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marcros

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I am confused by what product I need...

it is to be used outside, to support a piece of granite so the the overhang is reduced to 50mm. I was planning to use approx 1" thick, so 2 pieces of 12mm glued. In theory it shouldn't get too wet/weather beaten because the granite covers it, and it will be painted for aesthetics as much as anything although will be out of site from 90% of viewing angles.

Is WPB Hardwood faced exterior ply better that pine exterior ply? Genuine BS certified marine ply is very expensive and seems harder to get. Is "marine ply" used as a term more generally than meaning that specific grade of ply, such as a general reference to exterior ply?

The local place has:

https://www.woodworkstimber.co.uk/produ ... cale=en_GB

https://www.woodworkstimber.co.uk/produ ... cale=en_GB
 

robgul

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This may be useful - it's a pdf doc that you can either read online or download. https://www.google.com/url?sa=t&rct=j&q ... cYZEKJneDQ

Whilst plywood is described as "exterior" in my experience it's not very happy in exposed situations where it gets wet etc - marine ply (the clue is in the name) is OK . . . they build boats with it.

That said, what you're planning to do isn't totally obvious - what is the granite doing?
 

AJB Temple

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Either use Marine ply or something else. Any other form of ply will delaminate. Water will wick under from the table top.

All you actually need is a simple frame to support your granite, and if it were me I would do that using hardwood. I use oak for pretty much everything as I have a lot of oak, but some iroko or similar is not super expensive and will last many years.
 

marcros

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the problem with a frame, as I see it is that it isnt going to offer much support is it? Worst case, if somebody was to sit on the corner of the table (max overhang of the top), the frame is only going to have tenons holding it up.
 

ArferMo

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Tricoya is the upcoming stuff. 50 years life outside; so they say. Can you afford it is the question?
 

marcros

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I found a cheap place for the marine ply so will use that. I was a bit hesitant with using merchants that may have a sheet or two of marine in, because they have a habit of it either being damaged when you see it or they will sending whatever they think might be that spec but could be anything. "The computer says we have a sheet so it must be this one".

The place that I use when I am in the office is a specialist sheet material supplier so I will have a drive to that side of the city.
 

marcros

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ArferMo":h0gae149 said:
Tricoya is the upcoming stuff. 50 years life outside; so they say. Can you afford it is the question?
There is a disconnect between the depth of my pockets and the length of my arms when it comes to tricoya. I knew it was expensive but I hadn't realised it was quite so bad, marine was £36 Inc vat for a sheet of 9mm, tricoya is £107 or more on a couple of websites and I can't get it locally.
 

ArferMo

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marcros":ihefyefr said:
....I knew it was expensive but I hadn't realised it was quite so bad....
Mmm yes! Isn't it just? But on the other hand you can buy it coloured through and through to match whatever and it will never need painting or varnishing, ever. That is a cost saving over a lifetime; not sure if the savings balance out though.
If anyone should go down this route it almost demands the Lamello Zeta P2 plus a load of Clamex connectors for bragging rights when the neighbours come round; the ultimate knock-down garden table.
 

marcros

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the lifetime savings are always harder to justify when I dont charge myself for my time. if it were for a paying client, or if I was paying somebody to repaint it would be different.
 

Woody2Shoes

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I know I'm not answering your question, but I simply wouldn't use any kind of ply in that situation - in contact with the ground.

I'd use oak, or some other durable hardwood, or even Accoya, on the first six or eight inches above ground in any event. IME, all softwood and most Malaysian/Brazilian hardwoon of the sort that gets made into ply - even when treated with preservative - rots when in contact with the ground. Maybe modify your design to have four oak legs - with painted/treated ply as a sort of apron?

As I understand things, the main differentiator between ply boards made for "external" use is the type of adhesive used to hold it together - the designation says nothing about the duraibility of the plys when close to wet ground in service.
 

Woody2Shoes

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Sorry - I've just re-read your posts - if the timber is to be under the edge of the table top to form a lip, I'd just use a treated softwood roofing batten or some other treated softwood. Almost any kind of ply would be suitable under the zinc sheet - I'd give it a couple of coats of aluminium primer to seal all edges/surfaces first.
 

marcros

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Yes it is not on the ground, it is immediately under the top to reduce the cantilevered span of granite alone.
 
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