Can I use 5mm utility plywood for interior?

[DesertApprentice]

I'm working on the teardrop walls. I'm adding rigid form insulation: 3/4" insulation on the sides, 1.5" insulation on the top and bottom. So my wall is already heavy. For the interior walls, I'm thinking of using a lighter layer (not sure if that's a good choice).

I see this "1/5 in. x 4 ft. x 8 ft. Hardwood Plywood Underlayment Specialty Panel" from home depot https://www.homedepot.com/p/1-5-in-x-4-ft-x-8-ft-Hardwood-Plywood-Underlayment-Specialty-Panel-431178/203183010?source=shoppingads&locale=en-US&&mtc=Shopping-VF-F_D21-G-D21-021_001_PLYWOOD-NA-NA-Feed-SMART-NA-NA-New_Engen&cm_mmc=Shopping-VF-F_D21-G-D21-021_001_PLYWOOD-NA-NA-Feed-SMART-NA-NA-New_Engen-71700000086450526-58700007345542405-92700065818640363&gclid=Cj0KCQiA2sqOBhCGARIsAPuPK0g0oRHWVAfaUyIGcGcQjrsPqjjSaswYlmBDlaUSN26TtzJuWj_Y2RcaAk0rEALw_wcB&gclsrc=aw.ds#product-overview

That's the only option that's less than 1/4 plywood at home depot. It looks OK to me, but the product description says it's for sub-floor. Am being silly to even consider that? Any other recommendations?

Thank you!

[Tom&Shelly]

My experience with underlayment is that some brands aren't particularly waterproof. I bought a sheet from Home Depot and tested a chunk in water, and it started to become unglued. Not sure if it's the same stuff you linked to. Mine didn't look as nice as the picture on the web page (go figure!) Mine had a lot of wood putty filler etc. After all, sub-floor isn't meant to be seen!

On the other hand, Tony Latham, on this forum, got some good waterproof underlayment from his local lumber yard. I got the brand name and tried to chase it down, but they don't sell it in New Mexico.

We used Baltic birch for our interior. Comes in 5' x 5' 1/8 inch and 1/4 inch sheets, but not at Home Depot or Lowes. Try a hardwood plywood lumber yard.

Tom

[Woodbutcher]

I believe in using a good quality sound plywood. I don't care if it is marine grade or waterproof. All my trailers, including 2 Woody teardrops were made with cabinet grade interior plywood. For the interior the thing that is most important during building is quality joints and finishes.

[MickinOz]

I clicked the link and read the specs.
Noticed something strange.
So I googled Lowes and looked at how they report their plywood specs.
Same strange thing there.

Here in Oz, the type of glue used is generally reported in the specifications on the retailers website.
For example, Bunnings tell you that their Australian structural ply is constructed with type A waterproof phenolic resin.
I bought plywood from various suppliers. With two exceptions, It has always had the type of bonding printed on the back.
I look for A-Bond, or WBP (water boil proof). South American Aaruco ply is all made with WBP, even their structural grades. Love it.

The two exceptions were a piece of interior grade plywood that had a bright pink glue line which was clearly not phenolic resin, and some marine ply that had the relevant standard stamped on it (BS1088). That seems to be the standard for marine ply - it has two A-graded sanded faces, so rather than ruin one with a line of printing, they just stamp one corner with what standard it complies with.
So I can walk up to the rack in a hardware store, look at the back of the plywood and it will have the grading of the surface veneers and the type of glue used printed on it.

Do they not do this in the US? Can you not look at a piece of plywood and confirm it has the type of glue you require?

[working on it]

My experience with underlayment is that some brands aren't particularly waterproof. I bought a sheet from Home Depot and tested a chunk in water, and it started to become unglued....

On the other hand, Tony Latham, on this forum, got some good waterproof underlayment from his local lumber yard..

* I used thin underlayment on my floor, and due to good prepping, it has been flawless...as has my cabin structure.

* I started my trailer build using a 1/2" sheet of birch plywood that had been sitting unused in one of our sheds for twenty years. It was good quality, and hadn't warped or delaminated in any way, so it became the bottom of the floor (undercoated with automotive spray undercoat). I decided that I wanted a 3/4" floor, so I bought a sheet of Luan underlayment, which was 1/4" thick, and used Titebond2 and 38 Tek screws around the perimeter (plus eight 3/8" carriage bolts thru to the crossmembers) to securely attach it all.

* I made the floor before I learned of the polyurethane+paint thinner "mix" for waterproofing, but since I undercoated and filled all underside seams with PL adhesive, I figured that my floor would be effectively waterproofed after I put 2-3 ? full coats of polyurethane on the topside of the Luan. I guess it was sufficient since it once had two inches of standing water on it, overnight plus a full day, after I left a door ajar in a monsoon. No warpage or delamination, six years later.

...Here in Oz, the type of glue used is generally reported in the specifications on the retailers website.
For example, Bunnings tell you that their Australian structural ply is constructed with type A waterproof phenolic resin.
I bought plywood from various suppliers. With two exceptions, It has always had the type of bonding printed on the back.
I look for A-Bond, or WBP (water boil proof). South American Aaruco ply is all made with WBP, even their structural grades. Love it....

* My trailer is built from 3/4" Arauco plywood (no insulation), with phenolic resin between plies, except for the floor; I got a great deal on six sheets for $100 ??, with one side pre-sanded already. Once I studied the poly "mix" threads, I totally waterproofed the plywood before assembly, and again used PL adhesive inside and out (and in-between) all seams, for more waterproofing. 10-12 tubes. And afterwards did the same with poly "mix" basecoats, and multiple topcoats of acrylic farm equipment enamels. Ten years after the trailer was constructed/poly'd/painted, and after many modifications, there's been zero instances of wood rot or delamination. I love that plywood, too.

[mountainminded]

I’ve used the 5mm underlayment product from my local HD both as interior paneling and head liner with good success. I think the stock in HD varies by location and in my Oregon store it is a Birch panel made in Indonesia and supplied by a Bellingham Washington company called Swaner Hardwood. Look up in the HD racks for an unopened pallet of the product and the wrapping should give the name of the supplier. Before using it I contacted the manufacturer to find out more about the product, the glues used, etc. I also repeated a dunk and dry test numerous times where I submersed a scrap for several days and then dried it completely before putting it back in the water. The orange glue used (rated as interior glue by Swaner) showed no signs of failure and I was satisfied. Keep in mind that the veneer on these panels (like many modern plywood products) is micro thin and will not tolerate ANY sanding. A scotchbrite pad between coats of finish is about all it will take.

[tony.latham]

I'm thinking of using a lighter layer ....

I build my walls with 1/8" Baltic birch on the inside. The problem with the stuff you are looking at is the great unknown of HD plywood. It might be junk.

Get on the phone to real lumberyards, cabinet shops, or specialty plywood places and ask if they have or can get 1/8" Baltic birch. The stuff is exceptional.

Tony

[swoody126]

i keep several sheets of this stuff around most all the time

used for making patterns n templates

great for INTERIOR(never gets wet)

Screen Shot 2022-01-04 at 7.43.34 AM.jpg (148.08 KiB) Viewed 607 times

one side is always smooth and clear

finishes out natural beautifully

paints out very well/smooth

very flexible

the only issue i can imagine would be if you sand the veneer very much you'll sand thru it

sw

[Philip]

I used that stuff on the interior build of my van. After two years of the van setting outside or being on the road. I have had no problems with the ply. All of the ply is painted with an oil-based paint.

If you going to clear coat it. It seems to be a little rough of texture for that. Like stated sanding is a no-no. The plys are thin and disappear pretty easy with a sander.

[Shadow Catcher]

This is a section of wall from our tear. I can not say how many times I have said you are building an aircraft not a tank.

[Patrio]

I used Lauan for the interior panels in my camper. Puttied the seams and painted it white with exterior latex. It's held up beautifully for two years.

This is a pic from late in the build process.

[2bits]

I used the underlayment from Lowes and it was thinner than 5mm. Anyone who wants their wood to be "waterproof" must expect their camper to leak right? Build it so it doesn't leak. Even "Waterproof" wood will redirect water into the edges, then to the framing and onto the floor and ANY leak isn't good.