Grooving

[Bromley]

I am proposing to make a pair of external doors . They will largely be cosmetic, to hide a large and ugly window on what used to be a garage and was converted (before our ownership) into a room. It's now my workshop.
Anyway, the doors would be wood framed around the outside, and have a inner filling of 15mm exterior ply. I would like to enliven the look of the ply by cutting small v-grooves, to make it look as if it were tongue & grooved wood.
How should I best do this?
My wife would prefer to treat the finished doors with dark creocote or similar, rather than paint them. Any thoughts on what would last best - and, if using such treatment, how 'exterior' does the plywood have to be - what grade should I use?

 

[MikeG.]

Don't do that in ply. You'll cut through the laminations, it will splinter, and it will eventually delaminate. If the lining is internal, use MR MDF (I hate the stuff, but it's the best product for this job).

Here's one I did a couple of days ago:

The file, used at 45 degrees, chamfers the circular saw kerfs and makes them look realistic.

 

[Sheffield Tony]

I did that, with outdoor ply from Wickes, a clamped on guide like Mike's, but with a v bit in a router. It is under an overhanging roof (about a foot if overhang) so somewhat sheltered - but it has neither splintered or delaminated yet. It has been there 15 years. Not that I'd necessarily do the same again.

It is painted though.

 

[Cabinetman]

Hi, I agree with Mike on not disturbing the surface of the ply, unless you buy very expensive marine ply the stuff that we get, that is supposedly WBP water boiled proof, just isn’t. Most of it comes from the Far East and delaminates if used externally without a waterproof covering, varnish doesn’t last, I would suggest painting it – it may be that your wife is correct and creosote will do the job. (Sorry I’m not an expert) Ian

 

[Bromley]

Many thanks for those thoughts. I was a bit worried about splintering the ply. MDF in my limited experience seems much easier to use, and the suggested means of grooving (helpful photos), seems quite do-able. Would mr mdfvstand up to full-on weather, though?

And would it be possible to use creocote rather than paint on MDF?

 

[Steve Maskery]

If you do go down the creosote route, try to get the proper, old-fashioned, coal-tar stuff. You won't find it in B&Q but it still available online. It's what I've used for this.

 

[spb]

MDF isn't going to survive outdoors, unless you get (very expensive - think 6 times the cost of standard) Tricoya.

 

[MikeG.]

...Would mr mdf stand up to full-on weather, though?....

No. You did say the ply was going to be on the inside. Or at least, that's how I read it.

 

[Bromley]

Sorry - no, I meant the filling, with wood around the edges. Clearly, MDF won't do for that application.
I hadn't realised that creosote was still available, even though restricted to professionals, so that could be useful to treat the completed doors.
The Missus has now come up with the idea of gluing/pinning thin stripwood trim to the ply sheet, to give it interest, rather than cutting v-grooves, and that is probably the simplest solution.
Thanks for all the comments and advice.