Bedding compound vs. epoxy...

[mdevour]

Hello again, everyone.

This picture shows our boat jury rigged for display at school last year. All the ‘furniture’ is only attached with drywall screws right now. The first thing I’ll do when I start work again is remove the inwales, breasthook, knees, seats, thwarts, risers and trunk so we can prepare them to go together for real.

http://www.eskimo.com/~mdevour/other_pictures/woodboat_post1.jpg

The hull to this point has been glued up with epoxy. The instruction book basically says to go on using epoxy for everything. A couple of people have told me it might not be a good idea, and recommended bedding compound, so that 1) the joints can “work” as the boat flexes and, 2) I can take things apart again someday if I ever need to.

(I’ll ask about the trunk to keelson joint in a different thread. I know that it has to be handled differently.)

So I guess my questions start out with, should I start using bedding compound now? :confused:

Anything that’s been assembled so far had better stay together. If it doesn’t, it’ll be a major problem! I can see maybe using epoxy for the knees and breasthook, and for several fitted blocks that attach between the hull and risers to reinforce the thwarts, and then bedding everything else.

Is bedding compound the right stuff for this service? I assume so, but … it’ll be holding the mast up, y’know? ;)

Next issue:

For finishing, the designers are telling me to brush everything with 3 coats of epoxy, then paint or varnish as I see fit. I can see doing this to the inside as it is now, before everything else gets installed, but if I assemble it all first it would be a real pain in the ... ummm ... butt joint. :D

But what do I do as I install stuff? Epoxy coat each component, then bed it in place? Followed by paint or varnish?

Will the epoxy coating survive being flexed on things like inwales and seat risers that would be coated while straight and then sprung in place?

How does varnish hold up over bedded joints that are supposed to be a little flexible? I’m thinking particularly about the joints between the inwales and the knees and breasthook. If any joint is going to want to move a bit, I’d think those would be the ones.

Of course I’m reading a lot about CPES lately. My problems with it are 1) noxious chemistry that needs to be kept outdoors, which is not possible right now due to the cold weather, 2) the same noxious chemistry that makes it scary to use around a bunch of 12 year old girls, 3) the expense. If I forego the benefits of CPES I realize it’ll mean vigilance to keep the epoxy that encapsulates the boat alive for as long as possible, followed by a tougher refinishing job.

Please bear with me. As you can see I still need to pull all these bits and pieces of knowledge together so I actually understand. Hopefully this will be the single worst tangled mess of questions I have to ask. :rolleyes:

All your comments will be most welcome.

Be well,

Mike

[ 03-10-2003, 09:40 PM: Message edited by: M. G. Devour ]

[Old Salt]

I enjoy building with epoxy...so this comes from the perspective from which is not prejudice to the epoxy vs. traditional construction.

Mixing traditional and epoxy methods can lead to premature deterioration of your boat. Epoxy tends to attract moisture...kinda like salt...if you dont encapsulate all the wood the area next to the epoxy will tend to rot.

My two cents of advice is to go one way or the other. Epoxy the joints and encapsulate everything or use traditional methods and marine adhesives.

[NormMessinger]

I expect that you will get such a variety of responses to your questions that you may as well do what ever feels right. However, if it were I doing it....

What do you call bedding compound? 3M 5200, Sikaflex, roofing cement, tar? There won't be any give in 5200. I've not used the others. You don't want anything that will allow the pieces that are screwed togeather to "work", right? Use epoxy.

Three coats of epoxy seems excessive unless you are filling the weave of glass. Other wise one coat, sand and finish.

I'd hesitate to use CPES unless you had a big work area or good ventilation. If you use an epoxy coating no need for CPES. And visa versa.

Next.

[Bruce Hooke]

Two thoughts:

- As a general rule I think we usually do everything possible to STOP joints from working because working causes wear, breaks the finish which allows water in, and so on. So, I do not think that allowing the joints to work is a good reason to use bedding compound. It makes about as much sense as allowing wood to "breath" when the whole point of most finishes is to slow down the movement of water in and out of the wood.

- If you are going to coat everything with epoxy then as a general rule I would glue things down with epoxy too. I think you are quite right to be worried about the epoxy coating cracking if there is movement in the joint.

That said, my approach on a similar boat has been to consider which parts I am fairly certain I will have to remove and bed those rather than epoxying them. For example the rub strips are bedded (over an epoxy coated bottom) because rub strips are designed to wear out. However, I have also decided to only coat the plywood that makes up the basic hull with epoxy, and simply varnish or paint everything else. So, I am planning to bed certain parts such as the thwarts because at that point I am basically looking at traditional boatbuilding methodologies. The jury is still out on CPES as far as my boat is concerned for reasons similar to the ones you listed. However do note that CPES is pretty irrlevant if you are coating everything in epoxy.

You should certainly do everything you can to coat parts before you put them in the boat. You can coat all sides and sand while it is easy to do so. Then use epoxy to glue the part in place and simply wipe of any squeeze out, after which a very light sanding while leave the joint beautifully clean and neat.

[Bruce Hooke]

I'm going to disagree with Norm on the three coats issue. According to the Gougeon Brothers it takes two coats for epoxy to be fully effective as a coating and so they recommend three coats because you are likely to loose a total of roughly one coat in the process of sanding three coats. So, I would stick with three coats if you are going to use and epoxy coating. For large flat parts flowcoating in one thick layer also works well. See the Gougeon Brother's book for more details on this method.

[Carlsboats]

I am at a loss to see why people are so keen to put multi coats of epoxy on a wooden boat, prior to painting or varnishing. The only reason to do so, I believe, is if the boat is sheathed in glass cloth. Then, you have to fill the weave. For a regular wood or plywood boat, it is a real stinker to get several coats of epoxy put on smoothly, sometimes requiring a washdown and/or
sanding between coats. The stuff doesn't flow out well, to say the least, and it is not going to protect the boat any better the time-honored prime and paint method -- unless you are dragging the hull up sandy and rocky beaches, in which case you should get an unpainted aluminum boat or one of those molded plastic jobs. Plywood has traditionally been tough to finish -- the surface layer loves to crack over time -- but modern primers have greatly reduced that problem.
I spent a lot of time building up epoxy underlays on the bright work on a classic wooden boat, and then, several years later, spent even more time going back to bare wood and refinishing with regular paints and varnishes. Never again.
Several professional boat painters tell me that they too have had this sad experience, and no longer put epoxy on wood as a finish.
So I use it for glue, not finish.

[NormMessinger]

So there ya go. More agreement here than I thought there would be. So I'm reading along and Bruce disagrees with me which is fine and I figure if Geugon (You spell it.) recommends three coats and I have not read their litereature for years then okay, I can go along with that.

So then Carls comes along and agrees with me with far more experience in the matter than I have but his advice agrees with my preconcieved misconceptions so I'm back to where I started.

Where does that leave you, M.G.? smile.gif

The way the okoume plywood on Prairie Islander yellowed I'm sorry I used epoxy and not CPES (or nothing) under the varnish. Cleek warned about that but too late. The solid Hondurous mahogany has not yellowed however.

[John R Smith]

Just my (very) humble opinion.

All finishes, no matter what, will fail in the end. When they do, it's the ease of removal that counts. The worst possible scenario is a finish which has PARTLY failed, leaving the areas which are sound an absolute bear to remove. Epoxy is far more likely to behave like this than varnish or paint.

Remember, neither epoxy or CPES have any UV protection. They rely absolutely for the varnish or paint layer above them to provide this.

Epoxy makes a pretty good glue or filler. Varnish is varnish, and paint is paint ;)

John

[Scott Rosen]

Epoxy, paint and varnish can all be removed with the application of heat.

Fir plywood will develop checks over time, which can be prevented or slowed by epoxy coating. I do not think that CPES will prevent checking.

I would glue the joints in that boat with epoxy, not bedding compound.

[Paul Scheuer]

I don't think I've ever an entire boat dry fitted, including sails. Nice work.

To your question about flexing precoated pieces - should be no problem for the shapes that you mention. If you were steaming, that would be different.

[John Blazy]

Right on Scott. I don't know why epoxy removal is such a huge issue with people. Don't they own heat guns and RO sanders? I get major drips and thick spots when I glass areas and don't fret cuz the heat gun makes it scrape off like butter.
I also know for a fact that many, like myself at one time, put on too much epoxy under the varnish and blamed the epoxy. Its proven that just the right amount (sealed only with minimal film build) of epoxy, then varnish works better than either alone. Key, is just the right amount, not gobs and gobs. I'd rather have my finish last an extra year or three longer and put in a little more effort to remove the finish than refinish in years less because I didn't seal with epoxy. No wonder things don't work - everyone takes an extreme view rather than an objective evaluation.

M.G., if you want the benefits of CPES without the solvent smell, take a propane torpedo heater to your wood surfaces just before slathering on the epoxy. The heat will thin it almost like CPES, drawing in the epoxy, and air pressure will carry it further, then the residual heat will kick it off sooner.

As far as bedding compound, Norm is right with 3M 5200, and the loads cheaper, 99% equivalent, is PL Premium polyurethane adhesive found at any home center (in a caulk tube) that is second only to epoxy in strength if applied correctly. Much interior boat joinery (with large glue surface area) can be done with this stuff that has a LIFETIME warranty unlike anything else. It expands as it cures, with adhesion properties that completely blow away conventional adhesives and better than epoxy on (real) glass, metal and other dissimilar surfaces. Been using it since the eighties with no failures.

[Bruce Hooke]

Originally posted by Carlsboats:
I am at a loss to see why people are so keen to put multi coats of epoxy on a wooden boat, prior to painting or varnishing. The only reason to do so, I believe, is if the boat is sheathed in glass cloth. Then, you have to fill the weave. For a regular wood or plywood boat, it is a real stinker to get several coats of epoxy put on smoothly, sometimes requiring a washdown and/or
sanding between coats. The stuff doesn't flow out well, to say the least, and it is not going to protect the boat any better the time-honored prime and paint method -- unless you are dragging the hull up sandy and rocky beaches, in which case you should get an unpainted aluminum boat or one of those molded plastic jobs. Plywood has traditionally been tough to finish -- the surface layer loves to crack over time -- but modern primers have greatly reduced that problem.
I spent a lot of time building up epoxy underlays on the bright work on a classic wooden boat, and then, several years later, spent even more time going back to bare wood and refinishing with regular paints and varnishes. Never again.
Several professional boat painters tell me that they too have had this sad experience, and no longer put epoxy on wood as a finish.
So I use it for glue, not finish.In my (limited) experience paint applied over epoxy breaks down much more slowly than paint over bare (primed) wood. The key reason, I believe, is that paint failure is very frequently caused by water finding it's way behind the paint. This is much less likely to happen if there is an epoxy barrier to water behind the paint. Granted, if everything is built and maintained just right water should never find it's way behind the paint, but counting on perfect maintenance seems less than realistic to me.

Second, it seems to me that it's been pretty clearly demonstrated that an epoxy coating is very effective at keeping water out of wood and thus greatly reducing a boats vulnerability to rot. So, I think epoxy does protect the boat better than just paint and primer. Again, with the best maintenance of a primed and painted boat, water getting into the wood will never be an issue, but...

That said, as I noted above I have elected only to use an epoxy coating on the plywood parts of my current boatbuilding project. I decided that the hassle of applying epoxy to lots of small parts and then sanding it out was not worth the added protection on a boat that will be stored under cover when not in use. The plywood is joined at the chines via glass cloth and filets so at that point it pretty clearly made sense to continue the epoxy across the rest of the plywood.

If someone is worried that they will be lax enough in maintaining their boat that areas of epoxy may spend large periods of time with all the paint gone from them so that the epoxy is unprotected from UV radiation then there are additives that can be added to epoxy to allow them to withstand UV. Of course these additives will not work under a clear finish because they make the epoxy opaque. Since clear finishes are more prone to breaking down anyway, and since they do allow some UV through, I would be more cautious about using epoxy under a clear finish. In that situation I would be more likely to use CPES since it will not present as many problems as epoxy if it is exposed to UV for extended periods...

[mdevour]

Hello again, everyone! Great answers to my torturous questions. Thank you!

It's been over a year since I started this project, so I am getting a little foggy on the details. A careful re-reading of the plan book and my notes from the conversation with my old advisor are yielding a few corrections:

To give the designers, Butz and Montague, their due, they give you a couple of reasonable options for finishing with epoxy, paint and varnish. They are:

Option 1) glass the outside, with 3 coats of epoxy to fill the weave, and *ONE* coat of epoxy on the inside and gunwales, followed by a good "marine epoxy paint" and varnish for the brightwork. Ummm, I've never actually seen anything called "marine epoxy paint." Do you think they're talking about 2 part polyurethane?

Option 2) no glass, but 2 coats of epoxy inside and out followed by the same varnish and "marine paint."

They also tell you to finish the hull while the risers and seats are out of the boat, which makes darned good sense.

Some of my confusion comes from ambiguous instructions for the sailing vs. rowing vs. motor versions of the skiff:

Apparently, on the basic rowing skiff, they instruct you to put the risers and seats in dry after finishing the rest of the hull. At least, they don't mention glue or any kind of bedding, only screws. That strikes me as an oversight, since at least bedding compound ought to be used.

On the sailing version, they add some reinforcing blocks to the hull sides where the thwarts mount. You're then supposed to screw and epoxy the thwarts to these blocks and to the seat risers, yet they don't mention whether to epoxy the risers in place to begin with. :rolleyes:

Okay, so much for the instructions...

Everyone so far has agreed that we are not eager to see joints moving, so that is not a good reason to choose a bedding compound over epoxy.

Norm, the "bedding compound" I'm referring to is that stuff which may be described as, "a nonadhesive linseed-oil-based product with the look and consistency of peanut butter," that is available from most of the marine paint companies, and whose most endearing feature is ease of disassembly. At least I think so...

I realize there are other stickier "bedding compounds" of polyurethane or polysulfide, right on up to 3M 5200, which I'll be using for the trunk/keelson joint.

It looks like I need to read the Gougeon Brothers' book. However, it seems that whether I use one, two, or three coats of epoxy, they should be thin ones. And I should expect that someday I'll need to get it all off and may, indeed, regret putting it on in the first place. Scott and John, however, make the case for easy removal with heat.

Back to the other question, though: What about repairing or rebuilding things someday? Are we looking at destructive disassembly? We know that at some point this boat is going to become scrap. It's only plywood and plastic, after all. But it'd sure make life easier for us, and delay that mournful fate, if we can safely remove the seats and risers the day we want to put a new finish on everything.

What is the general repair and renewal experience of epoxy jointed boats as they age? Or haven't any of them aged enough yet? :D

I think we can all agree that there are usually several "right" ways for doing just about anything on a boat. My aim in asking for all your help is to be sure that I'm using at least *one* of them! smile.gif

For whichever options I choose, others will be set aside. Please trust me that they're *all* appreciated.

Be well,

Mike

[mdevour]

Paul Scheuer wrote:
I don't think I've ever seen an entire boat dry fitted, including sails. Nice work.
LOL... Well, it was a big show-and-tell for the school, and one of our milestone goals to have as much done for it as possible. smile.gif

Mike

[gary porter]

Mike, just to add another opinion and pretty much agree with the folks above.
You probably will never have to replace your rubrail unless its really treated
rough. If its just going to be used on an occasional weekend or such it will probably
last a long time without a lot of heavy maintenance. Anyway,, I'd epoxy all the parts except the thwarts, and the locker. Use 5200 on the locker and just screw the seats down with #12 Silicon Bronze screws. Being able to remove the seats will make what
later work you do much easier and they will still be quite strong if you use at least two
screws on each end. I'd coat , one or two, each part including the seats and the varnish.
A good quality paint, two part poly or easy poxy on the out side and in if you want. You may find that the wood inside, if you have used Okume is too pretty to paint. 5200 on the locker only. Anyway , whatever you decide, it will work. Have fun and enjoy your efforts.
Gary smile.gif

[mdevour]

Thank you for all the comments, folks. I think you've been able to hammer my thinking into something resembling sense.

Unless I change my mind... I will use epoxy to mount the breasthook, knees, and inwales, plus the blocks that tie the mast partners and trunk braces into the hull. For the sake of being able to get to the inside of the hull for refinishing someday, I'll install the risers, thwarts, and seats with screws and bedding compound (of the 'you don't have to splinter the wood to take it apart again' variety).

As for finish, I will brush on from one to three thin coats of epoxy on the insides, depending on how it seems to be going when I try it, followed by numerous coats of varnish (type to be determined). I'll epoxy and varnish all the "small bits" before they're bedded in.

It's certainly not the only way, nor by any means the best, but I 'spect it'll do. smile.gif

Time for a new question!!! :D

Mike

[paul oman]

Hello again;

We are probably the biggest internet supplier of marine coatings and epoxies on the internet (www.epoxyproducts.com) - but that said - my commnents are personal opinion and no better or worse than any of the others you read...

Don't overdue the epoxy stuff. Use to glue and fill. I would coat plywood with it, but not 'regular' wood - which has proved how durable it is for 100s of years. Plywood is another story.... Coat the plywood with at least one coat of solvent thinned epoxy (say 20% solvent not the 70% in CPES) to prevent checking in the years ahead. With one coat you might see shiny spots where the epoxy don't soak in very much, and mat spot where it did. If so, put on another coat of thinned epoxy (easier to apply thinned epoxy than non-thinned epoxy). or your topcoat will look different over the shiny vs. mat surfaces. A second coat will - should give you a uniform 'gloss' on the plywood. Then paint.... Enjoy!

paul

[NormMessinger]

Thinned epoxy? Why. Best check with the manufacture to see what they recommend. I won't argue with Paul with regard to the first coat but I would follow the manufacture's recommendation. Thinning subsequent coats accomplishes what? Uses up your supply of thinner, requires more coats to get a build up and probably weakens the epoxy. Go for it.

[frameshop]

Paul: what do you suggest for a thinner on that first coat of epoxy???? I understand the rational for the first coat to really soak in there with the thinners, but I must agree with Norm that if the thinned coat is for penetration it would not be needed for subsequent coats as it should have done its work on the first coat. I am about to turn over my hull and seal up the insides. If I get underneath it looks like Carlsbad Caverns. All the drippings hanging down from the joints. Its seems to me that when it is filpped I will have some starved glue lines on the chines and battens and keel that will need to be addressed with a thinned "goop" to get in the cracks and crevices and seal it up. Roger