Plywood

==Types==
[[File:plywood.jpg|thumb|right|Average-quality plywood with 'show veneer']]
[[File:multiplex.png|thumb|right|High-quality concrete pouring plate in plywood]]
[[File:Birke Multiplex.JPG|thumb|right|Extremely high-quality 29-ply [[Birch]] plywood]]

Different varieties of plywood exist for different applications:

''See also: [[pulpwood]]''

===Softwood===
[[Softwood]] plywood is usually made either of [[Cedrus|cedar]], [[Douglas fir]] or [[spruce]], [[pine]], and [[fir]] (collectively known as [[spruce-pine-fir]] or SPF) or [[redwood]] and is typically used for construction and industrial purposes.<ref>O'Halloran, p. 221.</ref>

The most common dimension is {{convert|1.2|x|2.4|m}} or the slightly larger imperial dimension of 4&nbsp;feet × 8&nbsp;feet. Plies vary in thickness from 1.4&nbsp;mm to 4.3&nbsp;mm. The number of plies—which is always odd—depends on the thickness and grade of the sheet. [[Roofing material|Roofing]] can use the thinner {{convert|5/8|in|mm|adj=on|order=flip}} plywood. Subfloors are at least {{convert|3/4|in|mm|order=flip}} thick, the thickness depending on the distance between floor [[joist]]s. Plywood for flooring applications is often [[tongue and groove]] (T&G); This prevents one board from moving up or down relative to its neighbor, providing a solid-feeling floor when the joints do not lie over joists. T&G plywood is usually found in the {{convert|1/2|to|1|in|mm|adj=on|order=flip}} range. 

===Hardwood===
[[Hardwood]] plywood is made out of wood from [[dicot]] trees (oak, beech and mahogany) and used for demanding end uses. Hardwood plywood is characterized by its excellent strength, stiffness, durability and resistance to creep. It has a high planar shear strength and impact resistance, which make it especially suitable for heavy-duty floor and wall structures. Oriented plywood construction has a high wheel-carrying capacity. Hardwood plywood has excellent surface hardness, and damage- and wear-resistance.<ref name="Handbook">{{cite web |url=http://www.forestindustries.fi/infokortit/handbookplywood/Documents/HandbookOfFinnishPlywood.pdf |title=Handbook of Finnish plywood |publisher=Finnish Forest Industries Federation |date=2002 |isbn=952-9506-63-5 |access-date=2007-09-27 |url-status=dead |archive-url=https://web.archive.org/web/20070927200306/http://www.forestindustries.fi/infokortit/handbookplywood/Documents/HandbookOfFinnishPlywood.pdf |archive-date=2007-09-27 }}</ref>

=== Tropical===
Tropical plywood is made of mixed hardwood species of [[tropical timber]].  Originally from the Asian region, it is now also manufactured in African and South American countries.  Tropical plywood is superior to softwood plywood due to its density, strength, evenness of layers, and high quality.  It is usually sold at a premium in many markets if manufactured with high standards.  Tropical plywood is widely used in the UK, Japan, United States, Taiwan, Korea, Dubai, and other countries worldwide.  It is used for construction purposes in many regions due to its low cost.  However, many countries' forests have been over-harvested, including the Philippines, Malaysia and Indonesia, largely due to the demand for plywood production and export.<ref>{{Cite web|url=http://www.rainforestrelief.org/What_to_Avoid_and_Alternatives/Rainforest_Wood/What_to_Avoid_What_to_Choose/By_Tree_Species/Tropical_Woods/L/Lauan_.html|title=Lauan (Shorea spp.)|website=www.rainforestrelief.org|access-date=2019-11-15}}</ref>

===Aircraft===
[[File:De Havilland DH-98 Mosquito ExCC.jpg|thumb|[[de Havilland Mosquito|De Havilland DH-98 Mosquito]] was made of curved and glued veneers]]

High-strength plywood, also known as aircraft plywood, is made from mahogany, spruce and/or birch using adhesives with an increased resistance to heat and humidity. It was used in the construction of air assault gliders during [[World War II]] and also several [[fighter aircraft]], most notably the multi-role British [[De Havilland Mosquito|Mosquito]]. Nicknamed "The Wooden Wonder", plywood was used for the wing surfaces, and also flat sections such as bulkheads and the webs of the wing spars. The fuselage had exceptional rigidity from the bonded ply-balsa-ply 'sandwich' of its [[monocoque]] shell; elliptical in cross-section, it was formed in two separate mirror-image halves, using curved moulds.

Structural aircraft-grade plywood is most commonly manufactured from African mahogany, spruce or birch veneers that are bonded together in a hot press over hardwood cores of basswood or poplar or from European Birch veneers throughout. Basswood is another type of aviation-grade plywood that is lighter and more flexible than mahogany and birch plywood but has slightly less{{Citation needed|reason=da012|date=April 2013}} structural strength. Aviation-grade plywood is manufactured to a number of specifications including those outlined since 1931 in the Germanischer Lloyd Rules for Surveying and Testing of Plywood for Aircraft and MIL-P-607, the latter of which calls for shear testing after immersion in boiling water for three hours to verify the adhesive qualities between the plies meets specifications. Aircraft grade plywood is made from three or more plies of birch, as thin as {{convert|1/64|in|mm|order=flip}} thick in total, and is extremely strong and light. 

Howard Hughes' [[H-4 Hercules]] was constructed of plywood. The plane was built by the [[Hughes Aircraft Company]] employing a plywood-and-resin [[Duramold]] process.<ref>Winchester, Jim. "Hughes H-4 'Spruce Goose'." ''Concept Aircraft: Prototypes, X-Planes and Experimental Aircraft''. Kent, UK: Grange Books plc., 2005. {{ISBN|978-1-59223-480-6}} p. 113.</ref> The specialized wood veneer was made by Roddis Manufacturing in [[Marshfield, Wisconsin]].<ref>[http://www.marshfieldnewsherald.com/article/20131023/MNH01/310230453/Marshfield-women-recall-building-engineering-marvels-skies?nclick_check=1 Marshfield women recall building engineering marvels of the skies] {{webarchive|url=https://web.archive.org/web/20141217024344/http://www.marshfieldnewsherald.com/article/20131023/MNH01/310230453/Marshfield-women-recall-building-engineering-marvels-skies?nclick_check=1 |date=2014-12-17 }}, Marshfield News Herald</ref>

===Decorative (overlaid)===
Usually faced with [[hardwood]], including [[ash (tree)|ash]], [[oak]], [[Erythrobalanus|red oak]], [[birch]], [[maple]], [[mahogany]], [[shorea]] (often called lauan, meranti, or Philippine mahogany, though having no relation to true mahogany), [[rosewood]], [[teak]] and a large number of other hardwoods.

===Flexible===
Flexible plywood is designed for making curved parts, a practice which dates back to the 1850s in furniture making.{{facts|date=December 2018}} At {{convert|3/8|in}} thick, mahogany three-ply "wiggle board" or "bendy board" come in {{convert|4|×|8|ft}} sheets with a very thin cross-grain central ply and two thicker exterior plies, either long grain on the sheet, or cross grain. Wiggle board is often glued together in two layers once it is formed into the desired curve, so that the final shape will be stiff and resist movement. Often, decorative wood veneers are added as a surface layer.

In the United Kingdom single-ply sheets of veneer were used to make [[Top hat|stove pipe hats]] in Victorian times, so flexible modern plywood is sometimes known there as "hatters ply",{{Citation needed|date=November 2010}} although the original material was not strictly plywood, but a single sheet of veneer.

===Marine===
Marine plywood is manufactured from durable face and core veneers, with few defects so it performs longer in both humid and wet conditions and resists delaminating and fungal attack. Its construction is such that it can be used in environments where it is exposed to moisture for long periods. Each wood veneer will be from tropical hardwoods and have negligible core gap, limiting the chance of trapping water in the plywood and hence providing a solid and stable glue bond. It uses an exterior Weather and Boil Proof (WBP) glue similar to most exterior plywoods.

Marine plywood can be graded as being compliant with [[BS 1088]], which is a [[British Standard]] for marine plywood and IS:710 is Bureau of Indian Standards (BIS) for marine grade plywood. There are few international standards for grading marine plywood and most of the standards are voluntary. Some marine plywood has a [[Lloyd's of London]] stamp that certifies it to be BS 1088 compliant. Some plywood is also labeled based on the wood used to manufacture it. Examples of this are [[Aucoumea klaineana|Okoumé]] or [[Shorea|Meranti]].

In the UK, one can find builders' merchants advertising a grade of ply as "marine ply" that does not conform to [[BS 1088]] - generally online adverts for these products will include a caveat along the lines of "not suitable for boat

In India,marine ply is popularly called "Kitply" after the brand which popularised the concept of water proof marine plywood in the 1980"s.

===Other===
Other types of plywoods include fire-retardant, moisture-resistant, wire mesh, sign-grade, and pressure-treated. However, the plywood may be treated with various chemicals to improve the plywood's fireproofing. Each of these products is designed to fill a need in industry.

Baltic Birch plywood is a product of an area around the Baltic Sea. Originally manufactured for European cabinet makers but now popular in the United States as well. It is very stable composed of an inner void-free core of cross-banded birch plys with an exterior grade adhesive. The face veneers are thicker than traditional cabinet grade