PVC Pipe Through 3/8" Ply: Caulking Or.... ?

That's what I would use.

Hi Pete,

Is that a shop vac, a generator, or something else? If the exhaust port of the device is plastic, you're probably fine using PVC. If the exhaust port is metal, you may want to use metal pipe instead of PVC.

I'm also curious why you reduced the full size port down to a smaller size? That would reduce air flow, which could be a bigger issue than the caulk. I would try to keep the same size pipe all the way out, especially considering the short distance you traveling.

Assuming the PVC pipe is appropriate for your situation, I see no reason why you couldn't use caulk to seal between the plywood and PVC. If the gap is larger than 1/8 inch or so, you might want to fill the gap with "foam backer rod" before applying the caulk. You can find that in various sizes in the home centers where weatherstripping is sold. It minimizes the amount of caulk you need to pump into the hole, but more importantly it allows the caulk to flex more than a big thick chunk of caulk. A thinner application will cure quicker too.

If you want to get fancy, they sell PVC trim rings to fit around PVC pipe. They're normally used where drain pipes penetrate sheetrock. Dab a little caulk underneath and slide the trim ring on. The trim rings are usually stocked in the plumbing area near the traps and valves.

I don't know what your application is, but you should probably install an elbow facing down on the exterior of your structure. This will prevent rainwater from blowing in and draining back to your appliance.

Good luck,

Anthony Watson

Dear (PeteCresswell), When I did heating and AC, we used Diversigum

item # 6-202-1 in the box. Roll it like Play-doh snake, push some around the outside much like caulk. Lasts nearly forever, and pretty much non hardening.

Some sizes of PVC pipe telescope within one another. So slide the next size up on either end and caulk the connection point.

Per bob haller:

That's what I spent a half hour rummaging though Home Depot's pipe section trying to find. Seemed like it would add a little bump resistance too.

Now that I know it's possible, I'll go back and look some more.

What is the budget?

Option 1 Machine a ring from 316 stainless steel exterior would have grooves to hold a Buna-N O ring on either side of the wall. Interior would have a silicone sleeve to hold the PVC in place and absorb vibration.

Estimated cost $176.50

Option 2 Silicone caulk