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How To Remove Mortar From Natural Stone [Clean Dry Cement]

Mortar is a necessary evil in stone patio construction, but that doesn’t mean you have to like it. Once your home is finished, the last thing you want is mortar residue all over your beautiful natural stone. This guide will show you how to remove mortar from natural stone easily.

Read on for tips on removing mortar from natural stones without damaging the surface! 

How Do you Remove Mortar From Natural Stone?

Removing mortar spills and how to remove cement from your natural stones is a DIY, especially if the contractors handling the patio construction don’t seem to mind leaving the splotches and streaks behind. The sight of the shoddy masonry work they leave behind can be heartbreaking, especially if they did a great job installing the stones.

Well, you don’t need to call them back; you can pick up a few tools and get the job done yourself. These tools include

  • Cement and lime film remover such as muriatic acid
  • Two buckets or a bucket with a garden hose or pressure washer
  • Stiff broom, scrubbing brush or long-handled masonry brush
  • Clean putty knife
  • Mop or damp floor cloth
  • Gloves
  • Mask
  • Safety glasses
  • Spray bottle

How To Remove Cement From Stone

This step-by-step process shows how to clean cement off stone.

 Step 1: Wet the Stones

Use a damp cloth, a mop or a garden hose to saturate the stones with water. Target the area with the dried mortar you want to remove, as pouring acid on dry stones can lead to yellow stains.

 Step 2: Muriatic Acid Dilution

It’s time to put on the gloves, mask and safety goggles. In a bucket, dissolve half a litre of muriatic acid, called hydrochloride acid as well, in five litres of water.

Always ensure you fill the bucket with plain water first, then pour the muriatic acid in to dilute it. Never attempt to make the solution the other way around. When you add acid into a bucket without water, you will cause a dangerous chemical reaction.

This short video shows how to use muriatic acid for cleaning patios

Step 3: Apply the Solution

Use a damp cloth or mop to apply the diluted solution to the wet surface carefully. Do not apply the acid solution to areas exceeding 10 to 15 square metres at any one time.

Additionally, allow the acid solution to dissolve the concrete or cement residue for a few minutes.  Note that bubbles on the water surface indicate that muriatic acid is working to dissolve concrete or mortar stains.

Step 4: Scrub the Stones

Pick up the hard bristle brush and scrub the dried mortar you had applied the acid solution. The goal here is to remove the cement spills. It requires working quickly to avoid having the acid sit on your natural stone for extended periods.

For hardened dolomitic cement stain, a clean putty knife works well. Carefully chip on the dried mortar with it. Remove dried cement and continue chipping and scrubbing to your satisfaction.

 Step 5: Rinse the Stones

Prepare another diluted solution; mix half a bucket with water with ammonia, half a litre. You can then use the mop to rinse the muriatic acid off the area where you applied it. The purpose of ammonia is to neutralise the acid and prevent it from reacting with natural stones.

Once done, fill your bucket with clean water and add soap. To ensure acid-free stones, pour the soapy water on them. This prevents more harm or a situation where the ammonia solution starts eating the stones.

If you’re using a garden hose, rinse the area with warm water as thoroughly and as quickly as possible, then use a mop to dry the area.   

Step 6: Clean the Remaining Area

Now that you understand what to do proceed with cleaning the rest of the area by repeating steps 1 to 5. If the stones still aren’t as clean as you’d hoped they would be, repeat the process until the stones get to the level you desire.  

This is also the same procedure of removing cement stains from sandstone slabs.

A Word of Caution

Do not attempt to clean wet mortar as you may end up causing further problems, which can end up negating all your efforts. The acid will start eating into the wet mortar, further affecting the underlying structure of the stone paving. Instead, let the mortar dry first.

When removing cement stains from sandstone, an easy solution is to clean them as soon as the mortar dries. The longer the mortar stain remains, the more difficult it becomes to get rid of it.

Don’t let the muriatic acid solution sit for too long, as it may end up affecting the natural stone. Observe the cement you want to keep for indications on how far the acidic action has reached to stop it from deteriorating.

Never attempt to use brick acid or other cleaners with high concentrations of hydrochloric acid since they are extremely harsh and corrosive. The brick acid is capable of chemically reacting with some natural stones.

This is particularly true if you attempt to use the brick acid or cleaning solution on stones such as granite, limestone, sandstone or slate. The brick acid first erodes the surface; then, it will draw iron deposits from within them. It makes the natural stone develop rust stains.

FAQ’s

Can I use vinegar to clean mortar off bricks?

Yes, it is possible to use vinegar to clean mortar off bricks, but you will require an alkaline solution such as dilute ammonia to neutralise the acid in the vinegar. Neutralising stops the acid from corroding the bricks. Always pour water to rinse the bricks after applying the diluted vinegar solution.

You can also mix 1 part of white vinegar with 4 or 5 parts of water, depending on the mortar you want to clean off the brick surface. Wet them using this solution and allow them to soak for five minutes. Use a stiff brush to scrub off the mortar.

Can you use baking soda on natural stone?

Yes, you can use it to remove stains on natural stone, but you must reduce its strength. As a general rule, only a weak solution is advisable. This is because baking soda is a strong alkali, and some formulations can make it almost as strong as ammonia. The result is a caustic solution that may easily mess with your natural stone.

A mixture of vinegar and baking soda is more effective. Even so, you need to rinse the surface well with clean water several minutes after application to avoid discolouration and porous stone surfaces.

Can you use OxiClean on natural stone?

OxiClean can be used as a sandstone stain remover; however, first, test it on a small area. This allows you to see whether it will react with your stones. Some natural substrates of marble, quartz and other natural stones react with OxiClean.

OxiClean contains two chemicals which, produce hydrogen peroxide when they react. The resulting product is a well-known cleaning agent that can also react with certain types of stone.

Last Word

Natural stone is a beautiful choice for homeowners, but it does have its drawbacks. One of the biggest challenges of natural stone surfaces is stains and discolourations caused by mortar or grout used during installation.

Fortunately, you can take simple steps to remove these unwanted marks from your sandstone or limestone surface, using a cement remover acid such as phosphoric acid, trisodium phosphate, and even vinegar.

Now you know how to remove cement stains from sandstone slabs or natural paving; they’ll look just as good as the brochure pictures.