Amine Blush/Bloom

Recently the weather here in Michigan has turned Winter Like. I am still in need of epoxying several components, Outer Sheer Rails, & Chine Logs, Seats, etc for my Drift Boat. So I moved the epoxy work indoors to a lower level room (partially in the ground) to do the Epoxy coatings to the individual pieces.
It's a finished family room insulated, carpeted, heated, etc. The temp with the heat on has been around 20* C (68*F), 65 % Humidity. The central furnace (source of CO 2) is in an adjacent room (no door).
So, here's my question, why am I still getting a stickey substance (Blush or Bloom????) on the pieces after 3-4 days in this heated room. Could it be just partially cured epoxy?
I have scraped it off, due to the fact that it just gummes up 80 grit paper if I don't. Could the furnace produce enough CO 2 to affect the result. Humidity and Temp are well within DOW's specs for this epoxy as well as West's recommendation. I am using Dow DER 331 resin and DEH 24 Hardner and using a 500 gram elec scale accurate to 0.1 Gram. Mixing for 2 mins per batch in yogurt tubs. Making ~ 60 grams per batch.
Any Ideas?

 

Heat increases air moisture (humidity )

"The best way to reduce blushing is to work in warm temperatures (the epoxy sets up fast, reducing the blush window) and with humidity at low levels. "

If you had a de-humidifier running, you would see a reduction.

http://www.yachtpaint.com/usa/diy/ask-the-experts/what-is-amine-blush.aspx

 

In spite of all the guidelines, for me blush is hit or miss.
Scraping works, but washing with a rag and water or a scrubbie is better, because it is easier to cover the entire surface.
Scraping as I have done it (large surfaces) has caused me to miss small areas, resulting in that absolutely putrid yellowish color underneath the next layer of epoxy or varnish.

Just wash everything you coat with epoxy when it is cured. You can sand then without clogging up the paper so bad.

This is another reason to fill all the cloth weave before stopping to let it fully cure. Trying to get blush out of unfilled weave is a fools paradise. I get little "pin hole" like spots of blush left even if I sand enough to ruin the strength of the cloth. Complete waste of time and money.

 

Use peel ply and never worry about blush again...

 

Unless you can absolutely control environmental conditions, you should assume you'll have a blush, which being water soluble is easily washed off. If you wash with a ScotchBrite pad, then you'll tooth up the surface, killing two birds with the same stone. Peel ply works, but has it's own draw backs.

 

A couple of questions,did this also happen in the summer in the shop?What was the humidity then?
Still sticky after 3-4 days?Doesn't sound like a blush problem.But I've never seen it so not sure.

 

The ambient temperature is sufficient to get a cure with DEH 24 after a few days, so maybe a mix issue, if still gummy.

 

Blush

Tunsten,
I am not 100 % sure it's blush. This condition wasn't occuring this past few months out in the shop. I don't know the exact humidity when I epoxied but didin;t do it during rainey days or the next days after.
The pieces are White ash, 1/2" x 1 3/4" x 13' & 16' Long. The stuckey stuff isn't consistent along the whole length. It seems to be stickey where the grain is somewhat distressed. This isn't quarter sawn lumber...
I am thinking it may have some influence by improper preparation. I have been using white terry cloth hand towels with solvents (Alcoh, Lac Thinner, Acetone) prior to coating wood with epoxy as opposed to while plain paper towels (West's recommended method).
I think the "Bounce" anti-static things we use to dry the towels after laundering may be putting Silicones in the fabric???? Also I have thought solvents were OK for removing blush and haven't used soap/ammonia as others above have recommended.
Anyhow, thing are going to change, PAR's simple method is the way it's going to be. I have sanded the above items and they are going to be properly preped prior to the next coat.
Thanks All for you input
Phil w.

 

I'm pretty sure "Bounce" uses animal fats, not silicone as a fabric softener. I don't know about towels, as I only use paper towels. The other half buys them in big lots, probably for me. I plow though a roll pretty quickly.

 

Blush/Bloom

on one site I read a paper which stated that if you let the mixed epoxy set a while prior to applying it it can/will reduce the formation of blush. Has anyone tried this, and did it work?
Just another variable, eh.....
phil w.

 

No, blush is formed as a reaction to the environment, so letting it "sit" in the mixing pot for a while, will just shorten the amount of working time you have. Which site made this ridiculous statement? Blush is a chemical reaction, technically it's the amine groups in the hardener reacting to moisture vapor and CO2 in the air, causing ammonium carbamate (the blush stuff) to form on the surface of the cured epoxy.

 

Amine Blush Cont'd.

PAR,
It took a while to find it today as it was the last place I looked (I origionally Googled Amine Blush). That was because it's in Dow's Technical Data Sheet on Amine Blush. Go figure.

Here's the direct quote, as follows: "Once the curing agent and resin component have been ixed together the chemical polymerization reaction starts. The further the polymerization reaction has advanced, the lower the chances of a reaction between the amine and the carbon dioxide and moisture of the surrounding air. Thorough mixing of the individual components and then leaving the binder to “rest” in the mixing container before application will accomplish this. The pre-reaction time, often referred to as the induction time, will react away most of the free amines (as these are typically the most reactive) and improve the compatibility between the resin component and the curing agent. Care has to be taken that the reaction does not advance too far; sufficient time should remain for the application of the whole batch"[I).
The link to the Dow Tech. Doc, Page 4
http://msdssearch.dow.com/Published...d.pdf?filepath=/296-01656.pdf&fromPage=GetDoc

I am thinking this might work by mixing small batches to avoid waste, but that makes the risk of ratio of hardener to resin more critical ( I have a 500 gram scale @ 0.1 Gr) . My enclosed room downstairs has a ceramic heater with blower and a de-humidifier in the adjacent furnace room. I can hold 80*F and 65% Humidity. I guess it's time to do some experimenting.
Let you know it works out.
phil w.

 

Induction time is a techniques used when working in cold and marginal conditions. This is done because the resin/hardener mix is more viscous and the chemical reaction takes longer to start up, compared to just mixing in normal temperatures. Not all hardeners are as prone to this difficulty as others and the usual route a pro will take is just a long er mix time. In normal temperatures (above 65) you can mix about a minute and get good chemical interaction. If colder, you'll need to mix longer, just to get the same level of mix, which is what forces the reaction to begin.

Every major formulator will tell you to warm the resin/hardener (independently) before combining and they'll also tell you to warm the work too. This makes mixing much easier and the reaction can begin quicker.

Now induction time is much more common in paints, which have several other variables to consider, but the usual choices in epoxy really don't need it, assuming a complete mix is insured, by some means (longer mixing times or warming the goo).

Smaller batches will not make much difference, unreacted amines will rise to the surface of the denser resin and interface with the environment. In most cases these sort of issues are procedure related, more so than goo formulation. Store your epoxy in a cardboard box and hang a 60 watt incandescent light, inside the box with it. This will keep the goo warm and lower viscosity, so mixing is quick and complete.

 

Amine Blush Cont'd.

PAR,
Thanks for your input. Your experience and knowledge is welcomed and appreciated. Tomorrow morning I'll do some controlled testing based upon your information and that of others on the posting.
The test samples will be a couple of pieces of raw Ash and a couple of the first ones that blushed (first coat) and which I scraped, sanded and and washed with water/soap/ammonia solution, and dried with plane white paper towels.
We'll see what happens.
thanks again,
phil w.

 

Skip the ammonia in future washings. I use dish detergent, I steal from the kitchen when she's not paying attention. Rinse well and dry. That's all there is to it. My procedure is to lightly scrub initially, with the ScotchBrite, lots of soap and water. I then get progressively more aggressive with the ScotchBrite, to get a good tooth and remove gloss, using less water and no soap. I could switch to wetdry paper at this point, but often don't.