Both waterborne and solventborne coatings come in two varieties: reactive and non-reactive. The reactive variety of wood coatings contain catalysts. Catalysts allow the molecules in the coating to bond together much tighter. That produces a more durable, better performing coating.
|Sanding & Finishing Webcast
I watched the webcast, âSanding & Finishing: How to Get
Green,â and liked it so much that I watched it again.
(If you havenât done that yet, then you should, at
For shops large and small, the issue of white wood sanding
and sanding between coats remains the same. Itâs not
negotiable. The quality of work done here will either make
or break your finish quality, your reputation, and the success
of your business.
The meat of the webcast was not about sanding. It was
about âgreen.â Waterborne coatings are coming of age.
Watch for significant strides in coming months. â B.B.
Waterborne wood coatings have been available for years as either acrylic or acrylic/polyurethane blends. Non-reactive waterbornes, as their title states, donât react with anything. They just cure through evaporation, because no chemical catalyst to activate the curing is involved. We see these in both brush and spray-grade products.
Now, enter the new age of low Volatile Organic Compound (VOC) coatings. This is the result of an explosion in new resin technology. That, accompanied by the need to make the rather benign (and at times temperamental) non-reactive waterborne coatings perform at the same levels as good solventborne pre-catalyzed and post-catalyzed coatings and, voila, we have pre-cat and post-cat waterborne coatings!
Whatâs a Pre-Cat?
A pre-cat coating is one that arrives at your door from point of purchase with the catalyst already mixed into the pail. A post-cat is one that you have to mix in batches to add the catalyst just prior to application. The reason for the existence of the two forms is that catalytic reaction is finite in length. Once it ends, the coating no longer performs per specification.
In post-cats we talk about pot life. In pre-cats we talk about shelf life. Typical shelf lives are 12 to 18 months. Pot lives are anything from 60 minutes to 2 weeks. The âstrongerâ the catalyst, the shorter the pot life. In pre-cats, by contrast to post-cats, the pot life is so long that the product can remain on the shelf for a long time and still be good when sprayed out.)
This new generation of catalyzed waterborne wood coatings has been formulated to be reactive. There is now a catalyst involved, working much the same way as their solvent-borne wood coating relatives.
There are waterborne pre-cats that have the same significant shelf life that we see today in solventbornes. There are post-cats that require us to mix in batches and have performance characteristics that closely approach solvent conversion varnishes. With this silent explosion in the field of resin technology, I predict that we will see even further advances in the next few years that will lift the performance standards of these coatings even higher. Until next timeâ¦spray on!!! CWB
Bernie Bottens (WoodworkingNetwork.com/blogs) teaches wood finishing in industrial woodworking to shop owners, foremen, spray technicians and finishers all over the Pacific Northwest. He is wood finishing specialist with Louis and Co., Portland, OR. Reach him at firstname.lastname@example.org.
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