Birch Plywood for Transom

[tonynoriega]

Just bought some 1/2" White Birch Plywood from the local wood shop... am going to use this for the outer section of my transom to replace the rotted wood that was there.

Anyone have any experiences with Birch?

Going to stain it something nice, and give it several coats of Helmsman spar urethane....

I have enough to make 3 pieces, so even it it lasts 3 or 4 seasons, I have some extras when the time comes.

Just wanted to see if anyone has had any experience, good or bad with Birch.
thx

 

[rscottp]

tonynoriega » 12 Mar 2014, 10:52[/url]"]Just bought some 1/2" White Birch Plywood from the local wood shop... am going to use this for the outer section of my transom to replace the rotted wood that was there.

Anyone have any experiences with Birch?

Going to stain it something nice, and give it several coats of Helmsman spar urethane....

I have enough to make 3 pieces, so even it it lasts 3 or 4 seasons, I have some extras when the time comes.

Just wanted to see if anyone has had any experience, good or bad with Birch.
thx

No no no! All the birch ply I have ever seen or used is for interior use only! If it gets wet it will delaminate and fall apart! Do not use it!

 

[tonynoriega]

What if I seal it with the Spar?

Does that not count for anything?

 

[jigngrub]

tonynoriega » 30 minutes ago[/url]"]What if I seal it with the Spar?

Does that not count for anything?

If you seal it real good with 4 coats of spar and seal any fasteners or penetrations with 3M 5200 it'll last a few years maybe.

The main thing when selecting plywood for use in a boat is to find out what kind of glue they use to hold the plies together with. There are 2 kinds of glue that're suitable for marine applications. One is WBP (water/boil proof) glue and the other is phenol (epoxy) resin.

Interior grade plywood is now made with a soy bean derivative adhesive that will delaminate the plies if it gets wet, and it doesn't have to get real wet for bad things to happen.

 

[SumDumGuy]

If you got the ply use it; no big deal.

At worst you will have to replace it sooner than something else, maybe. Replacing is ok 'cause it's something to do.

 

[tonynoriega]

What about using an epoxy resin to seal it up?

 

[rscottp]

That stuff will not last outside. You are wasting time and $ if you use it. Build something with it that stays inside!

 

[tonynoriega]

Would I just be better off buying something from home depot?

This is killing me... now I feel dumb...

I dont understand all the talk about epoxy resins, and spar urethanes if they dont do what they are intended to do?

Besides the glue... which it sounds like it is not waterproof, what about this type of plywood is unusable?

It feels solid... it has a nice grain to it...

Just looking for the "why" behind not using this stuff.

$30 mistake....

 

[rscottp]

tonynoriega » 12 Mar 2014, 16:49[/url]"]Would I just be better off buying something from home depot?

This is killing me... now I feel dumb...

I dont understand all the talk about epoxy resins, and spar urethanes if they dont do what they are intended to do?

Besides the glue... which it sounds like it is not waterproof, what about this type of plywood is unusable?

It feels solid... it has a nice grain to it...

Just looking for the "why" behind not using this stuff.

$30 mistake....

The glue used in that plywood is not designed to be exposed to the environment, it will fall apart in any type of moisture. You can coat it but water always finds a way to get into things. It just doesn't make sense to try to use tons of expensive epoxy to try to make it work. Just get some exterior plywood and coat it with spar. It will be much cheaper, faster and will last longer. I have also found that a lot of birch ply has voids in it, also not ideal for a transom.

 

[nlester]

I think the reply above says most of what is relative. You can use anything, it just depends on how long you want it to last. When I got my jon boat, I used what I had laying around to get it on the water. After a few months, it started delaminating but I still used it for over a year. It let me determine what I wanted to do next. I finally replaced it with a solid piece of pine covered in fiberglass and coated with epoxy. 3 years later I am still happy with it. Anything will work, the choices determine how long it will last but regardless of what you use, it will give you a better idea of your choices.

 

[tonynoriega]

Lesson learned...

Ill just eat the $30 and go get some marine grade...

Cant take it back because they ripped it from a 4'x8' sheet...

 

[Ringo Steele]

Marine works fine. Exterior grade also works (same glue) and half the price. If you use spar,use at least 4-5 coats.

 

[huntinfool]

Here is some info I copied from a site from Australia. It is no different than here in the U.S.<br /><br /> MARINE PLYWOOD EXPLAINED<br /><br />    <br /><br />Many Australians grow up with the belief that Marine Plywood is a ‘special’ product made with secret adhesives that make it virtually indestructible. This is an urban myth.<br /><br />The adhesive (glue) that is used to bond the veneers of Marine Plywood together is the same as any other structural plywood that is manufactured in Australia.<br /><br />What is Marine Plywood and why is it so expensive?<br /><br />A boat travelling through water is subject to plate action from waves and floating debris. Marine Plywood is designed to absorb these forces due to the fact that this plywood is the closest to solid wood. In fact it is better than solid wood with defects having been graded out.<br /><br />Marine plywood is manufactured using the highest quality grade of veneers.  These veneers don’t have defects and thereby eliminate core gaps when the sheet is cut. These veneers are not available in volume compared to lower grades. <br /><br />As these high grade veneers are used in every layer, marine plywood is dearer than other grades such as structural plywood<br /><br /><br /><br /><br />As I said there are no gaps in the wood. All perfect veneers that are glued together, making them very expensive. Same reason cdx is cheaper than ab plywood. More gaps in cdx. <br /><br />I have probably made well over 100 transoms in my lifetime. I started in '88. Since I did this for a living for almost 20 years, I'm not just giving opinion. Now days we don't make them out of wood. We pour solid glass transoms.<br /><br />I posted a thread here several years ago about it. <br /><br />Anyways, I'm not trying to come across as a know it all. I am trying to be helpful and informative to everyone here. Since this is the inter web and no one knows how I am saying this, I just want y'all to know. This is just informational.<br/>

 

[huntinfool]

I copied and pasted from another post. ANY wood will make a transom. Some will last longer than others. Two 3/4" plys bonded together with fiberglass or epoxy will be strong. Wrap that in fiberglass with resin or epoxy and they will last a long time. Or at least the ones I have done have lasted decades. My transom in my 1654 has lasted 5 years and is outdoors 24/7. No delamination and no fatigue.

Just some of my experiences and some info on what I have done and learned.

 

[ketchup sandwich]

I helped a buddy replace his transom. He was having a similar dilemma until someone explained it to him this way...."that rotting plywood transom you are tearing out was in there for the past 20-25 years." After thinking about it...2 pieces of 3/4 plywood, glued together with gorilla glue, and coated with 5 coats of spar....boom done, rock hard and hopefully another 20+.

 

[SumDumGuy]

ketchup sandwich » 17 Mar 2014, 22:46[/url]"]I helped a buddy replace his transom. He was having a similar dilemma until someone explained it to him this way...."that rotting plywood transom you are tearing out was in there for the past 20-25 years." After thinking about it...2 pieces of 3/4 plywood, glued together with gorilla glue, and coated with 5 coats of spar....boom done, rock hard and hopefully another 20+.

But just think, if ya'll would have used marine grade or maybe even super plywood the transom could last an extra 30 years.

:twisted: :twisted: :twisted:

 

[onthewater102]

I've wondered if you could make a corrugated / honeycomb material out of stainless or aluminum tubing nested with little 1.5" sections in a honeycomb near where the motor mounts then laminated between two pieces of sheet metal...I was thinking if you could weld or epoxy it all together it wouldn't ever need to be replaced...

this is a rather crude version of what i'm talking about - but it's the idea to what is between the laminating sheets

Probably be a good idea to case the whole setup in channel then fill with a sheet of the same gauge

 

[tonynoriega]

Well, I just went and bought a sheet of AB Marine Grade Plywood... sucks having to pay $75 for it... but oh well...

I will use the remaining for a removable floor mid ships...

Maybe I will use the birch for woodworking training with my kids... something they can cut up and build a bird box or something like that...

 

[thill]

Unless you like a transom that falls apart very quickly, you made a wise decision! I tried using some Sandeply, and it fell apart in MONTHS, not years! Fortunately, I hadn't mounted the hardware back yet, so I replaced it with some PT ply with a glass mat barrier and impregnated with resin. That transom will likely be there for a lifetime.

That $45 extra you spend for the good stuff will save you several days of labor, the time and $$$ of replacing is again, and the time lost not using the boat, not to mention the possiblilty of a bent transom skin and even possibly a lost motor.

NOT worth using the wrong stuff. Glad you listened to the majority on that one...

Epoxy is great to seal with, but make sure to paint, as the sun beats it up.

-TH

 

[SumDumGuy]

sandeply is not true plywood, it seems to have a couple layers of MDF type material in the sandwich. so....