Finishing coated plywood

[Dengue]

Bunnings is selling black coated form ply F14, and also Film Face Ply, which is also a black coating.

Can anyone please tell me the difference between these two, and how best to finish them for an outdoor cabinet application? I need to paint them another colour

[Master Splinter]

I think you'll find that one is just the cut down to smaller size version of the full sheets of formply.

[Bob38S]

I think the only way you are going to change the colour is to remove the black "film".

The original design of formply was to be used in the concreting industry where it was used in boxing which was reusable and did not require oiling to release from the concrete. The stuff I have used has more a brown coating rather than black but if the black has the same qualities then nothing sticks unless the surface is broken.

[Dengue]

Thanks Bob38s, you are correct. I spoke with one of the Bunnies managers and he said the surface would have to be at least etched and then primed, but there was no guarantee of a good finish.

I was hoping it was a way of avoiding having the cracks and grooves in a plywood finish

[malb]

There is a primer product designed for prepping the plastic faced random groove 3-4mm ply and simiar plastic faced products. Used it years ago to prep stuff and it worked quite well. Finish coats were still hanging tenaciously to the RG ply when my mate retired and sold the factory 15 years later.

Cannot remember the name of the stuff but it was still in Bunnings paint section a couple of years ago. It comes in a tall skinny metal can similar to the Triton finishing oils of old.

That said, form ply itself is not weatherproof and will delaminate, warp and bubble over time particularly if it gets moisture around the edges, so it is not overly suitable for your project. Sheets are quite often warped and twisted when purchased, relying on the pressure from a few ton of concrete and a lot of framing to flatten them. When used for boxing, Form ply is intended to release from the cured concrete without prior use of a release agent, primarily to avoid surface contamination of the concrete which may need it's own surface treatment later. Obviously oil or silicon surface contamination will adversely affect later surface finishing.

Film faced ply is a term applied to any ply coated with a plastic film, the random grooved that I mentioned before would be the other common example here. However in North America and possibly Europe, you can get decent film faced Baltic Birch for jigs etc but it is not cheap.