Plywood for the interior??????

Tim R. · Jul 17, 2009

The advantage of marine plywood is that it is constructed with little or no voids. The stuff from the big box store is full of voids. I say do it right the first time.

Bob McL · Jul 17, 2009

I worked a couple of months at Home Depot where one of the things I had to do was cut plywood. It was amazing how much of it had no glue at the center - just opened up after the cut. If you can't get marine wood, then find a cabinet shop supplier and buy Baltic Birch. It has seven or more equal plies, no voids, and comes in 60 x 60" sheets.

Ross · Jul 17, 2009

Jack, find a local yard that will sell you MDO plywood. That is mediun density overlay. made for outdoor signs and concrete forms. For anything special I try to go to the local lumber yards that sell to the builders. They can get anything.

Maddog · Jul 17, 2009

As a compromise, look for Baltic Birch plywood. Its the stuff with real thin layers, solid, no voids. I buy it at Homey-D. Seal it and on the interior, it will work fine for you.

sailingdog · Jul 17, 2009

I'd also point out that the glue used in marine plywood is far more water resistant and durable, as true marine plywood has to meet certain minimum specifications.

Ross · Jul 17, 2009

I use both Baltic Birch and exterior grade plywood and often boil a new to me piece of scrap. All of the plywood labeled "exterior" glue stays together in the boiling water test but Baltic Birch comes apart within a half hour. Oriented strand board stays together longer than interior grade plywood but it does come apart.

jibes138 · Jul 18, 2009

Sand Dollar

Hey Ross,
I'll try to make sure my sand dollar never falls into an ocean of boiling water.

How does boiling the water allow you to compare that test to real world conditions? The temperature may cause changes in the glue that will never happen in ambient conditions? Wouldn't a room temperature salt fog test be more appropriate? Of perhaps thermal cycling while simultaneously doing the salt fog? I agree it is an interesting comparison between similar objects to see if they withstand boiling, not sure it will reflect performance for the intended use.

RichBone · Jul 18, 2009

Are you referring to the plywood that covers the openings in the v-berth and settees?
For that I would just use 1/4" exterior ply from your local big box. Exterior ply uses the same glue as marine ply and it's not gonna be structural and can easily be replaced. Slap a couple of coats of varnish on it.
If you want to do it without voids buy 1/8' doors skins and glue up two layers.

Ross · Jul 18, 2009

jibes138 said:
Hey Ross,
I'll try to make sure my sand dollar never falls into an ocean of boiling water.
How does boiling the water allow you to compare that test to real world conditions? The temperature may cause changes in the glue that will never happen in ambient conditions? Wouldn't a room temperature salt fog test be more appropriate? Of perhaps thermal cycling while simultaneously doing the salt fog? I agree it is an interesting comparison between similar objects to see if they withstand boiling, not sure it will reflect performance for the intended use.

I could simply drop the sample into cold water and wait a week and get the same results. The rest of the test methods you suggest will yield the needed results after a time but boiling wioll give an answer in an hour.

kendall · Jul 18, 2009

I'd have to side with Dave here, boiling introduces a lot of stresses that will never be present in a boat.

Many of the glues used in making exterior plywood are thermosetting glues, so boiling WILL delaminate them, even if soaking would never cause it.

Exterior grades are extremely unlikely to have glues that will break down with simple soaking, interior grades will most likely break down with moisture. Most WILL delaminate when heat is applied.

Ken.

Ross · Jul 18, 2009

kendall said:
I'd have to side with Dave here, boiling introduces a lot of stresses that will never be present in a boat.

Many of the glues used in making exterior plywood are thermosetting glues, so boiling WILL delaminate them, even if soaking would never cause it.

Exterior grades are extremely unlikely to have glues that will break down with simple soaking, interior grades will most likely break down with moisture. Most WILL delaminate when heat is applied.

Ken.

And you know this how?
Boiling is a standard test for water proof adhesives.

Tim R. · Jul 18, 2009

I have seen boat builders use the boil test for glues. Somewhat common for testing waterproofness.

What happens when you boil a laminate glued up with epoxy? Contact adhesive?

Heat will soften epoxy but I am not sure if 212° is enough to cause delam.

Ross · Jul 18, 2009

Glue/Bond Information Phenol Formaldehyde is a two component synthetic glue. Phenol (with the chemical formula C6H5OH) is reacted with formaldehyde (CH2O) under controlled temperature conditions to produce a thermosetting (heat hardening) resin. This resin is a new chemical entity which possesses properties that are completely distinct from those of either phenol or formaldehyde, with the formaldehyde converted to stable methylene linkages which do not break down under exterior end use conditions. Phenolic resin is typically supplied to plywood manufacturers in a water solution premixed with a catalyst (caustic soda). Soda Ash and bulking ingredients called fillers and extenders (bark and wheat flours, for example) are added to improve gluing characteristics of the mix. Plywood is manufactured by bonding layers of wood veneers with the phenolic resin glue mix, and polymerizing (curing or hardening) the glue in a “hot press”. The hot press subjects panels to an approximate temperature of 150°C (300°F) and a pressure of about 1.4 MPa (200 psi), resulting in an inert water and boil-proof bond.

http://www.canply.org/english/literature_media/tech_glue.htm

Ross · Jul 18, 2009

Tim R. said:
I have seen boat builders use the boil test for glues. Somewhat common for testing waterproofness.

What happens when you boil a laminate glued up with epoxy? Contact adhesive?

Heat will soften epoxy but I am not sure if 212° is enough to cause delam.

Tim, I have used epoxy to glue knobs back onto pot lids and it always fails. polyurethane type glues work well. I posted a Canadian plywood association excerpt about glue bonds.

Mark Major · Jul 18, 2009

I used AB from Home Depot, put many coats of paint on it, and regret it. It was a lot of work to have to plan on doing over again.. Also, a boatbuilder/now lumber provider informed me fiberglass resin does not properly adhere to pine, but will stick to fir.

Ross · Jul 18, 2009

On anything where you have doubts make a test sample. Itis easy and cheap and can save a lot of work later.

Oldhokie64 · Jul 18, 2009

As a custom home builder for 35 years, ending with the present economy, I have run through a lot of plywood. My main lumber guy told me the difference in marine and exterior is the surface, marine being AA. The glue he tells me is the same. Plywood underlayment is SUPPOSEDLY assembled with no voids, unlike AB and the like. You always run the risk of the glue pot guy falling asleep and we have had several occasions where a number of sequential sheets would delaminate. I would and have gone for MDO for replacing access panels and such, it is available at any good lumber yard. Homer only carries 3/8 single sided. You can also get HDO which has surfaces close to formica, the better source for HDO would be a concrete form supply outfit.

zeehag · Jul 19, 2009

why not use clear penetrating epoxies--does it prevent delamination or is it a waste of money??