Cellular PVC, Anyone?

[Robbie Lee]

I discovered a first, over the weekend: 4' x 8' x 1/2" Cellular PVC sheets.

As I have a job requiring partial-burial -- namely, 5' panels that will have a 2' (above grade) reveal -- I'm wondering if anyone has actually made any "boxes" out of this stuff?

The project I've got in mind requires 3-sided, U-shaped, boxes that will be lined, on the inside, with Foamular 250 XPS. Once the XPS has been permanently glued to the inside
of the U-shaped fabrication, the entire contraption will be screwed against an (empty) ICF wall and, in the end, the entire wall will be filled with pumped concrete...and, in case
you're wondering, the point where the open part of the "U" meets the ICF forms will be cut open to allow for concrete "bump-outs" that will act as piers for I-beam base attachments.

Although it may read like a major project, I assure you that it's only for a 36 x 48 steel out-building that will, for all intent and purposes, be raised 2' above grade. By the way, I'm
seriously considering the PVC panels because they will be stay in place (inside the building), which means that 3' of each panel will remain below grade -- and cellular PVC should hold
up much better in ground contact than any wood product I'm aware of (not to mention the prevention of a subterranean termite super-highway).

If anyone has employed Cellular PVC to make boxes, I'd appreciate any productive thoughts on the best joinery method for the (2) 90-degree corners we'll need for each pier.

Thanks for your time...

[Chris Padilla]

Got a link or brand name we could look up?

[Eric Schmid]

I am just wrapping up a T&G porch floor made of PVC (Azek). The three craftsman columns wrapped around the roof posts are being trimmed out in 1/2" sheets. This product has no structural value and therefore needs to be mounted to a stable substrate. It is not at all rigid either. I would contact the manufacturer to see if there is a way to glue it to the insulation panels, assuming you can use these for rigidity.

As far as joining the corners, Azek makes a clear PVC glue designed to be used with their products. You could glue and clamp for a few minutes. If you don't mind fasteners, glue and stainless screws.

As far as rot resistance it's the perfect product for below grade applications. It won't rot and it does not absorb moisture.

[Peter Quinn]

Boxes yes, concrete forms no. I've done column wraps with tape miters and PVC cement, its strong enough to move around and set in place, don't know that it would hold up under the significant weight of a concrete pour. I guess I am not exactly understanding your application, why must the forms stay in place post pour? Do you have a sketch of this application? PVC does hand ground contact well, by the terms "termite super highway" and the description of what sound like grade beams sounds like you are in the southern part of the country? The 1/2" stuff is pretty flimsy, none of it is considered structural, seems like the ICF company should have some product to handle your form application that you can later wrap if required with PVC fro cosmetic purposes? Or build a break away plywood form with 2X outer ribs and an EXP core then cover the exposed sections later if required from grade up?

[Robbie Lee]

I am just wrapping up a T&G porch floor made of PVC (Azek). The three craftsman columns wrapped around the roof posts are being trimmed out in 1/2" sheets. This product has no structural value and therefore needs to be mounted to a stable substrate. It is not at all rigid either. I would contact the manufacturer to see if there is a way to glue it to the insulation panels, assuming you can use these for rigidity.

As far as joining the corners, Azek makes a clear PVC glue designed to be used with their products. You could glue and clamp for a few minutes. If you don't mind fasteners, glue and stainless screws.

As far as rot resistance it's the perfect product for below grade applications. It won't rot and it does not absorb moisture.

I think that you've hit the significant issue on the head here, Eric. Although the product we're considering -- Veranda HP Cellular Foam Sheeting -- has enough rigidity, even at 0.5" thick, it might not stick to the 2" Dow Foamular 250 XPS we have on hand. Put another way, there are adhesives out there that will bond XPS (aka, Extruded Polystyrene) to wood without breaking down its foam properties, but there doesn't seem to be an obvious choice when it comes to bonding XPS to PVC.

Thanks for the productive reply :)

[Robbie Lee]

Boxes yes, concrete forms no. I've done column wraps with tape miters and PVC cement, its strong enough to move around and set in place, don't know that it would hold up under the significant weight of a concrete pour. I guess I am not exactly understanding your application, why must the forms stay in place post pour? Do you have a sketch of this application? PVC does hand ground contact well, by the terms "termite super highway" and the description of what sound like grade beams sounds like you are in the southern part of the country? The 1/2" stuff is pretty flimsy, none of it is considered structural, seems like the ICF company should have some product to handle your form application that you can later wrap if required with PVC fro cosmetic purposes? Or build a break away plywood form with 2X outer ribs and an EXP core then cover the exposed sections later if required from grade up?

Well, Peter, your interpretation of the phrase "termite superhighway" is partially-correct. Although the steel/wood hybrid structure I [partially] described in the OP will be erected in the Berkshires, I'm a southerner with lots of [read: horrible] termite experience. No, there may not be as many termites up here, but I've seen enough damage to know that you should do everything you can to keep them out of a wooden structure, even a steel/wood hybrid.

In keeping with the purpose of ICF construction, all concrete foundation walls, including piers must be wrapped with at least 2-inches of either EPS or XPS rigid foam. In order to hold said foam in place during a pumped concrete pour, we're building the U-shaped forms I described in the OP and, more to the point, the foam must be bonded (i.e, glued to) to the substrate. As we're talking 5-foot foundation walls here -- and I obviously don't like the idea of burying wood -- PVC panels are being considered to fill the role of substrate. By the way, 16-inches will be the widest panel in these forms, so rigidity isn't really an issue -- I think that bonding the XPS to the PVC and joinery strength are the real issues at bar.

[Eric Schmid]

It sounds like you are planning on dropping the boxes into excavated holes, then backfilling before pouring. Is that correct?