Common Rot Repairs Using PVC Trim Boards

While having the pleasure of working in a beautiful neighborhood in Newcastle, NH recently, I was approached, on separate occasions, by 2 friendly neighbors. Both of these gentlemen were astute “Do -It- Yourselfers” in want of information. All of the homes in the neighborhood were built about 20 – 25 years ago and are beginning to have some of the same issues. They’ve got roofs that are starting to show minor problems, roof boots that have dried out and cracked, windows that have exceeded their serviceable life, and generalized exterior rot. Both neighbors seemed to want to see how we handle some of these things, and determine for themselves whether there is anything of value they might be able to take from it.

Because I want this blog and this website to be a resource, I figure I might as well share my approach to some of these things that people seem interested in learning about. In this case,

This is the bottom trim molding before.

the front door threshold had been replaced at some point with a pine threshold. It rotted at the corners, where the storm door side tracks sit on top of it. Also, the door surround had been patched with new pine in places, and it too was in need of attention. Originally, I didn’t think about writing a blog for this project, so the beginning pictures could have been better.

 

 

 

In this third picture, you’ll see the short section of pine that was used for a previous patch. The predecessor chose clear pine instead of primed finger jointed. Very conscientious. He/she also cut an angle at the top of the piece which created what we call a scarf joint, or some would call a weather cut. This is important. The patch had also been primed on all sides, including the scarf joint at the top. This is even more important when using wood.

But the patch, beginning at the top right corner, had begun it’s rapid descent down the drain anyhow. How come? Well briefly, (I’ll save the real meat and potatoes of this one for another blog post) because pine available today for exterior projects is complete garbage. Be as conscientious as you want, it’s still going to fail prematurely, everytime.

Step one: Drive screw with special driver (no pre-drilling).

So,I chose to replace these vulnerable components with pvc board and trim. Nothing comes without it’s pricetag, however. And these products have their pricey tag.

Additionally, they must be used with the utmost care and attention to detail, or suffer the wrath of buyer’s remorse.

The brand I use is Azek. A 1 x 12

Step two: Set pvc plug.

comes 18′ long and can shrink as much as 3/4″ lengthwise depending on ambient temperature. Typical wood boards shrink and expand with changes in

moisture, and in greatest fluctuation across their width (the 5-1/2″ width for a 1 x 6). Pvc boards shrink and expand with thermal changes, and in greatest fluctuation along their length (18′ for a typical board that is uncut). Therefore it can be entirely expected that if you install an 18′ 1 x 12 that butts into 2 perpendicular wood surfaces on an 80 degree day in the sun, and then come back to visit (this is where being a remodeling carpenter with repeat customers becomes priceless) during November on a

Final step: Gently tap flush with hammer.

40 degree day, you will probably see a gap at each end approaching 3/8 of an inch!!!!

But, with a whole bunch of awesomeness (I’m actually dusting off the tops of my shoulders while typing) these problems can be averted. I’ve built a deck, during the summer, with 1 x 8 trimboards totaling 39 feet joined together. I went back for another stage of construction during the winter, and none of the joints had opened a whisker.

I was very reluctant to use the super-spectacular new virtually invisible fastening method for these products, but with a bit of coaching from some of the younger guys that were more open to these things, I fell head over heels. The screws are made by Cortex. You just sink ‘em deep with no pre-drilling, and then tap in a pvc plug with your hammer. Boom! Nothing ever happened here. Stainless finish nails can sheer off under the right expansion and contraction conditions.

The glue we use for pvc joinery.

What about glue? We should use the Azek brand glue that Azek specifies, right? Wrong-o! This pvc is cellular pvc, similar to being blown up with air like a marshmallow. It’s not dense like pvc pipe. So, Azek specifies a light body pvc cement because it will not “bite into” their trim board too much and thus compromise it, according to them. I’ve seen this proprietary glue fail time after timeĀ  (could I please get Cyndi Lauper out of my head now!). I use a medium body pvc cement, preferably in a squeeze tube to fit neatly in my tool pouch. It “bites into” the trim board enough to hold the joint through the changes in seasons. This allows me to create exterior trimwork that water will never have the opportunity to infiltrate. It can join layers of trim on adjacent planes and at perpendicular angles. A trim product that doesn’t absorb water and adhesives and techniques that ensure tight joinery for years to come. I mean, what’s next? Are they gonna come out with commercial free radio stations or something?

Joining the upper wood with the new, lower pvc. Notice the Gorilla glue squeeze out.

The next thing to think about, with regards to this repair project, is joining the new pvc trim patch to the existing wood trim layers. I chose to save the upper portions of the wood trim that weren’t compromised. they will be out of the snow and rain, and I know we can elevate our game to keep water out of these joints. First, the lower product that would be catching all the water will be pvc. Second, we will use relatively small pieces for these patches so that the percentages that they will shrink with thermal changes will have a miniscule practical effect. Third, when we bond them to the wood we will use the best adhesive ever for this application…next time. I loathe making mistakes, and both times I’ve had a hard time reconciling it (laugh with me). However, I chose Gorilla brand polyurethane glue for this particular application, and then second guessed myself. To satisfy the second guessing, I did a test joint with a piece of wood joining to a piece of pvc trim. The next day it was no good. The glue didn’t bite into the pvc andĀ  I was able to force the joint apart with some effort. One of the reasons that I chose this glue, however, was because of it’s expansive properties. The other was because of it’s insane ability to bond to wood. Boil it down, and the glue I chose did not properly bond the two pieces. It did, however, expand to fill the entire joint 100% and form an unbreakable bond with the upper wood part of the joint. So, the wood end grain is well sealed forever, and the pvc trim board underneath it should not contract beyond a hairline. Lovely.

For the longer pvc trim boards, I made new nose pieces at the top that sit underneath the wood trim (For this whole paragraph, I have no pics…this blog post was an afterthought). I applied a heavy bead of Lexel caulk and then screwed these small pieces into the upper wood trim. I then applied a nice bead of pvc cement to the top butt edge of the long pvc board before butting it into this small pvc trim detail. Because we used the proper fasteners and adhesives, this perpendicular joint will not fail.

It’s alright to use stainless finish nails when using small components. Further, the nails are only going to be carrying the load until the glue sets up in five minutes or so.

The last thing to remember is to account for whether or not your pvc trim is going to be painted. It doesn’t have to be, but machine marks must be eliminated. They leave tiny pits that allow algae and mold to build up in. Raw edges, if unpainted and unsanded, turn almost black with these growths. Finely sand or paint all exposed cut edges. Also, paint doesn’t stick to sharp corners, so ease the outside corners of your work with a piece of sandpaper. Lastly, paint doesn’t stick to shiny pvc trim very well. I know, your painter and paint retailer will contradict me. That’s fine. I’ve been in the position to come back around to a project 6 months later, to see how the paint held up. The right paint, according to the manufacturer, didn’t stick. I now recommend gently scuffing the entire pvc surfaces to be painted to remove the “shine” from the board, beforehand. It is a price to pay, but remember that the new pvc trim will hold paint FAR longer than wood will, due to it’s moisture stability.

Finished product…before being painted to match.

By John Bradshaw

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