Exterior plywood

If you are using exterior grade plywood I would not worry too much, but a coat of exterior paint in the screw hole should be more than enough.

Just don't full tighten the screws when you erect it. Then loosen a screw at a time, paint it and then tighten up. Or even a silicone sealant applied again just before fully tightening.

 

If you use the correct size screw for the hole you'll be fine, maybe use stainless screws it you're concerned. To be honest, the paint cracking and trapping water over the years is more likely to be the problem.

 

If possible set the ply off the wall a tad using spacer, allowing an airflow around it, this will prevent damp on the back face from condensation.

 

All off the above and a thin strip of timber glued and pinned to the edges to stop water getting into the end grain.

 

my experiences of so called exterior grade ply haven't been that great if any part of the edge is exposed. Why ply?

 

The idea of glueing a strip around the edge is a good one, pu glue ideally, and leaving air space at the back, but ultimately it's down to maintenance as to whether it lasts.

 

What are you thinking, tricoya?

 

Exterior ply or not I would still give it a couple of coats of a clear wood preservative for wet rot, dry rot, insect attack etc.

 

I wasn't really, just my experiences of ply outside haven't been that great. I have a feeling that much of what is sold as "exterior grade" isn't. I have a round garden table base that a blacksmith made for me donkeys years ago. First it had a proper exterior grade ply top, and that one lasted 15 years. Since then the replacements have not done better than 3 years, despite me making it exactly the same way with supposed exsterior ply, and literally soaking the top in various preservatives. Also years ago had a shopfront myself, and the ply facade degraded very quickly.

Given a choice I would use anything but ply, unless, as chippie says, the exposed edge can be totally sealed. I guess you could use tricoya, or uPVC sheet or even waterproof cement board (sold for e.g cladding buildings).

 

Bring back enamel signs!!

 

If that was me, i would use Marine Ply and cover it in uPVC sheeting, as its for a shop front you want to make it look professional, clean and tidy and this is a good way to do it. If you didn't want to do that, simply coat your plywood in a preservative a few times, as others have mentioned leave it out from the wall a tad to allow air flow. Personally as its for a shop i would use the PVC method, but its your choice. whichever one you choose will suffice for your requirements.

Bertie

 

He will need a mortgage to buy marine ply

 

My now ex brother in law built a garden table top out of MDF years ago and it even had a hole in the middle for an umbrella, I didn't think it would last a year but it's been there at least 5 and has hardly blown at all, god knows what he painted it with but it would be something cheap.

 

Good old CREOSOTE with engine sump oil added.....................they were the days............. youngsters today ...tutttttt!

 

Did he like a Sunday morning fry up, well the fat had to go somewhere.

 

Sounds like dad's old shed.

 

The top coat was grey, probably DA's favourite.

 

grease the screw