Exposed Aggregate Driveway Thickness: Why is 6" Better Than 4"? -

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What Should Exposed Aggregate Driveway Thickness Be?

The Exposed Aggregate Driveway Thickness should be 6”, so that you can reinforce it with steel rebars, incorporate aggregates sized ⅜” – ¾” and be able to remove a bit of the top cement layer to expose the aggregates.

The slab thickness is an important exposed aggregate concrete specification, affecting the load bearing capacity of a driveway. Residential concrete driveways are usually 4” thick. This thickness is adequate to bear the load of standard passenger cars and pickup trucks.

The cost of installing an exposed aggregate concrete driveway is 2 to 3 times higher than a standard concrete driveway. A sizable portion of the cost can be attributed to the hiring of professionals to do the installation.

Exposed Aggregate Driveway Thickness: 6” vs 4”

Since you have already committed to spending a much higher amount, you should not cut corners on the specifications and materials. Exposed Aggregate Driveway Thickness of 6” will give you the following advantages over a driveway that is only 4” thick:

Exposed Aggregate Driveway Thickness of 6” lets you use steel rebars as reinforcement. The driveway will not only have higher compressive strength due to the extra thickness, it will also have higher tensile strength due to the steel rebar reinforcement.

Your driveway will be strong enough to bear the load of heavier vehicles such as RVs, motorhomes, garbage trucks, etc.
The thicker driveway will be a lot more durable. If built on a strong base, it will last for even 50 years, with regular maintenance.
Exposed Aggregate Driveway Thickness of 6” lets you incorporate stones sized ⅜” – ¾” for exposure quite easily.

A concrete slab with a nominal thickness of 4” is actually only around 3 ½” thick. On the other hand, a concrete slab with a nominal thickness of 6” is around 5 ½” thick in reality.
The removal of the top layer of the concrete slab, say a ¼” will bring down the real thickness of a 4” thick slab to 3 ¼” and that of a 6” thick slab to 5 ¼”. A 6” thick slab is 50% thicker than a 4” thick when we consider the nominal thickness but almost 62% thicker when we consider the residual thickness.

NOTE: A 6” thick concrete slab is typically more than twice as strong as a 4” thick slab but costs only 50% more.

How To Pour and Finish an Exposed Aggregate Concrete Driveway?

There are 2 popular ways you can pour and finish an exposed aggregate concrete driveway.

Adding the Stone Aggregates to the Concrete Mix

The process of adding all the stone aggregates to the concrete mix saves a ton of labor as the batching is done by the concrete ready mix producer. Professionals use this technique when installing large driveways.

Use 2X6s for the forms so that you get an Exposed Aggregate Driveway Thickness of 6” (nominal). Pour the concrete to the top of the forms. Screed the concrete, bull float it and complete the edging process (usually done 30 – 45 minutes after the pour).

Spray the top of the driveway with a retarder (aka deactivator) which essentially slows down the set time of the top layer. Sugar solution works just fine but is messy. Another favorite is good old Coke!

However, I think it is better to use a “deactivator” from a reputed manufacturer, such as Deco-crete Supply. The deactivators come with predetermined exposure depths. This ensures that you wash off exactly the right thickness of the top layer.

At the right time you can remove the top layer of the concrete by using a pressure washer and a buffer equipped with a medium soft brush. The brush does the removing and the pressure washer does the rinsing.

Seeding the Stone Aggregates on the Surface

Seeding is ideal for small surface areas such as stairs or garden pathways, but you can use this method even on a short driveway DIY project. A small 2 car driveway is typically 576 (24’X24’) sq. feet.

To end up with an Exposed Aggregate Driveway Thickness of 6” set up your forms using 2X6s. Pour the concrete in the form and hand float it such that it is about ½” below the top of the 2X6s.

Seed the concrete with stone aggregates within 20 – 30 minutes of floating. The concrete will be firm enough for the stones to not sink in but soft enough so that they can be pushed down with a jitterbug or a roller tamp.

The stones should be completely covered with the cement that rises up due to the tamping pressure. Be firm yet gentle and do not overdo the tamping.

You should then expose the stones using a wet horse hair brush or broom. Use the garden hose to gently wash away the loosened concrete. Do not use high pressure.

The remaining process of sawing control joints, curing and sealing are exactly the same as that for a regular concrete driveway.

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