Please ignore the subject line. I meant to say shellac, not lacquer.
I live in south Mississippi. The humidity here is probably highest un the US.
I love shellac and have had good results wwith it but this time of the year the humidity is almost always over 85% and hot. I have a walnut cabinet I need to finish. I am a pretty fair woodworker but I know little about finishing. I have a really good HVLP conversion gun(Accuspray) and would like to spray on lacquer.
Would some kind soul give me some tips on how to pull it off in my climate.
Also, I know that shellac does not keep. However, I have some super blond flakes. Will I be able to use “old” flakes?
Edited 8/11/2006 5:31 pm ET by coolbreeze
Replies
Lacquer or shellac? Flakes are for shellac, lacquer comes in a can.
cool,
Adding a small amount of retarder thinner to the lacquer will help keep it from blushing. It retards the evaporation of the solvents, and thus the chilling of the wet surface of the finish, which reduces the chance of moisture condensing on it from the air. Retarder should be available wherever you buy the lacquer.
If you can stand it, turning on the heat in the finishing area will also reduce the chance of condensation by increasing the amt of moisture the air can hold (reducing the relative humidity).
Regards,
Ray Pine
Of all the things I have lost in life, I MISS MY MIND THE MOST!!!:-(
I meant shellac!!!! That changes the discussion entirely. Please don't go away just because I am a dufus for the day. I need help on Shellac.
Coolbreeze
Shellac flakes have a long shelf and should work fine if they dissolve properly to begin with.
Have you tried the shellac and gotten blushing? Shellac does generally dry more slowly that lacquers so you may be OK. You might help the process by mixing the flakes with Bekhol (from Behlen). This is denatured alcohol that has isopropyl alcohol added to slow the drying time. (Isopropyl alcohol sold as rubbing alcohol in drug stores probably has too much water in it to work well.)
A very small amount of gum turpentine slows shellac drying, but I am not sure this would help with the blushing issue.
Thanks, Steve, for your reply. I have used shellac a few times. Once I got blushing but expected it. I guess it would help for me to know what is the upper humidity range for using shellac and get me a hydrometer.
Dp you know at about what humidity will shellac begin to blush?
coolbreeze, I think the important element in the equation is the dew point. If you are spraying shellac (or any other solvent based material such as pre-cat) in high atmospheric relative humidity then only a small cooling effect will cool the air enough to bring it to the dew point-- in other words any further cooling and water vapour turns back into water.
In my experience with spraying pre-cats which use a faster flashing solvent than shellac does I found I'd get blushing problems if RH was in the region of about 75% and above. For example, if you're spraying pre-cat and it's 90ºF and 75% RH then cooling the air by approximately 8ºF down to ~82ºF will bring the air to dew point.
The question is, will solvent evaporation from a freshly sprayed part (at 90ºF) cause 8º of cooling at, or near, the surface of the wet film? If it will, then bloom is the likely result.
My guess is that spraying shellac at about 80%RH is likely to cause problems-- but it is only a guess. Now, I've sprayed a lot of shellac over the years too, but I've never had a bloom or blushing problem. However, I've always managed to make sure that I spray it when RH is not that high. But somehow when I've experienced blush it's always been with the nitro-cellulose family of polishes.
One trick I've used in the past when I suspect bloom will happen is to spray and immediately switch off the extraction. It means getting the hell out of the workshop for a while because of the stink, but still air will hold more water vapour than moving air. Slainte.Richard Jones Furniture
Cool,
HAR!! Extreme embarrassment will cause blushing, as well as extreme humidity ;?))
Blushing on a wet shellac film only has been a problem for me when I apply a real heavy coat, but I'm not in Miss. either. I'd try Richard's remedy, isopropyl, maybe combined with turning up the heat in the finishing room, and multiple thin coats, rather than fewer heavy ones. Or a de-humidifier...
Ray
Joiners work. One of the things about this forum is that folks will come all the way from the UK to help. I'm impressed. I do believe that is where RJ is from.
I really appreciate yours and Richards effort to help. I was telling my wife about the problem and she asked about using a dehumidifier. I have access to a good one. Can that be a remedy???
Indeed I am UK based, coolbreeze. But I lived in Houston for ten years and I'm quite aware of high relative humidity, high heat, spray finishing, and the problems that can ensue.
In theory a dehumidifier should help. But it would rely on you spraying in a room that's been dehumidified, i.e., you wouldn't suck in fresh outside air that is highly saturated. Of course, if you're spraying you'll almost certainly be getting new outside air through the use of an extract system of some sort that removes the fumes spraying causes-- new air has got to come from somewhere.
Here in the UK better spray systems incorporate heated make-up air to replace the air that is extracted. Heated air effectively lowers the dew point by lowering the RH. I'd say the ideal system for a very hot and humid climate would incorporate an AC system at the input end. An AC is a dehumidifier of course because it makes air feel cooler by removing moisture from it by passing damp air over cold coils-- engine radiators in reverse in effect.
In Houston my solution was to try and avoid spraying in the morning when the RH was it its highest. In the am RH would often be at 90% or above. By mid or late afternoon, RH would usually drop substantially, usually to about 50- 65%. Of course, if it poured down with rain at lunchtime, and my could it rain hard in Houston, that could put the kybosh on spraying for the day, even with a ton of retarder in the mix, ha, ha.
Incidentally, I'm not a big fan of using lots of retarder at spray time. Use too much and you can end up with the polish remaining in danger of imprinting for days, not just overnight or 24 hours. Slainte.Richard Jones Furniture
Thanks, Richard.
Bought me a hydrometer today. Another thing that worries me about trying a humidifier is that the one I am familiar with move air in all directions. Seems to me that dust particles would also be moving with that air. I am in the process of making a KD spray booth but this case is 6' X 24" X 30 something. Too big for my KD booth.
I'm thinking you mean hygrometer, what type did you get?
I've been looking at this one.
http://testproducts.com/safecart/product_info.php/cPath/93/products_id/212?osCsid=d0600188173af709d16ed80c37becb34
Since the house is on fire let us warm ourselves. ~Italian Proverb
Edited 8/12/2006 9:43 pm by dgreen
You're right!!! I gotta stop doing this when I'm dead tired.
Did you notice the way I started this thread? This is just more of the same.
Howsomever, Thanks.
It was an inexpensive one. Cost about $16. I plan on checking how it tracks with a high tech one that a friend has at the University here in Hattiesburg. If it is not accurate, I will take it back and take a hard look at those in the link you provided.
They have Oregon Scientifics wireless weather station and I've been looking at it too. It does indoor and outdoor humidity along with everything else and can be hooked to the computer for logging. They want $399.00 for it but Amazons got it for $219.00, mixed reviews. Think I'll price shop the hygrometer too.
Since the house is on fire let us warm ourselves. ~Italian Proverb
coolbreeze, of all the weather station instruments that can be purchased the hygrometer is probably the one that is least reliable in terms of accuracy. I don't hink you need to get too hung up on precision readings. After all, if it's humid you can tell it is without a hygrometer.
A cheap hygrometer will give you as close a reading as you need to confirm what your body is telling you. The one in the attached image cost £15 at a local electrical outlet-- it's even got a clock which is handy I suppose. When I lived in the US we got one similar for about $19 from Radio Shack.
The one in the attached image is hanging on the wall in my house. Each day I note the high and low RH and the high and low temperature noted during the previous day. I want to create a graph of the annual range of RH and temperature in a typical UK residence to illustrate a text I'm working on. I know it's not spot-on accurate, but the figures it will produce will be more than good enough.
I don't see how you can incorporate your dehumidifier into your spray set up as you described. I'm not saying it can't be done. The sort of questions in my mind are: can you channel the dehumidified air the machine creates: will it shift enough air to keep up with your extraction system (whatever that may be): will it take enough moisture out of the air to make a significant improvement?
I just don't know the answer to these questions because I'm not looking at the machine and don't know its specs. Slainte. Richard Jones Furniture
Richard, I know what you mean. I have no idea how close mine is to correct calibration, but I DO know the safe setting where I can spray without blushing (the lacquer, that is). I'm in FL, and we have our share of humidity.
I kept up with temperature and RH today on my new hygrometer. At 8 AM, the temp here was 72 and the RH* was70. as the day went on, the temp rose and the RH dropped. I just checked it at 6:00 PM (US CDT) and the temp in my shop was 89 and the RH was 62. At that temp and RH, my body would have taken bets on a higher RH.
* the reading for humidity. Always thought it was called Relative humidity.
The way I have stumbled through this thread with a faltering brain cell, I thought I should insert that footnote.
I plan to spray Tuesday if all looks fairly constant.
Good luck with the spraying and let us know how the comparison with the universitys meter turns out.
Since the house is on fire let us warm ourselves. ~Italian Proverb
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