# Ply for Exterior Use



## lothian (May 25, 2018)

Ever use quality interior plywood, say baltic birch, for an external (meaning: full exposure to the elements) application and make it work? That's what this thread is about.

I'm tasked with building a "tiny library". I can save a lot of time simply sizing a sheet of quality plywood rather than edge-bonding cedar or PT boards. So I'm exploring this possibility.

Delamination is my concern... caused mostly from water penetration along the sheet edges. I figure some TB3-glued solid PT edge strips will fix the most egregious point of water infiltration, while the flats will get coats of poly prior to paint, cladding, or whatever. I know purpose-designed water-resistant exterior-grade ply exists. But that stuff is hurty-expensive, or in the case of PT seems of mediocre quality.

Thoughts? Suggestions?


----------



## GeorgeC (Jul 30, 2008)

You are asking for trouble trying to use an interior graded plywood for exterior applications. Use something that is rated for exterior or water applications, like marine plywood.
 Exterior plywood 

george


----------



## lothian (May 25, 2018)

Asking for trouble..? No. Risking it? Yes. 

I considered marine-grade ply. And since budget is a factor here, that stuff quickly fell from consideration. Thus the need that compels my post.


----------



## John Smith_inFL (Jul 4, 2018)

I have seen interior plywood on boats that last a few years that was heavily saturated with marine spar varnish.
BUT - any clear coat used outside is a maintenance project. "someone" must be tasked with the upkeep.
if you want 3 years out of the project with a clear coat, you will get it. but don't expect more.
TB3 and exterior primers and paints would be my suggestion. (never epoxy and polyurethane).


----------



## Kudzu (Dec 23, 2008)

I used Baltic Birch in my kayaks and it works well. BUT! They are wet a few hours then put up and dry out.

I tried the BB on roof platform on my jeep. 3 years old(?) and it is starting to delaminate. Same with a sign I made to go on my Kayak trailer. Great stuff but it will not hold up outside unless you find a way to totally seal the edges. Paint or varnish might work but it is going to need regular recoating if you expect it to last.


----------



## lothian (May 25, 2018)

None of you guys are addressing the edge issue. That's really the core of this discussion..


----------



## FrankC (Aug 24, 2012)

It will also depend on where you live, I certainly would not use it here on the West Coast.


----------



## kiwi_outdoors (Jan 15, 2020)

either take their advice and don't try it - or do it your way and prove the advisers wrong. The outdoors is a harsh environment. If you don't mind a finite life for you project, build it anyway that you want, and enjoy it for that limited lifetime.


----------



## Rebelwork (Jan 15, 2012)

lothian said:


> Ever use quality plywood, say baltic birch, for an external (meaning: full exposure to the elements) application and make it work? That's what this thread is about.
> 
> I'm tasked with building a "tiny library". I can save a lot of time simply sizing a sheet of quality plywood rather than edge-bonding cedar or PT boards. So I'm exploring this possibility.
> 
> ...



Lothian it's like anything else. If you can keep it sealed, it will last a long time. If it leaks then you have problems..

If I take particle board and leave it in the rain it's obvious what it will do, but if I seal and finish it with exterior finish and maintain it, then it could last a long time.

Just like your home. Normally cedar is used for rot and bug resistance, but not uncommon to see regular pine.. primed, caulk ed and painted it could last for ever with maintenance...


----------



## kiwi_outdoors (Jan 15, 2020)

For a "Little Free Library" - which we love by the way, perhaps you could get marine plywood some off-cuts from a local (marine) boatworks, especially if you explain, with a smile, what its for.

And do make sure that the roof overhangs the top of the door by a useful amount - we see a lot of LFLs that are not really well though out for exposure to rain.


----------



## johnep (Apr 12, 2007)

I needed to shield some T&G siding from the sun which was causing it to come apart and allow rain.
I used shuttering used for concrete work Full of filled knots ani I too worried about the edges. Used fence paint and knots seemed to vanish. Very happy. Shuttering is cheap. Cost me double the cost to have it installed.
johnep.


----------



## John Smith_inFL (Jul 4, 2018)

Lothian - I addressed it in post #4 = "heavily saturated with marine spar varnish".
we can only "guess" that you are wanting to use a clear coat on the beautiful wood ??
could you elaborate on the finish a little, please.
by "saturate" the plywood, I mean to reduce the varnish by 50% with 100% Pure Gum Turpentine.
Turpentine is a natural product that does not attract mold or mildew. (another personal choice).
reducing the first flood coat for maximum absorption into the end grain is a "sealer".
then, reduced 25% for the 2nd application also with Turpentine, 15% reduction for the 3rd application then 10% for an additional 5-8 coats reduced with 100% Mineral Spirits (Paint Thinner), all 24-48 hours apart for maximum protection.
and 3 years later, come back for a refresher coat of varnish - with a little sanding first.
I do not have any information on water based polyurethanes as I do not use it. (I use oil based only).
if you want to use acrylic or latex house paints, it will be oh so much easier than the clear coats.
for plywood that will be painted, after sanding smooth, I squish exterior latex caulk into the edge with my finger. depending on which brand and type you use, some will turn clear and some will stay white. (your choice). then paint with regular latex paint.
again - depending if you are wanting a clear coat finish or a painted finish.



















I make a LOT of plywood signs that are intended to be outside for years with little to no maintenance. Sealing the edge of plywood for outside projects will always be in the conversation of "how do I seal plywood" for the best results in my project.
the end result is left up to the builder: and their realistic expectations of their project as how to proceed and which methods to follow.


----------



## allpurpose (Mar 24, 2016)

Just some decent exterior grade plywood should do the trick just fine. I started a tiny library that got canned because the HOA never got back to me about it so I left it out in the driveway unfinished and uncovered last fall. it's still laminated just fine. it's certainly a lot less expensive than BB.. If I had coated it with a sealer I'd expect it to last a lot longer still, but since last fall it's rained a lot and still no visible signs of delamination to it..
Unrelated, but I absolutely HATE dealing with HOA's..


----------



## johnep (Apr 12, 2007)

Sorry, What is an HOA?
johnep


----------



## John Smith_inFL (Jul 4, 2018)

John - in a private community, you have to PAY a monthly fee to the managers of the complex so they can tell you what you can and can not do to the home you OWN and to the property that you OWN.
the HOA can actually tell you what color of flowers you can have (or not have) next to your home.
like a private golf community, you can not leave a parked car outside of your home at night - it must be inside your garage. and if you have a "hobby" that creates noise, like woodworking, it will make you cry.
THAT is called the "Home Owners Association" = HOA.


----------



## johnep (Apr 12, 2007)

Thanks John. We are just beginning to get these "gated" communities in the UK. We used to have a lot of rules set by the landowners which they they put in the deeds when they sold the land.one was No Fairgrounds or houses of "ill repute".
Most of the ancient lands belonged to the church and before Henry 8th, the abbeys. We were not supposed to have a caravan on ours as land originally belonged to Ely abbey. They used to have the Tithes under which 10% of income had to be paid to the church, We note that the US does not have fences at the front of properties and there are few here,
Originally they were the boundaries and to keep out rabid dogs.


----------



## John Smith_inFL (Jul 4, 2018)

let's not stray too far from the Original Post please.


----------



## lothian (May 25, 2018)

John, I genuinely appreciate your thorough response and sharing your experience.


----------



## JohnGi (May 9, 2019)

When you glue on an edge band you are relying on an adhesive to hold the edge band in place, which a wet use adhesive will do even when exposed to weather. An adhesive is different from a sealant, and you should expect that exposure to moisture will open up small gaps in the glue line through wood movement and (depending on your climate) freeze/thaw cycles. These will draw in water by capillary action, and the process will self accelerate. The adhesive will continue to hold the edge band in place, but internal degradation of the wood has started. A tongue and groove joint can slow this down since the side to side fit of the tongue in the groove isn't affected and it's much harder to shear this glue line, but this may not be an option for you.

John Smith is proposing you use a sealant which is intended to be a moisture barrier. To me this looks like simpler and more durable construction.


----------



## allpurpose (Mar 24, 2016)

Don't overthink it..Use some decent exterior grade plywood, slap some exterior paint on it and call it a day. Your neighbors will love you for it, take all the good books and leave all the crappy books you don't care about as payment.. Isn't that what good neighbors do after all?


----------



## kiwi_outdoors (Jan 15, 2020)

instead of trying to make it last forever, maybe plan on replacing the LFL every 5 years with a new one of a totally different style and color scheme etc. They are fun little projects.


----------



## RioVistaAndy (Feb 22, 2021)

lothian said:


> Ever use quality interior plywood, say baltic birch, for an external (meaning: full exposure to the elements) application and make it work? That's what this thread is about.
> 
> I'm tasked with building a "tiny library". I can save a lot of time simply sizing a sheet of quality plywood rather than edge-bonding cedar or PT boards. So I'm exploring this possibility.
> 
> ...


----------



## RioVistaAndy (Feb 22, 2021)

All plywood manufactured by reputable manufactures is made using waterproof glue. The difference between standard exterior ply and interior ply is the density of the wood plys. That said where the problems start are along unsealed edges. Exterior grade will hold up a bit longer as the water is not so easily soaked in. Both will eventually delam.
Your idea of edge banding will help, but only of you completely seal the cut ends prior to installing the banding. If I were you I'd seal the edges with a thin epoxy and when I installed the trim I would use a silicone sealer under the trim. This will help keep water from intruding in the nail or screw holes. Then plug all the holes and use a good exterior paint to finish it off.
Good luck, 
Andy


----------



## SA Schneider (Jul 11, 2020)

lothian said:


> Ever use quality interior plywood, say baltic birch, for an external (meaning: full exposure to the elements) application and make it work? That's what this thread is about.
> 
> I'm tasked with building a "tiny library". I can save a lot of time simply sizing a sheet of quality plywood rather than edge-bonding cedar or PT boards. So I'm exploring this possibility.
> 
> ...


Rust Oleum makes a product called Never Wet. It is a two part spray application that makes the base material water resistant.




I say resistant as nothing is really "..........proof"
I would experiment with it on some raw wood and also finished wood and expose your ends to water. Kind of an accelerated test.
Less is more when applying the two coats.
It would also be easy to reapply as needed.

SA


----------



## Rev. A (Jan 29, 2021)

lothian said:


> Ever use quality interior plywood, say baltic birch, for an external (meaning: full exposure to the elements) application and make it work? That's what this thread is about.
> 
> I'm tasked with building a "tiny library". I can save a lot of time simply sizing a sheet of quality plywood rather than edge-bonding cedar or PT boards. So I'm exploring this possibility.
> 
> ...


Save yourself from future headaches, use exterior plywood. Plywood is held together with glue and the use used on interior ply is not water resistant - it'll let go when it gets wet. If it's outside it will get wet unless encased in plastic.


----------

