? on poly and or epoxy

[timbecht]

i have my strings and new transom wood covered in poly resin but i need to know if i can use epoxy to put transom in and adhere to outer transom skin and the to put woven roven on hull to stingers

 

[Greg Mrozinski]

Re: ? on poly and or epoxy

Tim,

You should be able to. I would scuff up the side to be epoxied a bit first. You also might want to slightly thicken the epoxy some to help keep it from running too much before you clamp it into place.

Personally I would use PL premium to glue in the transom and the stringers. It's easy to work with since it comes in tubes. Lay it out and then use a 1/4" notched trowel to spread it around nice and even. Clamp it in place and let it sit for 72 hours. Clean up any oozing right away. For the stringers, just lay out a heavy bead and bed them right down in it. Again clean up any oozing right away.

Don't forget that you will need to filet all the corners with a PB mix or similar before laying your glass.

 

[Woodonglass]

Re: ? on poly and or epoxy

Epoxy will pretty much stick to anything. Poly will NOT. It pretty much just likes to stick to Poly. Make sure and sand your outer shell down to good bare glass. PL or Peanut Butter will work I prefer PB. It is stronger. Transom IS one of the Critical parts of the boat. Set the stringers in PL to allow for flex in the hull. Allow 72 hours for cure before you glass em in. Round over the corners of your stingers. Glass don't like square corners.


I'm just sayin...

 

[Greg Mrozinski]

Re: ? on poly and or epoxy

Wood,

I am just curious. How much stronger is epoxy over PL preminum? Does anybody have any data? I glued my transom in, bare wood to the outer skin, using PL. I cannot image that epoxy would be that much stronger then the wood grain itself. I am not for or against any one method, just curious.

 

[erikgreen]

Re: ? on poly and or epoxy

Sure.

PL premium has adhesion on the order of 500-600 psi when used for its intended purpose, on wood to wood bonds. For reference, see the data sheet for it (it's an older sheet, should still be valid though):
http://www.simplicityboats.com/PL Premium 2002.pdf

Note that strength increases over the first 7 days or so, and you may get a bit higher strength than this at the end of cure. Also, when using PL on non porous surfaces like fiberglass, you must pre-wet the surface to enable hardening - if water can't get to it, it can't cure properly (also mentioned on the data sheet above).

3m 5200 marine polyurethane is about 500-700 psi adhesion fully cured, but it depends on the substrate. Some materials are much lower. Reference:
http://multimedia.3m.com/mws/mediawebserver?66666UuZjcFSLXTtlx&EO8TVEVuQEcuZgVs6EVs6E666666--


Marine-tex epoxy putty, which is a popular repair putty for hull dings and (in the Gray) for machine work temp fixes, has an adhesion shear strength of about 1800 psi for the gray and 2300 psi for the white. Note that these aren't two strengths for the same uses, they're different formulations for different uses. Reference:
http://www.marinetex.com/marinetexepoxyputty.html


Ordinary marine epoxy used for layup varies, but for an example the MAS Epoxy sold on iboats has about a 2000 psi adhesion shear strength. Reference:
http://www.masepoxies.com/How_To/About_Epoxies__Vinylesters____Polyesters.html


I believe the adhesion shear strength of poly resin is about 200-ish psi. Ondarvr will know

To answer the question as to why it matters as long as the material fails before the glue does, keep in mind that a thinner resin or adhesive will soak into porous materials like wood much deeper than a paste like PL. So the actual surface area of the joint is considerably larger than PL, because it's thicker/deeper. Hence, epoxy makes a stronger joint, especially if you pre-wet the surface to be bonded with epoxy to let it soak in.

Since epoxy is a two part chemical, it'll cure without air, on non porous materials, etc. without a problem.

Plus epoxy is more waterproof.. PL absorbs up to 5% water and epoxy less than 1%.

If you absolutely have to have glue in a tube that's as strong as epoxy (more or less) then look up "Gelmagic" which is a two part epoxy that mixes in the nozzle and forms nice fillets without adding filler. It's expensive, but you may like it.

PL is great for some things in a boat. I personally don't believe critical structures like the transom and stringers should be among them.

Erik

 

[Greg Mrozinski]

Re: ? on poly and or epoxy

Thanks for the good info Erik. All makes sense. I guess like everything else, what is "good enough" is up to the individual owner/rebuilder.

 

[ondarvr]

Re: ? on poly and or epoxy

Erik laid it out well for each product. One thing that needs to looked at though is what amount of bonding is needed in a transom, because exceeding what's needed won't be of much value.

99% of the transoms on boats are bonded together with polyester resin and they appear to perform for decades with no problems related to bonding, the real problem is rot, related to water reaching the wood for various reasons.

The typical transom has several (6 or more is normal) somewhat good sized bolts running through it, so its clamped together fairly well. This further reduces the actual stress on the bond.

There was a thread several years ago where a frequent poster was talking about how poorly the inside fiberglass skin on the plywood transom core was bonded in place on his 30 year old boat. He said that while taking it apart he was able to grab a corner of the skin and pull it off in one large sheet without a great deal of force. What I pointed out was that in that 30 years of use the bond held up fine and the fiberglass was still stuck to the wood with no evidence of failure until he pulled it off. This proved that whatever the strength of the bond, high or low, it was good enough for its designed use.


All of this leads me to believe that if the product (polyester resin) with the weakest bond will typically survive the stresses of the real world for decades on these older boats, then whatever you use that is stronger, or better bonding than polyester should hold up just fine.

 

[ondarvr]

Re: ? on poly and or epoxy

i have my strings and new transom wood covered in poly resin but i need to know if i can use epoxy to put transom in and adhere to outer transom skin and the to put woven roven on hull to stingers

If you've already started the job with one type of resin, just stick with it for the entire job. Switching between the two can end up creating issues.

 

[erikgreen]

Re: ? on poly and or epoxy

Not to contradict you ondarvr, but thinking about this I figured out there's a potential for misperceptions of whether poly transoms are "good enough" or not based on anecdotal evidence, even many years of it like yours.

Keep in mind I'm just being anal here, or more precisely rigorously logical.

If transoms made with poly resin in general aren't strong enough, you'd see the same thing you're seeing now (with reference to the peeling skin story). The transoms that weren't strong enough would rot, fail, or otherwise not need the skin peeled. IE, we wouldn't see anyone say "the poly skin was weak"... if the skin was loose then water would get to the transom and rot it. We see that a lot, but we really can't tell what the cause was, because the skin at that point just covers a pile of mulch.

Of the boats that are made with poly transoms, we might hear details on the condition of one in a hundred. If 20 percent of these boats need transom repair after 20 years of use, we'd never know, because we don't get feedback from the owners. Sure, experience means we can intuit which boats are better built, but we can't truly be certain. Maybe those owners just junk the boats instead of fixing them. Maybe other problems cover up the failure of the poly based fiberglass.

Noting that most boats with poly transoms are fine for the duration of use because the ones we see with intact transoms (as opposed to mush) have skins in good condition is like noting that all cars on the road made from fiberglass survive crashes without being damaged. The ones that are damaged we tend not to see unless they are repaired.

This mental exercise aside, my gut says you're right about "good enough" but it also tells me to use the best materials I can afford, because any project that's as expensive and potentially dangerous as a boat I want to do as well as possible... as strong, as waterproof, etc. Hence my own bias.

Erik

 

[ondarvr]

Re: ? on poly and or epoxy

You are mixing two different types of failure, actually three, rot from water, not strong enough (as in under built) and the bond.

With how most transoms are put together it won't make any difference which resin is used, the failure is from unsealed screw holes, poor designs, sloppy workmanship, etc. It needs to be done correctly with any of the possibly products.

If it was designed to be strong enough with epoxy and it wasn't built up to spec, it would fail also. From the exact same set of production based issues that take place when hand built products are mass produced by poorly trained employees. First comes the leak, then rot, resulting in a big repair. It makes no difference which resin is used, if water gets in, the wood will rot. An unsealed screw hole doesn?t know if it went through polyester or epoxy, and the water doesn?t care either, it flows in and is sucked up by the wood, the barrier layer (resin) doesn?t make a difference in this failure.

A boat built with epoxy would be no stronger than one built with polyester, it would be lighter, but not stronger. The reason is the design is engineered to be a meet a certain specification, if stronger products are used, then less of it is needed to meet the spec. If you used the same amount of each product, then yes it would be stronger, but that?s not how products are designed and engineered.

Another failure is from uncoated wood, again if the wood isn?t sealed, it makes no difference which resin is used.

Another type of failure is from the product not being built up to spec. Not enough glass, the wrong kind of glass, unrolled glass, poorly cured resin, etc. Again, it makes no difference which resin is used.

Now a poor design. If it wasn?t originally designed to withstand the stresses it will see in use, it will fail, and again, it makes no difference which resin is used.

I have watched thousands of boats be built while auditing production plants to help fine tune procedures, some plants do a good job and some don't.

In the 60's and into the 80's there were hundreds of small, sort of fly by night companies that built cheap stuff and the wood rotted out, many of these are what get discussed here. As time went on production methods were improved, but still relied on each worker to do a good job and that's the problem.

From what I see myself, hear about, and read on this site, it appears water making its way past the skin through unsealed or poorly designed areas is the main issue, the bond doesn't come into play, in fact many people have a tough time removing the plywood that's not rotten. Frequently pry bars, hammers, come alongs, circular saws, chain saws, etc all come into play when trying to remove the good wood. And as I said before, if the glass was still bonded to the wood, no matter how poor that bond may be, it survived the real world and worked as designed.

Now if we?re talking about building a wood boat, it makes a big difference in which resin is used, but that?s a completely different subject.

 

[Woodonglass]

Re: ? on poly and or epoxy

Very well said Ondarvr.
Water intrusion is usually the Main culprit. There ARE some poor engineering jobs out there but even those can last as long as it remains watertight.

I'm just sayin...