Ask the Builder: Sealing your blacktop driveway is pointless

DEAR TIM: Can you settle a friendly argument? My wife insists that our blacktop driveway must be sealed. She listens to a local weekend home improvement radio show and tends to think everything the show host says is true. The show host tells callers about how important it is to seal blacktop, but one of his long-time sponsors is a blacktop sealer manufacturer. The cynic in me says he says he does this because he’s getting money from the sponsor. What’s your stance on blacktop sealers and what would you do if you had a blacktop driveway? – Stuart T., Hamilton, Ohio

DEAR STUART: I can speak to all your points. For 12 years I used to do a two-hour call-in home improvement show on a few commercial radio stations. When I negotiated my contract, I reserved the right to edit the wording of commercials I was asked to read.

I’d routinely change the wording in commercial copy because the salespeople made unsubstantiated claims about products and services. Soon they stopped selling ads for my show. My integrity was all I had, and I refused to say things that weren’t true.

Years ago, I fell under the spell of what many blacktop sealer manufacturers said about the necessity of sealing blacktop driveways. Much of what they said made some sense, but there was always a nagging thought or two in my head that conflicted with what I was being told.

First and foremost, I thought long and hard about blacktop roads in my city. They were never sealed. The asphalt cement used at the plant that makes blacktop for the city roadways was undoubtedly the same used to make residential driveways. Asphalt cement is the binder, or glue, that holds together the sand and stones that make up a blacktop driveway, road or parking lot.

The roads in my city got the same rainfall, the same snow and ice, and the same harsh ultraviolet light as my neighbors’ blacktop driveways. It was not uncommon for secondary side streets in my neighborhood to go 20 or more years before being repaved. That’s a very important fact you shouldn’t ignore.

I started to look at the average blacktop road and driveway. When you study them, you quickly realize that well over 90 percent of the surface is not asphalt. What you see are small stones and sand. The asphalt cement just shows up as a thin line in between the stones and sand. Remember, sand is just very small pieces of stone. The stones and sand in blacktop are immune to UV damage from the sun.

Last winter I did research for a book I’m writing about asphalt shingles. It turns out that the sun’s UV rays blast apart asphalt molecules, making it more susceptible to oxidizing. When its molecules oxidize and cross link with one another, asphalt becomes more brittle.

As asphalt becomes more brittle, it loses its ability to hold onto the sand and stones in asphalt roads and driveways. Keep in mind that this oxidation only happens at the very top of the asphalt that’s exposed to the sunlight, and it can take years and years for larger stones to become dislodged.

My current home has a blacktop driveway. I live in New Hampshire where winters are brutal with abundant snow, ice and harsh conditions. My driveway is 20 years old, it’s never been sealed, and a vast portion of the driveway is in excellent condition. The only bad portions are where the gravel base was not installed correctly and there are a few small areas that are beginning to deteriorate.

If you decide to seal a blacktop driveway, you open up a Pandora’s box of problems. The sealer is made up almost exclusively of asphalt. The UV rays will attack this thin coating and it will begin to harden and fail. If you don’t take off your shoes when you come into your home, you’ll track the asphalt indoors, discoloring vinyl flooring and carpets.

Once the sealer starts to wear off, your driveway starts to look bad. Your neighbors may think less of you because of the appearance of the driveway. You’re forced into an endless cycle of sealing your driveway, even though the driveway itself is in excellent condition.

The sealer manufacturers talk about the ability of the sealers to fill small cracks so water doesn’t infiltrate and cause greater damage. My driveway has only a few cracks after 20 years because the gravel base under the blacktop was put in correctly. I’ve filled the cracks using a strong epoxy that comes in a caulk tube. I press small stones and broadcast clean sand into the fresh epoxy so the crack matches the texture and color of my existing blacktop.

When a blacktop driveway is new, it’s as black as a moonless night because the asphalt cement has coated all of the sand and stones in the mix. Over time, this very thin coating wears off and you start to see the color of the stones and sand. Don’t discount this distinctive look. So long as the asphalt cement used at the blacktop plant was high quality, your driveway will not fall apart in a few years without sealer. If it does start to crack and crumble, it’s not a lack of sealer; it’s an indication that the gravel base was not installed correctly.

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