- 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?
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.