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Laminating plywood

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Grahamshed

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Hi again
I need plywood with a good veneer on both sides and it costs a bomb. I am debating the practicality of sticking two 6mm veneered face sheets together to produce a 12mm piece faced both sides but have in mind that plywood has to be made up from an odd number of layers. Sticking two together would obviously produce an even number. Is it a big deal ?
 

thick_mike

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I always thought that the reason for an odd number of layers was that the two faces have grain running in the same direction. I would have thought that an even number of layers would have been dimensionally more stable (very slightly).
 

Grahamshed

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thick_mike":31z19cnt said:
I always thought that the reason for an odd number of layers was that the two faces have grain running in the same direction. I would have thought that an even number of layers would have been dimensionally more stable (very slightly).
If the reason for the odd number of layers is merely cosmetic then that is great, it will be even more cosmetically pleasing when I have finished with it. :) I had assumed it was something to do with warping, a central core with an equal number of veneers on each side sort of thing.

I am doing up an old boat and want to replace the existing dark woodwork ( toilet wall and door, cupboard doors, seating partition etc with something lighter like ash or something. There is not much of it.
 

Yetty

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Indeed odd number of ply layers is for stability, the grain directions are balanced around the middle layer, so the effects of moisture are balanced, ideally.

Gluing two together is fine and works. Arranged with the glued faces each with grain in same direction, this effectively makes for one layer in the middle with double thickness – so it’s odd again.

Has worked fine for me, just make sure it’s kept flat as glue dries!
 

Grahamshed

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Two layers become one. Hadn't thought of it like that.

I have read somewhere ( maybe on here) that PVA should not be used with plywood. What would anyone suggest ?
 

Yetty

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Two possible reasons:
1, pva is not strictly waterproof, so might delaminate if exposed to water
2, pva is water based, so when applied to panel, the panel might expand across the grain width and cease to be flat. Before now when worried of this happening, I’ve applied pva to both contacting surfaces, fairly quickly, using a 6inch wide rubber roller, jointed, and then left it to dry under flat caul. No problem.

I dare say there are other reasons others can suggest??
 
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