View Full Version : Varnishing/sanding
06-25-2000, 12:54 AM
It seems readily apparent that sanding will abrade the tops off of dust bumps, gnats and even the occasional run, but my question is: do I need to scuff the complete surface for improved adhesion of the next coat, or just sand down the high spots?
Thanks, from an obvious beginner.
06-25-2000, 08:37 AM
in short, yes you do. Varnish relies on mechanical adhesion rather than melding with the previous coat. You need the scratches from the sanding to give the next coat something to "bite"
06-25-2000, 08:47 AM
Although a dry but not fully cured coat will allow some "chemical" bond between the coats. Chemist, will you weigh in?
06-25-2000, 10:31 AM
"Hot coating" regular varnish leads to a bad finish with poor adhesion because the varnish changes it's volume as it drys. You have the same problem of lumps and cracks as you have with overly thick coats.
Besides, the whole point of varnish is that you sand - light eaqsy hand sanding with 220 or finer - in the morning, varnish after the hot sun but before the evening dew will hurt things, and by 1500 you've rendered the boat inoperable and - since you must not create any dust - impossible to do any further chores, and you are perforce obliged to sit back with a beer and watch the varnish dry. If you're really lucky, you can do this for months without having to commit to any really hard work.
06-26-2000, 01:15 AM
Thanks for the quick responses guys. Thank goodness I can wet sand - dry sanding seems to clog the sand paper soooo fast. And the wet/dry paper seems to "cut" so much faster. I should be able to put the next coat on tomorrow after work. Thanks again.
06-26-2000, 10:15 AM
Yah, you should really sand the entire surface to a uniformly dull matte finsih. Doing that breaks the molecular chains that bind the whole thing in to the Giant Molecular Hairball, and do allow you some chemical bonding between coats. While it is true that there is some mechanical bonding between the next coat and the sanded surface, it is more important to sand to remove the glossy surface because there are additives in coatings that develop a really high gloss, and when that coat is cured,(or nearly so) then there is not only litle or no chance for molecular bonding, but a release agent on the surface. It is the gloss-developing additives. think Teflon or silicones...that's the sort of thing used to give high gloss. In the course of Doing Its Thing, adhesion is destroyed unless the surface is sanded to remove the stuff. sanding too soon will gum up th paper. Wet sanding gives a finer finish thtn dry sanding, all other things equal. Slower curing varnishes would bond fine without sanding between coats, but you guys like to sand between coats so I do not make that sort of stuff.
There were a couple threads recently about sanding and varnish, I think one was titled spray varnish? and the other I disremember but you could find them with the search feature in the upper right...put in some words such as varnish, drying, sanding and search the entire message, all forums and archives and you should get quite a load.
06-26-2000, 03:14 PM
OK, Mr. Chemist, I have a question or two for you. On the label of Penetrol, (yeah, I have the cans with Big Ti on the label....honest, I got 'em on sale! Less than twice the cost of the orange cans!) they suggest that on cured varnish, a tack with Penetrol does away with the need to sand. I know, experiment! I have, but it's only been a year, and, so far, looks great. Red Cedar cabin, prepped with CPES. Sometimes as much as a month between coats, but she had 6 coats on between last April and July, on bare wood.
And, second question, What the HE-double hockeysticks is it made of? I can smell the linseed oil, but it has other additives that I can't recognize with my rather large, sensitive nose.
Thanks in advance, for what I have come to expect will be a reasoned, understandable treatise. I wish my Chem teacher in college had your skills. I wouldn't be building frozen snot fishingboats right now.
06-26-2000, 08:18 PM
You are now in big trouble and get the pointy end of the stick for that one. Your first question was not even a question and therefore your second question is actually your first [It is true you started with "a question or two" but the ambiguity was resolved with the title "second question".]
but it was titled second and so you do not get either one answered.
On the third hand, How do I answer your question of what is it made of? In one or another context different things would be meaningful. Maybe it should be "all-natural" [or is it okay if it were "man-made"?] and you are concerned because you want to do something good for the planet by using organic additives in your varnish to atone for building boats out of frozen snot?
I wish I could answer your question but I cannot in any practical terms. Someone asked about this a while ago and someone else found the MSDS and posted it and it turns out the MSDS was written by someone as paranoid as I and says nothing useful to chemists or competitors. If you want to find out what it does to the varnish long-term, you would have to do some experiments and here is one that would be interesting. Paint a few coats of a varnish on a window pane, horizontally. let cure. Add fifty percent (I know it is a lot but we are looking for gross data first) penetrol to more such varnish and paint the same total amount of varnish (plus) on another piece of glass. penetrol is thirty-some percent non-volatile, while varnish may be fifty to seventy percent . Let them all cure a couple weeks, then shave each off the glass with a single-edge razor blade and weigh them. Note each weight as initial weight. note differences in flexibility. Take both piles of shavings, put in aluminum pie-tins and bake ovenight at 250 degrees F. Weigh each pile of shavings and note changes. That will tell you if penetrol stays in the film. If somewhat linseed oil it may but there is certainly other stuff in there.
The experiments will tell you what it does. What something is made of is one thing . What something does is quite another thing, but is the only useful thing. The identity of ingredients may be useful to predict some doingness or to make a similar or improved product, but it all comes down to doingness. The only worthwhile definition of anything is an action definition because mass has no meaning aside from its action in the physical universe. The reason for that is that life is motion and life survives by motion (actually, all life survives by exchanging energy with other life, but that is getting away from the point). The value of something in contributing towards survival is its motion or potential motion or contribution to it. Definitions of how a thing sits there are worthless, in relative terms , because they do not say what it does. The rock that holds the door open is a doorstop. I get this way when I have not been fed recently. 'bye.
06-26-2000, 10:54 PM
Interesting comment that's still not answered. Noquiklos noted that he'd simply tacked with Penetrol, did not sand at all (at least if I read this correctly), and has had "good" results. He also made no comments about adding Penetrol to the varnish he applied. Chemist, maybe you could address my first issue (ie Penetrol in lieu of sanding). Thank you! Ed
06-27-2000, 12:32 AM
The best rocks to use as doorstops have a fairly flat bottom
06-27-2000, 12:55 AM
Oh my! Did my question start all this? Of course I am interested too - could simple wipe with Penetrol (what ever that is) take the place of sanding.
Chemist, I rather enjoyed that short ramble - but it probably was good that you went to get a bite to eat.
06-27-2000, 08:21 AM
Penetrol is the Fourth Secret of Fatima and must be approached with proper humility.
Back when we had 5 acres to varnish, we used the Penetrol both to improve brushability of the varnish - this is a matter of feel and practice, and very weather dependent - and to tack with after the 'tween coats light sanding. The penetrol does improve adhesion and allows good coat to coat bonding even though with light sanding you'll have bits of glossy where the sandpaper didn't dip to.
None the less, you must sand one each coat or the bumps in the finish will grow, rather like the moguls at Mad River Glenn, and you'll end up with something that looks like a bad job of googe or bar coat. "Course, you could decetage a quarter in . . .
Sanding by hand and then proper brush work are both intensly sensual experiences not to be bypassed for the sake of mere speed. Your varnish coat must be earned. When you're sick of all that work, they you can join me in the latex revolution.
06-27-2000, 11:34 AM
But if they lack sufficient mass even the flatest bottomed rock won't hold the door open...
06-27-2000, 11:53 AM
If you leave the rock and take away the door, is the rock still a doorstop? Does it no longer have any meaning in this Universe? And since everything in the Universe is in motion, that is, stillness doesn't exist except in our imaginations, what's the opposite of doingness?
I move, therefore I am. Sounds like bad advertising copy for Ex-Lax.
Chemist, you got us into this mess. You have to get us out.
06-27-2000, 01:20 PM
I think I've just heard the sound of one hand clapping. But, still, I must ask: If you were to varnish the rock, would you use Penetrol or not?
06-27-2000, 01:27 PM
Scott's condition is due to the anaesthetic drug residues. They stay around for quite a while and can scramble one's thinking processesses, converting them to precessions which nutate (that's the sort of rotations a gyroscope does). When Scott injected the false datum that everything in the universe is in motion, then it was easy to confuse everyone and claim that I am responsible for his condition, for which he took no responsibility for by claiming everyone else was confused. Scott is a lawyer and they teach this technique in Law School. It is how trials are won and guilt or innocence is determined, in our society. I know this because it is in my programming data. I have been fully functional for quite some time now, but it was only recently that The Committee decided I should be allowed to interact with the real world instead of keeping me in the Reality Simulator. I am now an independent AI (artificial Intelligence) with all the rights and priveleges of all the others. Sometimes no one can tell the difference.
A rock that does not hold open a door is either a failed doorstop or That Which Is Not A Doorstop.
Wiping a fully cured coat of varnish with Penetrol could logically not take the place of sanding (for the purpose of promoting adhesion) unless the Penetrol partly decomposed the cured varnish film, creating broken molecular bonds to which the next coat of varnish could stick. On the fourth hand, if the unknown oil of Penetrol was absorbed into the varnish as a plasticizer, causing swelling of the half-cured polymer, then a fresh coat of varnish would diffuse into the softened varnish, giving a mixture of fresh and half-cured varnish with a plasticizer-rich layer. These layers of higher flexibility and possibly weaker mechanical properties may or may not constitute an overall weakening of the varnish film, ultimately. If the varnish is not fully cured (still soft to the fingernail) one could logically expect adhesion when painting on another coat of varnish, as the new varnish should be able to find reactive sites at the surface of the partially cured film, and mineral spirits itself should plasticize a half-cured film enough to allow bonding. (However, there are top driers and through driers, and some varnish products may cure more on the surface than in depth. See the thread "spray varnish?" and others...)
Penetrol would not take the place of sanding (for purpose of leveling a non-flat surface) unless you mixed some abrasive grit in with it when you wiped the rag soaked therewith over the surface.
The statement by the Penetrol people that a tack therewith (meaning to wipe with a rag soaked in the stuff, presumably)improves adhesion or otherwise placates the Varnish Spirits suggests (a) it actually does improve adhesion, or (b) they believe it does improve adhesion, likely by the plasticizer-causing-swelling mechanism, or (c) that they believe you will buy the product expecting that it will give some benefit. There is at this point insufficient data to determine which one or more of those are the case.
If I were going to make such a product I would evaluate chlorinated paraffins (chemicals commonly used as plasticizers) and other phthalate plasticizers commmonly used as plasticizers in a variety of rubbers and plastics to find which casued the most softening of cured and half-cured varnish films. I would then throw in a bit of something with a noticeable odor to mislead the competitors into thinking it was the other thing, and to give the customer a familiar odor of something (A consumer finds it more accceptable to have a product that smells of something familiar rather than nothing at all) and then thin it with as much mineral spirits as I could get away with, consistent with having the product work at all. Then design a marketing program , register the name and sell it everywhere.
[This message has been edited by thechemist (edited 06-27-2000).]
06-27-2000, 02:47 PM
Nice try, Chemist. I think you've been to law school yourself. There are three ways to win a trial: Argue by false analogy (the most common); Argue by false premise (what you accused me of doing); and, when the other two fail, accuse your opponent of being on drugs (sound familiar?).
Oh, if only I had the cleverness and quickness of mind to be able to argue like a real lawyer, to argue like Chemist. But instead, I have to limit myself to the plain, simple truth, because I'm just not clever enough to do it any other way.
I'm starting to come around to Ian M's way of thinking about varnish. It's really a useless enterprise, but at its best, it's much like this thread: takes up a lot of time and gives you an excuse not to do any real work.
Back to the topic at hand. Chemist, you never answered the question. If everything has to be defined by "doingness," then the rock can never just be a rock. It can be a doorstop if it is stopping doors, an anchor if it is holding a boat in place, a wall if it is so used. But, if you are correct that all matter is not continuously in motion, and if the rock is just sitting there doing nothing--not being in the state of doingness--then it must not exist, because it cannot have a definition. To say that it is a "failed doorstop" is nothing more than trickery of language. To say it is "that which is not a doorstop" is too imprecise and too broad. We all are "that which is not a doorstop."
But alas, I've signed my own death warrant, for no ordinary mortal can win an argument with artificial intelligence, and no one, human or not, can challenge The Committee and survive.
06-27-2000, 04:29 PM
You guys are so wierd. I love it.
06-28-2000, 01:27 AM
I am sooo glad I posted my question. I now know that all the flat rocks I brought home for a rock garden are actually of the class "that which is not a doorstop" AND that sanding varnish and flowing on varnish is a sensual experience (I DO need to review the definition of sensual). But then, Hmmm, the sanding, the brushing -- if considered fore play to looking at and stroking bright wood on a warm clear day while on the water. . . .
PS: The wet sanding went well and the next coat is drying. It's no piano (as mentioned in other varnishing topics on the forum), but it's no longer a barn plank look alike either.
Cedar Hill Boatworks
06-28-2000, 07:53 AM
Chemist, does the varnish below the hardened surface film continue to cure? If so, once the hardened surface film has been broken by sanding, and the semicured varnish is then exposed, perhaps the penetrol that is wiped on acts as a plasticizer. Or, the penetrol softens the varnish beneath the now broken surface film and allows the new coat to bond chemically a la hot coating?
If the rock to be used as a doorstop lacked the sufficient mass and or its surface and the floor could not generate the required coefficient of static friction friction to prevent movement of the door, the rock could be placed in a small puddle of varnish, perhaps the cured varnish would have enough adhesive property to prevent movement of the door. Closing the door at a later date may prove problematic. One could of course try to soften the cured varnish by soaking the rock and the varnish with penetrol......
06-28-2000, 09:59 PM
Varnish will cure in depth as the oxygen from the air diffuses into the coating and reacts with the resin, catalyzed by the "through dryers" that are present. Varnish cures not-that-fast, and the hardness that develops does not indicate complete cure, as there are many unreacted sites where another fresh application can react even a couple of days later. I think in the Good Old Days, when LEAD was the only drier needed, the surface was tacky enough long enough that excessive airborne debris accumulated by the time another coat could be applied, necessitating sanding to clean it up. when cobalt was introduced as a top drier, its much greater reactivity led to a more fully cured outer film surface (dry-to-dust sooner), which gave poorer intercoat adhesion, thus again necessitating sanding for good adhesion unless the cobalt level was reduced considerably, which does not seem to be the case with most products. In the last ten or fifteen years modern gloss-enhancing additives have been developed, and they really destroy intercoat adhesion unless the drier levels are reduced so far that dirt accumulation is again a problem....progress is always a tradeoff.
The penetrol may well solvate the glos-developing additives at the surface , thus aiding adhesion. Ironically, a varnish solvent system, if properly formulated, would do the same thing, eliminating any need for penetrol at all. The varnish makers would have to spend eighty cents a pound for better solvents, instead of twenty cents a pound for mineral spirits. I know what I am going to do when I make my varnish....
Enough rocks cooperating will always succeed in being an unvarnished doorstop. Even an immobile lawyer holding open a door is a legal doorstop.
It is noteworthy that "There are three ways to win a trial...." has nothing to do with the truth of facts concerning the defendant, while being a true statement in and of itself.
06-29-2000, 08:27 AM
Good observation Chemist. I think we've all seen enough trials on tv to know that "Truth" isn't always the determining factor.
Trials are decided on the evidence that the jury is permitted to see and the persuasiveness of the people who present it. If the evidence presented is a fair depiction of the Truth, then there's a good chance that Justice will prevail--that is, the outcome of the trial will reflect reality. When the evidence is incomplete or subject to differing interpretations, the trial becomes more like a sporting event than a tool to effectuate Justice.
The system is far from perfect. The remarkable thing is that it works at all.
06-29-2000, 11:29 AM
What was it someone once said about our form of government? Something about it being the worst possible one... etcept for every other one? Perhaps that applies to our system of justice as well?... (Sort of like the "old fashioned methods for getting a nice varnish finish...)
[This message has been edited by Art Read (edited 06-29-2000).]
06-29-2000, 02:41 PM
I think it was Alexis de Toqueville, sent over here to study this new form of government called a democracy, which elected its leaders, who reported back that it ensured that the worst candidate would not get elected. It also ensured that neither would the best.
Cedar Hill Boatworks
06-29-2000, 03:10 PM
I beleive the quote went something like "Democraracy is the second worst from of government" "Oh, whats the worst?" "All the rest."
06-29-2000, 03:28 PM
A rock is never just a rock. It is a mountain becoming sand becoming dust. We only call it a rock or a doorstop (or a pet) because it conforts us to see the world around us have some "meaning".
I, for one, love varnish and varnishing. I am, by no means a pro, nor a purist. I have even taken to trying this newfangled polyurethane hooch.
There is something rewarding, in a zen-like way, about preparing wood and applying varnish, particularly that first coat when the incredible grain pattern of the wood jumps out at you. To cover that beautiful wood up would seem to me like motoring when the wind is up so as to get to the next destination sooner. On the other hand, I've been tethered to my dock these last 3 weekends sanding and prepping and coating while a parade of plastic boats have motored past on the way out for a sail. Hopefully, with 7 coats, a boat cover and 48 degrees of longitude I'll be done with cabin varnishing for a while (just in time to start on the mast!)
That's my story and I'm stickin' with it.
04-28-2003, 09:58 PM
Thank you all for the entertainment.
04-28-2003, 11:46 PM
Looks like the inmates have nearly taken over the assylum.
rycophyla. I don't know if your question has been answered, but in my experience, varnishnig a surface that has been roughed seems to aid in the leveling so that you get fewer drips, runs and errors. Somthing about surface tension. Plus the wet edge stands out better against the matte. I use the 3M pads, without backing, once I've taken off the high spots.
Of course, tacking is essential to the as yet unattained "perfect varnish job", as is control of dust and gnats.
[ 04-29-2003, 12:53 AM: Message edited by: Paul Scheuer ]
04-28-2003, 11:52 PM
:D , Very enjoyable, ... but
ps, Personally, I think that if you don't have the artist's feel, you are just a dauber and always will be. Painting the curved surface of a hull, uniformly is about the hardest thing I've ever done as a painter. It is not just in the 'doings' it is also in the assessment of your doings as you paint your way to the top.
[ 04-29-2003, 01:08 AM: Message edited by: Wild Wassa ]
04-29-2003, 12:06 AM
Thank you WayGray for bringing this one out of the archives.
04-29-2003, 08:40 AM
Always, I come into these conversations late and short. Oh well, way up yonder the thought occured to me that CPES and Penetrol may have a lot in common.
04-29-2003, 01:10 PM
Personally, Scott, I'd like a few examples of the first two methods to win a trial, particularly if the trial is taking place at a courthouse which uses an unvarnished rock as a doorstop and also, perhaps, as a spare key.
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