Varnish Recommendations

[RussF]

... a lot of people these days operate on the "if you can smell it, it's dangerous" principle. Alcohol certainly won't hurt you when used responsibly.

I use alcohol for the reasons I stated. You can use either denatured or isopropyl (my choice) of at least 90%+ purity - available at pharmacies (or chemists for you Brits). 70% alcohol has 30% water and may also raise the grain.

Notice that I didn't mention lacquer thinner. While you can use it as an indicator of glue spots, it truly does have some nasties in it - MEK (Methyl Ethyl Ketone) for one. It will also permeate your skin, so it should only be handled with nitrile gloves and eye protection.

Acetone is good, but you have to be quick. Due to it high volatility, it evaporates very quickly. One other not of interest, a good friend of mine who is a retired chemistry professor from Cornell University once told me that the molecules of acetone are very large - too large, in fact, to easily permeate the skin. So while it may dry out your skin and you shouldn't drink it or directly inhale the fumes, it is much safer to handle than lacquer thinner.

 

[Bob Cleek]

I use alcohol for the reasons I stated. You can use either denatured or isopropyl (my choice) of at least 90%+ purity - available at pharmacies (or chemists for you Brits). 70% alcohol has 30% water and may also raise the grain.

Notice that I didn't mention lacquer thinner. While you can use it as an indicator of glue spots, it truly does have some nasties in it - MEK (Methyl Ethyl Ketone) for one. It will also permeate your skin, so it should only be handled with nitrile gloves and eye protection.

Acetone is good, but you have to be quick. Due to it high volatility, it evaporates very quickly. One other not of interest, a good friend of mine who is a retired chemistry professor from Cornell University once told me that the molecules of acetone are very large - too large, in fact, to easily permeate the skin. So while it may dry out your skin and you shouldn't drink it or directly inhale the fumes, it is much safer to handle than lacquer thinner.

A related question:

I understand that isopropyl alcohol ("rubbing alcohol") will dissolve PVA adhesives. I've never been able, however, to determine the extent to which it's better at doing so than ethanol ("ethyl alcohol.")

Thanks to "Google University," I have learned that rubbing alcohol is a polar solvent, meaning its molecules have a slightly positive and a slightly negative end. This polarity allows it to dissolve other polar substances, like water and some organic compounds. Ethanol is a non-polar solvent. PVA has polarity. Polar solvents are generally effective at dissolving polar solutes, while non-polar solvents are more suitable for dissolving non-polar solutes. Therefore, isopropyl alcohol should work better at dissolving PVA than ethanol does.

In the hope of avoiding doing the experimentation myself, I'm wondering if anybody has any experience with using both types of alcohol to remove cured PVA adhesive and can comment on how well each type works in this application. My interest is in the reversibility of adhesives. I am considering a method of mass-production block making which would involve gluing large numbers of pieces together for uniform machining and then separating them by dissolving the adhesive used. I would want to dissolve the adhesive completely from the glued parts. I am aware that fish glue is completely reversible with water and that is an alternative, although it is more difficult to source, must be refrigerated to maximize shelf life, and I'm not as familiar with using it as I am with PVA.

 

[RussF]

A related question:

I understand that isopropyl alcohol ("rubbing alcohol") will dissolve PVA adhesives. I've never been able, however, to determine the extent to which it's better at doing so than ethanol ("ethyl alcohol.")

Thanks to "Google University," I have learned that rubbing alcohol is a polar solvent, meaning its molecules have a slightly positive and a slightly negative end. This polarity allows it to dissolve other polar substances, like water and some organic compounds. Ethanol is a non-polar solvent. PVA has polarity. Polar solvents are generally effective at dissolving polar solutes, while non-polar solvents are more suitable for dissolving non-polar solutes. Therefore, isopropyl alcohol should work better at dissolving PVA than ethanol does.

In the hope of avoiding doing the experimentation myself, I'm wondering if anybody has any experience with using both types of alcohol to remove cured PVA adhesive and can comment on how well each type works in this application. My interest is in the reversibility of adhesives. I am considering a method of mass-production block making which would involve gluing large numbers of pieces together for uniform machining and then separating them by dissolving the adhesive used. I would want to dissolve the adhesive completely from the glued parts. I am aware that fish glue is completely reversible with water and that is an alternative, although it is more difficult to source, must be refrigerated to maximize shelf life, and I'm not as familiar with using it as I am with PVA.

I don't know anything about polarity. I've had good success releasing veneer banding with heat from a regular clothes iron. Actually, I have used the technique in reverse as well. When I've had to put a strip of banding on an irregularly curved edge where clamping was impractical, I have "painted" both mating surfaces with PVA and let it dry. Then, with the iron, I would "iron on" the banding. The heat softened the glue enough to get a very good bond. So, heat a small section, remove the iron and rub the area with a smooth block of wood to apply pressure while the adhesive cooled. Works a charm!

Doing a brief search on "reversible glue", it seems the everything I found was water soluble. So a lot will depend on your application and whether alcohol would work in its place. If you're talking about machining wood, I think water would be your enemy. It also depends upon how much surface area would be glued. Obviously, any solvent would have to work it's way in from the edges. The larger the area, the longer it will take.

I suppose you could try an ambroid (cellulose nitrate) type glue (remember the old model airplane glue - for balsa models?) I think that would dissolve in acetone (if you can even get it, that is.)

 

[Bob Cleek]

If you're talking about machining wood, I think water would be your enemy. It also depends upon how much surface area would be glued. Obviously, any solvent would have to work it's way in from the edges. The larger the area, the longer it will take.

I suppose you could try an ambroid (cellulose nitrate) type glue (remember the old model airplane glue - for balsa models?) I think that would dissolve in acetone (if you can even get it, that is.)

Yes, that's why I was interested in alcohol with PVA rather than water with the fish glue.

I've used the "heat cure" method with PVA and it's great. I tack down planking that way often.

 

[Roger Pellett]

I keep a tube of Duco cement on my workbench. This is a cellulose nitrate glue like Ambroid. It’s completely reversible in acetone. I understand from previous posts that unfortunately this and its acetone solvent are not available in California.

Roger

 

[RussF]

I keep a tube of Duco cement on my workbench. This is a cellulose nitrate glue like Ambroid. It’s completely reversible in acetone. I understand from previous posts that unfortunately this and its acetone solvent are not available in California.

Roger

As a funny tangent, in the hardware store the other day, I found a shot-glass sized measuring cup (made of clear glass) with markings printed on it for fluid ounces, milliliters, teaspoons and tablespoons. I grabbed it because it could come in handy. Then I noticed the big sticker with the warning, "Contains ingredients known to cause cancer in the state of California." The glass? The ink used to print the graduations? Probably the adhesive used to hold the stupid sticker on!

 

[Roger Pellett]

I’m sure that nobody analyzed the chemistry of that glass. This has become a meaningless catch all phrase imposed by legal departments to avoid litigation. If you look carefully you can probably find it somewhere on the glass written in Chinese.

Roger