s usually used for household cleaning, building construction and many commercial and industrial uses. You can get it from hardware stores, home centres, building supply stores and online. You need to dilute it before use and take precautions as it is a strong acid.

A concrete block wall

Needed materials:

  • Muriatic acid
  • Stiff-bristled plastic brush
  • Plastic bucket
  • Acid-resistant brush
  • A garden hose
  • Safety goggles
  • A respirator
  • Acid-resistant long rubber gloves

Steps to follow:

1. Wet the blocks

Prior to cleaning the mortar off blocks, you need to wet any block that might come in contact with the acid solution. If you don’t follow this step, you run a risk of damaging the blocks. Acid on dry bricks, stones and blocks ruin their colour. They will get a yellowish-green hue.

2. Dilute acid with water

It’s time now to put on your goggles and rubber gloves as you are about to deal with acid. Get a  bucket and fill it with 4.5l of clean water. Next, really carefully, pour a cup of muriatic acid into the water. Or else nine parts water to one part acid. Read the instructions carefully to know exactly how to dilute acid.

Never do it vice versa. If you pour water into acid, it creates a chemical reaction, causing the solutions to bubble and splash out of the bucket. What’s more, use a plastic bucket instead of a metal one, as the acid will eat metal.

NOTE: Instead of muriatic acid, you can use hydrochloric acid. However, it’s more dangerous to handle. Hence you need to wear protective equipment and test it first in a small area before applying it to the blocks.

3. Apply the solution

Using the acid-resistant brush, apply a layer of the solution onto a small portion of the concrete wall. Let the solution soak into the mortar for 5 minutes. To be sure that acid is working and reacts with the cement, it will start to fizz and bubble. Don’t let the solution dry on the blocks. It will damage them. 

4. Scrub the mortar

Then, start scrubbing the mortar with the stiff-bristled brush. Don’t scrub tho joints because you will weaken the mortar that holds the blocks. Keep scrubbing until you remove all the dried mortar.

5. Rinse the solution

Once you have removed all the dried mortar from the blocks, you have to rinse them. With the garden hose, rinse the blocks very well. As we’ve already mentioned, if acid dries on the blocks, it will weaken the mortar. 

IMPORTANT: If acid splashes onto your skin can cause chemical burns. That’s why you need to act quickly. Keep a box of baking soda near you while handing acid and pour it onto yourself if an accident occurs. Baking soda will neutralise the acid.

A concrete block with a trowel and cement mortat

Cleaning the mortar is an easy process. You just need to take precautionary measures, especially if you are using acid. Follow our step-by-step guide and clean your blocks off mortar. Repeat the above steps until you get a clean wall. 


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