Pothole Perils!

Heavy rains and freeze/thaw cycles can really take their toll on gravel surfaces, resulting in ruts and potholes.  The fixes are typically not difficult – you just need to know what to look for, the right materials to use and how to install them!   Read on for simple repair tips.

The foundation of any good driveway is its base.  The very wet winter we've experienced this winter in Charlotte has made mud of some driveways.  If there are areas that have substantial amounts of mud coming up through your gravel drive, then you no longer have a good base for your driveway.

The base material is what gives you something solid to drive on and keeps your car from getting stuck in the wet ground.  Most times the base is created using a crushed stone aggregate known as ABC.  ABC stands for aggregate base course and is a DOT terminology that refers to the base used for building roads.  This is, in fact, the material you see the highway department putting down and compacting before they lay asphalt to make the roads we drive on.

ABC is a crushed aggregate product that contains stones up to an inch in diameter and everything smaller down to a sand size particle called fines.  When wetted and tamped down (even by driving over it), the mixture of fines and aggregate will compact into a solid base material.  You need the mixture of sizes to achieve a good compaction – the larger pieces provide the strength and the small fines fill in the voids and allow the different sizes to bond.

ABC stone
If your existing driveway has lots of mud in it or has really deep pot holes, then you need to add some ABC to increase the structural integrity of the base.

Note:  There are different terms used for ABC.  You may also hear it called crush and run, ¾ minus, or simply base material.  All these terms refer to the same thing.  ABC is not the same things as pit run or pit gravel though.  Pit gravel has dirt mixed in with it and should not be used for a driveway.

To fix a pothole, you'll need to "square-out" your existing hole as best as you can so you no longer have a bowl shaped hole (this will keep the stone from sliding up the side slopes of the pothole when you drive over the area).  Then fill the hole with ABC – you will need to add at least 3"–4" of ABC to get it to compact well.  You'll want to slightly over-fill the hole since when you compact the ABC, it will shrink down to almost half of the depth you put down.  You can then dampen (not flood!) the stone and tamp or compact it by using a tamper or by driving over the hole a number of times.  The moisture and tamping will adhere the stone and fines to create a solid base.

Once you have a proper base for your gravel driveway, you can either use it that way or you can spruce it up a little with a top dressing.  Top dressing your gravel drive is done to improve the appearance of the drive, to keep the dust down during dry weather and also to prevent fines from the ABC being tracked into the house on people's shoes when the drive has moisture on it.  Fines are the smallest particles in the ABC mix and they can be like tracking sand into the house when the ABC gets wet after a rain.

The most popular type of top dressing is a clean, crushed, angular type stone like #67 stone (about the size of a quarter) or 78Ms (about the size of your pinky nail).  A decorative gravel such as Alabama Brown ½" can also be used for a top dressing to improve the look of your driveway.  These are top dressing aggregates and are usually put on about an inch thick or so.  Top dressings, if they are put down any thicker than two inches, tend to become difficult to walk on and will have too much rutting from tire traffic in driveway applications.

You do NOT want to put this top dressing into a pothole or other area where mud is showing through without first putting in the ABC base material.  While it may be tempting to skip the base material, you will end up spending more money in the long run because every time you drive over the area, the vehicle weight will push the loose gravel into the ground a little more and each time it rains, the mud will absorb the gravel a little more until you end up with your original problem all over again!

The same procedure is used if you want to start from scratch making a new gravel driveway or expanding a parking pad.  You will need to put in a 3"-4" deep base of ABC, dampen and tamp it and then cover it with a top dressing if you so choose.

To figure how much stone you need, measure the total length and then the width of the area you're trying to cover first.  Then you have two options, one is to call Blue Max Materials and let them compute your quantity or two is to follow these steps to compute it yourself:

Multiply the length and width of your proposed area together and this will give you the total square footage.  Then, decide how deep you want the material to be.  ABC should be at least 3 to 4 inches thick, deeper for commercial applications or for areas that stay wet.  Remember, this thickness will compact to about half of its original depth.  Most top dressing gravels are put on an inch or so deep.

So, for example, if your area is 11' wide by 20' long, to figure your ABC, you would do the following:

• 20 feet long x 11 feet wide = 220 square feet

• 220 square feet x .33 feet deep = 72.60 cubic feet (for a 4" deep application, take 4" ÷ 12"/foot = .33 feet deep)

• 72.60 cubic feet ÷ 27 cubic feet/cubic yard = 2.68 cubic yards

Note:  If you were ordering mulch for your yard, then the cubic yard amount is exactly what you need to know, because mulch is sold by the cubic yard.  Most gravel and dirt products are sold by weight and not cubic volume, so you need to convert the cubic yards into tons.  This is done by multiplying the cubic volume of material by what a cubic yard of that particular material weighs.  For ABC a cubic yard weighs 1.45 tons.

• 2.68 cubic yards x 1.45 tons/cubic yard = 3.88 tons of ABC

In the same fashion, to figure your top dressing on this area:

• 20 feet long x 11 feet wide = 220 square feet

• 220 square feet x .08 feet deep = 17.6 cubic feet (for a 1" deep application, take 1" ÷ 12"/foot = .08 feet deep)

• 17.6 cubic feet ÷ 27 cubic feet/cubic yard = .65 cubic yards

• .65 cubic yards x 1.35 tons/cubic yard = .87 tons (1 cubic yard of top dressing stone weighs 1.35 tons)

There you have it – you would need approximately 4 tons of ABC and 1 ton of top dressing for your new driveway!

As a side note, on construction drives when a new home is being built, you will sometimes see a larger #5 stone used for the base.  This is a bigger crushed aggregate that is more suitable for larger truck traffic and helps keep heavy delivery trucks from getting stuck in newly cleared lots.  It is rarely used in residential applications, since most cars have lower undercarriages which could get caught up in the larger stones.

Also, another alternative to ABC, especially if you are trying to save money on the base and will be top dressing the drive anyway, would be to use recycled concrete base or RCB.  RCB looks like and functions like ABC but is cheaper (almost half the cost).  It's not much to look at, so you might not want to use it if you are not going to top dress the drive with some other stone.  This is an eco-friendly product since RCB is created by crushing concrete that has been reclaimed from existing jobs, possibly a concrete driveway or sidewalk that was torn out because it was cracked or a section of road that had been changed.  This is concrete that will not end up in a landfill but as a base for someone's driveway or a new road.

Blue Max Materials is currently testing out a new driveway gravel mix called Driveway Max that contains several sizes of gravel (#5, #67 and 78M).  It has small particles to make the drive look nice and larger particles for a strong structural component.  Contact us to find out more about this product.

For more information about aggregate stone, visit www.bluemaxmaterials.com.