Effect of temperature and/or humidity on CA finishes

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JimMc7

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Well, I have to admit I was a bit skeptical when I read reports that CA acted a lot differently depending on the temperature and/or humidity. I thought folks must be using a slightly different procedure each time. Geez, was I wrong.

Last night I finally switched to wet sanding CA with MM and got my best CA finish to date. I don't know the humidity but the temperature was ~75* F. I was so pleased I refinished a couple of my old pens this morning and great results, too (again, temp <80*F).

This afternoon -- with the temperature in the mid-80s and 60% RH in my shop -- I've tried to re-finish 2 blanks and I can't bring a shine to the finish at all using the exact same procedure as last night/this morning.

I don't think wood type is the variable either because DI, boxelder burl and quilted maple finished great in the cooler temperatures. DI and Amboyna burl I can't finish at all in the warmer temperature. I actually had a decent glossy finish on the 2nd DI which I wanted to improve and now it looks awful.

I'll wait until cooler temperatures and re-try but, for now, maybe I'll just stick to acrylics when it's hot!

Not really looking for a solution here (unless you have one!) -- just confirming what I previously didn't really believe re how temperature can affect CA finish success.

Edit to add: I'm sure some of you get an excellent CA finish at temperatures >80*F and I'll believe you. Just pointing out my particular procedure doesn't seem to work at temps >80*F. My new procedure is a combination of that suggested by Russ Fairfield with the MM usage suggested by "greenmtnguy" (aka Alton -- not sure I got the name/id right and I apologize if wrong). Now that I think about it....maybe I should adapt a procedure used by someone in Texas or Oklahoma rather than those in Idaho & Vermont!
 
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Welcome to the world of Chemistry! :biggrin: But moving to a bit of shade tree science: CA can BURN the fingers and catalyzes (for want of a better word) - gets HARD.

With CA - Heat = Hard, but not always does it get HOT before getting hard. (Get your mind out of the gutter :eek: :biggrin:) So, temp does affect the setting of CA. Take the temp down 20°F and it takes longer for reaction to take place - with all other circumstances being equal. I know that I have more open time with 5 minute epoxy at 50° than I do when it is 90° in my little shop. CA is similar.

Next - Moisture . . or, the lack of does affects reaction in different ways, and affects differently at different temps ; A weird fact: Acetone dissolves CA . . . BUT some accelerants use acetone to make CA cure faster!

Water boils at different temps, depending on the air pressure (altitude). Chefs know well that ambient temp and altitude affect the outcome of their products; changes in ambient and altitude require timing changes. Relative Humidity percentage greatly affects some cooking. Dry heat and Humid heat affect living organisms in hugely different ways. CA, other glues, paints, finishes react similarly and yet each differently - with the variables being temp, humidity and air pressure. My knee certainly can tell the differences! :wink:

There is another world out there at the molecular level. :wink: :biggrin:
 
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Thanks, Lee. Seems temperature is my most important variable. I tried the problem DI blank this morning with shop temp at 72* F and finish was acceptable -- not quite as nice as the earlier DI blank but at least I got a shine! I guess this just becomes a +1 to all the other "I hate CA!" posts. Maybe LOML will let me put a finishing station in the formal living room we just had to have that no one ever uses :smile:.
 
I have noticed at lower temps also. Usually cold enough you don't really want to be in the shop doing a finish anyway. At those times I notice the Ca does not seem to want to cure.
 
CA's "cure" via a base-catalyzed polymerization. Like all chemical reactions, the rate of reaction is highly dependent on the temperature (colder = slower). This is true for epoxies as well. For CA's, there are really two reactions occuring -- the initiation of the cure and the subsequent polymerization of the individual cyanaoacrylate molecules. The initiation process for the cure is that the small amounts of moisture on the surface of the wood are a strong enough base to neutralize the acid stabilizers present in the CA. In very dry conditions, this also means that the cure process is slower because the initiation is slower. Cold conditions are also usually quite dry, slowing down both the first and the second steps in the curing of the CA. Accelerators all act on the first part of the process. They are virtually always weak bases in a solvent like acetone. Once the acetone dires, a very small amount of the base is present on the surface of the wood, which then neutralizes the acid stabilizer in the CA once the CA comes in contact.

More than you wanted to know.......
 
Here is the answer Russ Fairfiled gave me about this topic; in last year I have seen that it is 100 % right. It dependes on the temperature and moister inside the wood.

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Cold will affect the time it takes CA glue to cure. The curing is an exothermic reaction, and the cool surroundings keeps the necessary heat from developing. Therefore it takes longer to cure. Some moisture is also required, and there is usually sufficient moisture in the wood and the atmosphere. But, there is the possibility that very old wood can be very dry, and that also would retard the reaction.
 
george said:
Here is the answer Russ Fairfiled gave me about this topic; in last year I have seen that it is 100 % right. It dependes on the temperature and moister inside the wood.

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Cold will affect the time it takes CA glue to cure. The curing is an exothermic reaction, and the cool surroundings keeps the necessary heat from developing. Therefore it takes longer to cure. Some moisture is also required, and there is usually sufficient moisture in the wood and the atmosphere. But, there is the possibility that very old wood can be very dry, and that also would retard the reaction.
Click to expand...

I guess that would explain the very very slow curing of my CA finish in the last week. I live in central California and last Monday it was 101 while Tuesday is dropped about 20-25 degrees. There is very little humidity and I had already put on a layer or two of CA on my blank. It is in the mid 60's when I get home and go in the garage to play. Sunday as I was applying the CA it started to make the paper towel smoke within about 7-10 seconds after applying (nearly burned my fingers a few times). Tuesday evening it was taking well over 30 minutes before I was comfortable.

Chemistry is a strange thing.
 
Use acetone to wipe the wood before CA, and accelerator to cure every other coat and it will solve all your problems (when done right). I've been CA-ing for almost a year now, and in central VA it's 30% RH in winter and 65%+ RH in summer. I've done good CA finishes from 55 deg up to almost 90 deg. with consistent results, probably due to using stabilized woods, acetone and accelerant. Try it!
 
Thicker coats of CA

Results are improving after practice by re-finishing 20+ pens. I think my biggest problem is applying too thin a coat and sanding through by the time I've finished polishing. Still not sure why the higher temperatures make the process more difficult -- could be higher temperatures means less viscous CA resulting in thinner coats.

Before, I put CA on a Viva paper towel and wiped finish on the blank. I've changed application method to dripping medium CA on the blank and gently wiping smooth, waiting 10 minutes between each coat. After 7+ coats, I wait another 45 minutes or so after the last coat before I sand/polish. Finish is much better and, so far, no flat spots in the finish.

New process takes a long time but at least I get a repeatable decent result. I'll keep tinkering to reduce time required.
 
JimMc7 said:
Results are improving after practice by re-finishing 20+ pens. I think my biggest problem is applying too thin a coat and sanding through by the time I've finished polishing. Still not sure why the higher temperatures make the process more difficult -- could be higher temperatures means less viscous CA resulting in thinner coats.

Before, I put CA on a Viva paper towel and wiped finish on the blank. I've changed application method to dripping medium CA on the blank and gently wiping smooth, waiting 10 minutes between each coat. After 7+ coats, I wait another 45 minutes or so after the last coat before I sand/polish. Finish is much better and, so far, no flat spots in the finish.

New process takes a long time but at least I get a repeatable decent result. I'll keep tinkering to reduce time required.
Click to expand...
You answered your own questions there.....too thin of a coating will cause you to sand through it. Your new process sounds great, but honestly, try using a spray accelerant with a light spritz every other coat and you'll only have to wait 10 seconds, no 10 minutes b/w coats and you can sand almost immediately. I do 8 coats or more of thin with my process.
 
BigguyZ said:
Does anyone else use aerosol accelerator? I really like the Fast Cap stuff that WC sells.
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I do. Almost everyone else I know uses the liquid stuff, but I love the aerosol. It's just so derned fast and easy. I use thin CA anyway though, so I hardly even need accelerator!
 
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