Wood Glue or Epoxy? Laminating Transom Plywood

I'm sorry guys I looked at several threads on transoms but did not see what adhesive was being used to glue the two exterior grade 3/4 plywood pieces together with. I put one together with Titebond 3 and exterior screws, primed and painted it. Now I see where I should have sealed it first, so I stripped the paint off only to find the top ply on one side has bubbled up and has a big air pocket under it. DOH! I think the exterior plywood I got is maybe not so good so I am going to redo the whole thing with some better plywood.
So will the titebond work or should I use an epoxy like the Raka I have been reading about and if so which one of the Raka epoxies? Should I use screws or not? Exterior screws was a mistake, they should have been stainless steel. This will be for my 14ft 6 inch 1973 Starcraft Mariner, and I have a 1971 Johnson 50hp to put on it. I am thinking I will need a very strong transom for that motor.....
Thanks for any comments and I apologize if this has been covered somewhere already.

Dave, if you really wanted to beef up the transom,
you may want to entertain the idea of epoxy (I use Raka 900 medium).
and two or three layers of fiberglass cloth or mat between
the two sheets of plywood - before you cut to shape.
(make the transom a couple of inches over size all the way around).
put a lot of weights on it to compress it while it cures.
if you want to use screws just to hold it together, put your screws
on one end only - not all the way around or in the body.
Reason: when screwed together, that makes the two wood pieces immovable.
with screws only on one end, the weight can compress the epoxy, glue,
or whatever adhesive you choose to squish out and fill all the voids.
then after it cures, cut to shape that you need (make a template first).
then - seal and paint. A 50hp requires a bit more attention to detail
than a transom for a 15 or 25hp motor.
another note: your transom will not break - BUT - the corner and knee braces could fail.
so ensure all your structural components are sound and secure.

this is what I did - but went the extra step and laminated a piece of
1/8" aluminum sheet cut to shape to the front of the transom board.
Take into consideration that epoxy is not UV tolerant and must be
primed and painted accordingly to protect it.
You can find fiberglass mat on ebay for cheap.
2oz x 12" x 20' is what I purchased.
it comes in 3/4, 1, 1.5 and 2 ounce weights for what we need.

my next transom will be more cosmetically "pretty".
it will be 3/4" BDX plywood, 3 sheets of fiberglass mat and epoxy
with the show board being 1x3" Florida Cypress wood sanded smooth
with a dozen coats of clear marine spar varnish over the sealer.

for your sealer, mix up about a pint or so of this formula:





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Read through the thread in my signature for some thoughts. Thumbs up on Johnny's suggestions. If I were making another, I would oversize the 2 or 3 pieces, bond them and use weights as well as screw the outer edge all around. Trim using your template and cut out the edges with screws after cured. I don't have experience with Epoxy and fiberglass but there must be videos on utube. I used a PL product mentioned in several threads. Take some pictures and dig into the project after reading what others did.

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I did my transom out of 2 layers of 3/4" BCX plywood. Glued together with Tite bond lll. Then used the old timers formula to seal it.

2smknbrls - I have been using TiteBond yellow glue since it first came out in the '80s.
I bought it by the gallon and used it on all kinds of projects, inside and out. (mostly out).
The formula has improved vastly over the years through the I, II and now waterproof III grades.
There are sooooooooo many products available to the public today that
it makes the head spin trying to decypher the advertising hype.

here is a short list of adhesives/sealants/caulks that I have used and endorse for marine applications:

3M-5200 Fast Cure Marine Sealant
TiteBond WeatherMaster Polymer Sealant (caulk tube).
TiteBond II and waterproof III liquid [for wood-to-wood applications]
most of the Loctite products: Loctite PL Marine Fast Cure Adhesive Sealant (caulk tube).
Loctite PL Window and Door Polyurethane Sealant (caulk tube).
Gorilla Heavy Duty Construction Adhesive (caulk tube).
Gorilla Polyurethane (liquid) Waterproof Glue [for wood-to-wood applications]
WestSystem and Raka epoxy products
Dap 00203 1 lb Weldwood Plastic Resin Glue (powder form). [for wood-to-wood applications]
Resorcinol Marine Glue (powder form). [for wood-to-wood applications]

I am sure there are others that will work - it is just hard to keep up with the ever changing market.

CAUTION: most of these products say right on the container - compatible with aluminum
while a few will say NOT for use on aluminum. So read the instructions carefully.
anything with pure silicone should be avoided when working with aluminum.
anything with polyurethane is compatible with aluminum, wood and plastics.
any "polyurethane" varnish is for indoor use only - not in a boat for any reason.
~ use the correct product for your project and you will achieve satisfactory results ~

Disclaimer: this is just my personal professional opinions on these products.

** Read, Understand and Follow the instructions on the label
of any and all products you may use. Observe all safety precautions **




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Thanks All for your comments! The response is fabulous here and I have so much information now my brain can't handle it. DOH! I will take a little bit to try to digest the info and make a plan.

For your enjoyment I will share some photos I took of the mess that was the transom I am replacing.

SDC17722 by mrdaveusa, on Flickr

Check the damage and "repair" to the transom knee.

SDC17750 by mrdaveusa, on Flickr

Damaged knee

SDC17815 by mrdaveusa, on Flickr

Corner bracing.

SDC17813 by mrdaveusa, on Flickr


SDC17816 by mrdaveusa, on Flickr

The old transom-two untreated 3/4 plywood pieces set in place and bolted.

SDC17818 by mrdaveusa, on Flickr

Transom wood removed.

SDC17823 by mrdaveusa, on Flickr


SDC17807 by mrdaveusa, on Flickr

I am still not sure about the knee brace repair. I have shaped up some very thick aluminum angle stock that I will either bolt or rivet to the existing knee to allow fastening the knee to the new transom. I'm pretty sure the knee was originally fastened some way to the transom but as you can see was somehow damaged badly enough so that function is missing now.

whoaaaaa DUDE !! I personally would lower that new transom wood
down to about 3-4" from the bottom of the deck.
fabricate 3 new knee braces
fabricate new corner brackets out of 1/4" x 1.5" aluminum flat bar.
use the appropriate stainless hardware/fasteners where needed.

if you are still planning on putting a 50hp motor on that transom,
IMHO the whole rear end needs some work. a lot of work.

Thanks for the photos !!

Thought you might like that! Yeah the previous owner said it was water ready as is. After I got it home I looked at it closer and decided then and there NO WAY! I am sure glad I did not, looks pretty scary to me.
I will give some thought to strengthening this thing up. Agree with you Johnny, will take some work to get it done right.

Thick aluminum angle has been used before to fix knee braces on StarCraft boats.
Are you sure it's a Mariner? I was looking at brochures for '72 (no '73 brochures available) and they don't show a 14' Mariner. There are Sea scamp's and Sea farers. Those models don't have splash wells and have lower hp ratings.

lckstckn2smknbrls said:

Thick aluminum angle has been used before to fix knee braces on StarCraft boats.
Are you sure it's a Mariner? I was looking at brochures for '72 (no '73 brochures available) and they don't show a 14' Mariner. There are Sea scamp's and Sea farers. Those models don't have splash wells and have lower hp ratings.

Click to expand...

I have not been able to find this exact boat in any old photos or brochures. Here is a pic of the nameplate.

IMG_20170204_130259597 by mrdaveusa, on Flickr

I've put the "prototype" transom in place and clamped the aluminum angle parts I modded for a photo so you can see. This was my idea to repair the transom knee. I was thinking to bolt the parts to the knee. I made them so one of the motor mount bolts will go each one.

IMG_20170204_121457479 by mrdaveusa, on Flickr

I am not going to use the "prototype" transom in the photo. I will build something stronger. The plywood I used is exterior grade but really crappy as it has many voids and now plys are delaminating without any exposure to the elements yet. I may even consider some marine plywood and will use Johnny's glass mat idea in between the 3/4 inch plywood pieces.
The boat was rated originally for a 40hp, with careful strengthening of the transom I think the 50 will work. The idea intrigues me. Should make it interesting on the water.

my family heirloom boat is a '59 14' Crestliner rated for 30hp when new.
my brother had it for awhile and he put a 55hp Johnson on it to pull
water ski enthusiats and that big tube thing full of drunken fools . . . .
when it was my turn for possession - I had to rebuck most of the rivets
in the stern and knee braces.
a higher powered motor and excessive stress can reak havoc on a boat
that was not designed for it - from my personal experience.

That's pretty much how I've seen it done. Not as wide up top and the upper part came all the way down to the Z brace.

Dave I'm in the same predicament as you are in finding a solution to strengthen the transom. I have a long shaft 73 Johnson 50 hp and its one heavy rig. With mine im gonna completely replace the transom brace and add two more. Good to know someone else is trying to tackle this same issue. Good luck.

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on a personal note, I really don't trust a transom board that is
only 8" tall and one sheet of plywood resting on the "Z" brace.
"I think" this design was for the under 15hp outboards.
Once you start modifying the stern to accept a higher horse power
than what the boat was designed for, you must take the appropriate
measures to make it more stronger and ensure it is safe to do so.
This is where I recommend something in the middle of the transom plies.
either some fiberglass mat imbeded in epoxy or a sheet of 1/8" aluminum plate
with the appropriate addition of knee and corner braces.
for super strong, I would use 3 sheets of 1/2" BDX with fiberglass mat imbedded
between the plies. again, using screws only on one end to keep everything from
sliding around while there is a couple hundred pounds of weight on it for 12 hours.
VERY important to ensure grain of the plywood goes horizontal.

jus my Dos Centavos

Texas Prowler said:

Dave I'm in the same predicament as you are in finding a solution to strengthen the transom. I have a long shaft 73 Johnson 50 hp and its one heavy rig. With mine im gonna completely replace the transom brace and add two more. Good to know someone else is trying to tackle this same issue. Good luck.

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Click to expand...

I would be interested in how you fab up new knee braces. I have some ideas which will take a good aluminum welder to fabricate, then solid riveted to the hull. I've not seen where pre-made knees are offered for sale anywhere.

put aluminum boat transom brace in your search engine.

Johnny said:

on a personal note, I really don't trust a transom board that is
only 8" tall and one sheet of plywood resting on the "Z" brace.
"I think" this design was for the under 15hp outboards.
Once you start modifying the stern to accept a higher horse power
than what the boat was designed for, you must take the appropriate
measures to make it more stronger and ensure it is safe to do so.
This is where I recommend something in the middle of the transom plies.
either some fiberglass mat imbeded in epoxy or a sheet of 1/8" aluminum plate
with the appropriate addition of knee and corner braces.
for super strong, I would use 3 sheets of 1/2" BDX with fiberglass mat imbedded
between the plies. again, using screws only on one end to keep everything from
sliding around while there is a couple hundred pounds of weight on it for 12 hours.
VERY important to ensure grain of the plywood goes horizontal.

jus my Dos Centavos

Click to expand...

Johnny you knew what I was going to ask! Thank you very much for your comments! About the three 1/2 plywood fiberglass laminated stack, what weight cloth to use? Do I need to seal each one with the oldtimers formula before using the epoxy or resin? Epoxy would be stronger yes? Which epoxy to use with the fiberglass cloth?
I think this is worth looking into using the strongest plywood I can find, there is a shop close by that sells marine grade plywood, it is pricey but for the extra strength in this application would be worth it. I just have about zero confidence I can find a good piece of exterior plywood after what I have experienced so far.
A super strong transom with serious stout bracing is the order of the day here. Thanks to everyone for all your comments!

The is a brand of ACX plywood called Accurro (my spelling might be wrong) Menards carries it and others. It's about half the price of marine plywood but very high quality.
If you use the old times formula to seal the plywood you do that after you have glued the layers of plywood together and cut to it's finely shape.
If your using epoxy resin it will glue and seal the plywood and you don't have to use cloth but the cloth will add strength. If you use polyester resin you must use cloth otherwise the polyester resin will peel off.

do not seal or preserve the plywood prior to laminating.
cut transom boards a couple of inches bigger than what you need. (trim to fit later).
I use construction block, bags of cement, 5gl buckets of water - whatever I have on hand for weight. (not clamps).
transom must be on a FLAT concrete surface - not on sawhorses.
if your floor is crooked - your new transom will take on that shape.
place newspaper under the edges so you don't glue your project to the floor.
(you would be surprised at how many signmakers have done that !!!) [and yes, me too]
BDX/BCX is an exterior grade of pine construction plywood designed for outside use
as long as it is primed and painted. It must say that on the label when you buy it.
BDX/BCX has all the inside voids, knots and splits filled - CDX does not. (it has open voids).
there is no reason to spend the extra $$$$ for "marine" plywood if you can find the proper BDX/BCX grade.
once BDX/BCX plywood is properly sealed and preserved, it will last you a minimum of 10 years.
annual maintenance (cleaning and fresh varnish or paint) will make it last 40 years.
personally, I have switched from West System epoxy to Raka 900 epoxy. But both are very good.
I use 1.5 - 2 ounce fiberglass chopped stranded mat. "mat" is mostly for flat surfaces.
"cloth" is easier to work around corners and complex shapes. (either one will work fine).
avoid "waxed" polyester resin, if you use it - - - there IS a difference in the poly-resins.
avoid anything that says "polyurethane" varnish or paint - it is for indoor use only.

make a template of where it goes.
once you have your transom blank laminated, cut to desired shape and hit both sides
and all edges with the electric sander.
sand the cut edges smooth. Particularly the fiberglassed seam.
i like to butt the ends right up to the hull - so the backside must be chamferred to fit the
round corners. Vacuum all edges and surfaces.
Then - seal it with the Old Timers Formula followed by your choice of top coat.

that is just about as good as you can make it.

West System and Raka epoxy is available on ebay - as well as marine stores and online. https://www.raka.com
the fiberglass chopped mat and cloth is available in the same places.
if you are more comfortable with polyester resin - remember the "non waxed" formula.
the "wax" formula is designed to impede the curing of the surface so that successive layers
can be layed up during the manufacturing process in fiberglass boats, cars, bath tubs, etc.
(If you have ever used polyester resin and it never dries and stays tacky, that is the reason)
epoxy resin is not UV tolerant - so if you use that to coat the outsides of the wood,
it must be top coated with SPAR varnish (not spar urethane) or oil base primer and paint.
YouTube has many good educational videos on working with fiberglass

Read, Understand and Follow the instructions on the label
of any and all products you may use. Observe all safety precautions.

https://www.youtube.com/watch?v=9jHUI0CiYbs
https://www.youtube.com/watch?v=NGIveJSsWeI&t=955s

again - just my personal information

Edit: another plywood that is semi-weatherproof is the product called
MDO - Medium Density Overlay...... it comes in pre-primed (white color)
and natural - brown craft paper that is overlayed onto the plywood
with waterproof adhesive . . . . this is what sign makers use for long term
outdoor exposure. This is an excellent choice when using adhesives other
than resin or epoxy. such as Titebond III, Gorilla Glue or any other type adhesive.
more user-friendly in getting everything buttoned up watertight.
epoxy and polyester resin will NOT stick to the white (pre-primed) board.
my local Home Depot carries the brown MDO in 1/2 and 3/4" thickness.
This is an optional item for the Big Box Stores - you have to hunt for it.

https://www.andersonplywood.com/395/mdo-medium-density-overlay/
https://www.menards.com/main/building-materials/panel-products/industrial-panels/mdf-mdo-panels/roseburg-1-2-x-4-x-8-mdo-plywood/p-1444452504136.htm






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davedude said:

Texas Prowler said:

Dave I'm in the same predicament as you are in finding a solution to strengthen the transom. I have a long shaft 73 Johnson 50 hp and its one heavy rig. With mine im gonna completely replace the transom brace and add two more. Good to know someone else is trying to tackle this same issue. Good luck.

Sent from my LGLS991 using Tapatalk

Click to expand...

I would be interested in how you fab up new knee braces. I have some ideas which will take a good aluminum welder to fabricate, then solid riveted to the hull. I've not seen where pre-made knees are offered for sale anywhere.

Click to expand...

Well the plans for my transom braces are as follows. Since the center brace will carry most of the engines weight the current one from the factory will be removed( too small for my long to short shaft conversion).The plan is to have 1/8 inch 5052 sheet cut and bent by a local shop. This will provide support from the outboard clamps down further forward into the hull than the factory support, which Will be riveted to the hull and bolted to the transom. This support will span from the top of the outboard clamps down the transom about six inches from the bottom of the hull, then maybe fifteen inches forward into the bottom of the hull. The two other braces will be 1/4 inch and span from the two ribs on the hull up to the transom welded to 1/4 sheet. Both will be bolted at the connecting locations. I could draw up something if need be.

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