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Replacing rotten transom using epoxy

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Replacing rotten transom using epoxy

Old 02-23-2019, 02:19 PM
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Default Replacing rotten transom using epoxy

I just finished removing motors, OD/housings and rotten transom wood on a 1986 SR AJ. The complete transom was a rotten mess, not identified by a South Florida incompetent marine surveyor. I have done this type repair work before but I am getting old and I cannot remember if EPOXY requires wetted FG cloth between 3/4" plywood layers and boat's inside FG skin. If my memory serves me correctly, I first applied un-thickened epoxy resins on the inside FG skin surface and opposite surface of 3/4" plywood (wet both sides). Then, I applied trialed "thickened" epoxy to the inside FG skin using a grooved trial, followed by pressing and clamping the epoxy (non thickened) coated 3/4" plywood. The cloth was not needed between the layers. The thickened epoxy substituted for cloth. Cloth would have been needed if I had used polyester resin. After curing, I repeat the process with thickened epoxy on the second piece of 3/4" plywood clamped onto the first piece of 3/4" plywood. I have 1708, 6 oz. cloth. and matt. The STB MC transom assembly's bolt holes were somewhat "wallared" out and cracked due to the rotten wood giving way. I ground down from the inside and outside and have re-glassed with polyester and cloth. Both inside and outside FG skin surfaces are smooth. I have created 2x4 braces to sandwich the skin and plywood together for a flat surface and designed additional turnbuckles to force excess epoxy into voids. Any suggestions or disagreement would be appreciated.
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Old 02-23-2019, 03:08 PM
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You've got the game plan down pat. Only thing I'd suggest is to forget coating both sides with clear resin, not necessary when toweling on the thickened resin. Just mix that slightly on the runny side and go with it!
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Old 02-23-2019, 08:40 PM
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Originally Posted by bills106 View Post
You've got the game plan down pat. Only thing I'd suggest is to forget coating both sides with clear resin, not necessary when toweling on the thickened resin. Just mix that slightly on the runny side and go with it!
Id disagree with that, bonding to plywood improves when the surface is first saturated.
The thickened resin won’t penetrate very far into the wood, and your bond is only as good as the wood that it has saturated.
The thinner resin will soak deeper into the plywood.
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Old 02-23-2019, 09:13 PM
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REMEMBER if you using ply wood for anything the resin will only penetrate into the first veneer and no further because the glues stops it !!so thin veneers just penetrates a little thicker veneers penetrates further !
Ok what do you anticipate using to thicken the resin with ?? usually what is used weakens the resin and it becomes brittle and weak !! so you start with strong epoxy !!HOHOHO and then you weaken it !That's a good move ah !!
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Old 02-23-2019, 11:16 PM
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Originally Posted by nuffaredy View Post


Id disagree with that, bonding to plywood improves when the surface is first saturated.
The thickened resin won’t penetrate very far into the wood, and your bond is only as good as the wood that it has saturated.
The thinner resin will soak deeper into the plywood.
You may want to find out what Bills does for a living before calling him out on his methods.
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Old 02-24-2019, 12:01 AM
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The thinner resin will soak deeper into the plywood.
Only on the end grain that's all !The glue line in the first outer veneer stops the glue soaking any further !
So the less number of veneers to make up the thickness of the ply wood the better its is ?? maybe !! But take care to observe its structure by looking at the end grain , some times the outside veneer is very thin because you are being cheated by the inner substandard inner layers filled with poorer quality wood veneers and also gaps and voids and even bits missing !!
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Old 02-24-2019, 03:18 AM
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Originally Posted by tank1949 View Post
I just finished removing motors, OD/housings and rotten transom wood on a 1986 SR AJ. The complete transom was a rotten mess, not identified by a South Florida incompetent marine surveyor. I have done this type repair work before but I am getting old and I cannot remember if EPOXY requires wetted FG cloth between 3/4" plywood layers and boat's inside FG skin. If my memory serves me correctly, I first applied un-thickened epoxy resins on the inside FG skin surface and opposite surface of 3/4" plywood (wet both sides). Then, I applied trialed "thickened" epoxy to the inside FG skin using a grooved trial, followed by pressing and clamping the epoxy (non thickened) coated 3/4" plywood. The cloth was not needed between the layers. The thickened epoxy substituted for cloth. Cloth would have been needed if I had used polyester resin. After curing, I repeat the process with thickened epoxy on the second piece of 3/4" plywood clamped onto the first piece of 3/4" plywood. I have 1708, 6 oz. cloth. and matt. The STB MC transom assembly's bolt holes were somewhat "wallared" out and cracked due to the rotten wood giving way. I ground down from the inside and outside and have re-glassed with polyester and cloth. Both inside and outside FG skin surfaces are smooth. I have created 2x4 braces to sandwich the skin and plywood together for a flat surface and designed additional turnbuckles to force excess epoxy into voids. Any suggestions or disagreement would be appreciated.
The nice thing about boat restoration or repairs is that there are no hard and fast rules.

The thickened epoxy sounds fine. A layer of CSM either at the transom skin or in between the plywood layers would be fine and advisable if the mating surfaces were not very smooth.

Keep in mind that if you start with epoxy resin, you will want to stay with epoxy resin throughout your repair. Poly does not readily adhere to epoxy, because of 'amine blush'. Epoxy will adhere to poly though . . .

Post some pictures of your handy work.

BTW - "South Florida Incompetent Marine Surveyor" . . . sounds like it could be a company name . . . or SFIMS for short
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Old 02-24-2019, 03:48 AM
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So regardless, the cloth is not needed between layers, if thickened epoxy is used to laminate the transom skin to marine plywood?
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Old 02-24-2019, 03:58 AM
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mat between layers of plywood and thickener nott needed with epoxy. Prccoat plywood with epoxy and use peel ply to give some tooth before recoatingvand clamping.
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Old 02-24-2019, 04:01 AM
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You might want to use 60 grit sand paper and rough-up the surface of the plywood. It will remove any surface film that might inhibit the bonding. Do the same before applying 2nd coat of epoxy.
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Old 02-24-2019, 04:19 AM
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Most people don't realize that there are very few epoxy manufacturers.shell oil is one.
the name brand guys simply relabel it.
check out e bond epoxies.quality product at the best price. Also use a non blushing epoxy.
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Old 02-24-2019, 04:30 AM
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I would mix some milled glass in before thickening. Bumps the strength back up a good pit. Honestly, I would add some milled glass to anything touching the transom, especially wetting out between layers of core.

Everything tunnels and nuff are saying about wetting plywood sounds logical to me.

Are you replacing transom from outside or inside??

Rather than an notched trowel, get a bunch of cheap notched plastic spreaders. Less clean-up, just throw em away.

Something I think you might like, wish I had done it; prisma makes this mat that acts like CSM. "Trevira Mat". You can lay that on your inner/outer skin before bedding plywood. Fills rough/uneven surface from grinding/sanding very well and bonds "tenaciously". Won't replace spreading out thickened resin, but I think its pretty cool.
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Old 02-24-2019, 04:33 AM
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Originally Posted by tank1949 View Post
So regardless, the cloth is not needed between layers, if thickened epoxy is used to laminate the transom skin to marine plywood?
Correct. And use the thickened epoxy to laminate each layer of plywood together.
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Old 02-24-2019, 04:47 AM
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Originally Posted by tank1949 View Post
So regardless, the cloth is not needed between layers, if thickened epoxy is used to laminate the transom skin to marine plywood?
Correct. Structural glass weave is of very little benefit in the middle of a stack and does nothing to help bond strength.

When you glue in your first layer it may be a good idea to trowel the thickened mix to both the transom and the plywood going in. It will double the amount of glue but help bridge any imperfections left on the transom. Subsequent layers only need one side troweled.

Tunnels is spot on with his observations regarding the thinner outer veneers and resin penetration. Wait, did I just say that?
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Old 02-24-2019, 04:56 AM
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Originally Posted by tpenfield View Post
The nice thing about boat restoration or repairs is that there are no hard and fast rules.

The thickened epoxy sounds fine. A layer of CSM either at the transom skin or in between the plywood layers would be fine and advisable if the mating surfaces were not very smooth.

Keep in mind that if you start with epoxy resin, you will want to stay with epoxy resin throughout your repair. Poly does not readily adhere to epoxy, because of 'amine blush'. Epoxy will adhere to poly though . . .

Post some pictures of your handy work.

BTW - "South Florida Incompetent Marine Surveyor" . . . sounds like it could be a company name . . . or SFIMS for short
this is not the way to go...

first:

laminating with an epoxy - first,do a wet coat on wood core,followed by "buttering" with a thickened epoxy - do not thin epoxy with acetone...

before switching to using composites,years ago,i used wood,marine ply in transom recore jobs.i used west system epoxy,and their 403 adhesive additive.not cloth/mat is needed between laminates.chop strand mat should not be used with epoxies - the binder will dissolve..

epoxy and polyester products are very different chemically - amine blush is a by product of SOME epoxies kicking,SOME,not all,amine blush needs to be removed with soap and water only.polyester and epoxies wont chemically bond,they can mechanically bond.

wood - it requires a complete and total sealing,plywood does indeed soak water thru it's end grain.seal the end grains with epoxy,do not thin epoxy ! heating it slightly,that will thin it ...
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Old 02-24-2019, 05:13 AM
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Originally Posted by nuffaredy View Post


Id disagree with that, bonding to plywood improves when the surface is first saturated.
The thickened resin won’t penetrate very far into the wood, and your bond is only as good as the wood that it has saturated.
The thinner resin will soak deeper into the plywood.
Yes. This is correct. You need to prewet. If you go to YouTube and go to West Systems channel, you’ll find a bunch of helpful videos.

Brian
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Old 02-24-2019, 05:48 AM
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Those suggesting prewetting plywood might want to check how all the cold molded builders laminate, you know, the ones who do it all day long. I've been in every builders shop on the east coast and while there are different methods of mixing and spreading, none prewet plywood.

Solid woods, especially softer ones that soak like a sponge, maybe but not plywood with its thin veneers. The ideas behind the thickened resin is not only to aid even spreading on vertical surfaces but also to leave enough material in the glue line for a good bond.

We use a mix of cotton fibers to be that material and cabosil as a thickener. Mixed correctly to a wet slurry, resin will soak into the adjacent surfaces leaving the saturated fibers between. Mixed too dry (very thick consistency) might hold more resin in the glue line but theres a lot of room for error.

Try troweling out a piece then come back and scrape it off, you'll see wet plywood left behind immediately. Then try laminating a couple pieces together with offset edges and letting it cure. Then rip them apart. If they fail at the glue line and no wood comes with them you're doing it wrong but with the methods I've suggested 99.9% of the time they'll fail at a plywood glue line or the veneers will tear apart.

All this discussion of bondline failures is more critical with areas like hill sides and bottoms which have a lot more stresses than a simple transom panel but dont think for a second the cold molded builders havent thoroughly researched and tested their techniques!
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Old 02-25-2019, 02:33 PM
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Must I still remove the epoxy blush if I paint over finished job with true 2-part epoxy paint?

Will sanding the epoxy blush and then wiping with dry cloth or shop vac. brush work just as well as soap and water to remove epoxy blush?
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Old 02-25-2019, 03:40 PM
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Originally Posted by tank1949 View Post
Must I still remove the epoxy blush if I paint over finished job with true 2-part epoxy paint?

Will sanding the epoxy blush and then wiping with dry cloth or shop vac. brush work just as well as soap and water to remove epoxy blush?
A fresh water rinse will do more towards removing amine blush than anything else. No soap or any other chemicals, just fresh water. If the cured epoxy has gone beyond its "green window", it will need abraded with sandpaper to give a tooth for a secondary bond. Do NOT just sand and vacuum, all that will do is grind the blush into the surface. Just take a hose and rinse off, let dry and scuff. Ots really not that bad!
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Old 02-25-2019, 07:12 PM
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Arjay. Google it and educate yourself. I used it and it is awesome on transom/stringers.
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