Loss of Viscosity in Coatings on Storage

Manufacturer: I chanced upon your website by accident and am amazed by your effort in helping the latex industry in overcoming many of the common problems encountered by manufacturers. We only hope that there are similar consultants online who could also help us in the coating industry.

Since I'm already in your site I thought I should try my luck in throwing a question to you too.




We manufacture coatings and paints based on cellulose lacquers and Polyvinyl acetate/acrylics emulsions. Our problem is the loss of viscosity on storage. Any idea what causes this?

John Woon (Senior Latex Consultant): I'm no expert in coatings. However, certain aspects of the basic science and technology of latex are also applicable to the coating technology.

Let me make an attempt in answering your question and hope you'd find it useful.

1) Some cellulose lacquers are prone to loss of viscosity on storage. This might be inherently due to the base material - cotton. However, this only happens initially after production and it would eventually stabilise at some point. If higher viscosity is required, I suggest you start off with a higher viscosity.

Some basic salts in pigments (or even acidic materials) might degrade the nitrocellulose molecule and hence causing a drop in viscosity.

2) When pigments are not sufficiently wetted or the wetting process is too slow, the paint may lose viscosity as wetting proceeds during storage.

3) As regards the reduction of viscosity of paints based on emulsions (e.g. PVac latex), the cause could be the degradation of the thickening agent by bacterial attack.