Surface prep for epoxying wood.

I recently ran across a website that recommends an epoxy joint be planed to achieve the maximum amount of open grain for epoxy penetration. The logic makes a lot of sense, but is different than what I had in mind for my next project.

Personally, I was thinking of ripping planks with a fairly fine toothed sawblade to get a nice cut surface and still have some finer saw-tooth marks to create a mechanical grip through surface roughness.

My goal here is not to disparage a technique, but to confirm whether my thinking in correct. If the planing operation is not necessary, I would prefer not to expend the time and effort nor place the wear and tear on my equipment.

 

LP, if you are scarfing the wood, cutting with a fine toothed saw (say over 100) then the wood will be fine to glue together. The object of planing is to create a tight overall joint, not one with gaps. Done well, a swaed joint will be very strong when tapered and joined. The idea of a mechanical joint is quite good, as long as the fibres are not loose, and a fine saw blade will make a smooth surface, ready to join.

 

Actually the object of using a plane in a joint, that will receive epoxy as the adhesive is to sheer the tubules off clean, permitting the epoxy to penetrate better. Sanding or sawing rips the cells open and "fuzzes" up the wood. Epoxy doesn't penetrate this as well as cleanly sheered cell walls like a fine edged plane does.

The point is mostly moot as the bond (if properly prepared and applied) will be stronger then the wood, regardless of the joint cutting method, but from a technical stand point the issue is valid. On highly stressed pieces of a dainty nature, it would be a wise choice to increase the joint's survivability, but in most work, it's not particularly relevant.

In this same vain, high speed sanding and sawing make a lot more work for the builder/craftsman. Most aren't old enough to know the difference in a boat, a joiner has spent days smoothing, then one that's had a DA rubbed all over it's surface to fair it. There's just no comparison to a joined/scraped hull and a sanded one. Even our show winning yachts wouldn't stand a chance against a finely sculpted yacht of 100 years ago in regard to quality of finish. Take a scraper (a few swipes with a sharp blade) to a freshly sanded surface that your especially proud of. You'll immediately see and feel the difference and wonder why you've been sanding so much.

 

Isn't it the opposite?

Correct me if I am wrong (usually the case), but isn't a sanded surface best for epoxy?

For example, when planing (milling) softwoods such as Western Red Cedar, even the sharpest blades will compress the wood fiber surface, leaving a burnished (albeit smooth) surface. This "burnished/polished" surface can be even more pronounced in dense hardwoods. I have always thought a sanding with a coarse (80 grit or less) provided a better tooth for the epoxy to absorb and key into?

 

No PAR is technically very correct, the best wood finish is not achieved from sanding, it is from the use of edged tools.

I went to tech to learn boatbuilding at a later stage in life, thought that i could sharpen a chisel well, WRONG, it was two weeks of do it again and again till I learned the joy of a truely sharp blade. A scraper is also a blade, the working edge is filed across the top, causing a very fine bead of metal to roll off the top flat edge, it is this fine bead of metal that is the scraper, not the flat surface.

Once you learn to scrape with steel, the results are amazing.

But as he also said, it is almost irrelevant in practical terms, and we actually work in practical terms. That is the reason why amateurs can achieve better finishes than professionals, if they so desire, they have the time and the energy to do the job right, we have to work to time/money constraints. The pro can do it of course, but not economically, life is sad.........

 

A proffesional will abrade all smooth or shiny surfaces prior to bonding with epoxy. The time saved by not doing so is insignificant when compared to insurance liability in a structural failure, or at the very least, in reputation and lost man hours of a delamintation or aestheic creep call-back repair.

Congratulations, It's never to late to start and learn. For anyone else who is looking for the proper way to sharpen tools, there are many books and articles on the subject. The book I consider the most lay-friendly and comprehensive is "Guide to Sharpening" by Leonard Lee ( of Lee Valley Tools fame ).

Again, Congratulations on learning the proper use and preparation of a Cabinet Scraper

"Practical Terms" is applicable to both the proffesional and the amateur alike. The difference being efficiency and experience of accepted and known successful practices.

I don't want to fly off the handle, but.........

The original post starting this thread is in regard to bonding, not finishing. A Proffesional Finisher, can achieve a superior result in terms of overall quality and time expended, than can an amateur. This does not mean that some amateurs can't produce an equal result, It only means that you are are not a proffesional if you can't produce a top notch result, yet still pass it off as being "proffesional. The solution in this case, is that a "proffesional" will know to delegate the responsibility to an expert in the specific field, whilst the amateur is unlikely to have the neccesary resources of sub-ing out such procceses

I know how I am coming across in my reply, so I will apologize for it now. But as a proffesional, I strongly disagree with your statements.

LP, when it comes to bonding wood, there are a numbers of ways to create the best possible joint with epoxy.

With softwoods (Cedars, etc.) a sawn or sanded joint is perfect. If you would prefer using a orthogonal machine surfaced joint (Jointer/Planer), to avoid crushed fiber surfaces that will be burnished or rebound, you will need blades with a lower angle (do not use for hardwoods).

For hard/Dense woods you will need to use blades with higher angles.

The practicality of constantly resetting knives is nill. If you have Jointers and Planers, then the luxury is yours for the taking. If not, your best choice is giving the two mating surfaces a quick scuff with an abrasive

"The Pro" knows where the effort expended is most important, and how to utilize his skill most efficiently to acheive a proffesional result. There needs to be a standard by which a novice/amateur can start from. It is then through experience he can learn the most efficient practices, without sacrificing safety and quality, while maintaining a level a craftsmanship.

 

Ed 3,

Maybe I said it wrong, but what I was trying to say is that the pro is constrained by economics, the fact that we can make a beautiful hand cut dovetail is irrelevant if it costs so much time to produce the item that it cannot be sold for the hours of production. The amateur, on the other hand , is not charging out his time for the work done, so can spend all day doing four joints if he wants to, we have to do it in an hour to be "competative".
That is all I was trying to say.

 

Facts are facts, cell tubules sheered will accept a drip of goo, which a fuzzy sanded surface will not permit. This increases the sheer strength of the bond, much like honeycomb sandwich construction utilizes it's core as the skins are applied. It's not a debate, it's well proven and documented. As to the practicality of its employment in production efforts, moot as no one will pay for he effort, except full up racers that rely on extreme laminate or bonding schedules to get an "edge".

Practically is little more than what a client is willing to pay for, which is why many of the better methods and techniques aren't incorporated into new or redo construction efforts.

 

when all said and done, my guys used wide belt big boy sanders to finish joints, in oak, a dense heavy wood, you cant chisel of trim or plane small trims, at ends, we have never had a glue failure, using single pack glues too.
Dad was a furnuture builder and restorer, so everything was scraped, I have many scrapers some with long handles some short, some true , some cambered on the blade, I reckon I can strip a square meter of varnished top, in 30 mins,leaving no cuts, to flatten it true, I may use a longboard, diagonally, and then finish with the grain meanwhile your handyman is off to the store to get a chemical stripper, then he will hoe in with an orbital,
mind you, with these modern sliding compound saws, wide boy sanders are kinda obselete♠

 

US Forest Industries lab has a paper that indicates a surface from a sharp plane is good.

It actually doesn't seem to care how the planed surface is acheived - whether a power, hand or off a sharp tungsten blade.

The same paper is happy to recommend surfaces sanded with sandpaper of 100grit or finer where the sandpaper is SHARP.

Coarser than 100g or blunt paper will create the fuzz as PAR indicates.

There is a link to the paper and a summary here
Summary - US Forests Paper on timber surface preparation for gluing

Maybe a Professional is one who is paid and an Amateur is one who does it for fun?

Best wishes
Michael Storer

 

BOATMIX,

Maybe a Professional is one who is paid and an Amateur is one who does it for fun?

Well just maybe we have had a lot more practical experiences playing with the subject than an amateur would have. It is hard to do something for 50 years and not learn from your experiences.

 

I am glad you teased me back!!!!

One of the really strange things is that some amateurs also are very serious about developing their craft and have the free time to do so.

Most amateurs - including me - are just happy to get some kind of reasonable result - however there are a few that you run into on the net from time to time that have spent a lifetime focussed on perfecting their craft free of deadlines.

On the other hand there are professionals that don't approach your standards and knowledge (or mine for that matter - as low as my skill level is - did someone mention dovetails ?!?).

That is one thing that net has been good for - that we can sometimes catch a glimpse of the great work that everyone does. And also see the value of just doing it with a more modest set of skills and (probably) tools.

MIK

The farmer and the cowman should be friends,
Oh, the farmer and the cowman should be friends.
One man likes to push a plough, the other likes to chase a cow,
But that's no reason why they cain't be friends.
Territory folks should stick together,
Territory folks should all be pals.
Cowboys dance with farmer's daughters,
Farmers dance with the ranchers' gals.