Joining sheet goods

[John Craig Brown]

I am doing some wainscotting requiring seaming 3/4 plywood along a wall. As I intend to paint, what is the best method of covering the seams - spackle, cauk, woodfiller (Bondo like) etc.

[Eric Roberge]

Are you using GP bead board? They have a 3/4 bead board or are you making it yourself? The GP stuff is usually 1/4 or 5/16 with a half lap joint on each that fall within a groove. Should be near seamless. If not a little wood filler or caulk should do the trick.
Or are you doing 3/4 x 3.5 strips?

[John Thompson]

I would half lap it as suggested. You shouldn't have a problem doing that with 3/4" if I read the post correctly.

Sarge..

[JohnT Fitzgerald]

I've seen at least 2 VERY GOOD interior/finish carpenters use Bondo for filling seams like that.

[glenn bradley]

+1 for half lap at the groove, no filler needed.

[Peter Quinn]

Is this a but joint on flat panels or bead board? I too like a half lap for seaming plywood, little more than latex wood filler is required on a well made joint. Bondo is useful for filling deeper voids and defects on edges, but its strength comes at the expense of being more difficult to sand.

I am curious as to why a seam in the field would be necessary? I am willing to incur a greater waste factor and hide seems behind vertical moldings rather than risk seems developing site lines in the field of a wainscot pattern. Perhaps I am misunderstanding your application?

[Jim Becker]

A recent article that I read (I don't recall where specifically, but probably This Old House Magazine) indicated that caulking/filling the joints in wainscot can make the joints more visible over time. They suggested just painting. Based on my experience with the beaded hard-board I used for the wainscot in our kitchen, I have to agree with them. As the house moves, the seams move and the caulked joints have become quite obvious...from being partially opened up.

[John Craig Brown]

Thank you all for the excellent information. I said wainscoting to describe the work I was doing but I really meant 3/4 plywood, paint grade. The 1/2 lap is a great suggestion but the panals are already up and since I am going to paint the panals I would still end up with a seam. I have used Bondo in the past and it accepts paint fine and is quick to use. I was worried with wood movement with the Bondo and was considering using cauk instead but I will stick with the Bondo for now.

I am working on water damage that occurred in a 1930's home in Miami Florida - when I removed the preexisting 1/4 paneling the rest of the wall followed including the lathe down to the block outter wall - so instead of using sheetrock to covered with ply I opted for the 3/4 ply as the covering from the block to the existing (remaining) lathe/concrete/plaster covering is 3/4"

[David Keller NC]

I would use paintable latex caulk (not the silicone formulations) to fill the seams. The reason is that the latex will remain permanently flexible, while the Bondo will not. Ditto for "plastic wood" filler - it will dry to an inflexible, hard joint that will pull away from the plywood when the wall moves a little over the seasons and as the house settles. That pretty much guarantees a crack in the panels somewhere along the wall. With latex, as long as the wall doesn't moove all that much, it will give a little and remain intact.

[Prashun Patel]

For changes of plane, you could get away with caulk, but if you have to hide seams in the same plane, it's hard to beat tape and mud. For painting, a skimmed and sanded coat of dwall compound can fill grain and give you a cleaner painted surface also.