I'm doing some little sample panels for in the shop. Its 3/4" MDO (scrap). Normally I would "paint" the edge with Titebond II glue, then sand, then prime, then sand again, then paint.
Since these aren't going outside, I just primed one and painted it, and I skipped the prime and just painted the other one. The one that I just painted looks like it needs a second coat of paint, but the grain/edge didn't rise up as much, so it got me wondering...
Why bother to prime? What is the primer "doing" for me on bare wood? If i use two coats of paint, then my basecoat is the same as the top coat, and i get better coverage. with the 1-Shot, i have less sanding because the grain doesn't rise up.
I'm sure I'm missing something obvious, but I had to ask so I'd understand.
[ October 08, 2003, 11:22 PM: Message edited by: ScooterX ]
Posted by Richard Bustamante (Member # 370) on :
If you try to put a third and fourth coat you'll find that the paint just keeps on soaking through.
The primer is a barrior that keeps the paint from soaking in.
If your going to prime the edges with primer, the first coat should be sanded, and the second coat should go on smoothe. The third and fourth coat of enamel finishes the sealing.
If I'm not mistaken, TightBond II is not completely waterproof, and may fail after prolong exposure to the elements. (especially in San Fran)
Good Luck -Rich
Posted by Si Allen (Member # 420) on :
scooter...what are you using for a primer??
Posted by Jack Davis (Member # 1408) on :
Scoot, I think that the glue edge thing works well. It soaks in well and provides substance to the edges, but priming does the same for the rest of the project. The reason you have grain raising, is because the primer soaks in and gets a grab on the wood. It provides a grip surface for the OneShot. Without it, a moisture layer between the wood, and the OS can push the OS off later.
Posted by Ray Rheaume (Member # 3794) on :
Scooter,
I don't prime MDO boards. Never have.
I'm sure this is gonna raise a few eyebrows, but I've always looked at MDO differently. MDO has a laminate on it and I have always felt that your painting the LAMINATE, as opposed to only painting a wood surface.
Typically, I sand the edges scuff the surface with a scotch brite pad. After a wiping with a dry cloth rag, I roll on my backround paint right onto the board with a foam roller. No thinners, no reducers. I use a poly foam brush and tap the edges to "push" the paint in a bit, smoothing it where it gets over the edge and onto the surface as needed. I let it dry overnight, and the following morning the board will have a dull surface, like you described, since much of the paint soaks into the paper covering. I roll out a second coat and paint the edges again and can usually get a smooth, glossy coat. If not, I'll give it a few hours and apply a third coat while it's just a little tacky.
Latex is a definite "not in this lifetime" in my book. Every MDO sign I've ever had a customer bring in for me to "restore" failed because it was painted with latex and I won't use it on MDO.
For paint, I prefer not using One Shot for the backrounds. Typically I use Benjamin Moore Impervo paints, but when I need a special color, I use a good oil based paint (always by the same manufacturer) and can typically mix them to get the color I need.
Why no primer? I have always felt that some primers tend to just sit on the laminate and not really get a good "bite" into it, so, in all honesty, I just gave up on priming MDO years ago. Like painting a bare metal surface, many failures occur when you don't use a self etching primer and get a good adhesion to the metal. I figure why not just soak the paper with paint. The first coat of paint is my primer and I know it's gonna dig right in and grab the laminate. The second coat and/or third is gonna be for looks.
I know it's probably not "technically sound", but I have found it to work well. Never had a sign fail to date, and many have been holding up to this New Hampshire weather for 10 or more years.
My 2 cents... Rapid
Posted by Ron Percell (Member # 399) on :
primer is cheaper than paint and is also a good filler, that is why it is used first.
You can coat the edges with one shot, but it will take at least 3 coats, and some folks prefer 4.
Posted by Suelynn Sedor (Member # 442) on :
hmmm....I always thought primer was a prep coat to assist the paint in adhering to the background. I'm interesting in learning more.
Suelynn
Posted by ScooterX (Member # 2023) on :
Interesting discussion. Here are answers to some of the questions:
I've got about five different primers on the shelf. I want to try the Jay Cooke primer, but not until i use up some of the ones I have. I have the 1-Shot acryllic bonding primer, Zissner 123 Primer (water based) and Zissner CoverStain (oil based). I used the 1-2-3 on the recent job because it was tinted blue, and i was painting with blue paint.
I hate sanding primer, and wish it would level out better. It never seems to fill any scratches... it just leaves brush marks (if i brush a small area).
i never feel comfortable painting the 1-Shot over the primer until the primer is REALLY dry, and that means I end up waiting about as long as i would have waited before putting a 2nd coat of 1-shot on over itself.
As for pricing... the Jay Cooke primer is $8.25/qt and black or white 1-Shot is $8.59... not much of a savings... just an extra brush to wash.
I buy my MDO pre-primed (I don't use that much of it, so its not much savings to prime it myself), so all i have to do is the edges.
Posted by old paint (Member # 549) on :
being an old car painter and sign painter not using a primer is not a smart move. i swear by KILZ for wood and the house/home painting. ZINZER BULLS-EYE in good for furniture(all we used in wood shop in high school) not puting primer on metal your askin for failure!!!! with KILZ i coat out MDO, let it dry no more then an hour and either paint with a roller, an oil based background color, here we have a paint called NAM-E-LAC, and its the best for sign backgrounds. or i use automotive A/E as a top coat and spray it on the MDO. i can by prepainted mdo now....and usually do now.
Posted by Randy Campbell (Member # 2675) on :
I think a lot of people are in to much of a hurry to finish the signs.If you can't wait for the bluddy paint to dry do it in vinyl or spray the boards with a fast drying arisol.Don't use wood.I get a Latex paint with primer already in it.
Posted by Kelly Thorson (Member # 2958) on :
I was told that a primer contains binders which adhere to the substrate. I did a sample sign for my shop without it with alkyd paints and it peeled badly in a couple of years. To tell the truth the first signs I did - about 14 years now are still not peeling - the paint is getting quite chalky though. Those signs were painted with acrylic primer and Alkyd paints. I later switched to alkyd primers and alkyd paints, and those signs are peeling although they are up to 5 years newer. They have however stood up satisfactorily. I have recently switched back to the acrylic primers because time has proven them better in this environment. They are nicer to work with as well. I always try to let them dry a good day before painting with the oils. Just my opinion based on my experiences. Posted by Ron Costa (Member # 3366) on :
It is my understanding,that in the olden days, carriage woodwork was primed with a linseed oil process which took days to complete. The idea was to get as much penetration into the wood so that each layer grabbed hold of its predesessor. These were followed by filler coats and finally colors and varnishes. No one can afford that kindof time anymore unless you're into authentic restoration. I always use a primer designed for penetration and sealing.
Is that how it was done Si??
Posted by Mike Languein (Member # 319) on :
The best primer I've found is a 50/50 mix of Ronan Background White Enamel and Dana Blockout White. The Dana provides tooth (to grab the next coat), stops seepage into the wood and the Ronan allows more flow-out time. The only failures I've had were from trying all those other 'primers'. Of course now without any lead nothing will last very long. I never use any water base paints if I'm doing a nice job - it won't flow out and you can't sand it. Strictly for rush jobs, bang outs, and faux antiques.
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