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Treating plywood for external sign

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Daniel Evans

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Post Wed Jan 04, 2017 12:35 pm

Treating plywood for external sign

Hey guys

I need to make an external sign, been suggested to use marine plywood but due to the cost, the customer doesn't want to go for it, so will normal plywood be ok?

Basically, it's going to be a 4ft x 8ft sign with ACM on the front and screwed to 2 posts behind, i also thought of putting architrave around the edge to finish it off and just let the board sit inside that.

I intend to paint the whole sign to match their colour, so is there a certain paint i should use?

Thoughts?
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DavidRogers

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Post Thu Jan 05, 2017 4:21 pm

Re: Treating plywood for external sign

You'll get a good few years before it's knackered and delaminates with standard (fair quality) board...And moisture will get trapped between the ACM and the wood.
What will get spent on multiple coats of exterior paints over cheaper wood can be offset with exterior/marine ply... Especially when it comes to time spent. (Extra couple of hours painting and days drying)

Exterior paint will always add protection and colour, but given a say 10 year lifespan that extra £30 - £50 on wood isn't so bad.

Oh, and use non-rusting fixings if you can and at least 12mm wood (18 or 25mm better but weighs much more).

Dave
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Daniel Evans

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Post Fri Jan 06, 2017 10:28 am

Re: Treating plywood for external sign

Thank David

Decided to go with a 6mm marine plywood along with the 3mm ACM and use a frame to surround both.

Paint the frame and the plywood to match their colours and hopefully it should all look pretty nice.

Thanks for your help.
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Robert Lambie

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Post Fri Jan 06, 2017 10:40 am

Re: Treating plywood for external sign

If you are screwing into the sides of the wood, be sure to angle the screws slightly. More so along the bottom.
This is because as the wood gets wet or weathers around the parameter first and the plywood will expand/open. when this happens your bottom rail of trims weight will pull the screws out as they have nothing to grip.
angling the screws slightly like the following: \/ \/ \/ \/ \/ stops this from happening.
it is also better to use longer screws on the bottom length of trim for same reasons.
when i do the sides, i always angle the screw in a slight downward angle for same reasons.
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NeilRoss

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Post Fri Jan 06, 2017 11:00 am

Re: Treating plywood for external sign

For an 8' x 4' backing board I wouldn't use anything less than 12mm (half inch) ply. Have you considered using sign channel instead of the ply?
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Robert Lambie

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Post Fri Jan 06, 2017 11:18 am

Re: Treating plywood for external sign

NeilRoss wrote:For an 8' x 4' backing board I wouldn't use anything less than 12mm (half inch) ply. Have you considered using sign channel instead of the ply?


I meant to mention this too Niel, but then thought he maybe using a U-Shape trim to enclose both sheets right around the edge. actually this being the case, using a screw into a sheet that thin will just split it. bast going through the back if using U-Trim.
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Daniel Evans

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Post Fri Jan 06, 2017 11:44 am

Re: Treating plywood for external sign

Thanks guys

I was going to use the following trim in the attached image, this will allow me to insert both parts into the trim leaving a nice clean edge.

I can understand how this may be flimsy but this was the best way I could find doing a board with a nice edge, edge and back if the board needs to be green

https://signgeer.com/product/double-sid ... g-2-6m-522
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NeilRoss

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Post Fri Jan 06, 2017 11:58 am

Re: Treating plywood for external sign

Robert Lambie wrote:
NeilRoss wrote:For an 8' x 4' backing board I wouldn't use anything less than 12mm (half inch) ply. Have you considered using sign channel instead of the ply?


I meant to mention this too Niel, but then thought he maybe using a U-Shape trim to enclose both sheets right around the edge. actually this being the case, using a screw into a sheet that thin will just split it. bast going through the back if using U-Trim.


I wouldn't be happy putting my name to it unless it was of substantial build. An 8x4 board mounted on two posts will catch considerable wind so needs to be strong and rigid enough to stand up to that. If you're set on using 6mm ply, or even 12mm ply then you should have two or three rails fixed across the posts and then the ply screwed along them. Then the ACM (good quality) screwed through the ply into the rails. You can then frame it properly, fixing it into the rails. Also consider the height of the sign/posts - you'll need substantial concreted in footings for a sign that size. Your customer may not be happy with the price of a proper job, but when it all gets trashed in the first gale he'll be on the blower blaming you for using insufficiently strong materials and build practices.

There's always somebody down the road that will do it cheaper, but not always better.
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Robert Lambie

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Post Fri Jan 06, 2017 12:01 pm

Re: Treating plywood for external sign

I agree it will look nice when done mate.
trouble with that is you are going to have to glue that U-Shape wooden trim to the panels.
you may get some pin nails into it but careful not to split it.

how are you fixing the panel to the posts?
just asking as that wooden trim/moulding is double sided so the board will sit back from the moulding which will be touching the posts. you pay have to fit some packer straps to the rear.

should look nice once done.
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Daniel Evans

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Post Fri Jan 06, 2017 12:18 pm

Re: Treating plywood for external sign

There's some great points there, how would you guys make it, basically I know I'm using a 3mm acm board and I would like it to have nice edges
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Stephen Morriss

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Post Fri Jan 06, 2017 3:53 pm

Re: Treating plywood for external sign

Late to the party but..

Having used various ply boards over the years I'll only use marine or birch ply now, the cost of the materials is nothing compared to the time spent making and then replacing it. I had one set of signs made from water proof ply that all had to be replaced a few months later.
Also on a sign board 8'x4' I'd be using 19mm, I tend to go overboard sometimes but if it's only on 2 posts you'll get a lot of wind load. Make sure the posts are good ones as well, I've seen them snap from knotts.

Steve
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Daniel Evans

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Post Fri Jan 06, 2017 3:55 pm

Re: Treating plywood for external sign

Hi Stephen, thanks but what would you use for the edging?
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Martin Pearson

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Post Fri Jan 06, 2017 4:11 pm

Re: Treating plywood for external sign

Not really up to speed with current pricing as I don't tend to do a lot of work now days but I would have thought with the price of a suitable marine ply backing board |(like Steve 19mm would be my choice), plus trim round the edges of the boards & something to use as a sealer to help protect the backing board would you not be almost as cheap buying a 3mm aluminium panel with rails fitted ?
There is then no need to think about how well it will stand up to wind loading providing it is fitted to suitable posts which would also be true of the composite panel & wooden backing board :lol: :lol:
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Stephen Morriss

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Post Fri Jan 06, 2017 4:13 pm

Re: Treating plywood for external sign

I'm not sure really, it all depends on the use.
Aluminium angle, wood trim, lots of different styles of edging available and the 19mm edge gives you a good thickness to screw into. Also like Rob said angle screw as the bottom edge does hold water far more than you'd think.

Steve
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Stephen Morriss

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Post Fri Jan 06, 2017 4:17 pm

Re: Treating plywood for external sign

No idea of other locations but the last time I bought marine ply is was about £47+ vat, birch ply is slightly more but you don't get many defects in it and it's great for CNC V cut signs.
It's a few months since I last bought some so I suspect the price has jump since brexit :rollseyes:

Steve
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Daniel Evans

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Post Fri Jan 06, 2017 9:48 pm

Re: Treating plywood for external sign

Hi guys

It's for a Bowls club so It need's to look a little traditional hence going down the wood route.

Stephen, you mentioned there are loads of edging available, care to add a link? I can't find any other than the one I posted

Thanks

Dan
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NeilRoss

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Post Fri Jan 06, 2017 10:06 pm

Re: Treating plywood for external sign

Daniel Evans wrote:Hi guys

It's for a Bowls club so It need's to look a little traditional hence going down the wood route.

Stephen, you mentioned there are loads of edging available, care to add a link? I can't find any other than the one I posted

Thanks

Dan


Daniel - you can get GRP sign blanks moulded with edging like architrave. Don't recall many suppliers at the moment, perhaps Glasdon (glasdon.com)? Signmaster are another (signmasteruk.co.uk). There are other suppliers/manufacturers and they can often produce them in the colour of your choice. Maybe somebody else here can point you to a supplier. Very nice product and well worth considering.
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Stephen Morriss

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Post Sat Jan 07, 2017 11:49 am

Re: Treating plywood for external sign

Fair point Neil. Glasplas are a company I've used in the past and I seem to remember they have a long warranty.

Re edging, I tend to make it up. So for a ply sign I would get planed all over wood and glue and screw it onto the edge, insert the dibond sign board (after fitting to the posts) and then add a beading strip inside to finish it off.
This gives you a traditional-ish sign with a sign face that will last a long time.
Fit to some nice wood posts concreted into the ground and you have a sign that fits into most traditional backgrounds.

Steve
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Steve Morgan

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Post Sat Jan 07, 2017 7:28 pm

Re: Treating plywood for external sign

When I first started getting involved in sign making all the boards were timber, there wasn't really any other sensible options. On a board of that size we would certainly have used 5/8" or 3/4" (that's old money ha ha) 15 or 19mm but not always marine quality. Regardless of the board quality the whole board would have been given mulitple coats of primer, undercoat and gloss, the same would also have applied to the frame, which would normally have been softwood and fitted after painting. Generally speaking, we did not put any frame on the lower edge as it was always considered a water trap, and to further help the bottom edge we usually cut a fairly generous chamfer on the back of that edge to create a 'drip edge'

Obviously your project needs the frame all round so I would suggest drill a few drain holes into the groove that your boards will sit in, otherwise the painting regime could be the same.

In the end sadly, it's cost that will probably govern you and your clients decision.

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