Exposed Aggregate Concrete Sealer | Indoor & Outdoor – FAQ Video by CoverTec Products

The answer is yes. You can seal exposed aggregate, and it’s highly recommended.

Exposed aggregate concrete is a decorative way of finishing concrete. Instead of having just a plain look, you expose the top layer of the aggregate, and it gives the concrete a nice, rugged look. Depending on the aggregate you have, it gives the concrete different colors, and jazzes it up a bit if you like. 

It’s a nice way to finish exterior concrete, but you definitely need to seal it because concrete itself is very porous. And you need to stop chemicals, salt, mold and mildew, and moisture from getting into the concrete.

You obviously don’t want it stained, and sealing it will:

• Protect the exposed aggregate
• Give it much longer life
• Stop what we call pop-outs
• Enhance the concrete and the aggregate, and
• Give it more color, more of a wet look.  

Well, remembering that exposed aggregate concrete is naturally porous, if you don’t seal it, you’re leaving the surface open to contamination, and possible staining.

You have the potential for ingress of:

• Salt
• Moisture
• De-icing salts, or
• Chlorides from the atmosphere (if you’re around the coast).

And that moisture, if it gets into the concrete while you’re in a cold climate, you can experience “freeze-thaw,” where the water gets into the pores and expands and contracts.

This usually leads to break down of the concrete. You’ll notice cracking in the surface. It can weaken the surface and the binder that is holding the exposed aggregate together.

The resulting effect on the concrete with multiple holes in it is what’s called “pop out.” The aggregate itself will pop out of the top surface.

So, if you don’t seal it, you’re risking damage from:

• Freeze-thaw
• Chemical attack, as well as
• Unsightly things like mold and mildew.

It also makes the surface much more difficult to maintain and clean if you don’t seal the concrete.

Well, the first point is that you need to seal that concrete.

The concrete itself is naturally very porous and absorbent. So, we need to seal off the concrete to stop water and moisture from entering into the concrete, causing things like freeze-thaw, damage or cracking.

You also need to protect against staining from fluids like motor oil, brake fluid, hydraulic fluid etc. which happens to concrete driveways for example. So, it’s very important to seal. And by doing that, it’s going to make it much easier to maintain.

You should be able to use things like pressure washing. Now, you shouldn’t use heavy duty pressure washing. Just a light pressure wash to remove soils and dirt that are just sitting on the surface and are much easier to remove.

You don’t need to use harsh chemicals. It’s not necessary to use strong acids, strong alkalines, or degreasers, etc. You should dilute those products. Generally, a mildly alkaline cleaner is fine to use on a sealed exposed aggregate surface.

A good sealer should last two to three years. So, after that time it may not be necessary to pressure wash if the sealer itself is just dull and faded.

If you use a compatible sealer you should be able to re-seal without removing the existing sealer. So, plan to re-seal your surface about every two to three years, if you’re using a water-based sealer.

Use something like a urethane sealer, which is a much tougher sealer than an acrylic product. It should give you two to three years of protective seal on your surface.

• Much more environmentally friendly, 
• Less moisture sensitive and generally longer lasting. 

Professionals typically use sealers that are not moisture sensitive.

They prefer products that can be applied to concrete, without having to worry about it blushing or turning “water white” in the presence of moisture. And that’s usually something that has a high polymer content.

Off-the-shelf, big-box sealers are typically lower cost. The way you lower the cost of a sealer is to put less polymer or resin. Doing this will directly affect the long-term performance of that sealer. It will also result in a softer type of resin that will absorb moisture, and lead to blushing and “water white”.

So, make sure you’re using a high polymer content, hard-wearing acrylic or polyurethane sealer.

Professionals like polyurethanes because they’re much more durable. They’re a two-part product that you mix together. And even though they’re a bit more tricky to apply, they provide much better performance.

They are available in a water-based formulation. Something like our StrongSeal WetLook. And they can be applied after mixing using a pump-up sprayer or a roller. And two-part water-based products really bring out the colors of the aggregate and enhance the concrete, but still provide something that’s not moisture sensitive.

In some cases, with the StrongSeal Plus or the StrongSeal WetLook, you can apply soon after you’ve pressure washed the surface. This is a real advantage to a pro, because after they have cleaned and prepared the surface, they don’t have to wait 24 hours before applying the water-based sealer.

First you need to make sure that the concrete is absorbent.

That means that there’s nothing on the surface – like retarding agents or curing agents – that may prevent the sealer from adhering or absorbing into the concrete.

Often, when producing exposed aggregate, retarding agents are used. They make it easier to brush off, or sponge off the top layer of the concrete to expose the aggregate. That’s how it’s done professionally.

You also need to wait at least 28 days before you seal it. You need to make sure the concrete is fully hardened. The moisture is out of the concrete as much as possible. And if there are any cracks, you need to fix them before you seal the concrete.

Next, you need to make sure it’s clean. When you’re sealing it, you don’t want to seal in any efflorescence or stains that may be there. So, make sure you clean those off prior to sealing.

If you follow those key steps, you should be in a good position to seal your concrete.

• Make sure it’s absorbent.
• No barrier exists.
• Make sure any contaminants have been cleaned off the top.
• Make sure you’ve waited at least 28 days before you seal. 

We recommend you use something that has good polymer content, otherwise you’ll only get good performance for maybe one to two years before you have to re-apply the sealer.

All sealers get worn down. Reasons include:

• Exposure to weather.
• Repeated cleanings over time.
• Peeling and delaminating due to UV exposure.
• Moisture absorption and softening.

This is why the polymer content in a sealer is very important.

We prefer or recommend that you use water-based sealers. They’re much less sensitive to moisture, particularly during application, and they’re much safer and environmentally friendly.

You don’t have to worry about flammability. You don’t have to worry about pollution and fumes. They’re also safer to use around pets and around your lawn or grass areas.

A good quality penetrating sealer can last up to five years. Remember that this type of sealer gets into the concrete, rather than staying on the surface. So, there’s nothing to lift or peel.

Using a good quality topical sealer, something like the strong seal wet look, you’ll typically get three years of strong protection. Then, you should reapply another one or two coats, to revive that enhancement and color. 

If you’re using a topical sealant to enhance the exposed aggregate and bring out the color, it’s important not to apply the sealant too thick.

A pump-up sprayer is what we recommend to put a thin layer of sealer on the concrete. Then, you let it dry, and apply another layer. Typically two light, or thin coats, are better than applying one heavy coat. It’s a good practice to let the exposed aggregate be able to breathe.

Roller application is also another way of applying the product. But remember, the surface is a rugged, rough textured surface. So, make sure that the sealer itself doesn’t pond or puddle, because when it dries, it can leave behind foaming effect, or a whitish layer on your concrete.

Additionally, if you’re going to use a roller, be very careful about applying it too heavy. Professionals usually have a soft broom or brush handy to move away any sealer that’s puddled in an area.

When applying penetrating sealers, the objective is to get a good amount of the product into the exposed aggregate. So, you typically apply that in a heavier application, with the hopes of it to soaking in within 10 to 15 minutes.

If you notice that the penetrating sealer hasn’t soaked in thoroughly, you should brush or broom the excess away into another area.

If the penetrating sealer soaks in very quickly (within five minutes or so), you may need to apply a second coat, to the point where the concrete appears to reject the sealer.
You need to see the sealer refuse to soak in any further after about 10 minutes.

Well, if you have sealed the exposed aggregate concrete, that should make it much easier to clean.

It should be rejecting and repelling any contaminants from getting into the concrete. And dirt and debris should not stick easily to the concrete now.

Pressure washing at low intensity can work well to wash away any dirt or contaminants. Scrubbing or agitating with a soft brush is all you need to do. It’s not necessary to have harsh chemicals.

You shouldn’t be dealing with any dirt or staining. So, using mildly alkaline cleaners, like our SurfaceClean, is a good idea.

You can also use microbial cleaners like CoverClean AE, or CoverClean HC if you’re dealing with petroleum-based oils.
For example, if you’re on a driveway or a parking deck, and you want to clean off oil and brake fluid.

Again, don’t use:

• Harsh chemicals
• Acidic chemicals
• Anything highly abrasive.

This way, you don’t damage the sealer or the concrete itself.

If you use a good sealer, you can prevent a lot of cracking and patchiness, or what we call “pop out,” when the aggregate itself pops out of the concrete.

It’s also going to seal out the water and the moisture from getting into the concrete. It will stop what’s called “freeze-thaw” attack. It also stops the concrete dusting. And again, it will harden the concrete around the aggregate, so that it doesn’t pop out of the surface.

But if you are faced with any of these issues, then you can repair.

You can use adhesives like concrete mender. These are clear concrete repair products that you place into the concrete. And then you replace the exposed aggregate gravel, or pea gravel, and that adhesive will lock it in place.

You can also use surface repair products that are cementitious based.
Then you replace some aggregate, and brush or cleanse off the surface to create the desired effect.

So, using concrete menders to fix cracks and spalls in an exposed aggregate concrete is a little bit more of an art than a science.

But remember that prevention is better than cure. So, sealing the surface with a good quality, long-lasting sealer will prevent those problems in the first place.

Sealing the concrete should make it much easier to keep it clean.

But, you need to be careful that you don’t damage the sealer when pressure washing exposed aggregate.

We recommend against using a pressure washer equipped with a pencil tip.
Instead, use what we call a fan tip, about 12 to 18 inches away from the surface, to wash off the contaminants.

This way, you’re pushing off the contaminants, rather than cutting into the surface.

Join us again for another FAQ video from CoverTec Products.

About Our Expert | Charles Idowu

Charles Idowu started his career as a civil engineer in 1983 in the UK. After achieving his MBA and his Chartered Engineer qualifications, Charles quickly became the waterproofing and coatings expert for a renowned British construction company. His international work landed him in South Florida, where he combined his engineering experience and passion for business to start CoverTec Products.

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