Technical info about plywood types.

Ask your questions here. Guests welcome to post!
Site Admin
Posts: 4913
Joined: Fri Jun 18, 2004 8:14 pm
Type of boat I like: Wooden
Location: Greensboro, NC

Technical info about plywood types.

Post by jem »

Thanks for the research Jack.

Here is info from the Engineered Wood Association:

Plywood for Boat Building
Below is a copy of Form Q220, an APA pamphlet about the use of plywood in the boat building industry. Some remarks are necessary:

* Resin in the document below means polyester. Epoxy would work better but it was not tested.
* These are US standards but the information about plywood suitability for boat building is important for all builders. I will post some UK and French norms later.
* Redrying means drying the plywood before use, very important.
* Precoat all plywood parts with resin before any fiberglassing.
* If you use epoxy ( you should), there is no need to buy pressure treated plywood.

Points of particular interest to the amateur boat builder are: Types of plywood, classifications. Recommended plywoods for boat building Fiberglassing plywood

The Engineered Wood Association


The plywood industry consists of over a hundred mills in North America utilizing dozens of wood species for manufacturing. Since the major application for plywood has been for building construction, the standards and plywood specifications have been primarily geared to providing grades and layups that are optimized for construction applications.

However, structural plywood also has a proven track record in boat manufacturing. With the current grades, specifications and treatments available, it is the best structural material to meet many of the boat manufacturers needs. From the widespread use in PT boats during World War II to today�s modern composite hulls, plywood has been a preferred structural element due to its high strength-to-weight ratio, machinability and excellent fastener holding capabilities.

Given the unique requirements of the boating industry, APA has developed specific recommendations that best address the needs of the boat manufacturer combined with readily available preservative treatments, plywood can provide long-term structural performance as boat components. This guide provides specification details for best performance and provides reference to a vast information base on plywood.

Voluntary Product Standard PS-1 for Plywood

Plywood grade and workmanship quality are defined in Voluntary Product Standard PS-1. The standard defines the following panel attributes that are important for the marine industry.

* Wood Species. Over 60 wood species may be used in the structural plywood industry. Coniferous species are the dominant and preferred species for boat manufacturing applications. The most popular of such species is Douglas-fir. Other species include western larch and western firs.
* Veneer Grades. Veneer grading is based on the size and frequency of natural growth characteristics such as knots, knot holes and sputs. The common veneer grades for plywood are A, B, C, C-plugged and D. The plywood panel itself is defined by the grade of the face and back veneers (e.g., A-B or C-D)
* Bond Requirements. virtually all structural plywood made today uses waterproof phenolic resins which maintain their bond during moisture exposure.

APA Industrial Specifiers Guide

Today, manufacturers of industrial grades of plywood have very tight controls over how plywood is made. Current technology allows for production of specialty plywood with fewer core voids and gaps, which results in "tighter" panel construction. Such technology improves upon the prescribed combinations in PS-1 by considering exactly what attributes are needed by the industrial customer.

In order to fine tune the plywood grading system to more precisely meet the needs of certain manufacturing industries, APA developed an Industrial Panel Selection Guide. The grading system considers the following panel attributes in a four-number ranking known as the Industrial Category index, or ICI number. The four-digit ICI number consists of the following:

* Face Veneer Quality Ranking. A numerical scale indicating the solidness and smoothness quality of the face veneer.
* Back Veneer Quality Ranking. Similar to the face veneer, the ranking addresses the back veneer quality required for the specific application.
* Inner ply veneer under the face. These veneers are often important for applications with heightened fastener holding demands, and where panels are going to be cut into smaller parts.
* Other inner plies. Similar to the veneer under the face, these are assessed for solidness.

A copy of APAs Industrial Panel Selection Guide can be ordered by calling or writing APA at the address listed on the last page.

APA C-C Plugged, PS-1, Group 1, EXTERIOR
T the panel should meet an ICI Number of 7-3-3-3. Common Thicknesses Plywood 1/4� to 1-1/8� thick is available, with the most common thicknesses being 15/32�, 19/32" and 23/32".

*The best grade will vary depending on the application. Some boat manufacturers use treated panels with an ICI number of 4-3-3-3 for applications such as seats.


Plywood has a long history of good service in the boating industry. However as with all wood products, given extreme moisture conditions for a long period of time, plywood may be susceptible to some degree of fungal decay In many boat applications, the risk of elevated moisture conditions is mitigated by coatings, laminates, encasernent in fiberglass or other protective means that reduce the moisture pickup or provide sufficient drying rate in order to reduce the panel moisture content. For the ultimate assurance against the risk of decay, commercial preservative treatments are available. Since preservative treatments render the wood an unsuitable substrate for decay fungi, treated plywood can be considered at the top level of performance with respect to longevity.

Treatments and Standards

Treated wood products are readily available and are often used in construction where high decay hazards exist. Unfortunately, much of the treated plywood found in retail lumber yards may not have been redried to the degree required for boat construction. The following recommendations are geared specifically for treated plywood for boat construction. For best performance, care must be taken to specify and purchase treated plywood in accordance with these recommendations.

First, make sure the plywood comes from a mill that is a member of APA - The Engineered Wood Association. That is your assurance that the mill is subject to APA�s rigorous quality assurance program.

Treating is conducted as a secondary process following the commercial treating standards written by the American Wood Preservers Association (AWPA). The most common treatment and retention level for plywood used in boat construction is CCA (Chromated Copper Arsenate) at 0.40 pcf retention. Other treatments for boat use are ACA, ACZA and ACQ.

AWPA Standard C9, "Plywood - Preservative Treatment by Pressure Process," specifies that the preservative-treated panel be redried to a moisture content of 18% or less, unless waived by the specifier. For use in boat manufacturing, the redrying of the treated plywood is essential to good performance when laminating with fiberglass. Treated plywood purchased from lumber yards is often used in construction applications and is not necessarily re-dried after treatment. It is essential for boat manufacturers to specify redrying.

Treated plywood is trademarked by a grading agency that monitors treating quality. The trademark should specify the AWPA standard, treatment and treating retention. Many suppliers of treated plywood for the boat industry offer limited lifetime warranties. Check with your panel supplier for warranty information.

For BEST performance of plywood in boat manufacturing, APA recommends the use of treated plywood according to the following specification.

Treated in accordance to AWPA Standard C9 with < CCA, ACQ, ACZA or ACA> to 0.40 pcf retention. Kiln dry after treating (~AJ) to 18% or less.


Many uses of plywood in boats involve laminating fiberglass over a plywood boat component. APA recently contracted with a marine testing laboratory to study the strength of fiberglass bond using commercial resins applied to treated and untreated plywood. The objective of the study was to assess the effect of preservative treatments and panel moisture content on the strength of the laminate bond.

The study assessed the laminating strength on treated and untreated plywood. To study the effect of moisture content, half of the panels were humidified to simulate the upper range of moisture content of what may be expected from treated panels after redrying or from panels stored at a boat manufacturer's facility.

The treated plywood developed bond strengths similar to the untreated plywood.

As expected, the moisture content of the plywood influenced the strength of the fiberglass bond. However, even at the highest moisture condition, the ultimate test failure mode in the vast majority of the cases was wood failure within the plywood itself, rather than at the laminate bond interface. The influence of plywood moisture content reinforces the need to specify drying after treating when using treated plywood.


Like all materials used in manufacturing, plywood should be properly stored and handled to assure proper performance. Protect the edges and ends of panels during handling. Place panels to be moved by forklift on pallets or bunks when received to avoid damage by fork tines. Panels to be transported on open truck beds should be covered with tarpaulins. For open rail transport, use "lumber wrap" to avoid weather exposure. For best performance, store panels indoors away from open doors to minimize moisture differentials along edges and ends. Make sure the panels are not exposed to water, solvents or other foreign matter that may interfere with establishing the fiberglass bond. Covering and weighing down the top of the bundles assists in keeping the panels flat. Stack panels on 4x4 stringers or other blocking. To help assure continued panel flatness, use at least three full-width stringers or bunks to avoid bending of the unit. Covering and weighing down the top of the bundles assists in keeping the panels flat.


APA maintains a vast library of literature regarding plywood. A selection of titles follows:

* APA Technical Note: Fastener Loads for Plywood - Screws, Form E830
* APA Plywood Design Specification, Form Y510
* Consumer Information Sheet - Inorganic Arsenical Pressure-Treated Wood
* APA Product Guide Preservative-Treated Plywood, Form Q220
* EWS Technical Note; Controlling Decay in Wood Construction, Form R495
* Industrial Panel Selection Guide, Form T200


APA - The Engineered Wood Association is a nonprofit trade association whose members produce 70 percent of the structural wood panels made in North America.

APA has three main functions: 1) quality inspection and testing; 2) product and systems research; 3) promotion.

APA's Field Services Division is a national network of representatives with regional offices in major market centers across North America.

APA Field Representatives help users, specifiers and distributors market, design, and apply APA and APA EWS trademarked products for countless end uses.

Most importantly, APA Field Representatives are available to help you. If you have questions about structural wood panels or engineered wood products please call the APA representative in your area.

The Engineered Wood Association
PO. Box 11700, Tacoma, WA 98411-0700
(253) 565-6600 Fax: (253) 565-7265
Internet Address: See our resin-fiberglass basic tutorial for more information about the use of materials.

BS1088 (British Standard 1088)
is defined by the following 4 basic requirements

1. Same species of wood throughout
2. WBP Phenolic or Advanced melamine resin glue line
3. No core gaps, some small pinhole gaps are accepted
4. Whole piece face and back, no spliced faces, allowed Grade is normally an A/B

BS6566 (British Standard 6566)

1. Wood can be mixed in species, normally the core will be different from the face.
2. WBP Phenolic or Type 1 Ext Melamine glue permitted
3. Some allowance of core gaps permitted, recommend filling any exposed edges before further encapsulation etc.
4. Faces can be made up of one or more pieces, spliced together. Grade of face is normally a B/C

The BS6566 is recommended where the wood is being encapsulated, or at least fully sealed.
It is not as structurally sound as BS1088, and does not pretend to be.
This also includes bending strength and modulus of elasticity.
Sometimes, the factory producing the 6566 will manufacture the plywood which will exceed the above conditions, (for example, they may put whole piece faces on just to complete production more quickly for an order that needs to be exported) Customers must be aware that at any time, grade must meet the above to be approved under BS6566 .

I also found this at another site:
Noah's Marine sent me this information.

"The only difference between the 6566 and 1088 is the face. The 1088 has no
voids in face, the 6566 has some. People use the 1088 if they are going to
do a clear finish, if you are going to paint the plywood i would use the
6566,it's cheaper. That's the only difference between the two."

The following is the criteria that must be met for a panel to be "legally" marked and marketed as BS1088. I havent heard of any counterfeit BS1088 being marketed. All the BS1088 panels I have ever bought (I dont build with luan) had a Lloyd's of London stamp along with the BS1088 marking.
As far as I know there is no standard that Luan has to met. Any core material is OK, any glue is ok, variation in thickness is ok, any face veneer is ok. That is why I say that Luan bought in Florida may be (act) different than luan bought in Texas, Australia, Canada, England, Scotland, Maine, Iowa, North Carolina or even where I live in Florida. While any BS1088 bought from any of those places would act the same as a piece bought from anywhere else.


From Wikipedia:

In materials, the BS 1088 specification is a marine plywood specification that applies to plywood produced with untreated tropical hardwood veneers that have a set level of resistance to fungal attack. The plies are bonded with WBP glue. Although the initials BS are for "British Standard", the finished product does not have to be "British made". The standard is associated with Lloyd's of London since it performs testing of products to this standard.

WBP Glue Line -- BS 1088 plywood must use an adhesive proven to be very resistant to weather, micro-organisms, cold and boiling water, and steam and dry heat. The product's bonding must pass a series of British Standard tests.

Face Veneers -- These must present a solid surface that is free from open defects. Face veneers must be free of knots other than "sound pin" knots, and there can be no more than an average of two such knots per square foot over the entire surface of the plywood sheet. The veneers must be reasonably free from irregular grain. The use of edge joints is limited, and end joints are not allowed.

Core Veneers -- Core veneers have the same basic requirements as face veneers, except that small splits are allowed, and there is no limit on the number of pin knots or edge joints. However, end joints are not permitted.

Limits of Manufacturing Defects -- Defective bonds, pleats and overlaps, and gaps in faces are not permitted. Occasional gaps may be repaired using veneer inserts bonded with the proper adhesive.

Moisture Content -- BS 1088 plywood must have a moisture content between 6% and 14% when it leaves the factory.

Finishing -- Boards will be sanded on both sides equally.

Length & Width -- The length or width of a board produced as a standard size shall not be less than the specified size nor more than 6.3 mm (0.25") greater than the specified size.

Squareness -- The lengths of the diagonals of a board shall not differ by more than 0.25% of the length of the diagonal.

Thickness Tolerances -- Tolerances vary as follows.

* 4 mm +.02/-0.6 6 mm +.04/-0.65 9 mm +.06/-0.75 12 mm +.09/-0.82
* 15 mm +.1/-0.9 18 mm +.12/-0.98 22 mm +.16/-1.08 25 mm +1.8/-1.16

From the above we can assume that 6 mm material will arrive at thickness' between 6.04 mm and 5.35 mm.

Face Veneer thickness -- For any three-ply construction, which applies to 3 and 4 mm material, each face veneer shall be not thinner than 1/8 of the total thickness of veneers assembled dry. Since the dry thicknesses of the boards are 3.6 and 4.6 respectively, we can assume that for these thicknesses only the face veneers will be as follows:

* 3.6 mm dry x 12.5% (1/8 ) = 0.45 mm 4.6 mm dry x 12.5% (1/8 ) = 0.575 mm

Multi-Ply Construction-- This applies to boards thicker than 4.8 mm (3/16")

* Each face veneer shall be a minimum of 1.3 mm and not thicker than 3.8 mm.
* Each core veneer shall be no thicker than 4.8 mm
-Matt. Designer.
tx river rat
Posts: 989
Joined: Wed Feb 21, 2007 10:48 pm
Type of boat I like: <-- Please read instructions to the left and delete this text. Then, tell us what type boat you like! :-)
Location: Tx

Post by tx river rat »

See I told u polyester
Ducking :twisted:
Posts: 73
Joined: Mon Nov 26, 2007 6:33 am
Type of boat I like: <-- Please read instructions to the left and delete this text. Then, tell us what type boat you like! :-)
Location: Brisbane Australia

Post by lark2004 »

Good info there.

Poly... :roll: Fine I 'spose if you can glass the whole boat in one go..... not so fine a bit later when you want to modify it.. you'll be reaching for the epoxy then :P
tx river rat
Posts: 989
Joined: Wed Feb 21, 2007 10:48 pm
Type of boat I like: <-- Please read instructions to the left and delete this text. Then, tell us what type boat you like! :-)
Location: Tx

Post by tx river rat »

hey Lark
Just ribbing Matt ,
Butt modifying a poly boat is no problem.
Site Admin
Posts: 4913
Joined: Fri Jun 18, 2004 8:14 pm
Type of boat I like: Wooden
Location: Greensboro, NC

Post by jem »

ok boys... no hijacking the thread. Plywood! Plywood! :D
-Matt. Designer.
Kayak Jack
Design Reviewer
Posts: 1186
Joined: Sun Jun 20, 2004 8:03 pm
Type of boat I like: <-- Please read instructions to the left and delete this text. Then, tell us what type boat you like! :-)
Location: South-central Michigan

Post by Kayak Jack »

Matt, much of the info came from Danger Mouse.
Kayak Jack
Doing what you like is FREEDOM
Liking what you do is HAPPINESS
I spent most of my money on whiskey and women - and I'm afraid I just wasted the rest.
tx river rat
Posts: 989
Joined: Wed Feb 21, 2007 10:48 pm
Type of boat I like: <-- Please read instructions to the left and delete this text. Then, tell us what type boat you like! :-)
Location: Tx

Post by tx river rat »

Yes Sir
Posts: 73
Joined: Mon Nov 26, 2007 6:33 am
Type of boat I like: <-- Please read instructions to the left and delete this text. Then, tell us what type boat you like! :-)
Location: Brisbane Australia

Post by lark2004 »

:oops: sorry Boss
Posts: 116
Joined: Tue May 20, 2008 8:44 am
Type of boat I like: Okwata.
Location: Cundletown, NSW, Australia

Post by Earvin »

In my search for ply to start my first build I stumbled across this info relevant to the Australian members.

Plywood is classified according to grades, which are based on face and back veneer quality. The Engineered Wood Products Association of Australia (EWPAA) grading standards are as specified in the following table.

Grade A - A high quality appearance grade veneer suitable for clear finishing.

Grade S - An appearance grade veneer which permits natural characteristics such as knots as a decorative feature subject to agreement.

Grade B - An appearance grade suitable for high quality paint finishing.

Grade C - A non-appearance grade with a solid surface. All imperfections such as knot holes or splits are filled.

Grade D - A non-appearance grade with permitted open imperfections. Limited number of knots and knot holes up to 75mm wide are permitted.

Grade PG - A non-appearance grade that has open imperfections such as holes, knots, splits and rough grain.

Most local plywood conforms to the PAA standard with imported plywood in compliance with other grading standards such as:

BB/CC grade which conforms to the Japan Plywood Inspection Corporation (JPIC) standard. BB/CC grade plywood has a good face that may have small imperfections that are filled and sanded.

‘CC’ back may have rough patches and filled splits.

Overlay and Better (OVL/BTR) is more of an appearance grade plywood that conforms to the International Hardwood Product Association (IHPA) that uses more veneer in construction to produce higher stress grade plywood.

Glues used to bond veneers together are an element that influences the application of the plywood. Common glues are as follows:

‘A Bond’ (WBP) - a waterproof glue line produced from phenolic resins (WBP -Water Boil Proof adhesive) that will not deteriorate under extreme conditions. It is readily recognisable by its black colour. Type A bond is specified in AS/NZS 2272 for marine plywood.

‘B Bond’ - produced from melamine fortified urea formaldehyde resin and suitable for limited exposure.

‘C&D Bond’ – is produced from urea formaldehyde resin and suitable for interior use only.

Structural Plywood manufactured to AS/NZS 2269 Plywood - Structural is suitable for use in all permanent structural applications. A permanent Type A phenolic resin is used to bond the individual timber veneers. The Type A bond is distinctly dark in colour and is durable and permanent under conditions of full weather exposure, long term stress and combinations of exposure and stress.

Structural plywood is manufactured from a range of softwood and hardwood timber species. These timber species may not be durable when used in weather exposed situations. In exposed applications, structural plywood must be preservative treated to ensure it lasts its full service life and surface finished to minimise surface checking.

PAA branded structural plywood is manufactured under a rigorous product quality control and product certification system ensuring a quality controlled engineered panel of known and consistent physical and mechanical properties.

For assured performance, structural plywood should be branded with the ‘PAA Tested’ stamp.
The engineering properties of structural plywood are tabulated in both AS/NZS 2269 and AS1720.1. Structural plywood engineering properties are given for eight standard stress grades, F7, F8, F11, F14, F17, F22, F27 & F34.
Posts: 50
Joined: Thu Apr 15, 2010 5:59 pm
Type of boat I like: trapper

Re: Technical info about plywood types.

Post by ColCollyer »

Here we go
I have just received some Trapper plans from Matt, so now the questions begin
I'm in Melbourne, Aussiland, so I will need somewhere to buy plywood, and also some info on what to buy. It seems the choices are Gaboon, Hoop pine, Mahogany or Pacific Maple. What are the pro's and con's please...... what would you use. I wish to stain it.
Also some paddle shaft and gunnell material too, maybe laminate ?

I've had 40 + years with Balsa, but not much ply.

Have other questions, but need to cross this hurdle first !
Col Collyer
Post Reply