Latex for backgrounds on flat painted signs

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Mike Jackson
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Latex for backgrounds on flat painted signs

Post by Mike Jackson » Thu Jun 03, 2004 4:35 pm

Steve Vigeant called today to order a CD and was asking about latex paint. I know a lot of people use it for their backgrounds, but he pointed out something I notice here but has never affected us. When coating latex out on a flat board like MDO, it is difficult to get a smooth, even finish without roller tracks and blotchy areas. We use gloss black latex paint on the backs of our MDO signs because it is reasonably cheap and we can get three to four coats on in one day. Then we flip the sign over and prime the front with a couple of coats of blockout white and at least one finish coat--sometimes two.

However, when I look at the back side where we painted the black, I see a finish we could never sell if it were actually going to be the out facing side. We used to use latex A LOT on the sandblasted or carved wooden signs, but the smooth finish was not an issue on the textured backgrounds.

So, to answer Steve's question, what's the secret? Better paint? Better rollers? Paint additive to make it flow out? Spray coating instead of rollers? Only a problem if using gloss latex? Or just expect some flaws?

Thanks in advance,
Last edited by Mike Jackson on Fri Jun 04, 2004 7:55 am, edited 1 time in total.
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Steven Vigeant
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The latex in question

Post by Steven Vigeant » Fri Jun 04, 2004 12:42 am

I was attempting to use "the clients paint". It was low-sheen maroon. Inside I put on an almost perfect coat with a dense white roller (which by the way are impeccable for oil coats). I thought it would work well because dead flat white latex seems to go on super with these rollers. I installed the pre-coated boards which comprise a long run of panels and I wanted to hit them with one last coat. The coat was close to acceptable but still had some roller phase shine here and there. It has been dry in Berkeley but there was just no open time. I tried semi-gloss and it was worse. Zero open time. I admit I tried it in the sun at one point which of course didn't work.
The question is what is up with the zero open time? Can painting outside have a problem with internal board warmth? The thing was the clients door was brushed on with the semi and it looked great. I also suspect the dark color. (Paint that goes on pink and turns maroon gives me the creeps anyway) Can the tight foam roller be too dry? Has anyone had success perfectly coating boards with latex or Aquacote?
Thanks, newest member Steve

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Post by Danny Baronian » Fri Jun 04, 2004 1:54 am

I first started rolling latex with good success. I coat the panels out with a premium Sherwin Williams primer followed by 2 top coats of Sherwin Williams or Benjamin Moore paint, both exterior premium grade, rolled out inside or outside in the shade, never in direct sun.

Start with a 1/4 - 3/8" nap roller, sand with 220 grit between coats. If you want a smooth top coat, on the final coat switch to a foam roller. After the final coat, let the paint sit for 5 minutes - less if the temperature's hot, and roll over the whole board lightly with no pressure on the roller. Even much less if you live in Texas.

I currently have about 30 - 3 x 4' - 2 sided panels in the shop coated in this way with no variation, streaking or overlap lines. I've also tried several other methods to speed the process up - high end HVLP primer gun which requires too much thinning of the paint, conventional spray gun - too much overspray, and even bought a Wagner spray gun on the recommendation of another shop. The gun was too heavy and at times worked like a texture gun - laying down the paint with a heavy texture. Returned that for a refund.

All in all the best surface was with the roller. The trick is to get a good prime coat down with a longer nap roller, sanded then followed by a foam roller for a smooth surface. We've used both cheap and expensive rollers. As long as the rollers are clean and free of lint and don't shead, the cheaper rollers work just as well.
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Raymond Chapman
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Latex Paints on MDO

Post by Raymond Chapman » Mon Jun 07, 2004 4:59 pm

We use a lot of latex paints on MDO and have found little problem after the initial learning curve.

We use 100% acrylic paints made by Porter and ordered from Rhino Paint Co. - Gary Anderson in Bloomington, Indiana. He has special mixed some very deep, rich colors.

The paint is applied with a 3/8" nap roller cover (also from Rhino). Try not to overwork the paint or it will begin to get rough. Foam roller covers have never worked for us. In our Texas heat I had a little Floetrol which slows down the drying time and lets the paint settle out somewhat.

We have used Sherwin Williams and Benjamin Moore but have found that Porter is the best. If you plan to use vinyl on the latex it needs to be gloss or semi-gloss. You will get a much better finish with flat latex.

Latex paints can be applied with a HVLP gun if you get one with a large tip opening. David McDonald sprays his work with a HVLP.

Dan Seese
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Post by Dan Seese » Mon Jun 07, 2004 11:54 pm

I usually apply my latex paints with a HVLP. I do need to thin it with some water and some floetrol or airbrush additive but it dries quickly and with 2 or 3 coats it turns out very smooth.
Danny Baronian suggested sanding between coats when you roll. If I do need to sand, either with rolling or spraying, I like to use the green sandpaper made specifically for latex paints. It doesn't ball up with latex paint like other sandpaper (at least not as quickly.)

Doug Bernhardt
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Post by Doug Bernhardt » Tue Jun 08, 2004 10:04 pm

Just a quick aside....there are some great "no load" sand papers available. The green or very fine...probably 250 grit that Dan Seese referred to are especially wonderful if wet sanding. I'm still hooked on the oil primers and follow the old rules...2 primers (sand in between all coatings) and 2 oil gloss finishes. After long discussions with the local experts (Randall's) they recommended 2 oil primers followed by acrylic top coats. Flies in the face of everything I've learned ...BUT the job I tried it on 8-10years ago, still looks fine. (The acrylic colours were spec'd by a designer.)

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