Replies

1. 
   Guest_ | Nov 26, 1999 06:12am | #1

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   John,

   You will most likely get a few different replies to this question. Here's mine. You might hear people tell the you shouldn't "work" the brush to much that this will cause the air bubbles. Up until about ten years ago I believed this too simply because I didn't know any better. It does sound reasonable. . .

   What opened my mind was when I met and older guy who was at the time about sixty and was applying poly (varnish) for 45 of those years. The thing about this guy was that he worked the shit out of the brush! I mean he would slop it on and kinda like "push" it in and move it around a lot. Once the piece was completely covered he would just feather the piece with light strokes, commonly know as airplane strokes. This guy got GLASS when he was done. . . I asked why he did it that way, he replied because that's the way you do it! Ok, I'm not one to argue with success. I asked what type brush he used, he said china bristle. Ok, do you do anything to the ploy? Yes I add some turpentine and some boiled linseed oil to the varnish. That was all I got but, it was enough.

   So here it is. No matter what you do you will get bubbles when you first apply poly. By adding the turpentine and boiled linseed oil you make the poly less viscus. This is important because if it's to viscus the air won't be able to pop or brake the surface, the ones that do will only form little craters in the surfaces because the poly won't flow back to fill the crater. So just experiment with thinning the poly a bit till you get it right.

   There are other factors involved too. Moisture and temperature play a large roll in how poly dries. Good luck.

   Joseph Fusco

   View Image
   © 1999.

   "Whenever, therefore, people are deceived and form opinions wide of the truth, it is clear that the error has slid into their minds through the medium of certain resemblance's to that truth."

   Socrates

1. 
   Guest_ | Nov 26, 1999 06:15am | #2

   *Joe's advice sounds right on base to me.

1. 
   Guest_ | Nov 26, 1999 06:16am | #3

   *I've always believed that working the brush too much does add more bubbles to the finish. I still do think this is so.I've warmed up my poly before. I have a wood stove in my shop (I tend to collect alot of scrap lumber) and I set the can right on top of this (I use some sort of spacer - don't want a flash fire). This makes the stuff flow like water.Joe's right, the bubbles will float out if it's thin enough. I've thought about thinning it but no matter what the can says, I can't get the idea that my altering the mix might hurt it somehow. Probably not but just to be sure....

1. 
   Guest_ | Nov 26, 1999 07:17am | #4

   *Don't be afraid to thin it. Cut it 50:50 (or even 1/3 varnish, 2/3 thinner) and you get what is sold as 'wiping varnish'(at a fraction of the cost). Apply it with a soft cloth, just wipe it on, and after a few coats you start to get a superb finish, with no brush marks or bubbles. It takes a few more coats, but it looks as good as the very best sprayed finish, and it's tons better than brushed poly because each coat is thinner, and dries harder.What I do is: buy a gallon of varnish. Some of it gets cut with thinner (turps or paint thinner, doesn't really matter) and BOIILED linseed oil (has to be boiled, or it won't dry), proportions about 1/3 each to start, vary according to your likes. This is a long- oil varnish (Danish oil), and I use it for the first, penetrating coat. After that, I switch to the wiping varnish, based on varnish out of the same can. For the cost of a gallon of varnish, some boiled linseed oil, and some thinner, you can make your own Danish oil and wiping varnish very inexpensively. Bob Flexner has a book "Understanding Wood Finishing ' that covers this same territory.

1. 
   Guest_ | Nov 26, 1999 07:36am | #5

   * John,

   If you want to use a wipe on you just need to apply more coats. I usually apply between 6 and 10. If you want to make it yourself you can try this recipe. 1 part poly/varnish 1/2 part boiled linseed oil and 1/2 part turpentine. Here's a picture of how nice a home made wipe on poly can look. If you'd like some information on some books, try this.

   Joseph FuscoView Image© 1999."Whenever, therefore, people are deceived and form opinions wide of the truth, it is clear that the error has slid into their minds through the medium of certain resemblance's to that truth." Socrates

2. 
   david_sorg | Nov 26, 1999 09:26am | #6

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   Sorry, I'm going to have to disagree a little bit with each of the guys above. Never add linseed oil to your mix if you care about the properties of polyurethane in the first place. You will soften and yellow the finish anywhere from a little to a lot depending on how much oil you add. You can get the similar wonderful flowing high gloss properties that the oil adds by using a traditional alkyd varnish instead. Poly is a harder finish than alkyd, though not as pretty of a finish in my mind, but adding oil will alter its chemistry in a negative way. It's ok to add oil to an alkyd if you wish.

   Adding solvent will not alter poly's dried characteristics, and in fact, almost always must be done these days. Because of pollution laws, manufacturers have had to cut down on VOC's. They do this by reducing the amount of solvent, which is the main source of the VOC's, and sell a thicker product than they once did. So instead, the consumer has to add back the thinner. The thinner will give a longer open time as well as a physically thinner coat which allows air to escape.

   Doing the wiping varnish routine can work if you do it right. Polyurethane doesn't stick well to itself and can easily peel off if the previous coat is not still slightly "fresh" or well dried and throroughly sanded. It needs either the chemical or physical help to bond itself.

   So, thin it for sure, warm it if it's cold, make sure your substrate is not too hot to begin with or allowed to dry in direct sunlight, use a good brush, after distributing the varnish, finish it off with light brushstrokes.

3. 
   Guest_ | Nov 26, 1999 10:10am | #7

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   If your using water based poly it will foam. Oil based poly doesn't do the foaming.. I don't have trouble with oil. L. Siders

1. 
   Guest_ | Nov 26, 1999 05:05pm | #8

   *David; I'm going to agree with you that an alkyd varnish is a nicer finish than poly, and that if you have the choice,add tung oil to poly rather than linseed oil (but I've never had a problem with linseed oil). Also that poly doesn't stick well to cured previous coats. In fact the only thing I disagree with is that poly is a harder finish than alkyd; it's tougher, but not harder, which is important if you want to rub the finish out to a furniture grade finish. That's what I like about wiping varnishes, even if poly is the base; the thin coats are very hard, and you can rub them out (if you're careful).

1. 
   Guest_ | Nov 26, 1999 05:31pm | #9

   * david,

   I would just disagree with the use of the word "never". I've been doing this for quite some time and have had no ill effects. Though what you say is technically correct, it just doesn't to seem to have been a problem. I have used both tung and linseed oil with great results. Have you ever personally experimented with this? If so, what were you findings?

   Joseph FuscoView Image© 1999."Whenever, therefore, people are deceived and form opinions wide of the truth, it is clear that the error has slid into their minds through the medium of certain resemblance's to that truth." Socrates

4. 
   david_sorg | Nov 27, 1999 12:19am | #10

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   I'm not saying never as in, nasty things will happen and in X years it will all fall off. In fact, linseed oil is usually an ingredient of polyurethanes. I meant to state that you are partially defeating your reason for choosing a urethane in the first place by adding extra oil. The addition will result in a softer final finish. Softer in terms of sandability/rubability, and softer in terms of abrasion resistance, and, with the addition of lots of oil, the permeability will be increased and you would lose water resistance.

   I haven't done any experiments with this, nor would I; the manufacturers have already devoted far more assets and science to it than I could. Adding mineral spirits does not change the ratio between oils and resins and other additives in the cured product. Obviously, adding oil does. This changes the chemistry, including all that fancy cross-linked long molecular chains stuff that you just paid extra to get in the first place.

5. 
   Guest_ | Nov 27, 1999 01:59am | #11

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   david,

   Thanks for taking the time to reply.

   My statement wasn't meant to amply you said that either. My secret formula of polyurethane is; for a pint of finish I add 2 cabs full of MS or turpentine and one cap full of linseed oil or tung, whichever I may have on hand at that moment. That's it.

   My statement wasn't to amply either that if you catastrophically alter the chemical makeup for the product (varnish / polyurethane) that bad things can't happen. As far as your statement "and, with the addition of lots of oil, the permeability will be increased and you would lose water resistance", by having a higher ratio of oil to resin you actually increase the water resistance. That brings me to say that if you should happen to add to much oil, you will in effect be making a spar varnish.

   Joseph Fusco

   View Image

   © 1999

   "It is better to be feared. . . Then loved!"

   Machiavelli

6. 
   david_sorg | Nov 27, 1999 03:32am | #12

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   Sorry Joe, you're wrong about the function of oil and resins. Re-read the appropriate parts of "Understanding Wood Finishing." Oil provides the flexibility in a varnish, NOT the water resistance.

7. 
   Guest_ | Nov 27, 1999 04:31am | #13

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   Sorry david,

   I'm being to see why you have a fondness for andrew. It must be that 'birds of a feather" thing. I would recommend that you confine your preaching to FWW. The word "WRONG" is such a destructive word in the months of, well you know.

   This is the excerpt from Bob Flexner's book pg. 176 chapter 10.

   This should pretty much put an end to you. BTW you were quite easy. . .

   

   
   

   Joseph Fusco

   View Image
   © 1999.

   "It is better to be feared. . . Then loved!"

   Machiavelli

8. 
   andrew_dicgless | Nov 27, 1999 05:00am | #14

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   Ouch. Some ringer you were.

   andrew dic.

9. 
   Guest_ | Nov 27, 1999 07:38am | #15

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   With enemies like these ... who need worry?

10. 
    david_sorg | Nov 27, 1999 08:30am | #16

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    Joe, you're giving me a backache stooping this low; cut it out, willya? Your underlined words are just right, -it is you who are upside down on which is which. If you must, turn your scanned page back to 175, read the second paragraph, think about it, maybe sleep on it or consult with someone you trust.

    Don't take advantage of my sweet disposition, now...

11. 
    Guest_ | Nov 27, 1999 05:26pm | #17

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    david,

    Actually, you should be getting a nose bleed. Here's the whole page. Now go crawl back under your rock. . .

    As cousin Vinny would say; "I'm through with this one."

    

    Joseph Fusco

    View Image
    © 1999.

    "It is better to be feared. . . Then loved!"

    Machiavelli

12. 
    John_Vavala | Jan 04, 2000 11:44pm | #18

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    how do i apply polyurethane without creating a lot of bubbles