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I've been asked to shiplap an area where one "wall" is the back side of an 8' tall Ikea wardrobe (technically it's one wardrobe and a portion of another). The back panel is flimsy 1/8" hardboard, and the side walls are 18mm (.7") particleboard. The shiplap is 5.5 x .5 pine.

I can think of a few ways to do this, each with drawbacks.

  1. Brad nails straight into the frame (wardrobe side walls). But I don't really trust the nail holding power of particleboard and a misfire could stick through the side of the panel and be difficult to repair. Probably a nonstarter for that reason.
  2. Use construction adhesive. But the back panel is flimsy, and I don't think there's a good flat surface for adhesion along the edges.
  3. Screw some 1x2s (or 2x2s?) into the particleboard frame (from the back) with coarse threaded #8 screws (carefully predrilled), and then nail into those with the Brad nailer. This is my leading option.

When I get to the corner where the shiplap will meet the other wall (already shiplapped into studs in the photo below) I could also theoretically shoot some short brads on an angle to attach the shiplap on the wardrobe to the shiplap that's already installed.

Carpenters of StackExhange, what do you advise?

Close up of back panel and seam.between the two cabinets

You can see there are actually two cabinets, about 24" wide total, with a seam about 5" from the end.

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  • maybe consider attaching the lap to a 0.25" OSB/plywood panel that you then rest/tack/glue to the cabinet.
    – dandavis
    May 23, 2022 at 20:57

2 Answers 2

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Little brad nails are more than sufficient to hold the back on the cabinet, I'm not sure why they wouldn't be sufficient to hold the ship lap on to it, too. You trust those little nails to hold the back on and prevent the whole cabinet from falling sideways, so if one or two of your additional nails should happen to fail to hold, it'll only be holding on the ship lap that will be held on by other nails and the boards above/below it, and still won't allow the cabinet to fall over.

Note that the nails that hold the back to the frame are roughly in the middle of the thickness of the verticals, therefore, you have a fair bit of "wood" to hit with your nailer.

Nails can wander when driven into real wood because they hit the grain and will follow it. Particle board, however, has no grain, so that shouldn't be a concern. The stuff is going to be harder than regular wood, so you might have to step up a nail gauge or two, but I doubt it.

A misfire would end up not shooting a nail, while a poorly aimed nail would cause you problems. However, as you build up your layers of ship lap, you'll know exactly where the frame edges are because you'll be able to see them clearly exposed above the new piece of wood you're adding. You just have to confirm for this piece where the existing nails are and try to avoid hitting them. Taking your time to carefully set and line up the nailer so it's 90° to the vertical and you should be fine. It'll take longer, but less time than it would to fix one missed nail.

FWIW, I'm building my own "flat-pack" cabinets to match some IKEA cabinetry we already have since they can't tell me how long it'll be until all the parts I need for their exorbitantly over priced versions will be available. Once the carcasses are built, I'm planning on using either a nailer or stapler to attach my 1/8" plywood backer to it. I'll take my time to make sure each fastener is lined up before pulling the trigger.

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  • My only concern would be if there was too much distance between uprights for just brads on the ends. You might get some bowing in the middle depending on the board length. I'd lean toward #3.
    – RetiredATC
    May 23, 2022 at 17:25
  • Ship lap would go on long-edge vertical. I suppose it could sag over time, but I wouldn't think it would sag much. In that case, vertical lath to give an intermediate support could be beneficial I suppose.
    – FreeMan
    May 23, 2022 at 17:30
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    I'm not talking about vertical sag, but instead bowing (not laying perfectly flat against the board behind it). Short distances probably will be fine, longer distances, maybe not.
    – RetiredATC
    May 23, 2022 at 18:23
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    I ended up going with this approach. I did mis-aim a couple of nails over the course of the panel, but they both poked through the side that was going to be shiplapped next, so they're hidden.
    – Aaron
    May 28, 2022 at 1:31
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I would use construction adhesive to attach the shiplap to the back.

But first, is the back shiny? If yes, get some 80 grit sandpaper on a random orbital sander and scratch up the back so the adhesive has something to grab on to. Make sure to clean all the dust off the surface. A shop vac will probably do the job.

If it still feels flimsy afterwards, you could install some 1x2s on the inside of the cabinet like your option 3. Screws are overkill if you have a brad nailer. Especially if you also use construction adhesive.

Also, I would finish the corner with some wooden outside corner molding painted white.

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  • My concern here is that if there's any bow in the shiplap (either now, or after a humid summer), there won't be anything to keep it flat. The flimsy backing will just bend along with the shiplap.
    – Aaron
    May 23, 2022 at 20:02
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    I think you're worried about nothing. But if you really have to do something about potential warping, then cut the boards a quarter inch short short so the corner molding allows the boards to expend and contract. Also paint both sides of the shiplap before you install it so that moisture absorption is uniform instead.
    – longneck
    May 23, 2022 at 21:25
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    Or you could mount some plywood to the back of the cabinet and glue the shiplap to that. But now you've spent more than the cost of an IKEA cabinet on a hidden piece of plywood.
    – longneck
    May 23, 2022 at 21:26

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