Any paint chemists here?

[Willemjm]

We use a lot of Sherwin Williams Pre-Cat.

I purchase from their industrial outlet in Charlotte and always ask them not to add the catalyst, giving only 3 months pot life. So I add the tiny bit of catalyst 3oz per gallon ratio when I spray.

The smallest quantity one can buy is one gallon, so I always wonder if their pre catalysed lacquer with short shelf life is designed to sell a whole lot more paint, being the main reason?

 

[Mike Davis]

Not a chemist, but in the late 70s to early 90s I bought about $300 a month from Sherwin-Williams mostly high gloss enamel and One-Shot sign paint.
Your reasoning is solid, I believe they do everything they can to optimize sales even at the expense of the end user.

 

[cyclopentadiene]

Lacquer can be one of 3 types. Nitrocellulose is the classic chemical and has a long shelf life. It is hard to spray but provides a strong durable finish. Polyacrylics are considered lacquer and are easier to apply but have comparable durability. Catalyzed depend on the formulation but will polymerize on their own (slower)or with catalyst so the shelf life suffers. I have not looked it up but most likely the SW product is called a proprietary blend so it would be tough to answer your question. However, I am sure they have stability data with and without catalyst and will share this if you call

I am an organic chemist but my knowledge of coatings is limited.

 

[Willemjm]

Lacquer can be one of 3 types. Nitrocellulose is the classic chemical and has a long shelf life. It is hard to spray but provides a strong durable finish. Polyacrylics are considered lacquer and are easier to apply but have comparable durability. Catalyzed depend on the formulation but will polymerize on their own (slower)or with catalyst so the shelf life suffers. I have not looked it up but most likely the SW product is called a proprietary blend so it would be tough to answer your question. However, I am sure they have stability data with and without catalyst and will share this if you call

I am an organic chemist but my knowledge of coatings is limited.

 

[Mike Davis]

It says the customer can add the catalyst so you could buy the gallon paint and the 3oz cat and split them into 4 equal parts each.
Must be stainless or plastic container.

2 years shelf life before adding the catalyst.

 

[cyclopentadiene]

If you purchase and split, you may want to use Bloxygen before you seal the can. If the polymer is a polyacrylic, a small amount of oxygen could be enough to catalyze the cross linking of the polymers thereby shortening the shelf life they suggest when uncatalyzed. Generally oxygen is much slower than the catalyst but it could shorten the life by half of the recommended.

 

[marinosr]

If the product had a longer shelf-life, it would take too long to reach final hardness. I don't think there's a conspiracy going on... the product spoils precisely because it's doing what you want it to do, except it's doing it in the can instead of on your project.

I use MegaVar post-cat from Benjamin Moore and it is a good product that you add catalyst to at the time of application. The pot life is much shorter because it's designed to be mixed and sprayed, but it also hardens much faster than pre-cat.

 

[TB2]

Willem, I too spray Sherwin Williams pre cat lacquer but have been catting myself as needed. Asked Manager Dwight about the shelf life of the catalyst and was told indefinitely. You may know him. He was at Southern Pines store before the move to Rockingham. Hope he’s correct.

 

[cyclopentadiene]

I think most of these use a mild acid like p-toluenesulfonic acid as a catalyst. Generally the SDS sheets do not disclose exactly which acid. However, these molecules are extremely stable for years.

 

[Willemjm]

Thanks for all the responses.

I purchase the catalyst per gallon, comes in a plastic ( HDPE) jug. Then when I spray, around 1 1/2 table spoons of catalyst goes into my 24oz spray gun disposable container.

I have uncatalysed product over a year old, which still works just fine that way.

Initially, Sherwin Williams Industrial told me they cannot sell Pre-Cat uncatalysed as it is not a post cat. I managed to get them on board though.

I tried their conversion varnish which is a post cat, with up to 16% catalyst added for a while, however my results were not as good as with Pre-Cat. Their Post Cat is a more durable product, but it needs to be applied under perfect conditions, being temperature, humidity and industrial spray equipment, which is not suitable for our one off small jobs.

We typically spray the one or two doors which got damaged by the trades after our install or the one off items we could not purchase as part of an install.