Technical, Techniques, Hints, and Tips > Wood Care:

Plywood

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badbunny:
What is Marine Ply? Is it the same as the plywood you get from B&Q? If I am looking at some, can I tell what type it is?

Are there different grades of ply, ie better quality laminates less prone to splintering?

Where is the best value place to buy good quality ply (particularly very thin sheets)?

Thanks,
Peter.

anmo:

--- Quote from: badbunny on October 03, 2007, 08:52:56 am ---What is Marine Ply? Is it the same as the plywood you get from B&Q? If I am looking at some, can I tell what type it is?

Are there different grades of ply, ie better quality laminates less prone to splintering?

Where is the best value place to buy good quality ply (particularly very thin sheets)?

Thanks,
Peter.

--- End quote ---

badbunny, the last thing I want to do is discourage a new forum member, but all these questions you're asking on plywood/paints/clear coats etc have been covered repeatedly, many would say "ad nauseam" on Mayhem already. The info you seek is all there if you look for it, how about trying the Search facility?

badbunny:
It may seem that it has been discussed, but I have used the search facility, and have found the following.

1) Marine ply - I cannot find anything about marine ply on here. If you google it you can find technical descriptions of marine ply, but that doesn't help me to identify the stuff!

2) Clear coats - If you use the search for clear coats there are LOTS of hits with discussions mainly in builds. I have looked through a LOT of these, but different people have different methods and if you read them and their little hints n tips, you will find contradicting information. I haven't been able to find a dedicated discussion of the subject - if you know of a thread that does this, can you please point me at it.

3) Acrylics vs enamels for a working boat - I can't find anything on this topic.

I think for experienced modellers, who see these topics touched on time and again, it can seem like they have been dealt with in depth. However for someone inexperienced, trying to piece together fragments of information from lots and lots of threads it can be very difficult.

Thanks,
Peter.

DickyD:
Exterior grade plywood (WBP - Weather and Boil Proof) is specially made using a water-resistant adhesive to withstand a certain amount of moisture and can be used for outdoor constructions - sheds etc. and is sometimes used as a cladding material, particularly for insert panels under windows. WBP does require additional protection (paint or varnish) to protect the outer veneer.
Internal plywood is of a similar quality as Exterior grade but it does not use water resistant adhesive. It can be used for wall panelling, flooring and furniture.
Shuttering Ply is used in the construction industry for making shuttering boxes for containing concrete while it goes off. Although water resistance to a degree, the sides of this material are not finished with a decorative veneer and is generally not suitable for use where a quality finish is required.
Marine Plywood is made with waterproof adhesive so that it will stand immersion in water, the veneers themselves will not last forever under water so the material should still be finished with paint or varnish.
Plywood is normally available in 2440 x 1220 sheets (or subdivisions) and in thicknesses from 3 to 35 mm.


Working with plywood

If the sheets are to be used in a centrally heated room, store them in similar conditions before use so that the moisture content of the sheets will stabilise before installation - this will avoid shrinkage later.

Cutting

To avoid damage to the finishing face, cut into the panel from that face - for hand sawing have the face upwards, for power sawing have the face downwards. To reduce the damage, score through the outer veneer on both sides of the sheet using a sharp knife before starting to saw.

Thin sheets (up to 3mm) can be cut using a sharp knife.
From 3 to 6mm use a tenon saw.
From 6 to 12mm thick, use a fine tooth panel saw.
For thicker sheets use a coarse tooth panel saw.

Power saws can be used with thicker material but are more likely to damage the outer skin where the saw cuts away from the material.

Fixing
Plywood may be fixed in place with adhesive and screws or nails.

Generally only small screws grip well in thick plywood itself but even then they will not stand up to repeated changes in force. When fitting hinges to any thickness, use bolts with large washers and nut to 'squeeze' the sheet. It is not practical to screw or nail into the edge of plywood.

Where a corner joint is required, fit a softwood batten in the corner so than both sheets of ply can be fixed to it.

For thin material, always fix plywood to a pre-made frame, use glue and panel pins (on about a 200mm pitch), use a punch to knock the head of the pins below the surface. The frame should support all edges of each plywood sheet and at about 400mm centres (for 6mm ply), 600mm centres (for 9mm) or 900mm centres for thicker material.

Knocks to the edge of ply can cause damage to all the veneers which is hard to rectify, so fit a thin strip of softwood along the finished edge or put a rebate in the frame so that the edge of the plywood can be recessed. This will also improve the appearance as the edge of plywood is not very attractive.

When gluing plywood, roughen the surface with coarse abrasive paper and brush clean before applying the glue. Spread the glue evenly and apply pressure.

Finishes


Plywood which is supplied with a decorative veneer can be varnished or painted but to get a really smooth surface will need good preparation as most plywoods are not as smooth as planed timber.

kayem:
The adhesives used in the manufacture of BS1088 marine ply are more or less the same as WBP Water and Boil Proof ply, and marine ply is guaranteed to have fewer voids so the quality can be better, but the main difference and most of the reason for the much higher price are the woods used for the laminations, which have to be tropical hardwoods. Most plywood sold as WBP is made from birch or something similar, usually from Scandinavia. Apart from the price, there are other disadvantages to using BS1088 marine ply, it's much harder and heavier than birch ply, which means it's more difficult to work, it will blunt your tools, and the finished boat will be much heavier. Part of this comes from the fact that most marine ply is 6mm thick,and few suppliers stock anything thinner than this. It is also available at 4mm, but that can be difficult to find. Forget about marine ply for a model, unless you want a very heavy boat stand that you can leave out in the rain.

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