56-yr. old 3/8" Redwood Siding Separating Non-Detracting Slat Additions

[3/8RRWsiding]

We have a guest house with 56-yr. old, 3/8" shiplap siding, built in 1968, that began shrinking in width over the years The siding was originally fastened using one nail center-stud placed every 16".
Because the planks are only 3/8" and face east, the top thinner edge warped first.
At the time of first repair my only option available was to fasten the thin, bowed edges with a wood screw into a stud only until the top thin-edge got recessed under the overhead overhanging lap that wasn't seated on top of the thin edge at all.
I would like to use redwood material from this stack of 16' x 3/8" T&G butt joint planks that were salvaged from a 16' wide garage door covering. The tongue & grooves are only 1/4" so the joints are not usable in my siding repair situation.
I could rip strips from the stack of planks to any width needed if I wanted to scab a strip (one nail) to studs along the warped edge, under the thick (bottom) edge of the lap above it, but the planks would be the same 3/8 thickness - and when the two edges are butted-up, rainwater has a great tendency to move inward through the gap. Exterior gluing the butted edges together would not survive expansion and contraction exposure.

Any thoughts on how I can utilize the materials I have on hand to eliminate rainwater intrusion would be greatly appreciated. Thanks

 

[Greenman]

From your description and pictures, the siding has failed. Without a lap the only thing preventing water from getting into the stud cavity is the tar paper behind the siding. That paper is most likely baked at the laps from exposure to the sun.
There isn't any practical fix. A few cases of caulking and a couple coats of elastomeric paint will buy you a few more years of service, but the material is toast.
You can have matching material milled if you want to maintain the look, but you'll pay through the nose for it.

 

[3/8RRWsiding]

Thanks for the opinion. How about if I rip a 3" strip from my 3/8's plank pile, with the table saw blade angled to its most critical bevel (@ 45-degrees)? The tapered bevel can be stuffed under the overhanging (thick) lap edge above it, and then when water sheets down the siding on its way to the ground, the tucked-bevel edge would prevent rainwater from backing up (as physics dictates) into any gap it could find that would allow water to enter the structure? I could use only one galvanized nail through the strip at the inner wall stud positions to allow for some heat/cold flex of the strip, and the taper of the beveled edge to repel water - with the help of a thin bead of GE® 100% silicone into/along the new seam where the bevel meets the overhanging lap above it?

 

[Greenman]

I think tucking that strip into the channel above it will split the boards. If you want to do something like that use sheet metal. I also wouldn't use silicone as caulking, it doesn't accept paint, and will quickly look really bad.

I'm sure you'll be able to squeak a few more years out of it, but keep a careful eye on the interior as you will get moisture damage.

 

[3/8RRWsiding]

Sheet metal sounds good. I can prime and paint it to match. Very good suggestion. Would never have thought of it. Thank you. Great site for Q&A. Thanks to all

 

[3/8RRWsiding]

I researched and found that this is the best caulk for redwood. Can be used on damp surfaces. Can be painted. And, it does not adhere to any silicone or silicone residue, so until this arrives I will use wide blue tape to repel rainwater that is soon to be sheeting down the shiplap. Any comments to contrary would be appreciated.

Lexel Adhesive Caulk, Clear​

Amazon.com

 

[Greenman]

Lexel is horrible stuff to work with. I used it once and swore I'd never touch it again.
Sikaflex is a very good product that I've used often. Harder to work with than latex, but much better quality.

 

[3/8RRWsiding]

I'll check out Sikaflex, limestone is the color I've chose, wish it came in clear, but what is the workable problem specifically with Lexel? I bought the Lexel for temporary water sealing around the vinyl frame and non-sealed redwood framing on their exterior side of double-pane bay windows. After the storm season, I'll be removing the exterior redwood framing strips, and Lexel caulking around the perimeters of the 5-windows before re-installing redwood framing strips again.

 

[Greenman]

I found it to be runny and sticky. Didn't like the it went on or tooled.
If it works for you then by all means use it.

 

[3/8RRWsiding]

"runny and sticky". The facts I was looking for. Might work on my window/trim sealing task using a steady extrusion amount, producing a flat bead without wiping. All in the size of the tip hole. Cut a tiny opening and run a test bead on something until it suits your purpose. Stays clear for a long time exposed to sun its said. - thank you!

 

[Sukhoi]

Yeah Lexel is fine if you don't need to touch it and don't care about the final surface, but it doesn't tool well. I used it around the windoors on my truck camper shell that leaked from nearly day one, and it's held up well so far for five years.

 

[3/8RRWsiding]

Good to know. I am using it between exterior window framing to prevent water from entering between contact surfaces of wood and plastic window surrounds.