Here in Norfolk, VA, we have many beautiful slate roofs on homes throughout the city. It saddens me to see so many of these roofs covered with caulk and roofing cement. This type of repair does not last long because once the caulk or cement hardens it cracks and the leak starts again. Although the repair does not last long, the ugly tar-like substance lasts forever on these roofs. The only way to remove it, is to remove the many slates infected when originally there may have only been one or two slates in need of replacement. Replacing slates is not brain surgery but some rules must be followed if you expect the repairs to be effective.

Do you need slate repairs?

Stand in your yard and look at your roof to determine if any slates are missing or have slid down from their original position. Any missing or displaced slates should be replaced immediately. If 1/3 of your slates are missing or damaged it may not be cost effective to do repairs, at this point you may want to think about getting a new roof. Another major problem can be that your slates were installed with the improper nails. If you have a large number of missing slates this may be your problem. If your nails are rusting and the slates are sliding out, eventually every one of your slates will come loose and slide out.  Slates last anywhere from 50 to 100 years or more depending on the type, so if you can repair your roof it is a good idea to do so.  The next time it rains heavily go into your attic with a flashlight and look at the underside of all the roof deck and pay special attention to any penetrations in the roof (pipes, vents, etc.). If you see any dripping or any wet spots this should be addressed immediately. If the wood deck under a slate roof rots extensive labor is involved in the repair because all of the slates in that area must be removed to change the damaged wood.

Be careful traversing the roof!

Walking on a slate roof can be dangerous for you and your roof. Slate can be slick and walking on it can crack the slates, sometimes in places where the cracks can’t be seen until the roof begins to leak. Just having someone walk on your roof can cause many more leaks than you already have if they do not know where to step. Always step on the bottom 2 inches of the slate, this way the load is transferred to the roof deck preventing the slates from cracking.

Repairing the slate roof.

First thing is locating the proper size and color slate. As far as the size goes the thickness is more important than the width because slates can be cut down to the proper width but not shaved to the proper thickness. The exact color may not be able to be found because of the rate of fading or color change due to iron content which varies from slate to slate. Having more than one place to buy slate will insure that you get as close to the existing color as possible. Synthetic slate should not be used to repair natural slate roofs. Since slates can’t be nailed in the traditional way on repairs synthetic slate tends to curl up on the sides when the sun heats it up. When removing the damaged slate great care must be taken or many more slates will be damaged in the process. When installing the new slate there is one method that should be avoided. Many leaks that we have found on slate roofs are from previously repaired slates. This method of repair is when the slate is slid in, then a hole is punched in the slate and a nail is driven into the hole. After that a slip-joint or bib is slipped in to cover the nail. The problem with this is that if the bib slides out water can run directly into the nail hole and often does when this method is used. A hidden clip method is the best because it does not compromise the integrity of the slate and doesn’t run the risk of cracking other slates in the process.

Hopefully this information will take some of the mystery out of slate repairs for you. If you have a slate roof, you have one of the building systems and materials that has stood the test of time. When properly installed and repaired, slate roofs perform as well as they did in the Colonial days.