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PostPosted: 19 Feb 2010, 21:13 
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Hi Can someone please tell me the difference between lacquer and varnish?
I'm showing my ignorance, I know, but I've done very little in the way of finishing :oops:


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PostPosted: 19 Feb 2010, 22:31 
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I don't think there is a (straightforward) difference, they seem to be pretty interchangeable terms.


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PostPosted: 20 Feb 2010, 12:12 
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Froggy wrote:
Hi Can someone please tell me the difference between lacquer and varnish?
I'm showing my ignorance, I know, but I've done very little in the way of finishing :oops:


There are basically three types of finish:
* evaporative
* reactive
* coalescing


In simplified terms evaporative and reactive finishes work as follows:

Evaporative finishes use alcohol, acetone and lacquer (cellulose) thinners as solvents and thinners. Lacquers and shellac fall into this group. The solids are soft and string like in solution but as the solvents evaporate they lock together in a solid mass like dried spaghetti. Successive layers burn in to one another and form a contiguous whole. The solvent will re-soften the film, eg, lacquer thinners will soften cured lacquer, and alcohol softens cured shellac.

Reactive finishes use solvents such as white spirits and naphtha. Oil varnishes and linseed oil are reactive finishes change chemically when they cure, unlike evaporative finishes. At cure the solvent/thinner evaporates the resin cluster tighter together, and then a chemical reaction occurs causing the resins to cross link in a different chemical format-- it's sometimes described as being like loose scaffolding that suddenly bolt together. You need to scuff sand between layers of cured finish so that the subsequent applied layer has something to grip on to effectively. The solvent won't re-dissolve the cured film, eg, white spirits does not soften cured oil based varnish.

You didn't ask about other finish types so I won't describe them except to say that water based finishes generally fall into the coalescing category. Slainte.


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PostPosted: 20 Feb 2010, 12:23 
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Sgian Dubh wrote:
Evaporative finishes use alcohol, acetone and lacquer (cellulose) thinners as solvents and thinners. Lacquers and shellac fall into this group. The solids are soft and string like in solution but as the solvents evaporate they lock together in a solid mass like dried spaghetti. Successive layers burn in to one another and form a contiguous whole. The solvent will re-soften the film, eg, lacquer thinners will soften cured lacquer, and alcohol softens cured shellac.



You seem to be equating lacquer with cellulose there, Richard?

There are plenty of products on the market which call themselves waterbourne lacquers (I assume they fall within your coalescing category) and plenty which call themselves 2 pack/part waterbourne acrylic lacquer. As those are 2 pack, they have to be reactive I assume.

Even if that is just sloppy usage, the terms don't seem to have any really distinct meaning at least that I can discern.


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PostPosted: 20 Feb 2010, 13:07 
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Jake wrote:
You seem to be equating lacquer with cellulose there, Richard?


Yes. Cellulose polishes and thinners and lacquer and lacquer thinners are the in the same family of finishes. Lacquer thinners, aka cellulose thinners do come in different flavours, eg, 'hot' or 'fast' thinners and 'cool' or 'slow' thinners depending on how the formulation is meant to perform.

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There are plenty of products on the market which call themselves waterbourne lacquers (I assume they fall within your coalescing category)


Yes.

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... plenty which call themselves 2 pack/part waterbourne acrylic lacquer. As those are 2 pack, they have to be reactive I assume.


Correct as far as I am aware.

Quote:
Even if that is just sloppy usage, the terms don't seem to have any really distinct meaning at least that I can discern.


It's amazing how creative 'creatives' in the advertising game are when it comes to meaningless and obfuscatory text. Slainte.


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PostPosted: 20 Feb 2010, 14:33 
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Thanks for that Sgian and Jake, Could you give me some examples of when you would use lacquer instead of varnish and vice versa please?


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PostPosted: 20 Feb 2010, 15:57 
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Froggy wrote:
Thanks for that Sgian and Jake, Could you give me some examples of when you would use lacquer instead of varnish and vice versa please?


Well, that's an open ended question if ever there was, ha, ha.

I certainly wouldn't use any of the spray applied lacquers if I didn't have spraying facilities.

You can apply oil based varnish with a brush, with a rag, and a spray gun, but you can only apply nitro-cellulose lacquer, pre-catalysed, post-catalysed (acid catalysed) lacquer and other related formulations with a spray gun.

I sometimes use oil based varnish when I want a quite thin wiped on appearance. Oil based varnish is also good around hard used surfaces, eg, kitchen tables, coffee tables, etc and is usually brushed on, although it can be wiped on too-- you need more coats to build up a suitable fim thickness, typically three to five wipped on coats equals one brushed on coat.

Acid catalysed lacquer is good in these situations too, but the stumbling block of course is the need for a spray gun. If you don't have one, along with a sutable spray facility, you simply can't use it. Slainte.


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PostPosted: 20 Feb 2010, 17:08 
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Part of the reason I asked the question in the first place is that I have a spray gun that I've never used (and compressor obviously) and I've never used lacquer. I've just made a pine table (red wood). It's only a small one, more like a butchers block table and wanted to try a lacquer on it. If I can spray the lacquer all the better...I kill two birds with one stone :wink:

Thanks Richard

By the way where abouts in Leeds are you? I'm from Birstall near Batley and went to school in Leeds.


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PostPosted: 21 Feb 2010, 17:59 
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Froggy wrote:
...where abouts in Leeds are you? I'm from Birstall near Batley and went to school in Leeds.


North side. Estate agents probably gentrify where I live by calling it Monkswood, but I think it's really on the edge of Seacroft. However, Roundhay Park is just around the corner and open countryside is within about 500 yards of where I live.

Yorkshire and Leeds are both a 'foreign' country to me, but I've found I rather like the north east of England, particularly as you head even further north through the relative emptiness of Durham, Northumberland and up into the Borders. Slainte.


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PostPosted: 21 Feb 2010, 20:40 
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Yep...I'd definety rather be in Northumberland than North leeds!!

Thanks for your previous imput. Some of it went over my head but I get the general idea.


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PostPosted: 21 Feb 2010, 20:51 
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Sgian Dubh wrote:
Acid catalysed lacquer


Sorry to ignore all the good advice you're been given and obsess about terminology, but acid cat is another contradiction - if a reaction is being catalysed, that's not an evaporative finish. So those categories of yours sound more useful distinctions (if more clunky) than the varnish/lacquer one. Unless I'm missing some link somewhere.


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PostPosted: 22 Feb 2010, 23:04 
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Jake wrote:

Sorry to ignore all the good advice you're been given and obsess about terminology, but acid cat is another contradiction - if a reaction is being catalysed, that's not an evaporative finish. So those categories of yours sound more useful distinctions (if more clunky) than the varnish/lacquer one. Unless I'm missing some link somewhere.


Actually you're not Jake. I'm guilty of typing faster than I should have been thinking.

The evaporative finishes include shellac and nitro-cellulose lacquers.

The pre-catalysed and post catalysed lacquers (aka acid catalysed lacquers) are reactive finishes (as are the oil varnishes) and I should have been clear in my original post when I said lacquer that I meant specifically nitrocellulose lacquer.

The oil based varnishes dry from the top down by reacting with oxygen. The catalysed lacquers dry from the bottom up (which is like the evaporative finishes) and the solvents migrate upwards to the film surface and then out leaving behind molecules that then crosslink.

Incidentally, tung oil and linseed oil are reactive finishes that cure by reacting with oxygen, but these do not really form film finishes when cured. Wax on the other hand is really an evaporative finish because it is dissolved in turpentine or petroleum distillates to make the familiar soft paste. After these distillates evaporate all that's left is the wax.

I have a feeling the sloppiness between my thinking and my typing earlier may have caused yourself, froggy, and perhaps others confusion. I've half a mind to go back into my earlier posts and do some editing. On the whole I probably ought to leave things as they are and hopefully anyone reading the thread will get to this point and work out what I should have said. Apologies for the errors on my part. Slainte.


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PostPosted: 22 Feb 2010, 23:15 
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No need to apologise at all, and you didn't confuse me, I was really just pursuing my doubts that "lacquer" has any precise meaning, at least now, when it refers to all sorts of things.

Maybe there is a common link, which differentiates them from other finishes, but I have no idea what it is.


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