We recently talked with Durabrac owner, Mike Sheehan, about the properties and abilities of cellular PVC when it came to load bearing issues. Mike has worked with PVC/vinyl for over 25 years, first molding it into various creations for his custom sign business then eventually taking his knowledge and applying it to a full-time manufacturing business of exterior components such as brackets, rafter tails, sawn balusters and more.
Q: Some refer to PVC as “plastic wood”. How similar is PVC to wood when it comes to building brackets and other components?
MIKE: Cellular PVC has a density weight similar to pine. This similar density makes it easy to alter its shape with wood-working tools. I like to think it’s the perfect marriage of wood and plastic. Cellular PVC’s main quality is its uniform density. It’s the same board after board. A painted cellular PVC component crafted by a skilled woodworker is very hard to distinguish from wood. But really, cellular PVC is nothing like wood. It’s 100% plastic. That can be good and bad. As a vinyl resin, it is unaffected by moisture which allows for excellent paint adhesion with no swelling or cracking. But, because it’s plastic, it can become very malleable when heated. That’s great for forming, but risky for handling weight.
Q: That leads us to the next question: can cellular PVC be load bearing?
MIKE: Some will argue that if you laminate enough thick layers together, it will hold a fairly heavy load. This is true… at first. Because it’s cellular, over time those cells of PVC will compress and begin to sag under the weight. It will take time, but eventually gravity will win. Cellular PVC has none of the interlocking fibers and grain that give wood it’s load-bearing strength. Cellular PVC is made up of individual expanded PVC cells. Each cell is bonded to adjacent cells to form sheets and boards. This configuration is great for material that will be cut or machined, but not so good for material that needs to provide support under stress.
Q: So, it’s not possible to have a structural support with PVC?
MIKE: I wouldn’t say impossible. We’ve actually come up with a solution to achieve the durability of PVC decorative brackets while maintaining structural support: use traditional angled braces of wood or steel to support the load and cover the structure with the PVC bracket. It may not sound original, but how it’s done is and solves a major installation problem in the field
Q: So, what makes your solution different?
MIKE: Architects and contractors use faux covers all the time. The difficulty arises when you want to hang a decorative bracket with an open center (such as the Durabrac 0512) between a load-bearing brace and the supporting wall.
Our solution is to allow for the walls of the open center to be installed in the field after the bracket is slipped over the load-bearing brace. We create a notched ledge for the inside faces to rest on; providing a secure and accurate positioning in the field. Without the ledge, a potentially ugly seam where the covers meet the sides would be seen.
Q: So what adhesive do you use when adding the center covers?
MIKE: PVC doesn’t bond well with many adhesives. You could use traditional PVC cement or epoxy designed specifically for PVC, but those tend to be messy and hard to use. Cleaning up PVC cement that squeezes out is not an option. Epoxy requires mixing, is expensive and requires a time consuming additional step to clean off the exposed epoxy that squeezes out. A better way is to adhere the faces in place with latex caulk. Latex caulk is not traditionally used as an adhesive. You wouldn’t think it has a lot of bonding strength, but it has a surprising amount of holding power when used for this type of installation. Apply a bead of caulk to to the inset notch. Clean up any that squeezes out with a damp rag. Use masking tape to support the faces in place while the caulk dries. The caulk is perfectly suitable for this type of adhesive situation.
So, Durabrac has created a clever way to create “structural” PVC brackets. Refer to the installation video here to view a graphic demonstration on how the installation and final product works.