Q. I have concrete tiles on my roof, and some are cracked. What type of adhesive should I use to glue them back together? I have the pieces, they are mostly small triangles from the corners of the tiles, and I do not have whole tiles to replace them.

A. There are a number of adhesives that are formulated specifically for concrete roof tiles and most of them are readily available at your local roofing supply house. Some of the more common brands are RT600, Rainbuster 850 and Geocel 3500. The trick is to not use too much. If you cut the tip of the adhesive tube only enough to allow about a sixteenth of a bead out, you will be well served.

Q. How long does it usually take for repair tile (new) to fade and blend with the existing (old) tile on the roof?

A. Since there are a number of variables that can affect the weathering of tile, it is difficult to say precisely when a replacement tile will match the shade of the existing roof. Likewise, different types of tile will have different rates of weathering depending on whether they are surface colored or integrally colored. The weathering process happens gradually so I’m not sure that anybody has actually measured the rate of assimilation but I would expect that once the surface sealer has worn off, the tiles would be reasonably close in appearance. The sealer loss also occurs gradually depending on exposure but most of the visual effect of the sealer will be gone after five to ten years. It should also be noted that darker colored tiles are most likely to exhibit contrast between the color shades of the new and old tiles. If the contrast of the replacement tile is considered a significant problem, it is quite common to harvest tiles from another, ideally isolated and hidden, part of the roof to be used for the repairs and the new tiles may be substituted onto the vacated area where they will gradually begin to match the original roof without causing a visual distraction.

Q. Our new home (built and occupied in Nov. 2000) recently had severe roof damage due to snow sliding off the roof. It slid both as an avalanche, sliding all at once, and as a glacier, moving slowly. We used a standard weight concrete roof tile. The installation was made with standard horizontal battens over a cold roof. Is there something we can do to prevent this from happening again?

A. To prevent the type of damage that you described, it is recommended that snow retention devices be installed on the roof. Snow fences, individual snow brackets, or a combination of both have been shown to be very effective in preventing damage to tile roofs in alpine conditions. To get specific information regarding which system would best suit your needs, I would suggest that you contact Tile Roof Accessories (TRA) at 801 756-8666. This company specializes in snow retention systems, many of which are designed specifically for concrete tile roofs.

Q. I bought a home with a lightweight concrete tile roof. I was told not to walk on the roof, or the tiles would break easily. The valleys get a lot of leaves in them all year from the oak trees. I was also told to keep the valleys clear, or leaks might occur. What should I do? Can I walk on the roof?

A. The concern for maintenance of valleys in situations such as you described is best addressed at the time of installation but I will try to give you some suggestions that may work for you. I would concur with the advice that you received but, not having the specifics of your roof design, I will give a number of potential options for you to consider. The first one, which you’ve probably already considered, is to use an extension device to rake the leaves from the valley from a ladder set up at the eave. This option is practical for short valleys but may be impractical for longer runs. Another option that is best considered during the original construction is to cut the tiles away from the center of the valley far enough to allow you to step on the valley metal rather than the tile as you clean the area. This method also greatly reduces the concern for roof leaks since the water runs more freely down the center of the valley. It is possible to have the valleys cut open later, but it is much easier during construction. Valley metals with additional longitudinal ribs on the sides will also help to prevent clogging and lateral water diversion. If neither of these methods is feasible, you might consider using padded walk boards that are commonly used by painters or other trades who have to work on roofs of this type. There are commercially prepared versions of these or you may consider fabricating some from sections of plywood with padding attached. This method should only be used on reasonably shallow roof slopes and caution should be exercised to prevent slipping. It may also be possible to find contractors in your area who actually specialize in providing this type of service. The other option that has just recently become available is to apply EPS or polyurethane foam beneath the tiles in the areas that you need to access. The polyurethane foam in particular may be viable in your case since it often may be applied without removing the tile. The only problem you may encounter in that regard is finding a qualified roofer in your area since it a relatively new process on the west coast.

Q. I have a 50 year tile roof that has developed a leak. How can I find out if it was properly installed? The valleys are butted against each other. Is this proper? 1 tile broke and slipped down a few inches; I caulked it and pushed the tile back together. Should it be replaced?

A. There are any numbers of reasons that your roof may be leaking and having a broken tile is certainly a way for water to enter into the system. Caulking on a broken tile will usually work as a stopgap measure but this tile should be replaced as a permanent solution. Since you mentioned the closed valleys, am I to assume that the leak is occurring in that area? If this is the case, it may be necessary to clear away any debris that may have accumulated there. You did not mention which tile profile you have but if it is a flat tile, you may want to consider having the tiles cut away from the center of the valley to allow better drainage. Even though closed valleys are an accepted method of installing tiles in your area, they may become problematic if there is any debris accumulation that creates water diversion off of the valley metal. Sometimes it is sufficient to remove only those cut tiles that are creating dams or diversions in the valley. Another option, if you desire to keep the closed valleys is to use a ribbed style valley metal to replace what is probably a standard flat valley metal or to install a fitted valley guard system. This is a little known but very affordable and effective option developed by my associates and me.

Q. We have a buff colored concrete tile roof on our home in Santa Barbara, CA. We spec’d the tile when we built the home in 1992. The tile is developing a discoloration that appears to be mildew growth. I have read your bulletin on your web site re mildew growth, but it does not offer instruction on removal.

A. There are a number of variables that affect the procedure so it is very difficult to come up with a “one size fits all” solution. Rather than wait for a formal document, I wanted to at least respond to tell you something about the process. The most common method for cleaning moss and algae from the roof is to soak the roof in a diluted solution of bleach and then power-wash to remove the debris. Typically, a 10 to 15% solution of bleach (5%, if pool chlorine is used) is sprayed onto the roof in an amount that soaks in rather than runs off the roof. After it dries, the roof may then be power-washed to remove the debris. To slow the reoccurrence of the problem, the roof may be sealed with a high grade acrylic tile sealant that optimally has 33% solids with a wetting agent. This sealant should be applied to a thickness of 1 mil for normal wear.