Cheap plywood: Bad idea?

[Davepat76]

I'd like to build a sailing canoe with plywood. Funds are limited.

The plans call for six (6) sheets of 4' x 8' x 1/4" plywood. I priced "Marine grade plywood, 1/4 inch" at a specialty wood store: CAD$88 per sheet. Then I went to a big box place: 1/4" Aspen ply for $53; 6mm Sanded Fir ply for $56; 5.2mm RevolutionPly for $33.

The plans say to fibreglass the outside of the hull and epoxy coat inside surfaces, as well as paint or varnish all surfaces. With this accomplished, does it really matter what quality of plywood I use?

Thanks!

Dave

[wizbang 13]

Yes it do.
It also matters the quality of plans you use
quarter inch glassed both sides sounds heavy for a canoe ?

[John Meachen]

I've only built one plywood canoe,it was stitch and glued with just a 2 inch strip of glass tape along the seams and while it might horrify some,I only used polyester resin.The canoe itself was built of 4mm exterior ply and lasted well enough as I stored it under cover.I wouldn't be keen on any plywood that wasn't rated for exterior use as it essentially becomes a disposable object.Six sheets plus glassing will make a fairly heavy canoe and it will take some lugging around.I don't know how much epoxy costs in Canada but suspect that the cost of epoxy and glassing will be a fair bit.

[Autonomous]

Sharing your plans could help us get you a better boat for less.

[upchurchmr]

Wood is biodegradable.
Cheap plywood is even more biodegradable.

What do you want for a Boat?

A few years?

Part of the problem is that cheap plywood often has voids, which severely affect the strength locally.
If any water gets past the epoxy then the voids lead to rot.

Perhaps you could show us your expected cost for the hull, mast, fittings, rudder, centerboard (leeboard or whatever), sails, trailer, ropes/pulleys, etc.
You will see the ply is not so major a cost.

[wdr99]

Cheap 1/4 inch is probably three ply, it’s really not good hull material, good marine ply is usually 5-ply. A void in three ply is a way bigger problem than a void in 5 ply. Anyone I’ve ever talked has advised against the cheap stuff.

Also, I built a boat with 1/2 Doug fir marine ply and the boat is fine. But, then I built a boat with Okoume marine ply and I was astonished how much better it was to work, finished way better, and how much better result it yielded. I actually laughed out loud making the first cut in the good stuff. It’s just more fun.

Bill

[stromborg]

Boats tend to have curves.

Curves do a great job of revealing voids in the inner plies by breaking the plywood.

It doesn't take many broken parts before you'll have used up any initial savings by buying another sheet or two.

[sp_clark]

Garbage In, Garbage Out.

The ply is the skeleton of your project, the fiberglass & epoxy the soft(ish) tissues that protect the skeleton from the elements.

Without a viable skeleton the rest will be mush before too long, and likely unsafe as well way too soon.

If you value your time and effort, don't waste your money on the cheapest ply you can find. You'll have Builder's Remorse that'll severely – in the (-) direction – affect your motivation towards your next project.

[Davepat76]

Thanks for the input, everyone. The build is a Tamanu sailing canoe. I don't want to have any regrets later on. Therefore, I will wait until I can afford the good stuff.

D

[Clinton B Chase]

Cheap plywood is realllly BAD idea for the reasons already specified. In addition, people think epoxy coating allows you to get by with cheaper ply but it is a falsehood of the greatest degree: epoxy will only seal in the voids and the boat will rot from the inside out.

[swoody126]

nuthing less than EXTERIOR GRADE plywood

exterior (clearly marked on each sheet) will provide a life expectancy of about 5 years if the boat is dried out after each use and stored indoors

BCX-YP might get you a coupe extra years w/ excellent care

jumping to doug fir marine plywood can bump you up to about 10 years

okume or miranti marine plywood w/ good care could become a family heirloom

big box store 1/4" plywood is 3 ply w/ unknown center layer and a good chance for numerous internal voids

ALL VOIDS will end up w/ moisture in them and begin rotting from the inside ... failing when you least expect

doug fir marine 1/4" ply can be 3 or 4 or even 5 plies w/ minimal internal voids depending on the manufacturer

there is no way(short of completely fiberglassing) to prevent checking

surface layers are not expected to be flawless and can have "football" patches and bunches of them

11 footballs in 16x36.jpg (this is a 3' section)

okume and miranti 1//4" marine ply comes in 2 grades

British Standard 6566 (BS6566) & British Standard 1088 (BS1088)

both grades will have 5 layers of the same quality veneer w/ teeny tiny voids if any

1/4" BS6566 can have thinner outside veneers(somewhat easy to sand thru) w/ the inner layers not being as pristine

1/4" BS1088 will have 5 layers of relatively equal thickness AND quality(no voids)

good enuff quality that the edges can be very attractive when finished bright

when the surface finish is maintained properly there will be very little if any checking

IMG_1065.jpg

all the above will have either the same or virtually equal quality glue

i personally live just north of the DFW metroplex and have found driving to houston for HYDROTEK saved me money over the years

buying in Ft Worth i could only get doug fir marine and i eventually lost my politically correct vocabulary skills while working with the stuff

this information is based on my personal experiences and not hearsay

bon chance

sw

[Dusty Yevsky]

Lots of great advice above. Let me add one more bit. Save up the spondulicks and get NAME BRAND marine ply. Lots of shady third world plywood mills slap a BS1088 sticker on their inferior product and call it marine ply. These days it means the producer has a stamp and an inkpad, nothing more.

Stick with producers like Joubert or Bruynzeel. They still fabricate to a high standard and have a reputation to uphold. Once you work with this stuff you will not regret the premium price.

Buy the best and cry only once.

[MushCreek]

Part of the problem is the huge decline in plywood quality over the years. Back in the early 70's, I was building cheap rowboats for sale out of A/C exterior plywood. The stuff was fine. The boats were rugged and held up to abuse. By 1980, the same stuff had degraded to the point of being unusable. I can tell just by glancing at the stuff at the big box stores that it has only gotten worse. I nearly cried buying 5 sheets of meranti for the 18' rowboat I'm building, but as others have said, it sure is nice to work with.

[wizbang 13]

Part of the problem is the huge decline in plywood quality over the years. Back in the early 70's, I was building cheap rowboats for sale out of A/C exterior plywood. The stuff was fine. The boats were rugged and held up to abuse. By 1980, the same stuff had degraded to the point of being unusable. I can tell just by glancing at the stuff at the big box stores that it has only gotten worse. I nearly cried buying 5 sheets of meranti for the 18' rowboat I'm building, but as others have said, it sure is nice to work with.

I still carry Jan’s el Toro, 45 year old acx fir. Yea it’s tired, but still working. Now I only recommend strongly against using it. Had she been Aquatek.. she prolly be only be middle aged.

[Skegemog]

I built a duck punt out of 3/8" marine grade fir a couple of winters ago. I am a professional cabinetmaker and have access to wholesale pricing from multiple industrial vendors; I used fir for it just to see what I would be giving up using it rather than the Okoume, Sapele, Meranti joubert/brunzeel/aquatek/hydrotek I have used for all my other builds, as I was afraid I was being a bit too precious about my materials. What a nightmare, never again.

[johngsandusky]

How long will it take to save for better materials? If months, wait and buy the best you can afford. If years, build and enjoy now.
Another alternative is to build a different construction that doesn't require much plywood. I suggest looking into Skin On Frame boats.
Good luck, keep us posted.

[devout]

Boats tend to have curves.

Curves do a great job of revealing voids in the inner plies by breaking the plywood.

It doesn't take many broken parts before you'll have used up any initial savings by buying another sheet or two.

Just so. Even if it doesn't break, the bending stresses expose the voids and you will have strange bumps and valleys as the cheap sheets will not bend into fair curves. I built a few dog kennels from my first cheap hull sheets.

Regards

[P.I. Stazzer-Newt]

Yes it do.
It also matters the quality of plans you use
quarter inch glassed both sides sounds heavy for a canoe ?

And six sheets sounds like a lot - but a little googling found https://duckworks.com/tamanu-plans/

20 foot seagoing outrigger canoe with 80 sqare feet of sail - and suddenly it makes more sense.

[pablobesser]

good ply is a good idea unless you dont had any access to it.

i tried this year, to get 6 mm, 1/4 plywood for a rowing wherry , here in chile and was impossible. all the old plywood factories who produce native or marine plywood are gone. they move to only make pine , radiata or insigne or fir plywood. the same stuff you use and buy cheap on USA. many come from arauco plywood and cmpc selex plywood (this is really bad, they save on glue badly). arauco is good stuff, almost no voids, waterproof resorcinol glue, only the wood is too prone to checking. so rot ressistance is mild but the funny thins is the same with okume and meranti, both tropical woods not very rot resitance but without voids....

to my if the plywood is 5 layers, no voids and glued with good resorcinol waterprof is called good. meranti, okume ,or pine or fir will be glassed to me anyway. not just epoxy painted, glassed.

a bad exterior grade plywood boat can be a surprise if you work properly on it....

20220829_175547.jpg


20230104_201546.jpg

and on this case the ply was only 3 layers,

but almost no voids, but with some channels on one face to look more fancy, called colonnial plywood so i fill all this channels, at expense of some weight but not a big diference...

you can see here when scarfing the layer, are almost no voids on it.

20220921_163329.jpg


IMG-20220815-WA0008.jpg

[Jack Loudon]

I think a counterpoint to the above opinions is needed. I've built two small boats in the past 2 years, the first in 5mm underlayment plywood from Home Depot and the second from 6mm Joubert Okoume. The Joubert boat should last longer, but it's too early to say. Both boats are sealed in epoxy and mostly stored inside when not in use. If moisture gets to the wood of either boat, the okoume is just as likely to rot as whatever the underlayment ply is made from (Indonesian origin). Jim Michalak is one designer who has built boats of underlayment ply and says they have held up. The OP's boat at 20 ft is probably too big for 5mm ply so my comments are more about keeping an open mind with regard to plywood types.

Before committing to the underlayment ply, I left a piece outside over the Seattle winter, and also boiled a piece for 15-20 minutes. No delaminating, in spite of claimed interior grade. The underlayment is 3 plies, with two additional paper-thin veneers on the outer faces. I have made hundreds of rips of this stuff, including 1 inch rips of scraps for kindling, and have never yet seen a single void or failed glue joint. It was easy to work with (really no different than the Joubert ply), the only problem was the thin outer ply was too easy to sand or plane through. I vastly prefer 5mm underlayment to 1/4 inch ACX/BCX fir ply, which can be full of plugs, voids, and starved glue joints.

I do think that saving money on plywood is generally poor economy, and any subsequent boats I build will be with Joubert or equal. But for some people the difference between $20 underlayment ply and $100 Joubert may mean the difference between building a boat and not building a boat. And realistically, a small boat that lasts 10-15 years is enough for most; at that point they're either ready for a bigger better boat or they're done with boating and onto something else.

[wizbang 13]

Ten to fifteen years is the day after tomorrow .
That is how long a good paint job lasts .

[Dave Hadfield]

I've designed and built several plywood boats, up to 18 ft. Build A Lightweight Plywood Canoe – Dave Hadfield



The thing about using underlayment is that it's quite variable. You have to look closely at the laminations. If it's a thick core with two very thin surface veneers, it's garbage. Too weak. But if there are 3 laminations all about the same thickness, it'll be OK.

Rot resistance doesn't matter if the boat is being stored under a roof, as most canoes are.

[keith66]

Thirty years ago or more you could get away wiith exterior. Not any more. As has been said by others the quality has become truly dreadful with glues that for all the world are little better than wallpaper paste or flour & water.
I remember making a set of floorboards for a rowing skiff, coated in epoxy & painted I put them in the boat & they looked great. A month later they started to delaminate & a month after that were completely gone. A great waste of good epoxy & paint. Can you imagine how i would have felt if i had built a boat with that garbage?

[sp_clark]

Only motivation I'd have for using big-box thinnish ply'd be to do a 'proof of concept' full size prototype just to see if the idea I wanted to spend good money and lots of time a'building was at all practical in actual use. I wouldn't expect it to last too long, the idea being that if the concept was worthwhile for my purpose, I'd have proven my theory in practice and could justify spending time & money on better materials for a longer-lasting end result.

There are contests that have teams building boats out of corrugated cardboard & PL Premium in a couple of days. They then go out in them on the water for a race.

It's a not a rare thing to have most of those last long enough to actually get to the finish line but I'd never expect one to last too long, or be safe to venture out in again after a couple of weeks.

30+ years ago I bought six sheets 4'x8'of 1088 6mm Okoume from Harbor Sales for close to $40.00 a sheet. Today they sell the same stuff for $98 each.

Simply factoring for inflation in that interval, those sheets'd be selling for $91.11 in today's US $.

[Edward Pearson]

The only 'cheap' ply I've found over the years that I'd contemplate building a boat from is the Birch ply from Latvia/ Finnland/ Russia. A few built on here (a Phoenix) by a boat by Vivier and Wharram have all held up ok.

Now it's twice the price (£40 instead of £20) but on the good side it had the full number of veneers, thick (non sanded) outer veneers, waterproof glue and pretty clear faces. Birch has the natural advantage of peeling with few defects, which means I've never found a hole any bigger than very very small, no bigger than you might get in the most expensive Lloyds stamped plywood that has also crossed my palm.

Its heavier but proportionately stronger, so a design that might call for 8-9'ish Occume might be planked in 6mm Birch for equivalent strength/ bend resistance and you dodge the weight penalty.

It does however have low rot resitance and that means dry storage, prompt use and good epoxy/ paint coverings, covers, ventilaton, drains etc. Stuff that's good practice anyway, but you're going to have to look after it accordingly. Drill, fill and redrill fittings etc.


The plywood you'll find in builders merchants will usually have heavily sanded outer veneers. If your design is glued only, that could more easily delaminate under stress. You could get around this by building a glued and screwed ply on stringer approach to reduce that vulnerability. Often 'cheap\ builders ply will have fewer veneers say 5 instead of 7 or 3 instead of 5. Sometimes the inner veneers will be of a lower quality wood with less rot resistance or have more holes in them. Often the glue is not waterproof. BS stamping is completely worthless - its not inspected.

But now and again, you'll be staring at some plywood that looks good and isn't so dear that you wondering where's the catch. I think sticking a test piece through the dishwasher a few cycles is how it can be tested in short order.

Cost is for you to determine depending on what you want the boat to do, how long in needs to last, and wether you expect to resell it and for how much. £2000 of plywood is alot, but if you sell a boat built for £5,000 for £9,000 it's a shrewd investment. Saving £1500 and spending £500 on ply and selling a boat that's cost you £3.5k for £2k, not so much, but at least you went sailing!

Generally you want to be building in Joubert Occume in the USA as something that's usually good quality, not the most expensive, not going to fall apart, right number of veneers and not heavy etc That's the ballpark 'normal stuff' I believe over your side. I think its what CLC boats use for example. You could spend more on more durable plywood or less on heavier plywood.

It's a shrewd builder who has in mind what he roughly wants to build, then looks for the plans in the building method that suits the local wood availablility. If you can't find African deforestation products locally and don't want the carbon footprint of it, building from local softwood in either strip plank or cold molded is the right way for you to go. It's likely your local softwood hasn't risen on price nearly as much as imported plywood will have in the past few years. If you're back in the box store, the roofing timbers are usually the clearest, they are graded/ inspected to be so, and quite alot of hull material can be had if you can cut one up. Even after losses from saw kerfs, planing and having a greater thickness (about 30%) over plywood, it'll work out cheaper. A fraction of plywood cost per boat. And find some cedar and it can be no heavier than occume, sometimes lighter (white cedar). Recyling beams from old buildings being demolished is a source of old growth American Pitch Pine here in the UK. If you want to cut one up yourself, google 'chainsaw mill'.

The place to go though is your local Forest, there may be a small painted sign 'The Mill', uually just a gap in a fence, a long muddy track, three guys and some 'ol iron'...that's where local softwood at the cheapest price and smallest carbon foorprint will be found. hey don't take phone calls, you gotta go and interupt them. Now your a pain in the ass to to them, wanting so little, so go in with your game face on, take cash, tell them what sizes (length/ thickness etc). They'll tell you is x dollars per cubic foot, and you'll need to know the volume of what you're asking for to figure the cost. It will rough sawn, so you'll need to add a few mm either side to plane down to thickness and a clean surface and it'll shrink as it dries. You'll really need a thickneser and table saw to resaw thicker pieces. And don't ask for quarter sawn, vertical grain coz they'll laugh. They'll just be chucking it 'through and through', but if you can deal with them and pre think what you need, dry it and then clean it up and cut it as necessary it can be a good value and even pay for the machinery. Big long lengths too. Wear your wellies and a decent jacket. It will be cold, noisy, wet and muddy. There will be a big dog.

[sp_clark]

Lovely post Edward. Were I the OP I'd take your advice & run with it. Strip-built canoes have been built and sailed for decades.

[Jack Loudon]

I did a 30+ minute boil test of three 4" x 4" plywood scraps: 5mm underlayment, 1/4" ACX fir, and 6mm Joubert Okoume.

All three LOOKED fine after the boil test, no delamination or wrinkling.

But with the 5mm underlayment, I could get my fingernail between the plies and pull them apart, like they were held together by strong double stick tape. I then put the underlayment ply in a low oven to dry it out, and the glue seemed to regain its strength, making it nearly impossible to pry the plies apart without first destroying the wood.
I then boiled another piece of underlayment for 2 hours to try for complete failure, but ended with similar results. No self-delamination, just a very slight wrinkling of the outer veneer, but the laminations could be pulled apart. Added boiling time did not make it fail further, and it re-adhered after drying out. So a fail but not a catastrophic one. My kayak made from this plywood has held up fine and I expect it to remain so for the foreseeable future, used for afternoons on the water and otherwise stored inside. But I would not trust it for multiple weeks on the water, say to Alaska or down the Rio Grande.

The 1/4" fir passed the test, as I couldn't pry the plies apart. The Joubert of course passed.

Based on the above, if strapped for cash, I would not choose 5mm underlayment, but instead go with ACX fir ply.

[Davepat76]

Wear your wellies and a decent jacket. It will be cold, noisy, wet and muddy. There will be a big dog.

Ha! That last part drew a grin. I have seen such places.

Joking aside, you seem to have tapped into my own thoughts: Why pay lots for imported, likely endangered wood? Why not look for materials locally?

I'm in a good position for this, actually: We own a forest property that is brimming with mature Eastern White Cedar. I own a chainsaw, and have recently priced those "chainsaw mills"; they're quite reasonable, actually. A friend owns a thickness planner. Going this way would certainly prolong my project plans, as I would have to harvest, mill, and then dry the wood first (especially since there will be snow on the ground for another 4 months). But that's actually fine. I have more time than I have money.

Now, this would mean looking for a new plan (the Tamanu is plywood). Perhaps I'll go back to my original plan: an Ulua sailing canoe (cedar-strip + glass)?

Many things to consider. Thanks for your input, Edward!

D

[sp_clark]

Cut your EWC now while the ground's frozen & the sap's down. Fell 'em easy so your boles don't shatter when they hit the ground, paint the ends then mill to rough thickness, get 'em out of the woods & onto a solid base with stickers between & under cover.

Wood'll dry faster, more evenly than sawlogs left to dry after painting the ends & be less likely to check when resawn for strippage.

[upchurchmr]

If you use a chainsaw mill to make boards from logs, be sure to get a "ripping" chain. Don't use the normal cross cutting chain.
The cross cut chain will dull quickly when ripping -even though it will still work good for crosscutting.

Realize you are going to lose lots of wood due to the width of the chain. If there is a bandsaw mill located close it will offer much less waste. But more cost.

[Edward Pearson]

Nathaniel Herreshoff clinker/ lapstrake planked his dinghies in Eastern White Cedar. Its regarded as one of the best timbers for small boat planing in the world...when it can be found. Winter is the best time to fell them but i think needs to be done gently as the ground is hard and you dont want internal shakes. You’ll have your choice of natural crooks too at the bends and branch points. Thin planks of softwood will air dry in no time. If you need to minimise waste from a chainsaw kerf, there are guys with a bandsaw mill that will do it for you on site. If you have plenty of EWC on site you’re set for life for small boat construction. You could fell one or two extra and sell the air dried planking to pay for sails and trailer etc. That’s about the most premium timber you have and air dried is better than kilned. Natural crooks can also save alot of time and glue if you makes some basic templates to offer up from you selected plans/ lofting. Keep extra crooks for the next boat’s breasthook, knees or inner stems etc.

[sp_clark]

+ 1 on upchurchmr's post there, unless you can afford wasting wood to the kerfs. Crosscut chains get all fouled from stringy long-grain cuts since they're shaped to cut short shreds out of cross-grain. Heat kills cutting edges. Bandsaw mill's the ticket, and you just may find a local who's got a portable unit if you ask around.

There's a guy about three blocks from where I live who's got one parked next to his driveway. Blades I have no idea how long, but it's ~ 1-1/2" wide & maybe four or five teeth per foot. Kerf's half what the skinniest chainsaw ripping chain I've ever seen has. Carriage looks to be maybe 18-20' long when assembled.

[Davepat76]

Cut your EWC now while the ground's frozen & the sap's down. Fell 'em easy so your boles don't shatter when they hit the ground, paint the ends then mill to rough thickness, get 'em out of the woods & onto a solid base with stickers between & under cover.

Wood'll dry faster, more evenly than sawlogs left to dry after painting the ends & be less likely to check when resawn for strippage.

Thanks for the advice! I might be able to drop a few of them shortly. They'll have 3 feet of snow to fall into. Won't be able to do any milling until thaw though.

[Davepat76]

If you use a chainsaw mill to make boards from logs, be sure to get a "ripping" chain. Don't use the normal cross cutting chain.
The cross cut chain will dull quickly when ripping -even though it will still work good for crosscutting.

Realize you are going to lose lots of wood due to the width of the chain. If there is a bandsaw mill located close it will offer much less waste. But more cost.

I will look into that type of chain. As for a bandsaw mill, our property is an hour away from civilization, and I don't have a way to get heavy logs out of the woods. I will have to do the milling onsite.

[Davepat76]

Thanks for the advice, everyone! I am certainly rethinking my project now.