How to make proper installation of cement siding

Q. The cement siding on parts of my house is disintegrating. When my builder sold me on this fiber-cement siding, he claimed it would last forever. Is my cement board siding defective, did the builder make a mistake, or is it a combination of these two? What are the best practices that should be followed when cement siding installation is part of a new-construction or remodeling project?

A. Based on your photos, it's my professional opinion that your fiber-cement siding installation was doomed from the start. Because the crumbling cement siding is in just a few areas and the siding on the rest of the house in is perfect condition, the problem is a workmanship error. Cement house siding is a fantastic product when installed correctly.

Installing fiber-cement siding is not hard, but there are published best practices that the major cement-siding manufacturers make available. Follow these instructions and your fiber-cement siding can last over 100 years.

Your cement siding failed at three locations: front porch, rear deck and along one roof edge. The reason is simple: The siding was installed too close to these surfaces. The best-practices installation guide shows that a 2-inch gap should exist between the bottom of the siding and each of these horizontal, sloped or vertical surfaces. 

The crumbling is most pronounced at your porch and deck because the cement board siding is in direct contact with the porch and decking. Water that accumulates on these flat surfaces soaks into the siding. In cold weather, this water-soaked siding freezes. Since water expands approximately 9 percent when it turns into ice, this expansion blasts the siding apart. Creating the 2-inch gap prevents the siding from sitting in water, and it promotes rapid drying after the storm has passed. 

Cut or sheared edges of cement siding, while inherently durable, can have extra protection added if the carpenters use finish paint during installation. If they apply a heavy coat of urethane acrylic exterior paint to the cut edges, it prevents any splashed water from soaking into the siding. It's extremely hard to paint these edges after the cement lap siding is installed, especially the angled cuts where the siding abuts a sloping roof. It takes just a minute to paint each cut edge, but this practice can add decades of life to the tender edges. 

Before you or a contractor attempt to install fiber-cement siding, read the instructions. Some manufacturers have different instructions for different regions of the country. Be sure you have the correct set of guidelines for your fiber-cement house siding. These can be obtained for free online. 

You can't assume that the carpenter, builder or subcontractor will do the job right. It's your responsibility to know how the job should be done and it should be in your contract that the written instructions are followed to the letter. 

The best-practices guidelines cover many aspects and details you'll encounter when you or your contractor start to work with fiber-cement exterior siding. Cutting methods, flashing details, nailing suggestions, use of water barriers and more are discussed. These practices are not difficult to implement, nor do they require expensive tools. 

Note that the building code can be in conflict with the best practices for installing cement siding. The code may have more stringent requirements. For example, instead of the 2-inch gap called for by the siding manufacturer at a horizontal grade application, the building code may call for a gap of 4 or 6 inches. Be sure you have a full grasp of the building code as well as the best practices so you don't have to correct a mistake. 

Asbestos used to be the aggregate that was mixed with cement paste to make cement home siding. This process essentially created thin sheets of solid rock. This is one reason why many older cities and towns have cement siding houses that are still in service. Many of them only need a good washing to look like new. 

Because asbestos has been linked to lung cancer, its use in building materials has been halted. Wood fibers were substituted in fiber-cement siding. Try to locate a fiber-cement siding whose wood fibers have been treated to prevent wood rot. Untreated wood fibers are susceptible to rot if water gets into the siding. 

One of the best characteristics of cement board siding is its ability to hold paint. Cement siding is not hygroscopic, so it doesn't expand and contract like regular wood siding when wet. This means paint sticks to cement siding like it sticks to metal. If you apply a urethane-acrylic exterior paint to clean cement siding, you may not need to paint again for 15 or 20 years.

selected from https://www.silive.com/homegarden/homeimprovement/index.ssf/2009/02/properly_installed_cement_sidi.html