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Composition Board Siding

By Tim Krof



Composition siding is a composite wood product made from wafers of wood pressed together and coated in resin, then formed into a board. Composition board siding had a rough beginning.   Weyerhauser was one of the first major producers and their product did not fare well.  As is the case with many new products, it has been improved.  But, even with all the improvements made in siding material over the past 20-30 years, all wood products, pressed or natural, must be kept sealed. What is being ‘sealed out’ is moisture.  This ‘seal’ consists of the caulk and paint that was applied to the product at new construction.   The key is to maintain that ‘seal’ over the years to ensure the longevity of the product.

Caulking usually lasts anywhere from 3 – 8 yrs, and exterior paint has a life span of 7 – 12 yrs, depending on the product.  Caulking is required more often than painting. It is important to caulk around nail heads and seams. Those are the two most likely areas for moisture penetration, and need to be maintained in order for the product to last.  The bottom edge also needs a good coat of paint the same time you’re a caulking, to keep moisture from wicking up at the base.

Today there are three types of composition board siding:

Masonry Composition Board Siding (Fiber Cement):   The sturdiest and most expensive, this is marketed as a lifetime siding and it very well could be.   This material will not swell and get soft.   It is more difficult to install and will expand and contract, thus expansion gaps are needed.

Hardiplank:   Wood chips are glued together for this product.   It is a sturdy product that has recently been introduced.    It is less likely to swell when compared to composition board siding.

Composition Board Siding:   This material is basically saw dust and wafers of wood that are held together with exterior glue, and a water proof membrane.