Picking the Right Paint: Blocking Test

I do a lot of painting in my shop. It’s a huge part of what my company does and I’m very particular about our techniques and materials.

I know that a good paint job is possibly the most pivotal way to protect your work, especially in the outdoors. When a paint job wasn’t done properly, wood starts to rot, doors and windows fail to open, the surface looks blotchy or covered in brush marks. There are a ton of ways that bad painters and their work can destroy an old house.

I’ve written in the past about the techniques behind getting a lasting and attractive paint job here:

How To: Paint Your Historic House…Properly

6 Secrets to Silky Smooth Paint

But, just as important as knowing the right techniques, you also have to use the right products.

For years, I have just relied on what manufacturers have told me their products do, but not anymore. I have been testing wood fillers for a couple years now and starting today, I am publishing my first tests on paints for you.

What is Paint Blocking

This test is an immensely important aspect of any paint I use. Paint “blocking” is an adhesion problem that occurs when two freshly painted surfaces stick to each other when pressed together. When the surfaces are pulled apart, the paint can peel and cause the other surface to pull away.

This is a big problem with doors and windows. Over time, the paint builds up and the windows become harder and harder to open until finally people give up and paint them shut for good.

Door are often mottled around the edges where they rest in the jamb from blocking. It’s unattractive and annoying to hear that peeling sound every time you open the door, along with the added effort required to operate it.

The Blocking Test

I mainly use Sherwin Williams paints because they are readily accessible and make, in my opinion, an excellent product. So, I decided to test four of the most common paints I use in my shop on a weekly basis to see how well they prevented blocking.

I do not receive any money or benefits from Sherwin Williams. These tests and results are entirely based on my own objective observations.

The Products

1. Porch & Floor Enamel

I’ve used this paint for a lot things, but mostly windows, doors, trim, and as the name suggests, porches and floors. It is a water based acrylic paint, available in Satin and High-Gloss. I used the Satin for this test. It is very easy to work with, lays down nicely, and doesn’t gum up my brushes easily.

2. Sher-Cryl

This is from Sherwin’s industrial line of paints. It is considered a high-performance marine grade acrylic. I figured that if it could be used to paint boats, it would hold up nicely in the wet Florida weather. It has some of the best adhesion I have ever seen in a paint. And it is conveniently water clean up.

3. ProClassic (Acrylic/Alkyd)

ProClassic has been around a loooong time. There is an oil-based, water-based, and the hybrid acrylic/alkyd, which is the one I used for this test. The hybrid gives you a water clean up with a hard cured oil-based performing finish. I use it mostly for trim and molding and sash interiors since it is not an exterior formulation. Of all the water-based paints I have used, this lays down for the smoothest, most brush free finish I have ever seen.

4. SnapDry

This is a new paint from Sherwin that really was what inspired this test. They claim it is extremely resistant to blocking and quick drying (2 hrs to re-coat instead of 4 hrs like most every other water-based paint) and still lays down to give you a nice smooth finish. I have found all of their description to be true in the last couple months since I started using it, but was curious to test the blocking.

The Test

I cut eight pieces of 1x common pine stock into small blocks and primed them all with an oil-based primer. After they were dry, I lightly sanded the primer with a fine sanding sponge and wiped off the dust with a tack cloth.

I then applied one fairly thick coat of each paint to two blocks, doing my best to get as smooth of a finish as I could. I let the paint dry for a full 24 hrs and then clamped the two blocks of each paint type together for 24 hrs.

I didn’t clamp them extremely tight, just bringing the clamp down so that the blocks were meeting and giving the trigger 1/2 a pull to snug it up.

After 24 hrs, I removed the clamps and checked to see how difficult it was to remove the blocks from each other and how much paint pulled away from the surface. I realize that the amount of blocking I might get for a specific paint may vary widely if I had only let them dry 8 hrs or had given them a full 7 days, but I felt that for my purposes, 24 hrs of drying time was the right timing.

The Results

Here are the rankings from worst to best.

4. ProClassic (Acrylic/Alkyd)

This one was a surprise to me because once cured, it feels so hard. But, after removing the clamps, it was extremely difficult to separate the two. It took an act of Congress and an aggressive 5-in-1 to pry them apart. The end result was a lot of damage to the paint surface. About 10 different spots were peeled and 6 or 7 of them went down to bare wood.

3. Sher-Cryl

When the clamp was removed, these two pieces had become one as well. It took about the same effort to separate as the ProClassic, but they finally did come apart. The damage to the paint surface was apparent in about 4 spots, 2 of which had pulled the paint off all the way to bare wood.

2. Porch & Floor Enamel

I was pleasantly surprised that there was no noticeable blocking. When the clamp was removed, the pieces stuck together briefly, but came apart before I had the opportunity to pull them apart. The surfaces were unmarred and the paint looked fine.

1. SnapDry

I figured it would be a good performer, but as soon as I began to remove the pressure from the clamp, the blocks fell apart onto the table. No marring of the surface whatsoever! It really does what they said it does.

Final Thoughts

This test was really designed to determine only one thing, and that was the blocking that occurs with each of these paints. I’m not saying that SnapDry is the perfect paint now, but I’ll certainly be doing some more testing to see how I might use it more in the future.

These tests are so important to my work and I hope you find them useful. I’m happy to do the work for you, just let me know what kind of testing you want me to do and I’ll see if I can make it happen!