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Thread: Marine Ply Or Exterior?

  1. #1
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    Default Marine Ply Or Exterior?

    Hi All, just sent off for plans to build a Selway Fisher Prospector 15'8" and was wondering had anyone out there built a similar craft using exterior ply instead of marine. The cost of marine is quite high compared to exterior ply and really difficult to get hold of up North.If the canoe is going to be fully sheathed with glass cloth do you think she would be hardy enough?Any advice would be gratefully apreciated

  2. #2
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    Bulkington Warwickshire
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    Hi

    I am building a Peterborough -same process
    My local plywood supplier (a real woodyard!!!) refused to sell me exterior ply when I told him what I wanted it for - he doesn't stock marine ply - even when I explaned that I would be covering it in epoxy etc.

    Eventually bought 4 sheets of 6mm Marine - 20 / sheet

    Probably been said before but - all sheets of marine ply should be stamped - BS 1088 (I think!) this ensures 'proper' glue has been used etc
    Gary
    Paddling my own path

    www.elsonairtightness.co.uk

  3. #3
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    Ulverston, Cumbria
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    Default

    A lot of boats are built with exterior - mine will be. One thing to bear in mind is that exterior is good enough but marine is better - it is stronger and lighter usually. (assuming a high quality one compared to bog standard exterior grade).

    The number of plys are the key part. Cheap ply is usually 1 thick ply and 2 thin veneers, more expensive plywoods have plys of the same thickness which is much better for strength etc.

  4. #4

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    Unless you go for the staggeringly expensive Bruynzeel stuff WBP exterior grade is more than adequate, as long as you make sure you seal all the cut edges. You need to be sure it is certificated as such and is'nt the cheap knock off exterior which really won't do.

    There seems to be some dissolusionment with marine ply at the moment, things are not being checked as they should. Companies like Robbins do stock good quality marine ply at a reasonable price, with a guarantee, but do you really need to go that extra bit when the whole thing will be epxied?

    I have a new project on the go and having talked to the guys who have done the same job beforehand I'll be following their example and using WBP exterior grade, eposeal and epoxy.
    Obscured by Clouds

    Clipper Prospector 16

    http://lostcoast.blogspot.com

  5. #5

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    Quote Originally Posted by simon3009 View Post
    Hi All, just sent off for plans to build a Selway Fisher Prospector 15'8" and was wondering had anyone out there built a similar craft using exterior ply instead of marine. The cost of marine is quite high compared to exterior ply and really difficult to get hold of up North.If the canoe is going to be fully sheathed with glass cloth do you think she would be hardy enough?Any advice would be gratefully apreciated
    Hi
    I notice you live in preston, why not try Preston Plywood one of the best stockist of both marine and exterior ply there is also a firm in Darwen who stocks marine ply down to 4 mm

  6. #6
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    Default

    I nearly always use exterior ply.
    Don't know where you get marine ply at 20 a sheet. Round here exterior ply is about that price. Marine ply is up to 60 a sheet for 6mm.

    The main thing to look out for is voids in the inner layer(s). If any are visible on the edges then there are probably some in the sheet. Marine ply is void free.

    I have only had one sheet that has delaminated. this happened in storage luckily. This sheet was obviously different to the rest purchased at the same time. It had a much darker appearence and I suspect it was interior ply. (not waterproof glue)

    None of my home made boats have been coated with anything other than paint and varnish. the oldest being 37 years old now and still as strong as new. This one was made out of marine ply and has been dry stored when not in use but has had no other special treetment apart from it has been repainted three times.

    The oldest exterior ply boat I still have is about 10 years old now and is also rot and delamination free although the ply has discoloured under the varnish in a couple of places.

    Hope this helps.

    Steve

  7. #7
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    Port Erroll, Scotland.
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    Default

    I have had a major problem in the past when I was sold an 8' x 4' sheet of 9mm exterior ply by mistake instead of the marine ply I had been using regularly for years. Within just a few days, during which it did rain, delamination began with large areas even in the middle of the sheet splitting along the grain and bursting open.

    On phoning to explain, Travis Perkins - used to be Index, I was asked if I had coated it in varnish/paint or had left it untreated, untreated I replied, ah well there you are, what do you expect you have to treat marine ply I was told.

    I pointed out that I had loads of offcuts of marine ply I had previously bought from them which had been outside through several winters untreated without any problem and asked if I could possibly have been given a sheet of interior ply by mistake, I was told that the lowest grade ply that they stocked was exterior.

    I explained it was my understanding of marine ply that it was impregnated and bonded with resin so as to render it impervious to damp, it is after all used to make boats from (forgot to mention canoes, rather agitated at the time as I had had an 8' x 4' sheet of crap which wasn't worth a on my hands). No, no you have to coat marine ply to protect it I was told . . . mmmmmh !

    Long story short, after refusing a refund of half the cost in the form of a credit note and informing them I was going to get it independantly analysed I finally got a replacement sheet which has shown no delamination after several months open to the elements . . aye, untreated !

    Assuming that what Travis Perkins told me to be true, regarding the lowest grade of ply they stocked being exterior, then my experience with exterior ply is such that there is no way I would take the risk of using it for canoe making, though I appreciate others have apparently used it very successfully.

    It's also my understanding that though resin is water resistant it is not 100% waterproof especially if used for prolonged periods submerged and with this in mind I personally would be very concerned that a slow water migration/penetration would occur and in my experience the exterior ply would react by delaminating.

    I appreciate that many of you guys have used it very successfully without any issues and I am only conveying my very limited experience of exterior ply.

    I'm aware that there must be several different grades of marine ply and exterior ply, the 8' x 4' sheet of 9mm Malaysian marine ply only costs me around the 32 mark, including VAT, and I have been told by those more knowledgeable than me that it should be almost three times that. However even with the presumably lower grade of marine that I am accustomed to using, the difference in actually working with marine compared to exterior is very noticeable with virtually no splintering as the jig saw blade glides through the marine . . . very smooth edged finish presumably due to high resin content, compared with extremely jaggy/rough finish with the exterior.
    Last edited by Hairy Frog; 16th-September-2008 at 01:52 PM.
    "It's not the direction of the wind that determines your destination but the setting of your sails"

  8. #8

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    I've tried to source 4mm BS 1088 marine ply in Preston and area, all suppliers who list it have been unable to supply it in the end.

    I have built my first SF peterborough 15'8" from WBP exterior and have used over 7 sheets where 4 are required, big internal voids, delaminating veneer repairs etc, not good stuff, I've persevered and once everything is glassed, epoxied, varnished and finished and on the water I'll no doubt forget all the frustration, unless it breaks up and sinks when I finally wet it.

    I have now bought Robbins Elite 4mm from Fyne Boats up Kendal way for canoe number two, its really quality stuff and Lloyds registered too, having cut sheet 1 for templates its the dogs cojones to work with over ext grade dross, wish I'd bitten the bullet and worked overtime instead of phoning plywood suppliers who haven't got the goods. A point to note is that no 4mm is made with equal thickness veneers, as BS1088 requires a minimum of 3 layers, also the veneers aren't equal gauge the middle is much thicker, still better though.

  9. #9
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    Bamber Bridge,Lancs
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    Thanks very much guys for the input.When you're planning your first build you try and take on board as much information as you possibly can get, although after a while too much info results in 'brain meltdown'. After weighing up the pros and the cons I think the sensible option is going to be the marine Ply.Price wise I'm looking at another 70 ish.
    I would imagine there would be nothing worse than spending most of the dark winter months building your pride and joy, only to see part of it 'de-laminating'.As far as suppliers go, I gave Fyne boats a call in Kendal and they could supply top quality 4mm Marine ply for approx 35 a sheet.The gentleman I spoke to was very helpful and advised me against the use of exterior ply!
    Thanks again all.
    Last edited by simon3009; 16th-September-2008 at 05:10 PM.

  10. #10
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    Oct 2007
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    Chesterfield Derbyshire
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    Default No suprise there!

    Quote Originally Posted by simon3009 View Post
    35 a sheet.The gentleman I spoke to was very helpful and advised me against the use of exterior ply!
    Thirty five quid a sheet! No wonder he advised against exterior ply!
    My one and only canoe is made of 'ten quid a sheet exterior stuff' from Jewsons. The previous fishing punt, exactly the same only without a drop of epoxy or fibreglass! Just cascamite, exterior enamel and yacht varnish from B+Q. 23 years later and one 'repaint' it's as good as the day it was built. It is kept off the water and undercover and is absolutely fine!
    Having said all that , if I could afford marine ply the only reason I would use it would be to build a lighter boat!
    Good luck (and post pics if you do build!)
    Older, but no wiser!

  11. #11
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    Ca. United States
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    Default

    Here in the states the "exterior grade" was really good about 10yr's ago.
    Now it's garbage. 6mm is 3 ply. The center ply is full of voids. The outer
    plies are paper thin, with mickey mouse patches all over. They even skim
    the cracks/splits with silicone caulking. Ridiculous!! I got 6 sheets of 6mm
    bs1088 from a supplier in Los Angeles. It's really nice. 5ply and the faces
    look to be "A" an both sides. It's so nice I'm afraid to lay my hands on it.
    You pays your money, you takes your chances.

    Coogs


    He think's thats funny

  12. #12
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    Sep 2008
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    cleveland uk
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    Default marine or not?

    Hi Simon, I have built 2 ply canoes, 1 with free plans, the second with bought plans, an 18 footer, get this I chopped the rear 20inches off giving me a flat transom to stick an outboard on when I fancied, both exterior grade ply with no problems,as you said it will be sheathed in part in fibre glass and when painted with resin. mabe even painted with marine paint, I think the only differance between exterior grade and marine apart from cost is more care is taken,in the layering,wood grade,mabe,mabe better quality glue,if possible have a look at some marine ply and compere,but I think for a canoe exterior grade will be fine,I hope this helps.good luck.bigH.

  13. #13

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    arh, if I were to cross oceans in a boat that spent its life afloat, then no doubt I would use marine, but what percentage of the time is your boat really in the water. -I wish mine was afloat more often.

    4.46 a sheet I think my ply was.

    Granted, I built a quick, dirty and cheap boat, but it gets me along just fine.
    S/F PETERBOROUGH 15' 9"

  14. #14
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    Oct 2008
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    Addington, Surrey
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    Consider birch ply as a good inbetween ply, it's also exterior grade but a much more dense ply with higher strength and thinner laminates so more layers. It's about half way between the price of standard exterior and marine.

    the 2 main supplies I use for plywood are;

    W T Eden

    and

    Panel Supplies
    Harvey Road,
    Burnt Mills Industrial Estate,
    BASILDON,
    SS13 1ES
    01268 729 100,

    very competitive prices

  15. #15

    Default

    Hi, interested to know if anyone else has experience of using Birch Plywood for building canoes? I'm looking for some FSC certified exterior plywood and Birch from Ridgeons seems a good option (all their exterior has an 'MTCC' certification which according to Greanpeace is totally bogus).

  16. #16
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    Sep 2009
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    High Wycombe
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    Quote Originally Posted by simon3009 View Post
    The cost of marine is quite high compared to exterior ply and really difficult to get hold of up North.
    Well I live down in the South East, but Jewsons were able to supply BS1088 marine ply. 6mm was about 20 a sheet and had 5 plies. They didn't stock it in the shop, but supplied it within two days.

    My understanding is that BS1088 has specifications of the (lack of) voids in the timber and the quality of the surface.
    Well the forecast said it would be good...

  17. #17
    Join Date
    Aug 2007
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    Mid Wales
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    Default 5 ply 6mm marine ply at 20 a sheet !!

    Quote Originally Posted by jameshcox View Post
    Well I live down in the South East, but Jewsons were able to supply BS1088 marine ply. 6mm was about 20 a sheet and had 5 plies. They didn't stock it in the shop, but supplied it within two days.
    I,ll have ten sheets of that stuff !
    At that price I think they must have made a mistake !
    Get back there and buy all they,ve got !
    You could supply folks on here at a reasonable profit I,m sure ,
    Still It,s a long way to come from Wales to get a few sheets of plywood
    It certainly seems you got a bargain there jameshcox !
    Noel
    Last edited by KeithD; 2nd-November-2009 at 11:12 PM. Reason: quotes

  18. #18
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    Default

    Quote Originally Posted by Nomad Rush View Post
    I,ll have ten sheets of that stuff !
    At that price I think they must have made a mistake !
    Get back there and buy all they,ve got !
    You could supply folks on here at a reasonable profit I,m sure
    I am sure I could, but then where would the time for paddling come from? Of course the mistake could be that its labelled BS1088 but isnt, or he charged me for WBP but delivered marine, or may just their purchasing power lets them have low prices.

    I think it came from the Abingdon branch, the following was from their web site:


    Branch Manager - Jeff Allen
    Opening hours - Mon - Fri: 7:30am to 5pm - Sat: 8am to 12pm
    Contact details - tel: 01235 536036 fax: 01235 538914
    Jewson Ladygrove
    Drayton Road
    Abingdon OX14 5HX
    Oxfordshire

    The following specialist services are offered in this branch:
    Tool Hire
    Chain of Custody for certified timber
    Insulation Centre
    Well the forecast said it would be good...

  19. #19
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    Jul 2009
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    North of the Trent, East of the Weaver
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    Default

    "Marine ply for a boat that will stand in the water all the time, exterior for one that will be stored in the garden," was the advice that made sense to me.
    I used exterior, and finished my build last month. There have been no problems with the ply so far.
    Andy

  20. #20

    Default

    http://www.jewson.co.uk/en/templates...mId=prod350053

    Worth a look, they list it for sale. Have to go there for prices.

    I know someone who works there as well

  21. #21

    Default

    Quote Originally Posted by minotaur View Post
    http://www.jewson.co.uk/en/templates...mId=prod350053

    Worth a look, they list it for sale. Have to go there for prices.

    I know someone who works there as well
    Having clicked the above link I am a bit concerned by the specification

    It is recommended that all edges and faces of the board are sealed before installation to prevent moisture absorption


    • Hardwood plywood
    • Conforms to BS EN 636-3
    • Complies with BS1088-1:2003
    • FSC certified
    • Marine Grade
    • General Moisture resistant applications - not suitable for boat building
    • E1 Glue




    Not sure that this can be marine ply.

  22. #22

    Default

    Hi,

    Not sure if it helps but I usually go to Selco to purchase the marine plywood I need. Their prices are always good and the quality of the wood is one of the best I've used.

  23. #23

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    Hi,
    our boat was constructed a good 15 years ago. It was from a kit so I can' t be sure but it looked like WBP.
    One issue I noted recently when refurbing it is that the internal ply, which had been painted with interdeck paint, had shrunk across the grain leaving what looked like small cracks in the paint. Presumably the ply has dried out over the years.
    We did not glasscloth the inside other than the tapes. I would recommend as a minimum a couple of coats of epoxy on the inside to avoid this.

  24. #24

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    Exterior grade means the glues will hold up in a humid/moist environment. There are no assurances regarding the quality of the veneers or voids there-in.
    Marine grade BS-XXXX means it meets a Lloyd's standard, the veneers should be void free and of equal thickness.

    The former is a gamble. The latter, less so.

    If the 100 quid saved is important. Gamble.
    If not. Don't
    Trevor Paetkau
    Ashes Still Water Boats
    Canoe Plans | Custom Boats

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