Catalyzed Varnishes, Offgassing, and Odor

Occasional bad smells associated with conversion varnish, explained in terms of chemistry. February 23, 2008

I sprayed a set of cabinet doors with Valspar conversion varnish over Valspar oil base wiping stain. Luckily, I did not have to install these doors right away because I now have noticed that they have not lost the CV smell after days of sitting in my shop. The only thing I can think of which may have caused this is that the CV is having some kind of reaction with the stain. Of course I allowed the stain to completely dry out before applying the CV, and the CV has dried normally and looks good. I did not use any thinner with the CV since it comes quite thin from the can, so there's no way I could have unintentionally adulterated it. I have previously used Sherwin Williams over oil base stain and had no problems. Has anyone else had this problem?

Forum Responses
(Finishing Forum)
From contributor J:
All CVs outgas for a while - it's part of the curing process. Over catalyzing can make it worse. One thing about Valspar CVs is they do not all have the same catalyst ratio. The vinyl sealer, for instance, is 2%, not 3%. Valspar makes a number of different CV products, different VOC levels are given different names and product codes. Which products specifically did you use, and how were they catalyzed? Colder weather can slow down curing too, prolonging the outgassing. Another common cause is when cabinets are assembled after finishing but before full cure and doors left shut, trapping the gas and smell inside the cabinet.

If it was Valspar's Graintone Plus wiping stain, I doubt that had anything to do with it as long as the stain was used correctly and completely dry. This stain is meant to go under just about any Valspar topcoat.

From contributor D:
The smell that you are mentioning is the formaldehyde that is given off from the urea in the CV. Several companies today will use a low formaldehyde urea, and this will reduce the irritating odor. You will most likely find this chemistry with companies that have a history in Europe, as they seem to be more proactive in environmental issues.

It is unlikely that the stain has anything to do with the formaldehyde odor, as well as too much catalyst. Too little catalyst will slightly slow down the cross-linking of the co-resins, and the smell may linger a little longer. Too much catalyst will likely dissipate or form a slight haze on the surface. The catalyst is usually made up of nitric or sulfuric acid, or a blend of the two. The acid initiates the cross-linking of the hydroxyl function of the urea to the co-resins. These co-resins will likely be a combination of alkyds, lacquers, or acrylic. I have found that the CV that requires a diluted catalyst is easier to use because it lowers the error factor when measuring. It is easier to over-catalyze when measuring 2-3%, as compared to 10-12%.

As to cure, contributor J is correct - cold temps or humid days will slow down the reaction. I often will refrigerate leftover CV to use several days and perhaps a week later. You will find that good air movement and heat will cure this material quicker and minimize the residual odor. Time will eliminate this smell.

From contributor J:
I should have been more clear. Too much catalyst dissipates with an acrid, almost vomit type odor, often accompanied by a pinkish color shift and/or haze. This is a different smell than the normal outgassing of formaldehyde. In my opinion, companies that use a diluted catalyst are just trying to sell more product. A gallon of catalyst at 3% lasts a lot longer than a gallon at 10%. 3% ratios are not difficult to measure with reasonable accuracy.

From contributor D:
I'm not sure about the odor of over-catalyzing conversion products. I do know that the catalyst will cause a haze as the extra catalyst will have no hydroxyl functionality with the resin.

As to your comment to the level of catalyst, a 10% catalyst rate does not indicate a shorter pot life, it is just cut with solvent, most likely methanol. The value of catalyst is determined by the volume solids of the resin to be cross-linked. The pot life is not effected, because only a certain level of catalyst is required to complete the hydroxyl function. Companies that have a higher level of catalyst may not be trying to increase use. The catalyst is often cut in solvent to extend the shelf life and prevent the catalyst from oxidizing. Other reasons will include the handling of corrosive material, shipping restrictions, along with the selection of plastic containers capable of holding up to corrosive materials. Other issues may be the restrictions placed by other counties.

From contributor J:
I was not talking about pot life with a diluted catalyst. I was talking about how much is used (sold) per gallon of finish. A 10% ratio means you will have to buy over 3X the amount of catalyst for a given amount of finish than at 3%. And since the diluted catalyst is cut with solvent, this lowers the solids content of what you are spraying, leading to more coats necessary for a given mil thickness. Thus you have to buy more finish too.

Okay, this may not be much for the end user in the per gallon scheme of things, but think what it amounts to in sales figures per year for a company with a 10% catalyst ratio. And if it's necessary to use more catalyst that's cut with more solvent and spray more coats, I don't see how this is environmentally proactive.

From contributor D:
Contributor J, I can argue your comments by comparing cost per square foot coverage, however, I think that this would make no sense to you. If you think that any major paint company is reaping huge profits by increased catalyst ratio, then you are mistaken. I work for a major paint manufacturer, and I can't help but smile at your response.

From contributor J:
"I work for a major paint manufacturer, and I can't help but smile at your response."
One with a 10% catalyst ratio, no doubt.