Lower Maintenance Cellular PVC Products for our Climate

Today’s consumers demand lower  maintenance, sustainable building products that last.  Manufacturers have responded to this need by offering non-wood alternatives for doors, siding, decking and more.  Exterior trim is the most recent category to experience a major shift from wood to alternative materials.

Traditional wood products used in exterior applications experience many challenges:

  • Wood products tend to cup and warp, especially in the longer lengths used in trim installations.
  • Almost all contractors complain that painting is a problem at some level. Knots bleed through paint, requiring special primers/coatings to treat them.
  •  Wood products absorb moisture causing them to rot and deteriorate over time, especially if they are not installed and maintained properly
  •  Insects love wood, and often time’s natural wood becomes the home and food to termites.
  •  Wood can be heavy and difficult to handle in many exterior trim applications
  •  Only 3% of contractors in a recent survey reported having no problems with exterior wood trim.


It is clear that regular maintenance is required on all wood used in exterior applications to avoid potential problems like weathering and insect infiltration.  And, even with on-going maintenance the deterioration of wood used in exterior applications is inevitable.

Building product manufacturers have introduced several alternatives to painted wood for use in exterior trim applications:   

  • Engineered wood products like hardboard and OSB
  • Fiber Cement
  • Vinyl/Aluminum Coil wrap
  • Cellular PVC
  • Wood Plastic Composites – Decking and railings

Of these alternatives, cellular PVC appears to be the substitute product of choice with consumers and contractors because it looks more like wood than the other alternatives, can be installed with the same tools as wood by the same people, and is low maintenance.



Cellular PVC trim does not absorb moisture so it will not rot and is also highly resistant to insects.  It can be applied in direct contact with the ground, masonry or brick.  Unlike wood, Cellular PVC will not rot, split, cup or warp so it can be used in the harshest environments without concern for durability.

Since cellular PVC is extruded in a continuous process it is available in premium lengths up to 20’, which reduces the number of joints required in long runs, improving the finished appearance.  It has a consistent cell structure that grips fasteners securely and is easy to work with using the same tools and techniques as wood without nicking, chipping or cracking.

Heat blankets, ovens or other heating appliances can be used to heat cellular PVC to approximately 270o so it can be heat-formed to create arcs and radiuses in an easy cost-effective way.  Cellular PVC is so versatile it can be used to created one-of-a-kind decorative pieces to create true homes of distinction.

The surface of cellular PVC has a pleasing matte finish that resembles primed wood.  It is white throughout its thickness and remains white without protection, even in direct sunlight.  It doesn’t require paint for protection, but readily accepts standard 100% acrylic latex exterior paint.  And, since cellular PVC trim products don’t absorb moisture, they are not subject to the same moisture-cycling problems that wood products experience, so paint last significantly longer on cellular PVC than it does on wood.

There are two ways to manufacture cellular PVC trim and, the process selected will determine many of the physical characteristics of the product. This diagram shows the Celuka process of manufacturing cellular PVC:

In the Celuka process the ingredients used to make the PVC product are dropped into an extruder and mixed with a blowing agent to foam the PVC.  In a process known as extrusion, the foaming PVC is pushed through a die by the screw.  As the foamed material is pushed through the die, it is forced around a “torpedo”, creating a low pressure cavity that the two “melt streams” of PVC foam into.  The two “melt streams” that are created by the torpedo are reunited as they exit the die and enter the “calibrator”.  The calibrator is set to the actual desired thickness which continues to force the foaming of the PVC inward, which is why the Celuka process is sometimes referred to as an “inward foaming” process.

The outside edges of the PVC are cooled very quickly in the calibrator, usually by circulating water, which sets the thickness of the board and creates a hard, smooth outside surface.  The inside continues to cool at a different rate from the cooled outside surface, typically resulting in density variations between the surface and core. The final product is a Cellular PVC whose surface is smooth, hard, and glossy, with an inside that is typically rough and contains voids.

The second process used to manufacture cellular PVC is called “Free Foam”.  As with the Celuka process, the ingredients are dropped into an extruder and mixed with a blowing agent to create the foaming process.  Unlike the Celuka process, however, there is no torpedo and as the foaming PVC exits the die it doesn’t enter a calibrator.  Instead, free foam PVC is allowed to expand freely after exiting the die. The thickness of the board is controlled by a series of cooling rollers that cool it more slowly than the calibrator does in the Celuka process. This gradual cooling process allows the surface and interior to cool more uniformly, producing a more consistent density and cell structure throughout.  It also reduces the surface hardness and shine, creating a matte finish.

Compared to Celuka PVC products, Free Foam PVC products, typically have a more uniform density that is similar to white pine, have a matte finish similar to primed wood, have smooth edges when milled or moulded and can be heat formed to create curves and arches.  The characteristics of Free foam PVC allow installers maximum versatility in creating products at the jobsite so it has become the preferred manufacturing method and represents the majority of the cellular PVC products available today.

Cellular PVC works in any non-structural application, in high-moisture environments like bathrooms and laundries, in the ground, attached to masonry, brickwork, tile or stone.  It can be used to wrap posts or columns, to create seamless cornerboards or deck trim, and fascia and soffits.  It can be used on porch ceilings or to create millwork items like raised panels and wainscoting.

In general, most cellular PVC manufacturers and distributors like Universal Provision Group LLC. (UPG), have standard product offerings that include trimboards, sheets, beaded products, pre-made corners and mouldings.  These products can be used in combination to create unique architectural details that truly differentiate one home from another.   UPG also provides custom fabricated commercial and residential building components per the client’s desire and the architects design.   The company President, Johan Rostad confirmed the recent supply and delivery of a variety of custom components during this past year, including projects at The Albany Development, Baha Mar, Lynden Pindling Airport and a variety of residential homes throughout the Bahamas.  (See pictures below)

As discussed earlier, moisture can cause wood to swell and, as the wood dries out it often shrinks.  Cellular PVC does not shrink and swell like wood because it does not absorb moisture.  It does, however, expand and contract with changes in temperature.

The Coefficient of Linear Expansion for most cellular PVC products is approximately 3.3 x 10-5, which means that an 18’ piece will expand and contract approximately 3/8” for every 50oF change in temperature if left unrestricted.  With the use of proper installation techniques, the expansion and contraction can be reduced to approximately 1/8” for every 18’ of cellular PVC with a 50oF change in temperature.  It should be noted, however, that stable temperatures throughout the year in warmer climates (like the Caribbean) help keep expansion and contraction to a minimum.

The proper fastening, both type and quantity is critical to ensuring a good installation.  Stainless steel or hot-dip galvanized nails with smooth shanks and round heads, or exterior grade trim-head screws should be used to fasten cellular PVC. The fasteners should be placed no more than 2” from each end and spaced evenly across the face of the board.  8” or narrower boards require two nails across the face of the board and 10” or wider boards require three nails across the face of the board.   UPG recommends the CORTEX system for fastening PVC trim.  Cortex fasteners include a stainless steel screw with a pre-cut PVC plug to fill the hole where the fastener is countersunk, and leaves a clean smooth surface that does not need patching or filling.

UPG also recommend use of proper PVC Adhesives and fillers to properly fill nail holes and to glue PVC to substrates and other materials.  PVC adhesives match the same white color of the materials and can be sanded and painted as well.  The Cortex fastening system and the PVC adhesives should be considered when working with “free foam” PVC products.

Cellular PVC trimboards should be fastened to a flat, continuous solid substrate that is at least 1-1/2” thick wherever fastened, and the fasteners must penetrate into the substrate at least 1-1/2”.  Any premium quality, flexible acrylic or urethane exterior caulk or exterior spackle may be used to fill the nail heads.

To accommodate expansion and contraction, it may be necessary to leave expansion spaces.  If the cellular PVC is installed at the lower end of the area’s annual temperature range, slightly more than a 1/16” expansion space should be left at each end of the run for every 18’ of material installed.  If the cellular PVC is installed at the upper end of the area’s annual temperature range, slightly less than 1/16” expansion space should be left at each end of the run for every 18’ of material installed.  The closer the temperature at the time of installation gets to the extremes of the annual range, the greater the change in the space required.

Cellular PVC can be cut using standard woodcutting saws, like circular saws or chop saws.  It can be drilled using standard metal-cutting drill bits and shaped using routers or moulders.  Carbide tipped blades or bits are recommended for the best results.  Depending on the cellular PVC selected, cut or milled edges may display interior texture.  For a cosmetically smooth finish, edges may be machined, sanded, filled with spackle or painted.

When creating long runs with cellular PVC it is often advantages to glue the butt-ends together to avoid joint separation.  When doing so, the use of #20 plastic biscuits in conjunction with a good quality PVC adhesive will ensure that the joint is flush and strong while the adhesive cures.  Alternatively, a 30o or 45o scarf cut can be made and glued together.

If thicker products are desired, pieces of cellular PVC may be laminated together.  For best results, the faces of each piece should be sanded prior to gluing to ensure a solid bond.

Remember, cellular PVC does not need to be painted for protection.  It can, however, be painted to reduce dirt build-up after installation or simply to better coordinate with other exterior colors.  Typically, 100% Acrylic Latex Paint may be used to paint cellular PVC.  Because none of the paint will be absorbed into the cellular PVC like it normally is in wood, it may take a longer for the paint to dry (up to 48 hours).  Once fully dried, however, paint typically lasts longer on cellular PVC than it does on wood.

The use of darker color paints on cellular PVC may increase the product’s expansion and contraction.  The Light Reflective Value scale is helpful in determining if standard Acrylic Latex paint can be used to paint cellular PVC with a given color.  Most paint manufacturers include the LRV (Light Reflective Value) on their color chips. 100% Acrylic Latex paint should only be used with colors that have an LRV of greater than 55%.  If a color is selected that has an LRV of less than 55%, a coating that is formulated specifically for use on exterior vinyl products is required.

So remember, the application of trim to the exterior of a house serves not only to break up large areas of siding, but also to produce architectural details that differentiate one house from another.  For exterior trim applications like rake or fascia boards, window or door surrounds, or even the most elaborate architectural details like brackets, corbels and columns, wood is no longer the best option.  Today’s consumers demand lower maintenance products that last a long time.  Cellular PVC products from Kleer™ Lumber offer the same traditional look of wood, but with the added benefit of being truly low maintenance.  For exteriors that are meant to be enjoyed, not maintained, choose cellular PVC products.

Universal Provision Group LLC.

Please contact Universal Provision Group LLC. by;

Phone:  978-973-4548 Fax: 978-626-1277 or email: jrostad@upgco.com


Local Supply

Cariluxe Bahamas Ltd.

#16 Gladstone Agro-Industrial Park

P.O. Box SP61312

Nassau, NP



Bahamas Local: 422-2PVC

Office: 426-4858

Fax: 978.347.7043

Skype:  johan.rostad



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