Exterior trims provide the benefit of an improved aesthetic appearance at exterior building joints and they also help make the buildings wall assembly more water resistant. Below is a list of trim materials commonly used and their benefits:
Plastic – Polyvinyl chloride (PVC) or Polyethylene (PE) are available as exterior building trims. Polyurethane can often cost a bit more than PVC but offers greater density and is ready for direct paint. PVC on the other hand must be sanded/prepped before paint. Plastic trims can be custom fabricated and molded into special designs which resemble hand carved wood. Plastic trims won’t rot and are resistant to shrinking and swelling.
Wood – Wood has historically been the go-to material for exterior trim and can be had in solid boards or finger jointed pieces. Southern yellow pine, Douglas Fir, and Hemlock Fir are commonly used wood choices and tend to cost less than other choices like red cedar or redwood. Red Cedar and Redwood however are easy to work with and are not conducive to warping or rotting like other less expensive woods.
Hardboard – Hardboard trim is made of chips and glue which are heated with water and steam and compressed into stock. When compressed a component called lignin found in wood cells starts to flow and works as a natural glue to hold the board together. Hardboard must be installed with care and concealed well as gaps or holes letting in water can work to rot and destroy the board. Eventually, hardboard will swell over time.
Fiber Cement – Fiber-cement trim is made up of cement, sand, and wood-fibers. It is resistant to fire, insects, rot, water and is also very durable. Fiber cement trims must be cut with a carbide tipped blade for the neatest edge. It’s dense material characteristic will often require a new blade much more frequantly than with wood or other lighter duty materials. With it’s water resistant nature, fiber-cement trims will hold paint for much longer than wood because the bond is almost never compromised between the paint and the material.