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-   -   Does Primer need topcoat? (http://www.diychatroom.com/f4/does-primer-need-topcoat-98678/)

michaelcherr 03-17-2011 09:07 AM

Does Primer need topcoat?
 
This is probably a stupid question.
I know about the need for primer, but what does topcoat do?

Is it mainly aetshetic, or does it have a significant coating/protecting function?
This question is mainly aimed at interior paint, but I also recently had a section of an asbestos sided house painted primer only.
I manage rental units that get painted frequently. I guess I was hoping to prime, then paint a year later.

Windows 03-17-2011 09:36 AM

The main function of primer is to promote adherence between the old coating (or substrate) and the new finish coats. The finish coats provide decoration and protection for surfaces and provide other capacities, such as allowing surfaces to be easily cleaned. Many primer/finish coat systems are designed to be applied in close succession (often within a month of each other) for maximum effectiveness so priming and then waiting a year to finish coat may not be entirely a waste of time, you are definitely not deriving all the benefits from your coatings as you could be. In fact, depending on you substrates, and what type of old coatings you are covering, priming could actually be the superfluous step.

jsheridan 03-17-2011 09:45 AM

Primer serves the purpose of being the primary sealer of the substrate, and what bonds all subsequent coats of paint to the substrate. Primer bonds to the substrate, top coat bonds to the primer. It's the topcoat that actually provides the protection of the substrate against the elements. They each serve a purpose that the other, in general, does not. Certain primers will specify that if the finish is acceptable, it can stand with no top coat. (Hold on, I'm bracing for the coming flak). However, those are rare. That said, primers must be top coated, and most have a specified time in which that must happen. If the window closes, they'll recommend a new prime coat prior to finishing. Exterior is a larger concern to me because of the elements. We had a heated thread here recently where the topic of leaving primered ceilings unfinished was discussed. Personally, I couldn't see the problem with since ceilings take no abuse and have no element exposure. (hold on, here comes another round) I wouldn't leave the walls just primed though.

michaelcherr 03-17-2011 10:08 AM

These were the replies I expected: Just couldn't find it discussed. Thanks

DangerMouse 03-17-2011 11:41 AM

I've painted new drywall using NO primer, just Dutch Boy white, and 10 years later, it's still there...
It was in my old garage, so who cared? But still... why primer if it's not necessary? I guess we'll never know, huh?

INCOMING!!!! :laughing:

DM

jsheridan 03-17-2011 11:51 AM

The problem with finish over bare rock is a bonding one. Finish will not bond to bare drywall. If you put tape on it will pull finish. Probably not a problem in your garage, but could be in a customers living room. A lot of guys take that shortcut, two coats of finish and done. It could lead to a lot of headache over time.

Windows 03-17-2011 12:43 PM

Another problem with primer over bare sheetrock is sealing. Sheetrock is porous and absorbs the paint at different rates so your topcoats won't look uniform. If the space is unfinished like a garage, or you don't otherwise don't really care how it looks, then yeah, you could skip the priming. You can also apply a greater number of topcoats and eventually that will seal the substrate, but at greater expense, and as jsheridan points out, you may have adhesion issues.

Gary in WA 03-17-2011 01:14 PM

A good picture of what Wndows (previous poster) pointed out is here; http://books.google.com/books?id=lO8...um=9#PPA159,M1

This is why the drywall manufacturers have priming before texturing (A.1.3) and priming prior to painting (A.3.3); http://gypsum.org/pdf/GA-216-2010.html for their warranty.

Gary

Gymschu 03-17-2011 01:37 PM

I really can't explain why, but, as a painter, I just feel so much better about my work if I have primed before painting, especially drywall. Since I sand after letting the drywall primer dry for a day or two, it gives me a great surface upon which to sand. You can get interior walls as smooth as a baby's butt if you properly prime, sand, clean, finsh.

As for exteriors, I have used primer as a finish coat..........after a year or two it looked like crap. That finish coat has the binders, mildewcides, etc. to make it last......no sense taking shortcuts.....do you really save anything by doing so?

jsheridan 03-17-2011 01:39 PM

Gary, I've never seen a case of photographing that extreme before. Also, I read a page or two and he says he uses flat latex wall finish as a primer. I take issue with that advice he gives. I know that finish over bare drywall is a failure waiting to happen. How does he get away with that? The only finish I know that claims no primer is needed is Behr, and we all know how that goes over around here. I believe SW Duration says the same thing, doesn't it? No primer necessary. If I'm missing something about his advice, clue me in. Thanks,

DangerMouse 03-17-2011 02:20 PM

Quote:

Originally Posted by jsheridan (Post 611393)
The only finish I know that claims no primer is needed is Behr, and we all know how that goes over around here.

:laughing:

DM

Gary in WA 03-17-2011 04:49 PM

First three words of post #8....... He is a good drywall pro, though. I only had it in my library for the picture.... LOL, thanks for pointing that out! Now I have to read it......

Gary

chrisn 03-17-2011 06:58 PM

Quote:

Originally Posted by jsheridan (Post 611393)
Gary, I've never seen a case of photographing that extreme before. Also, I read a page or two and he says he uses flat latex wall finish as a primer. I take issue with that advice he gives. I know that finish over bare drywall is a failure waiting to happen. How does he get away with that? The only finish I know that claims no primer is needed is Behr, and we all know how that goes over around here. I believe SW Duration says the same thing, doesn't it? No primer necessary. If I'm missing something about his advice, clue me in. Thanks,


restraint, restraint, restraint :laughing:

Matthewt1970 03-18-2011 08:46 AM

Truth is, can you get paint to stick to drywall without primer? Yes. Will you have the same durability? No.

Ole34 03-18-2011 03:53 PM

let me explain it this way..............PVA drywall primer costs about $8 per gallon so what in gods name do you thinks in there ?? some mirical product that promotes adhesion and whatever else ??? lmao noooooooooooo its pure crap that's all it is an that's why its only $8 per gallon !!!!! if that crap actually did anything it would cost a hell of a lot more don't you think ??? like I said its cheaper then finish paint an that's why its used ...............I base coat with M.A.B wall sheild .........almost covers bare rock in 1 coat and ill give anybody $5,000 if they can peel it off after it cures lol . I find that flat finish seals the rock better then the so called ''Primer'' but whatever ...to each his own


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