- Q. Is it okay to butt fiber-cement siding against aluminum-clad windows and aluminum soffit, or will the fiber-cement cause a reaction that damages the aluminum?
A.Corresponding Editor Paul Fisette responds: Portland cement is highly alkaline. Any cementitious material, including cement-based siding, can attack aluminum if the aluminum is not protected.
According to Miguel Gonzales, national accounts manager at Tamlyn & Sons, a manufacturer of vinyl and aluminum trim products, Tamlyn does not recommend that its aluminum trim products be used with fiber-cement siding.
If you do choose to use aluminum trim, it should be anodized. Virtually all major window manufacturers anodize their aluminum trim. Aluminum windows used with stucco siding have a long history of successful performance.
To be safe, I would be sure that any cement-based siding is fully primed on all sides and the ends before installation, in order to minimize the alkaline bleed. Carefully prime the ends of the siding at field cuts. This will help minimize any possible reaction with aluminum.
