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flyfisherman 01-05-2009 09:12 PM

Painting over 4 year old primer coat
 
Greetings all!

My first post to this forum:

I finished buliding a house 4 years ago...due to other projects and lack of time I never painted the walls and ceilings. The drywall just had a sand-textured primer coat sprayed on it by the drywall subcontractor. Anyway, now I'm getting ready to paint it. One of the guys at one of the paint stores said that I should probably reprime the walls since the old primer has likely "degraded" and is not sealing the wall like it would if it were new.

Have any of you ever heard of this before? Needless to say, this was not welcome news. I was hoping that I could just dust off/vacumn the walls real good and have at it.

I'd appreciate any advice.

Jim

Nestor_Kelebay 01-06-2009 12:03 AM

Quote:

Originally Posted by flyfisherman (Post 207673)
The drywall just had a sand-textured primer coat sprayed on it by the drywall subcontractor.

That concerns me cuz normally it's necessary to backroll sprayed on primer to ensure that it's forced into the porous surface of the paper and joint compound for proper adhesion. Do you know if that sprayed primer was backrolled? If not, you may have adhesion problems with it.

Take some regular (yellow) masking tape, stick it to the primer, and pull it off quickly. If the primer comes off with the tape, then it wasn't backrolled, and that primer isn't sticking well to the walls (and ceilings too, prolly).

Quote:

One of the guys at one of the paint stores said that I should probably reprime the walls since the old primer has likely "degraded" and is not sealing the wall like it would if it were new.
Don't seek his advice anymore. He doesn't know squat about the products he's selling. That primer is as rough now as the day it dried, and the underlying paper and joint compound is as plugged up as the day the primer dried as well. So, the primer is as effective as a primer and a sealer as it was 4 years ago.

Quote:

I was hoping that I could just dust off/vacumn the walls real good and have at it.
If you're a perfectionist like me, you'd clean the inside of exterior walls (that are likely to be the dirtiest due to something called "Brownian Motion") with a Magic Eraser to remove any dust/dirt that's settled into the rough surface of the primer. If you can see vertical lines of dirt on the walls or ceilings spaced 16 inches apart, and therefore revealing where the wall studs are, I'd definitely clean off those vertical lines with a Magic Eraser. But, if you see no such lines, vaccuuming the walls and painting over them would work too.


PS: "Brownian Motion" is named after the English botanist Robert Brown, who noticed that tiny pollen grains floating in water would appear to slowly move about when viewed under a microscope. Einstein investigated this phenomenon and was able to show that the pollen grains moved the same way as an object of equal mass would when it was being bounced around by the random impacts of much smaller objects. (That is, O2, N2 or H2O molecules hitting the pollen grains would make the pollen grains move.) Einstein reasoned that very tiny particles (like soot from burning candles) behave very much like large molecules, and would move when O2 and N2 molecules in the air bump into them. Similarily, such tiny particles would lose energy when they bump into a cold wall. And, when they lose energy, they stop moving and remain on the surface of that cold wall. THIS is why dirt and dust will accumulate over the studs on an exterior wall, and accumulate most heavily right over top of where the drywall nails or screws are located, cuz that's where the wall is coldest.

Ya gotta know about Brownian Motion to get your DIY'er arm badge in Painting.

If you don't see any such lines on exterior walls, then I'd be inclined to just paint over what you have. If you do see parallel lines of dirt over wall studs and ceiling joists, then you really should clean them off before painting.

http://www.aip.org/history/einstein/brownian.htm

PS2:
And, truth be known, it's too bad that you have to go so much smaller than airborne dust particles for quantum effects to become important. Otherwise we'd probably know more about the world we live in than we do.

flyfisherman 01-06-2009 10:10 AM

Great! Thanks for the reply! I did the tape test....it seems fine.

May you always have the Brownian Motion where you need it!

Jim

sirwired 01-06-2009 04:37 PM

If this was an exterior job, the bit about the primer "degrading" might make sense. But not in an interior, unless there has been actual damage or staining done to the primer. Certainly, if the primer has been extensively scrubbed or if it is stained, you will need to fix that up; but otherwise there is no need to reprime.

SirWired

slickshift 01-06-2009 05:09 PM

The old primer will be extremely "thirsty" and tough to paint and easy to flash
I'm the first to speak out against over-priming, but in this case absolutely prime first

Nestor_Kelebay 01-06-2009 07:51 PM

Slickshift:

What would change in the primer over 4 years that would require it to be re-primed?

If oil based and latex paints last well over 4 years between coats, why would the old primer need a new coat?


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