Nails can make difference between good, bad roof

Sun., July 5, 2015

DEAR TIM: I’m getting bids on a new roof and some of the roofers want to use a nail gun to install the shingles. Is this a good idea? I’ve also heard stories about inferior galvanized nails that don't hold up and start to rust soon after being installed. What type of nails would you use when installing shingles on your home and why? How can you tell the difference between different galvanized nails? – Cheri B., McAlester, Okla.

DEAR CHERI: Roofing nail guns are mainstream now and accepted by just about every roofing material manufacturer that I know of. It's important the guns drive the nails correctly per the written instructions of the shingle manufacturer, so be sure to take the time to read the written installation instructions about this.

While you’re checking out the instructions, pay attention to the type of nail the shingle manufacturer recommends so you don't void the warranty. Realize the fastener is the lifeline of the roofing material. It's vital the fasteners last longer than the actual roofing material. If the nails or fasteners rust and fail, the shingles can succumb to gravity and/or be blown away in a moderate breeze.

You should be very concerned about using inferior roofing nails. I’m in the process of reroofing my home. It was built just 14 years ago, not by me. It had a heavy-duty architectural shingle on it that was supposed to last 40 years, but it started to fail two years ago. Now that I’m taking off the curled, brittle shingles that are losing granules by the minute, I see the roofer used cheaper electroplated galvanized nails, many of which are rusting.

When it comes to galvanized nails for roofing, the gold standard is hot-dipped galvanized nails. These steel nails are cleaned chemically and then immersed in a vat of molten zinc that sometimes contains some lead. The molten zinc is very hot, usually between 815 F and 850 F.

It doesn't take long for the steel nails to rise up to that temperature. When they do, the steel atoms vibrate rapidly and interlock with the zinc atoms, creating a zinc-steel alloy that resists rust quite well. When the nails come out of the molten zinc, they also have an additional coating of pure zinc on them. Zinc doesn't rust, and the coating protects the steel from the ravages of water. The best nails get a second dipping in the molten zinc bath.

There are other processes for galvanizing nails, but they simply don't offer the level of protection that hot dipping does. Hot galvanizing, for example, is a process whereby zinc dust or chips tumble in a hot drum with cold steel nails. This process doesn't sufficiently heat up the steel to produce a zinc alloy on all the nails. It is, however, cheaper for nail manufacturers.

Another process is to plate nails mechanically with zinc dust. The cold steel nails tumble around with the zinc dust, tiny glass beads and a chemical. The glass beads and the chemical work to apply a thin coating on zinc on the nails. Once again, this process doesn't create the all-important alloy, and the zinc coating can be uneven and thin.

A third process is electroplating. Here the cold steel nails are immersed in a chemical liquid and electricity is applied to the solution. The result is a very thin coating of zinc on very shiny nails that almost look too good to be true. They don't have much zinc on them and, as I can attest, they rust in short order when exposed to the elements.

Years ago it was impossible to locate hot-dipped galvanized nails that would be compatible with nail guns. Fortunately it's possible to get them for just about any roofing nailer. Be sure your contract with the roofer specifies hot-dipped galvanized nails, and pay close attention to the minimum length called for by the shingle manufacturer.

If you’re applying a thin shingle to a wood surface and no other shingles are present, you might be able to get by with nails that are only 1 1/4 inch long. The shingle warranties are very specific about the nail length, and you want the right nail so they have enough holding power to resist blowing off in strong winds.

To tell the difference between nails, you probably need a little bit of experience. The first thing to look at is the labeling on the boxes or containers the nails come in. The wording must say hot-dipped. If you just see the word galvanized, that's not enough. Don't be fooled by the words "hot galvanized" either. It's got to say hot-dipped galvanized.

Hot-dipped galvanized nails not used in a nail gun are usually very distinctive. Often they have clumps of zinc on the shaft or the coating of zinc is somewhat uneven on some of the nails. You may even discover small ingots of zinc in the box or nail container. Other methods of galvanizing leave a much smoother appearance on the nail surfaces than hot dipping.

I’m using hot-dipped nails because I want no rusting. I want my realistic and gorgeous synthetic slate shingles to stay attached to my roof when a punishing nor’easter pummels my house with gale-force winds. I have a feeling I’ll be out the next day helping to secure my neighbors’ roofs because their roofers chose to use the cheaper nails. Don't you make that mistake.

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