Spraying BW...advice needed

[mrkln]

So I have my 90" screen up on the wall. I don't think that I would go this route again but I have a 1/2" piece of mdf screwed into the studs. I have sprayed at least 9 coats of Kilz on it to seal it up but I am having trouble with the paint laying down uniformly. At first I thought it was the mdf absorbing the paint but this many coats into it I'm not so convinced. I am running an HVLP gun and am much happier with the atomized finish as opposed to rolling but I just can't get a uniform finish across the screen. I have attached a shot that shows the non-uniform spray pattern (see the horizontal and vertical lines?). Looking straight on at the screen, you can't see anything and it looks great when projecting an image onto it, but with the projector off and looking at the screen from an angle, the spray pattern looks horrible. I want the screen to look as good off as it does on (sorry, I'm like that). I think my problem has to do with the narrow field of paint the gun is throwing down and me not making my passes close enough together. However, I'm worried about getting my passes to close together, not going straight up and down or left to right and creating runs by putting to much paint in one spot. I am using the 1.4mm tip and amrunning 40 psi at the gun with the trigger pulled.

My question is, does anybody have any recommendations for correcting my problem? If not, then I am looking at just rolling on the BW paint. I really want the fine finish of spraying but if I can't get it on uniformly, then what good is it?

Anybody with any thoughts or opinions? Here is my frustration. Thanks in advance.

[mechman]

How long does it take you to do the whole screen?

Do you have a work light set up off to one side shining on the screen at about a 30 degree angle? I use a twin halogen tripod light.

How much do you overlap each row?

My thoughts are that you're either not using enough paint or you're not overlapping your rows far enough.

The vertical lines have me confused...

[mechman]

Have you tried a projected image on it yet? Are these things noticeable?

[mrkln]

How long does it take you to do the whole screen?

It probably takes me just under 10 minutes to spray the screen. When I sweep the gun the spray mist appears to be about 8" wide but when you look at the width of the paint that is actually laying down on the screen, it appears to only be about 2"-3" wide. Is this about right? That would be a lot of passes accross the screen.

Do you have a work light set up off to one side shining on the screen at about a 30 degree angle? I use a twin halogen tripod light.

No. I forgot about that one. I am simply using the overhead lighting in the room. I read about using the halogens but I completely forgot about it. Oops.

How much do you overlap each row?

Well, I am overlapping the total fan that is coming from the gun by a couple of inches. However, like I said, there is the entire fan width and then a much narrower fan that is actually laying down a track of paint (I can see it from the reflection from the overhead room lighting).

My thoughts are that you're either not using enough paint or you're not overlapping your rows far enough.

I'm sure that you are right. I was/am just extremely leary of getting to much paint down at once and having a run. I guess the worst case scenario is that I would have to wait for it to cure so that I could sand the run down and respray it.

The vertical lines have me confused...

They are there because I was using vertical strokes with the gun as well.

Have you tried a projected image on it yet? Are these things noticeable?

Yes I have. The are not noticable at all. But like I said, I want the screen to look perfect when it is not on. The screen is in our living room so it will be a definate conversation piece when we have entertain and it isn't on. That and I'm incredibly about things looking perfect. Just ask my wife.

[Harpmaker]

I would recommend thinning your Kilz2 or Kilz Premium a full 40% with distilled water. The secret to getting a wide fan is to have the paint thin enough so the air will atomize it properly. I try to keep the gun about 1 foot away from the screen and move left and right at about 1 foot per second. If the paint is going on too thick and looks like it might run, just speed up the spraying motion to compensate. I have sprayed at up to 2 feet per second.

I recommend starting to spray at the top-right corner of the screen and move left until you get to the end, then drop down so your next row overlaps the previous one by 50 to 70 percent as you spray from left to right. Also, start your gun before you get to the edge of the screen so you have an inch or two of over-spray and keep spraying when you get to the other end so you have an inch or two of over-spray before you let to of the trigger. Also try to over-spray 1 or 2 inches top and bottom as well.

To help insure you don't get horizontal strips, after the coat dries and it's time for the next one OR if the paint is going on thin enough so you can immediately put on more paint without risk of runs, start the next pattern at the top-LEFT of the screen and spray to the right. This will help prevent putting down paint in the exact same place each time. At least it works for me.

Under NO circumstances should you spray up or down unless you adjust the gun to change the fan shape to spread horizontal instead of vertical!!! This would almost ENSURE that you would get vertical strips since you would have no fan at all going vertically!

Was the paint dry when you took that photo? It looks like parts are still wet. Always wait until the whole screen has lost it's "wet look" before putting on another coat.

Again, if the paint is going on thin enough so it looks like you can put on more paint after you have sprayed the whole screen, do so. I call this "making another pass" and sometimes I will spray 2 or 3 passes before it looks like any more paint would cause runs; that is the point where I say I have done a "coat". If you find that you have to do more than 3 passes per coat then I could recommend adjusting your gun so more paint is being pulled through the gun (usually this means opening the needle adjustment a bit).

[mrkln]

I would recommend thinning your Kilz2 or Kilz Premium a full 40% with distilled water. The secret to getting a wide fan is to have the paint thin enough so the air will atomize it properly. I try to keep the gun about 1 foot away from the screen and move left and right at about 1 foot per second. If the paint is going on too thick and looks like it might run, just speed up the spraying motion to compensate. I have sprayed at up to 2 feet per second.

Well, I had it thinned by 40% to start with but it was way to thin. Either that or I wasn't moving the gun fast enough. I guess for clarification, when you say that you thin by 40% does that mean that you add 4oz of water to 10oz of paint or do you add 4oz of water to 6oz of paint. I think that may have been my problem. I went with 4oz of water to 6 oz of paint. I then went to 2oz of water to 8oz of paint. That is what I painted the screen with. If the calculation is 4oz of water to 10oz of paint then I was spraying to thick as I was only thinning by 16%. I, of course, am mixing in larger quantities. I'm just stating easy numbers for clarification.

Under NO circumstances should you spray up or down unless you adjust the gun to change the fan shape to spread horizontal instead of vertical!!! This would almost ENSURE that you would get vertical strips since you would have no fan at all going vertically!

I did rotate the nozzle on the gun to change the orientation of the fan. I thought going the perpendicular direction would help uniform coverage.

Was the paint dry when you took that photo? It looks like parts are still wet. Always wait until the whole screen has lost it's "wet look" before putting on another coat.

No. The paint had cured about 20 hours. I was just trying to catch the screen in the light so that you could see the non-uniform finish that I am talking about.

FYI, I was only holding the gun approximately 6" away from the screen. I think that is also adding to my troubles.

Thanks.

[Harpmaker]

I guess that I should add that I have only sprayed with my single gravity-fed HVLP gun, and that while I have read books on spraying, and researched it on the 'net, I have learned to spray by experience and was not taught by a pro or a school etc. I just know what works for me with my equipment. I also learned that pressure at the gun isn't the only thing that affects how the paint sprays. I tried adding a water filter in-line right below the gun and it cut the air volume so much that I had to remove it.

I keep forgetting to define what I mean by thinning by 40%. My bad! Using you example, I add 4 oz. water to 10 oz. primer. I get that figure by multiplying 10 by 0.4. BTW, I find that I thin my BW mixes made with Behr or Valspar paint by around 30% (multiply the mix amount by 0.3). I never count my added water as part of the volume of paint I want to go on to the screen since it evaporates and doesn't stay part of the screen. It is only added to aid in getting the paint thin enough to spray without spitting. By thinning using 4 oz. water (BTW, I mean fluid ounces when I say ounces, I never weigh my paint ) to thin 6 oz. of paint, that comes to thinning 66.66% by my method of calculation; as you found, that is too thin (it should have made a wide fan though!). I haven't found a latex primer that will spray well though my equipment with only 25% thinning; the fan is short and it tends to spit and sputter for me. BTW, my gun is my avatar here.

I will admit to never trying to spray vertically. I would imagine that, I personally, would have problems trying not to tilt the gun slightly up as I move toward the top of the screen and slightly down as I approach the bottom of the screen. Since you are readjusting the shape of the fan correctly, I see no reason you couldn't spray this way if you can control that. No matter what direction you spray in the gun nozzle should always be 90 degrees to the screen otherwise more paint will be applied to the area of the screen that is closest to the tilted fan. In my experience, the slower you move the gun and the more paint you put down at one time the more little mistakes in 'gun tilt' and general gun position and movement will show up.

Due to space limitations, I have not set lights up at an oblique angle to my spraying area either, but have depended on a hand-held flashlight. I need to change that somehow.

From the sheen in your photo I would assume that you are using Kilz Premium (which I personally like), but I don't remember it having that much sheen; but then I usually only spray small test panels with it. Size does matter.

My guess is that if you were under-thinning the primer at 25% or 16% the mix would be so thick that your fan would be very short and you would have to spray with the gun very close to the screen. I think thinning with 40% water, as explained above, will fix that problem. Yes, less paint goes on per pass, but you can make several passes per coat and I have found that with the aid of a small box fan the screen dries to the point where I can repaint in about 10 minutes. Even thinning this much, I find that I can spray more paint than I can roll in a given time, and the result is almost unbelievably smooth.

[mechman]

Use a plastic fork to determine how thin the mix needs to be. When the paint drips from between the tines quickly, it should be thin enough. If the paint sticks between the tines, it's not thin enough.

I'd stay away from the vertical spraying.

You should have at least a 6" wide strip of paint if everything is done correctly. Mine is usually around 8-10" and I overlap 4 inches on each pass. Remember to start half on and half off the screen with your first and last pass. Hold the gun back a bit further.

After 20 hours the screen should have been dry. It takes 15 minutes or so for each sprayed coat to dry normally. This does depend upon humidity though.

What type of gun are you using? Is it a Wagner or a gravity feed gun with air compressor?

How much paint do you use after 6 coats? After 6 coats on my 100" screen, there was roughly 4-6oz left over from a start of 48-50oz. That's 32oz BB, 8oz AAA-F, and 8-10oz water. Harp needed more water than I did. That will all depend upon the gun and thickness of the paint from your local store. And you'll need more water for Kilz as that stuff is very thick!

It's good that you're getting this worked out with the primer coats! Get that light set up! It will help quite a bit!

[mrkln]

Harpmaker wrote:

I haven't found a latex primer that will spray well though my equipment with only 25% thinning; the fan is short and it tends to spit and sputter for me. BTW, my gun is my avatar here.

I believe you and I are using the same gun. I have a Harbor Freight (43430) HVLP gun and a 60 gallon compressor single stage compressor. Aside from the non-uniform finish, I am laying down a finely atomized and smooth finish. It looks much better than if I tried to roll it.

mechman wrote:

After 20 hours the screen should have been dry. It takes 15 minutes or so for each sprayed coat to dry normally. This does depend upon humidity though.

It is taking at least 45 minutes for each of my coats to dry. I have been waiting basically an hour to shoot the next coat.

mechman wrote:

How much paint do you use after 6 coats? After 6 coats on my 100" screen, there was roughly 4-6oz left over from a start of 48-50oz.

I wasn't really paying attention to the best of my recollection, I had probably gone through at least 60oz of paint in the first 6 coats. On the bright side, I'm sure I have plenty of base of to seal up the mdf.

Thanks for the tips so far guys. I would say that my paint mix was definitely to thick. I will work on thinning it up some and go for round 2 (or 10 but whose counting )

I hope to do a little more work tonight as long as I get the time. I really want to at least be done with the base by this weekend as I'm having some guys over to watch the fights Friday night.

[mechman]

mrkln wrote:

Aside from the non-uniform finish, I am laying down a finely atomized and smooth finish. It looks much better than if I tried to roll it.

Smooth finishes are overblown in my book. Not that you don't want a smooth, blemish-free finish. Just that it can only be achieved with an HVLP gun. Most of the high end screen materials from Da-Lite, Elite, Beamax, Vutec, etc. all have texture to them. The key to it is to make it uniform. It seems like the smooth materials are the cheaper products such as the CineGray and CineWhite from Elite and the Carada products. This isn't to say that these won't give you as great an image as the 'high end' materials. Just that there is texture out there and it's prevalent on some high end screens.

I've gotten some pretty smooth finishes with a 1/4" nap roller.