It is an unfortunate fact that many of today’s historic slate roofs are being destroyed by roofing contractors. Often, roof owners must hire incompetent, ill-informed, inexperienced roofing contractors and pay them good money to have their own roof defaced and abused. One of the most unpleasant tasks of competent slate roofing contractors today is the removal and replacement of bad repairs, which often amounts to 50% of a competent contractors workload.

How can you tell if the contractor you are considering hiring is a Neanderthal? Here are some things to consider:

Replacement Slates

Ask them how they attach replacement slates to the roof. There are only two generally acceptable methods: a nail in the slot covered with bib flashing, or a slate hook. The nail in the slot should be a 1.5″ copper roofing nail (not an 8 penny nail). This method is illustrated on this web site here. Replacement slates should not be face-nailed (nailed through the exposed face, leaving exposed nail heads – this is only acceptable in very rare circumstances). Nor should exposed straps be used to hang slates. The straps are unsightly and unnecessary and will eventually fail. These techniques are popular among Neanderthals. Replacement slates should only very rarely be cemented into place. Furthermore, the contractor should have replacement slates that match in size, type, and shape.

Getting Around on the Roof

Contractors who use ropes and walk on the slate roof should be avoided at all costs. They are Neanderthals. The generally accepted method for working on slate roofs is via the use of hook ladders, which hook over the ridge of the roof and allow the contractor to walk all over the roof without putting any weight on the roof itself. Aluminum hook ladders do not need to be padded. Contractors *can* walk or crawl on the ridges, in the valleys, and sometimes on the hips if they know how to do it properly. If the roof has no ridge (such as a hip roof), then roof jacks and planks will create a platform on which to rest a roof ladder. [Note: An experienced slater who knows what he is doing *can* walk carefully on a slate roof without damaging it. But this is done only when needed, not routinely.]

Proper Tools

Every competent slate roofing contractor will have a slate ripper, slate cutter, and slate hammer (not to mention ladders and ladder hooks). A Neanderthal will not have these tools.

Roof Cement

Roof cement is not an acceptable material for repairs, except under very limited conditions. Roof cement (tar) should never be applied to the exposed face of a slate anywhere on the roof (a limited exclusion to this rule is made for sealing chimney flashings as a form of temporary repair). The slots (narrow spaces between slates where they butt side-by-side) should NEVER be cemented. If valley metal is cemented, the slates alongside the valley should NEVER be cemented under any circumstances. If you see black tar spots on the roof, or, worse yet, large areas covered with tar, your contractor is a Neanderthal.


Roofers installing slates should not be walking on them during the installation. If they are, they’re Neanderthals and you will have lots of slates to replace in a short period of time. Many new slate roofs today are losing 50-100 slates in the first ten years or so due to the slates cracking during installation by Bigfoot Contracting, Inc., and falling off later (after the contractor is long gone and won’t return your calls). Slate should be installed with 1.5″ copper nails using a slate hammer (not a nail gun). The slate should not be nailed too tight or not tight enough, it needs to be nailed with just the right amount of pressure. If a slate is nailed to tight it strains the slate nail to nail and it can break. If a slate is nailed to loose the nails act as pilings holding up the next course of slate.

Be Informed

Education is always the answer when it comes to slate roofs. Make sure that you are as well informed as possible. We try to provide as much information as we can on this web site, but there is always more. Check out the education section of this web site and others to teach yourself as much as possible before investing in a slate roof. If when you approach a contractor and it seems that you are teaching them about slate RUN!!! and find another contractor.