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 Post subject: Lacquer Cure Time
PostPosted: Mar Thu 01, 2018 8:02 pm 
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Excuse me as I am sure this has been discussed before but I had no luck with search. How much time should be typically allowed before I rub or polish this finish out? There are two coats of sanding sealer and 5 coats of Watco semi gloss lacquer . Looks good but I want it smooth. Thanks, Bill


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 Post subject: Re: Lacquer Cure Time
PostPosted: Mar Thu 01, 2018 8:57 pm 
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Many factors involved, depending on where you live and the temperature etc ,etc, thin coats ? Think coats?
I live in sydney and its summer time.
Nitro i let cure for 5 days
Oil varnish the longer the better.
Just test it in a area that wont be seen, but you want a good dry surface to cut into so let it cure, although nitro does not technically ever cure.
Pete

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 Post subject: Re: Lacquer Cure Time
PostPosted: Mar Fri 02, 2018 9:49 am 
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Location: Sunnyvale CA
EX COT wrote:
Excuse me as I am sure this has been discussed before but I had no luck with search. How much time should be typically allowed before I rub or polish this finish out? There are two coats of sanding sealer and 5 coats of Watco semi gloss lacquer . Looks good but I want it smooth. Thanks, Bill



As long as you can stand it. I would be inclined to say a month, but it could be less if it is warm and dry. You *can* do it the next day, but you will be back doing it again later.

Brett


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 Post subject: Re: Lacquer Cure Time
PostPosted: Mar Fri 02, 2018 11:45 am 
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Where i live its summer, 40 degrees often thats 100c some days its too hot to spray. But you want it well and dry before cut it, or you will be stripping it again. It takes a long time to do either nitro or oil varnish.
But both are beautiful when done

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 Post subject: Re: Lacquer Cure Time
PostPosted: Mar Fri 02, 2018 5:42 pm 
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vintage pete wrote:
Where i live its summer, 40 degrees often thats 100c some days its too hot to spray. But you want it well and dry before cut it, or you will be stripping it again.


I am not sure what you mean by "stripping" it, but normally, the problem is just that the grain will pop back up as the material shrinks, and you have to cut and buff it again - not that the coating will have to be removed completely and the whole whole thing redone. Of course, if you go through to the wood in the "cut" part, then yes, then you have to redo the entire job.

Brett


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 Post subject: Re: Lacquer Cure Time
PostPosted: Mar Sat 03, 2018 12:10 am 
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If the surface is not dry and he buffs it , its going to be re-do.!
This is his first lacquer finish, if it gets damage ,he is not going to able to re-activate and patch up like you and i can. So it would be a complete re do if the lacquer is not cured .
That will depend on temperature and how thick or thin the nitro was sprayed.
Ive seen people who have never done it before and they spray one thick coat on not knowing any better. Lacquer is a nice finish, but temperature and coats must considered or you will get problems.

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 Post subject: Re: Lacquer Cure Time
PostPosted: Mar Sat 03, 2018 3:19 am 
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vintage pete wrote:
If the surface is not dry and he buffs it , its going to be re-do.!
This is his first lacquer finish, if it gets damage ,he is not going to able to re-activate and patch up like you and i can. So it would be a complete re do if the lacquer is not cured .


I think we are probably not quite communicating clearly, this is in no way controversial or out-of-the-ordinary.

You can easily rub it out the next day, it will sand and leave dust, and otherwise look good. What will usually happen if you do, however, is a few weeks later, all the grain will show back up, since the thickness in the pores is larger than on the surface, when it shrinks, it will sink and every grain will be a depression.

Normally you would want to wait until most of the shrinking is done.

Brett


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 Post subject: Re: Lacquer Cure Time
PostPosted: Mar Sat 03, 2018 4:04 am 
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Brett is 100% correct.

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 Post subject: Re: Lacquer Cure Time
PostPosted: Mar Sat 03, 2018 7:14 pm 
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Yes shrinkage I agree!
But as i stated in my first post cure times depends on many factors , location, temperature, application, Im in sydney where the temperature is often 113F its like an oven. This summer it was the hottest place on earth.
I dont get shrinkage on nitro after a week here. I also use Wattly which is not Available in the usa, but the principals are the same no matter where you are, nitro must be hard and cure before the cut.
If a person is doing his first nitro finish as above it is easy for him to cut ,sand or buff through the finish as he does not have the experience, if he did that , Than its a redo ,because he wont be able to patch up.
We must consider he has not done it before, has it got 3 coats on it or 10???
In a perfect world for nitro finishes we would let it cure for ages, but thats not always possible or practical .But i agree the longer it sits the better. Nitro actually never cures so what looks hard or sands lightly is deceiving because it can stil be soft.
Here where I live its oil varnish that you wait for ever for, not nitro so much but i only spray in summer.
Pete

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 Post subject: Re: Lacquer Cure Time
PostPosted: Mar Sat 03, 2018 9:51 pm 
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vintage pete wrote:
Yes shrinkage I agree!
But as i stated in my first post cure times depends on many factors , location, temperature, application, Im in sydney where the temperature is often 113F its like an oven. This summer it was the hottest place on earth.


As noted, yes, if it is abnormally hot and dry weather, it won't take as long. But right now, according to Weather underground, right now, it's 73 degrees and 86% humidity in Sydney, and assuming you applied it successfully without blushing and without retarder in other conditions - since this is FAR too humid otherwise - I would certainly wait at long as possible, because those conditions would result in very slow drying. Even longer if you had to use 10% retarder. The reason it takes a long time is the same effect that causes it to dry also causes it to trap the solvent. Compare this to an automotive clear where the flash-off of the solvent is much faster than the cure of the two- or three- part chemical reaction. Almost all of the solvent evaporates, then the finish cures hard.

I suppose the point is - one of the fundamental flaws with lacquer and other solvent-evaporation materials to one degree or another is that they shrink a lot, and for a long time, and nitrocellulose lacquer is one of those that shrinks the most and for the longest. This is inevitable because by the time you spray it, it might be 75% (or more) solvents - some that came in the original unthinned can, required to get it to be a liquid at all, and then whatever thinner or retarder you added later. That means whatever film thickness you have when it first hits the surface is 4x as thick as it will eventually end up when all the solvents have evaporated.

Note that is also important with toned lacquer, because the color tends to darken from the original instant of application. If you make it look just right while you are spraying it, it will get too dark over the next 8-12 hours as the pigment particles get closer together.

Bottom line, and as originally stated - you can do it any time you want, but the longer the better, and I would wait around a month for nitrocellulose furniture lacquer.

Brett


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 Post subject: Re: Lacquer Cure Time
PostPosted: Mar Sun 04, 2018 11:08 am 
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Summer in Sydney.
Spring Sep ,oct, november
Dry!
December, jan, feb summer
December is dry, January is dry,
The end of February is Humid.
On the 28th of February summer ends and its Autum. If i spray in the summer dont need to wait a month for nitro., if you do well thats what you have to do , I dont and ive been doing a long long time and i started spraying way back in the Acrylic car era and right through to 2 pak and from cars to furniture restoration.
So my system has worked well for me and continues too in the summer months and in my first post i made it completely clear that curing time depends on location and temperature and was in sydney not the USA and i dont have to wait that long!
Btw it Autum here now ! The turnaround for a nitro finish is slow at the best of times, if you have to leave every job for a month to cure before the cut, its going to be one very very slow business .
The furniture finishing business is terribly slow at the best of times , when we are dealing with the traditional finishes any waiting time i can save without causing a problem in the finish i do!
All the best pete

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 Post subject: Re: Lacquer Cure Time
PostPosted: Mar Mon 05, 2018 12:28 pm 
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vintage pete wrote:
Where i live its summer, 40 degrees often thats 100c some days its too hot to spray.

I hope you meant 100ºF.


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 Post subject: Re: Lacquer Cure Time
PostPosted: Mar Mon 05, 2018 2:30 pm 
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I can only agree with the at-least-a-month wait time. I've finished several guitars, and found the best thing is to just put it somewhere I can't see it so that I'm not tempted to go after it too early.


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 Post subject: Re: Lacquer Cure Time
PostPosted: Mar Mon 05, 2018 4:10 pm 
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johnnyreece wrote:
I can only agree with the at-least-a-month wait time. I've finished several guitars, and found the best thing is to just put it somewhere I can't see it so that I'm not tempted to go after it too early.


Exactly!

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 Post subject: Re: Lacquer Cure Time
PostPosted: Mar Mon 05, 2018 4:30 pm 
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Location: Sunnyvale CA
johnnyreece wrote:
I can only agree with the at-least-a-month wait time. I've finished several guitars, and found the best thing is to just put it somewhere I can't see it so that I'm not tempted to go after it too early.


That is far and away the hardest part!

Brett


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 Post subject: Re: Lacquer Cure Time
PostPosted: Mar Mon 05, 2018 7:26 pm 
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We used Lacquer paint at Van Masters when I worked there in the 80's. You can machine buff it in 15 minutes with a drying
boost from a heat gun. That was on metal, doubt if wood would be much longer to dry.

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 Post subject: Re: Lacquer Cure Time
PostPosted: Mar Mon 05, 2018 9:06 pm 
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glue_ru wrote:
We used Lacquer paint at Van Masters when I worked there in the 80's. You can machine buff it in 15 minutes with a drying
boost from a heat gun. That was on metal, doubt if wood would be much longer to dry.


With metal you have a constant film thickness, so 25% shrinkage is .001" everywhere. On wood, you might have .002 total on the high points but .020 on the low points (where the pores are). 25% of .002 is .0005, 25% of .020 is .005, so you have a a million little divots .0045" deep that stick out like a sore thumb, particularly if it is glossy.

I will add - I am hardly a world-class furniture refinisher but this is pretty standard basic stuff.

Brett


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