In the construction industry, whether it be residential, commercial, or industrial, concrete plays one of the most crucial roles in the completion of a project.
Its strong and durable qualities, as well as its versatility, make it the perfect construction material. However, when it comes to pouring concrete, there is one issue in particular that can cause problems: air bubbles, also known as surface voids.
Surface voids appear like air bubbles and pinholes, and they can be a real headache for concrete construction professionals.
Not only do they have an unsightly and unfavorable effect on the surface’s aesthetic, but they can also lead to a reduction in the concrete strength, or even its complete failure.
Causes of Air Bubbles or Surface Voids
Concrete surfaces can be easily damaged if not taken care of properly. Unevenness and voids are some of the most common issues that occur when there is a lack of attention to detail during the installation process.
There are five most frequent reasons why surface voids arise in concrete:
Entrapped Air
Entrapped air is usually the cause of surface voids in concrete, as a result of poor handling or compaction during installation.
Improperly mixed concrete and weak forms can also contribute to entrapped air bubbles. When concrete is poured, the water and cement portions of the mixture begin to bond, creating bubbles that get trapped within.
This process is referred to as hydration and it’s normal for there to be some air pockets created as a result. The problem arises when too much air gets trapped, causing large holes at the surface level.
Improper Curing
Another common cause of voids on concrete surfaces is improper curing. For concrete to set properly and achieve its full strength potential, curing must take place over an extended period of time—typically 28 days or more.
Without proper curing methods in place such as damp-curing or ponding, the moisture content within the concrete will not be sufficient enough for it to properly set and fully harden.
As a result, surface voids may form due to structural weakness caused by running short on water content during this process.
Excessive Water in the Concrete Mix
When the mix contains too much water, it creates a weak surface layer.
This layer is often filled with air bubbles that can cause voids when left unattended. The excess water also affects the chemical and physical properties of the concrete, leading to inadequate strength and durability.
To prevent this issue, builders should always use the right amount of water in the concrete mix as advised by their suppliers.
Improper Compaction and Vibration
Another common cause of air bubbles or surface voids is improper compaction and vibration.
The compaction process helps fill any voids in the concrete mixture before it cures, ensuring an even surface without any lumps or bumps. However, if this process is not done correctly or if there isn’t enough vibration applied to the area, then some voids may remain which could later lead to surface imperfections like cracks or hollow spots.
As such, builders should make sure that they are properly preparing their surfaces before pouring any concrete.
Improper Application of Release Agents
Release agents are materials that are used to prevent concrete from sticking to the formwork and molds during the casting process.
It’s important to use the right type of release agent for the material being cast, as incorrect application or choice of product may cause surface voids to arise.
If too much release agent is used, bubbles may form on the surface as the air gets trapped in between the coating and concrete mix, leading to an uneven final product.
How to Repair Air Bubbles on Set Concrete
The sight of air bubbles on newly set concrete can be disheartening, but fortunately, these blemishes don’t always mean the concrete needs to be replaced.
We often see tips on how to avoid air bubbles, but not too much is being discussed on how to fix it once the concrete has hardened.
Gather Your Supplies
First and foremost, prepare the area and gather everything you need before getting started. For this, you’ll need a measuring cup, a bucket to mix the concrete with, repair mortar, and repair colorant.
Prep the Surface (Spray Water)
Once you have everything ready, start prepping the surface. Start by lightly spraying water on the affected area to make sure that it’s damp.
This will help your mortar bond better and form a strong seal. Depending on the size of the area and the number of bubbles, you may need to use a sponge or brush to spread the water evenly across all surfaces.
Personally, I’d like to get a garden hose and spray it over the entire area where the bubbles are visible. This makes sure that I’m not missing any spots and that the area is uniformly damp for easy repair.
Mix Cement and Water in a Bucket
Next, you’ll need to mix your cement and water in a bucket. Start off by measuring out the amount of cement you need according to your project’s specifications. Then, add enough clean water to make a paste-like consistency.
Mix everything until it’s thoroughly blended and has an even, smooth texture. Make sure not to add too much water, as this will weaken the mortar’s strength when it hardens.
Add Cement Coloring
Before adding the mortar mix to the surface that needs repair, add a few drops of cement coloring to your bucket. This will make sure the patched area matches the rest of the concrete’s color.
Spread the Mix and Fill the Holes
Using a trowel, spread the mix over the area that needs repair. Make sure to go slow and fill in any gaps and holes. Use a damp sponge to smooth out the surface and make sure there are no air pockets or ridges.
Go an extra step and use a cement sealer to ensure the patching job is long-lasting and durable.
This will keep the patch from cracking due to the expansive pressure of freezing/thawing cycles or other environmental factors.
Tips on How to Prevent Air Bubbles on Your Concrete Surface
Air bubbles on a concrete surface can be an eyesore and affect the aesthetic of a concrete structure. While there are added steps to take if you’ve experienced this issue, there are many ways to prevent it from happening in the first place.
Here are some tips on how to prevent air bubbles when pouring concrete:
- Ensure that the concrete mix is properly prepared. Start by measuring out your dry mix precisely, and make sure that all ingredients such as cement, sand, and water are evenly blended together. If you have to, increase the time you spend when mixing together the ingredients.
- Use a vibrator or trowel to release any trapped air and ensure that all the mixed components are evenly distributed throughout.
- Make sure that you use the right amount of water in your mix. Too much will make it too runny, while not enough may cause dry spots as well as air bubbles.
- Consider using aggregates such as gravel or pebbles to reduce the chances of air pockets forming in your cement mix.
How to Fix Air Bubble in Concrete: Final Thoughts
Ideally, what we want is to prevent air bubbles or surface voids from occurring in the first place.
This means ensuring the correct ratios and cement and water are used, as well as making sure that all concrete mixes are carefully and properly mixed together.
In the event you’ve noticed that air bubbles have started to form, the steps outlined above should help you fix any air bubbles in concrete.
All you need is the right materials such as cement, mortar, and repair colorant, as well as a bucket to mix the concrete with.
