polyurethane techniques

[woodguy1975]

J John, respectively if I had your talent and was into making what you make, I would agree with you, I would use a shellac, lacquer, or varnish, most likely lacquer. But us folks who are making stuff for everyday use, really need something durable, especially if kids are involved. Shellac, lacquer, or varnish are beautiful finishes in their own right, but I think you would agree their not all that durable. I also think you would agree they scratch and stain pretty easy?. I like the idea of being able to clean with soap and water or maybe even windex, I wouldn't dare try that with a shellac, lacquer, or varnish finish.

One of the main reasons I prefer gloss, is the sheen can always be adjusted downward, by rubbing out the final coat with fine steel wool or if your a real glutton for punishment, pumice or rotten stone. But flat simply can't can't be adjusted any higher than flat.

Everyone has their preference, that’s why there are so many different finishes out there. I try not to discount any of them; they all have their purpose in life. Ranging from a fine museum piece, to a young boys toy box.

Please keep in mind this is my 2 cents only and I'm not trying to be contentious in anyway. I'm sure you cover finishes and their intended uses in your finishing class.

Thanks

Jeff, you are correct about intended use. When I make a peice I make it for heirloom quality. If you are making something for kids to tear up maybe poly would be a good choice. Conversion varnish though is tougher than poly.

On rubbing out I'm only responding so the guys can learn something they might not realize. First of all most newbies finish with gloss and don't know how to properly rub out and end up with a superglossy piece. Big mistake for most projects. You should only use gloss when you are using lights reflection as part of the design feature. In my chairs I put in hardlines that the gloss shows the viewer. It is a matter of reflection and shadow lines. I'm taking a viewer through a visual and tacktile journey. You can rub a flat to a gloss and vice versa. That is a common mistake to think that you can only rub down and not up. You can rub a satin to a beautiful gloss and depending on the finish not get any masking of the grain from the flatteners in the finish. Some finishes do mask the grain when you try to rub up due to the flattening agent used. Most high quality finishes don't have this problem. In fact one of my teachers, Jerry Terhark a professional finisher and teacher at MASW, taught using satin for everything and rubbing up or down for desired sheen level.

Just remember if you make something make it to the best of your abilities. Our peices from a simple pen to a rocking chair speak to the user about the craftsperson.

This has been a good discussion. I think a lot of good information has been passed in this tread.

John

 

[chris99z71]

I'm assuming they used Shellac or Lacquer? Can anybody tell me the chemical makeup of those two?

Al, you're such a hopeless polymer chemistry dork! :rolf: As if I'm not the pot calling the kettle black...

Good info all! Thanks!

 

[NZAPP1]

Wow
John I agree there has been a lot of great information passed on in this thread:eusa_danc :icon_thum Thanks All

 

[SteveColes]

:rolf: :rolf: :rolf:

Thin/dilute with turpentine or mineral spirits, NOT with mineral OIL !!!!!!!

 

[OriginalChong]

Al, you're such a hopeless polymer chemistry dork! :rolf: As if I'm not the pot calling the kettle black...

Good info all! Thanks!

At ease the noise, you. :slap:

 

[OriginalChong]

I'm going to try the dilution technique this weekend on a board and batten door I'm building. I'll take pictures and show you guys how it turns out. Thanks to all again. I'll keep you posted. :thumbsup:

 

[Howard Acheson]

Getting a good finish with any oil based paint or clear finish is primarily learning the correct technique and then practice.

First, sand the project surface up to 180 grit using a sander and finishing with 180 grit paper mounted on a rigid sanding pad. Sand in the direction of the grain. Use a vacuum to get off all the sanding dust.

If using a non-gloss finish, gently stir the product 100 strokes in one direction and then 100 stokes in the other being sure to keep you stirring stick in contact with the bottom of the can. There are flatteners in the finish to make it non-gloss and these must be stirred into suspension. Pour some finish into a clean container and seal the original container. Thin the first coat about 25-30% with mineral spirits so that it is deeply absorbed.

Use a good, natural bristle brush. Brushing technique is to first dip the brush into mineral spirits and wipe dry by stroking onto paper towels. This prepares the brush and minimizes finish getting up into the furrell where it can damage the brush, Dip the bristles into the finish about 1/3 to 1/2 the length of the bristles. What you want to do is to flow on the finish with long, slow strokes minimizing back and forth brushing. Let the first coat dry 24 hours. It will not look good at this point.

When it is dry, use 320 sandpaper on a sanding block and sand the surface flat. If the surface sort of "corns" let it dry another day. When you have the surface flat, vacuum off the dust. Pour out some new product into your working can. Thin the next, and all subsequent coats 10% with mineral spirits to promote good flowout or leveling of the finish. Again apply in long, slow strokes with minimal back and forth brush. It's fast brushing that created bubbles. After getting a surface covered with finish, it's time to "tip off". This involves removing most of the finish from the brush by lightly dragging the bristles on the edge of your working can. Hold the brush perpendicular to the surface and with the bristles lightly touching the wet surface slow brush the full length of the surface in one continuous stroke. Tip off the whole surface. This breaks up any remaining bubbles and smooths the surface. Let it dry 24-48 hours and then sand with the 320 paper but this time sand lightly. Do two coats this way.

For the finish coat, finish your scuff sanding and vacuum off the surface. Get out your finishing supplies. Now clean up the area. Vacuum everything. You must try to make the area dust free. Dust is what will leave nits in the finish. When you finish vacuuming, get out of the area for two hours. After the two hours, change your clothes and go back in being careful not to stir up any dust. Get your finish ready. Wipe the item down with a rag lightly dampened with mineral spirits to remove any remaining dust. Now apply your final coat being a careful as you can. When you finish, get out of the area or room. Clean you brushes somewhere else.

Done correctly, you should have a smooth, nice finish.

Also keep in mind that you should never work out of the original can of finish. This will cause you to be putting dust back into the clean finish.

Never pour unused working finish back into the original can as this puts contaminates back into your finish.

If using non-gloss, always stir after opening the can. Re-stir every 5-10 minutes as the flatteners fall out of suspension.

Always clean your brushes after each coat. Again, you will be putting contaminates back into or on you new coat of finish.

Finally, brushing on a finish is a learned process. It takes a while and practice. When I learned in a marina, I painted lots of non-important surfaces before I was allowed to do an appearence surface.

 

[Travis Porter]

Howard, you obviously know A LOT about finishing, more than most.

Where/how did you learn all of this?

 

[jeff...]

John agree with you on conversion varnish being one of tougher finishes out there, but the down side with conversion varnish is it's not easily repaired. Scratches and worn spots will never look right after being repaired on a conversion varnish finsh. Poly urethane on the other hand is just as easy to touch up as a laquer or enamel finish. Again it's a trade off and what works best for oneself and the use of the finished piece. Furniture gets used, no matter how careful we are with it, it's going to get scratches and wear marks. I wouldn't want to be the guy to have to strip down a table top in order to repair a couple of dings and scratches. If that were the case, I would have to quit my part time furnitre touch up and repair job and all the classes I've taken over the years would be useless.

With regards to rubbing out a finish I further agree one could buff a flat finish smooth as a babies butt. But I'm not convinced by doing so it would have the same clarity and depth as a gloss finish would. Simply because of the dulling agents embedded in the finishing medium whos' jobs is to absorb light, that' why it's flat. Gloss and high gloss finishes are pretty much free of dulling agents, so they will reflect light. When you get right up on a gloss finish and at the right angles you can clearly see the wood underneath the finish in all it's glory. Gloss simply provides higher clarity and depth than a flat finish. I really don't know about using a different finishes for lines and shadows, you lost me there.

Anyways this is just my 2 cents worth, I think this is a good conversation to have, there's a lot of good information being discussed and it's nice to be able to talk a topic on friendly terms without having to worry about emotions getting in the way. I can appreciate and fully accept your stance on polyurethane - I have a similar one on wood stain, I don't stain wood at all and think stain is a bad 5 letter word .

Thanks

 

[woodguy1975]

Jeff, to me poly is the thoughest finish to repair. You can't just wipe another coat over it for a repair because it won't chemically bond. If you have a deep scratch you can't buff it out like you can with lacquer. A deep scratch with lacquer I'd apply lacquer to fill the scratch and buff out the whole surface. That repair is invisible. You can't do that with poly. Besides for restoration work the only solution for removing poly is sanding.

Try applying satin lacquer to a board and buff it up for yourself. You'll see a slight difference, but not much. Especially when you use a high clarity lacquer like Behlens. I've taken flat Behlens and sprayed it besid gloss and rubbed them both up. There was next to no difference in the clarity. I know this seems odd to think about rubbing up and is against standard convention, but I hold my stance on it. The classical example of a table with a glossy top and satin sheen base comes to mind. It is a lot easier to rub up a flat table top surface to a gloss than rubb down a ball and claw foot or some other non flat surface to a satin from gloss.

It's just a different way of looking at things. I hope everyone is enjoying this tread. I get a kick out of conversations and debates like this. In the end the right answer is up to the end user. What is right for you is right for you.

 

[DaveO]

I know polyurethane is synthetic in nature and probably went into production about a hundred years ago or less. So, historically speaking it won't be found in antiques. I'm assuming they used Shellac or Lacquer? Can anybody tell me the chemical makeup of those two?

Here's a little info on the make-up of Lacquers:

http://pubs.acs.org/cgi-bin/abstract.cgi/iechad/1928/20/i02/f-pdf/f_ie50218a027.pdf?sessid=6006l3

And a little on Shellac...it's bug spit :lol::lol::lol::lol:

The Story of Shellac on the Natural Handyman home repair and do it yourself website


HTH, Dave

 

[OriginalChong]

Here's a little info on the make-up of Lacquers:

http://pubs.acs.org/cgi-bin/abstract.cgi/iechad/1928/20/i02/f-pdf/f_ie50218a027.pdf?sessid=6006l3

And a little on Shellac...it's bug spit :lol::lol::lol::lol:

The Story of Shellac on the Natural Handyman home repair and do it yourself website


HTH, Dave

Dude, thanks. Those sites are great. Read carefully on the second site though. We don't use natural lacquer anymore. It's all synthetic now. So, it's no longer "bug spit". I'm going to try to find out how close to its origins is the chemical nature of the new lacquer.

 

[jeff...]

John, I know you'll probably never have the need to touch up a polyurethane finish since you don't use it. But Mohawk's Finish-Up works great to repair a wide variety of finishes including polyurethane requiring touch-up. That is if your looking for a pre-canned solution. http://www.mohawk-finishing.com/catalog_browse.asp?ictNbr=214

Sometime I might get hard knox on a finish and re-flow re flow it with a acetone mist or a 0000 piece of steel wool moistened actone and a hair dryer, it all depends on what I'm working with, there are times when a finish just needs to know who's the boss ;-).

Stripping and sanding is for the birds man, old tired finishes can be rejuvenated and repaired with the right solvents pretty easily, providing their in fair shape to begin with no (silicon wax / pledge / paste wax).

What kills me is when a piece has been stained and a customer wants it lighter. That's a lot of work, they don't call it penetrating stain for nothing. I usually am very quick to say no, because I'm destined to fail from the start.

Stain, just say no! :lol:

 

[woodguy1975]

There is solvent for everything. Now would you want to use all of them......



That is some good refinishing info Jeff.

John

 

[chris99z71]

Good article, DaveO.
From what I can figure out, the solvent based lacquers are nitrocellulose based, with the product containing various solvents to dissolve the nitrocellulose.
But then I also found a lot of papers talking about polysaccharide lacquers of asian origin. I'm wondering if these might be the water based lacquers? Anybody?

Incidentally, nitrocellulose is also gun cotton (think flash paper). The first projector films made by Kodak were nitrocellulose. So lets take an explosive and run it right next to a hot light bulb...
That's why there were so many theatre fires back in the day.

 

[chris99z71]

Dude, thanks. Those sites are great. Read carefully on the second site though. We don't use natural lacquer anymore. It's all synthetic now. So, it's no longer "bug spit". I'm going to try to find out how close to its origins is the chemical nature of the new lacquer.

Actually, Shellac is still from the bugs. The article talks about other synthetic polymers that "replaced" shellac after WWII such as lacquers and urethanes. Also about machine produced shellac, but that's just the commercial scale preparation of the bug stuff. I don't think there's actually a synthetic shellac.

 

[jeff...]

There is solvent for everything. Now would you want to use all of them......



That is some good refinishing info Jeff.

John

John, I really like chatting with you in these forums, you a man with a wealth of information and the ability to communicate it in easy to understand ways. I'm planning on taking your finishing class, you mentioned somethings such as sheen adjustment that I really would like to understand further. I've learned a lot in this thread, thanks for the information sharing and I'm looking forward to jumping in on your finishing class.

BTW I mainly only use three solvents, they range in strength from weak to strong. Denatured Alcohol, Mineral Spirits and Acetone, of course I'll use others too but I consider these three essential just like earth-tone pigments and blacm and white for color matching.

Nice chatting with you - thanks again...

 

[woodguy1975]

John, I really like chatting with you in these forums, you a man with a wealth of information and the ability to communicate it in easy to understand ways. I'm planning on taking your finishing class, you mentioned somethings such as sheen adjustment that I really would like to understand further. I've learned a lot in this thread, thanks for the information sharing and I'm looking forward to jumping in on your finishing class.

BTW I mainly only use three solvents, they range in strength from weak to strong. Denatured Alcohol, Mineral Spirits and Acetone, of course I'll use others too but I consider these three essential just like earth-tone pigments and blacm and white for color matching.

Nice chatting with you - thanks again...

Acetone will take care of most tough stuff. That is one solvent I don't have in the shop. I do have MEK though. Pretty nasty stuff, but takes care of just about everything including cured CA.

 

[PeteM]

OK I'm glad we all agree . . .
The best finish is a bit of BLO, a few coats of shellac and a nice coat of wax!!!
:lol::eusa_danc:lol::roll::icon_thum:eusa_thin:slap:

pete

 

[Travis Porter]

Some of the solvents are wicked. Lacquer thinner, xylol, acetone, Naptha, Denatured Alcohol, and Mineral Spirits. Knowing which one to use and some of the additives is a science in and of itself.