What you really need to understand about Paint Shrinkage

above is our Direct to metal and rust 2K urethane primer after 7 years of outdoor testing. 

Paint shrinkage

There was a video that someone tried to put on the 411 page supposedly showing the differences of shrinkage of primers.  They compare Tamco to other primers.   I didn’t allow the video to go through because people who do so-called shrink test are basically comparing apples and oranges and have no concept of what they are doing.  Youtube is full of videos that purport to be factual, but in reality, are junk science.

R.e0e154513a654c94ff62aeb94c80ea74Product can only shrink to the degree of solvent that has been added to it either in the formulation or what is post added before spraying so to determine shrinkage on any material all one has to do and we do this in the lab at all times, is do a drawdown of the product.  Spraying a product will not give accurate results.  We mix the product as per instructions. We add no solvent. We then use a draw down panel that measures exactly 4 Mils. You then then you bake it for 1 to 2 hours at 200°

You take it out and you do two things: One,  you do a mill reading to see what it will be and you also do a weight reading because there is a difference between volume solids and weight solids and honestly weight solids are not as important as volume solids here because sometimes weight can have heavy Solvents in them heavier than the resins in the solids. For example Oxsol,  a low VOC solvent that’s mandated in California paints, weighs 11 1/2 pounds per gallon!  Almost twice the weight of other solvents and since that leaves the film the weight of the product is misleading compared to the volume of solids

That means our HP 5310 has a volume solids after catalyzed a 45%, it has a weight solids after capitalization at. 57%. The primer itself is 65% solids before mixing.

This means that 10 mills of our primer, Will end up being 4.5 mils. (volume) and weigh 57% of the initial weight.

The problem with these tests you see on YouTube is there is no scientific principles being applied.

First of all they’re spraying the product and there is nobody that accurately sprays evenly.  Also, they fail to mention if the ADDED solvent! How much they reduce the product in order to get it through their gun when we do a test we mix at 4 to 1 and we do a draw down we don’t spray it that’s your accurate reading.

If you load it with solvent in order to spray it through your gun the product is going to swell when wet --- the Talc and the clay will actually grow so you’re going to get a false millage reading higher than it really is.   The Internet is full of misinformation and downright lies, so no I didn’t let the video go through but I’m explaining anytime you see a video you will know that most of them are based on false science and deception.

The next point that’s important to know is what is called shrinkage is not shrinkage. Real shrinkage is the evaporation of solvents that occurs after the product has curedand continues to lose volume and that is usually a formulation of a product that is not chemically put together correctly and a full cure is not occurring and this happens in many peoples primers and that’s why you see sand scratches come through 2 to 3 months later, something you will never see it happen with Tamco epoxy or urethane primers.

The choice of resins also may lead to post curing shrinkage. Most primers are made from Alkyd enamels which actual can continue to shrink for months. The resin we use.  From the Data Sheet

Key Features

  • Excellent Flexibility
    • GoodWeatherability
    • GoodWaterResistance • Low Shrinkage

Urethane paint must be made to a formula which results in 100% curing within a certain amount of time and a certain temperature.   If the primer is way over catalyzed or under catalyzed there will be problems in the long-term shrinkage of the product.

I have sprayed 5310 over 180 grit scratches on steel panels with unreduced three coats of primer at 75° allowed it to sit three full days sets and took a mill reading and three coats of primer that had a wet mils of nine to ten BUT had a dry mill a 4.7 to 5.0.

However, what is the real important test here is 60 days later a second mill reading was performed and it was still 4.7  to 5.0 mils, meaning no further shrinking after curing.

That is what’s important in a primer -- not these tests do you see on YouTube

Paint shrinkage