A study of clears - part two

[mechman]

Part one is located here.

Work on the Black Widow paint project has taken up a considerable amount of my time as of late. And my keen interest in 'taming' the 3:1 mixtures has inevitably led me back to clear coats. Through many trips to home improvement stores I have always taken note of clears they stock. Home Depot stocks Behr 780 Matte Polyurethane and then the various Minwax products. Lowe's stocks Olympic, Valspar, Minwax, some Varathane, and other miscellaneous products. I could not find the American Traditions products described elsewhere in either of the stores close to me other than a clear gloss. All of the Varathanes at Lowe's are of the floor coating variety and only sold by the gallon for the cost of ~ $50. I mention this because as I was nearing the end of testing, benven mentioned that he used Varathane exterior polyurethane in his CGiv formula. While I haven't yet completed my search - I have a couple of Home Depots to check yet - I will keep looking and add an addendum when found.

So this brings us to an interesting point to consider right from the start. Exterior poly vs. interior poly. Exterior poly is used mainly as it has better UV resistance. That UV resistance will help in the long run from your screen shifting colors. Interior polyurethanes are less UV resistant than their exterior brethren. So what does that mean? UV stands for UltraViolet light. This light is produced naturally by our sun. It is also produced from black lights, mercury lights, and fluorescent lights. If you don't have any of these lights in your theater I wouldn't worry about using an interior grade poly. As to the sun, most windows will block a lot of the UV radiation from the sun.

		Ordinary window glass passes about 90% of the light above 350 nm, but blocks over 90% of the light below 300 nm. Source - Wikipedia

If your theater is like mine and the sun never hits your screen and yet you have a bit of ambient light, you can be safe using an interior polyurethane.

The other question is to the quality and opacity of the polyurethane. Behr 780 has been used for quite some time as it is the only matte polyurethane available that I'm aware of. I have two rolled coats of Behr 780 on my Wilsonart Fashion Grey screen to eliminate the hot spots. There are spectro numbers on both poly coated and non poly coated Fashion Grey laminates in the Master Screen Data Index. The one thing that a lot of people have noticed however, is that it tends to soften the image very slightly and if it's rolled on thick it yellows as it dries. This is even in a non UV environment. So where do we go from there?

On one of my many trips to Lowe's I noticed a Valspar Clear Protector. They come in gloss, satin, and flat finishes. They are located, as the Behr 780 at Home Depot is, by the faux finishes and are intended to be used as a protector for faux finishes. One thing they did not have was a matte finish, but that's easily remedied by mixing equal portions of both satin and flat.



The bulk of this investigation will focus on the Valspar Clear's (VCP) and flat/satin combinations.





This next graph shows how much of a change there was in each particular color on the Winter Mist panel.



mech

[mechman]

Initial testing of a flat topcoat on Black Widow.

"Why?" You might ask... well because one of our beta testers had created smudges on his samples with his hands. Smudges which I was able to recreate using my own hands on my samples. The difference being that it took quite a bit of rubbing (friction) for me to recreate it, but I could. Another potential issue was sparkles. So far I think we can write that off as an application problem - spraying. I had no issue with sparkles when I used a 1/4" nap roller. The few panels I did with a foam hot dog roller, however, there were some slight sparkles.

Another issue that we're still looking into is how to make the 3:1 mix better. If you had a chance to look at the 3:1 pictures, the panels exhibited graininess and areas which there appeared to be roller marks. I can assure you there were no roller marks.

So on to the initial testing. I took three panels and coated one half of each of them with Valspar Clear Protector flat.





As you can see from the above pictures it was a failure. While it eliminated any sparkles, it also eliminated any of the advantages that the aluminum offered us.

Here are some close ups:

This is a close up of one of the 3:1 panels. I took this in one of the areas that appeared to have roller marks



Here's a shot of half with no CCP and half with CCP



Here's a close up of a 3:1 panel - note the top left area and areas which appear to have roller marks

[mechman]

So what next? The only matte that I know of is Behr 780 and it's known to yellow!?!?!? Well I headed back out to Lowes and picked up another quart of the flat VCP and a quart of the satin VCP. I already had a gallon of Minwax satin Polycrylic. I also picked up a quart of Olympic water based satin polyurethane. I have yet to use the Olympic in any of the test mixes yet but intend to add it next week.

Now the question is why 50/50? Why not 60/40? And which finish ratio? So I donned the lab coat, carried my True Value Winter Mist panel out to the garage and started mixing poly's. I went from 80/20 down to 50/50 and varied the mixes from satin to flat. This was all done in Valspar Clear Protector. I then added a mix of 60% flat VCP to 40% Minwax satin and a 50% flat VCP to 50% Minwax satin.

On the left side of the panel we have:

1. 80% flat VCP / 20% satin VCP
2. 70% flat VCP / 30% satin VCP
3. 60% flat VCP / 40% satin VCP
4. 50/50 flat and satin VCP

On the right side of the panel we have:

1. 80% satin VCP / 20% flat VCP
2. 70% satin VCP / 30% flat VCP
3. 60% satin VCP / 40% flat VCP
4. 60% flat VCP / 40% satin Minwax
5. 50% flat VCP / 50% satin Minwax

[mechman]

Here we have the Luminous White 3:1 BW panel. On the right is VCP flat.

On the Left:

1. 50/50 VCP flat/Minwax satin
2. 60/40 VCP flat/Minwax satin
3. 50/50 VCP flat/satin
4. 60/40 VCP flat/satin

For BW it appears that the VCP 50/50 flat/satin is the most beneficial. After viewing these images though and completing the test, I believe it may be encouraging to try a 60/40 satin/flat combination as well. I chose the 60/40 flat/satin combo mainly because of the color shifting and the added sheen that more satin resulted in.

[mechman]

Conclusions

Looking at the numbers, it appears that the more flat the less color shift. For my purposes though (finding something suitable for a 3:1 BW), the higher amounts of flat is proportional to the amount it eliminates of the purpose of aluminum. And because of this and the amount of the color shift, I decided to try the 4 test areas on the LW3:1 panel. To me it seems the 50/50 VCP flat/satin would be the best option for a BW screen. If you're painting a screen that needs protection such as a neutral gray, you may want to stick to a flatter combination in order to retain the neutral qualities.

Let's just say that with the comments in this post and the comments in the post previously, there more than likely will be a part three to clear coat testing. And if I can wrangle up some Varathane, more than likely a part four.

mech

[mechman]

Still a bit shocked this one never caught on in any discussion...

mech

[muzz]

Looked like it turned it into a flat grey......

Not sure it's worth discussing much.

[Harpmaker]

There's a whooole lot of info to wade through here mech.

To tell ya the truth I got busy with my own experiments (and the new spectro) and forgot about it.

After re-reading some of this, it appears I should try to spray some LW/He558 3:1 and see what it looks like. How was this mix for neutrality?

[mechman]

While the testing was done on a 3:1 panel, the topcoat added nothing and subtracted quite a bit from the aluminum mix, as muzz said. The gist of the experiment was for those who required a topcoat for whatever reason. And how it affects the paint.

To me the most base neutral looking topcoat was the 50/50 VCP satin/flat. I still have this panel, maybe I should get some spectral response curves.

mech

[mechman]

I've let the Winter Mist panel sit out in the garage for 5 months and yesterday I put it on the hood of my truck all day long while I did yard work. Yesterday was a sunny beautiful day here with a temp of 82. It's time to check it for yellowing or color shifts.

This is the original chart I did 5 months ago:



I'll post up screen grabs of BabelColor. Both the pertinent RGB data and spectral curves. For the RGB data, a reading of the Winter Mist panel is on the right side. For the spectrums, Winter Mist is the black line.

All of these topcoats are of Valspar's Clear Protector in differing ratios of flat and satin. At the end I substituted Minwax Polycrylic Satin.

We'll start off with 50/50 flat and satin:





60% flat to 40% satin





70% flat 30% satin





80% flat 20% satin





The Minwax values - all satin ratios are the Minwax Polycrylic satin

50% flat 50% satin





60% flat 40% satin

[mechman]

The satin numbers

No more Minwax - all Valspar Clear Protector

80% satin 20% flat





70% satin 30% flat





60% satin 40% flat





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