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konsole 11-08-2010 12:59 PM

How paint primer actually works?
 
It seems to me that the properties of primer that make it stick better to unpainted surfaces and make paint stick better to it, can be introduced to the regular paint so if you have a smooth unpainted surface you can skip the primer, with maybe a bit of sanding. I understand the benefit of having something cheap to fill in the imperfections on the surface but if there are virtually no imperfections on the unpainted surface then a little sanding and then right to the regular paint seems attainable.

Is there a reason why regular paint isnt given the attributes of primer and if so then what is it about primer that makes it stick so well to unpainted surfaces and then the regular paint sticks so well to it?

Windows 11-08-2010 03:45 PM

Quote:

Originally Posted by konsole (Post 530857)
It seems to me that the properties of primer that make it stick better to unpainted surfaces and make paint stick better to it, can be introduced to the regular paint so if you have a smooth unpainted surface you can skip the primer, with maybe a bit of sanding. I understand the benefit of having something cheap to fill in the imperfections on the surface but if there are virtually no imperfections on the unpainted surface then a little sanding and then right to the regular paint seems attainable.

Is there a reason why regular paint isnt given the attributes of primer and if so then what is it about primer that makes it stick so well to unpainted surfaces and then the regular paint sticks so well to it?

Primer does not smooth and perfect the substrate, and acting as a binding agent is only part of its function. Many substrates (like drywall boards for example) absorbs paint at different rates altering the sheen and making them 'flash' and the finish look blotchy. Priming in this instance involves sealing the surface so the finish coat can be applied evenly.

As to how paint and primer achieve their goals - i don't rightly know. If I were to guess I would say that asking the finish paint to physically and chemically bond to the substrate, have good coverage, contain favorable additive like mildewicide, be (mostly) non-toxic, be affordable, look beautiful, and be durable is simply too much to expect from a single resin, so they offload part of the function to a primer.

DIYHelper 11-08-2010 09:06 PM

Quote:

Originally Posted by Windows (Post 530928)
Primer does not smooth and perfect the substrate, and acting as a binding agent is only part of its function. Many substrates (like drywall boards for example) absorbs paint at different rates altering the sheen and making them 'flash' and the finish look blotchy. Priming in this instance involves sealing the surface so the finish coat can be applied evenly.

As to how paint and primer achieve their goals - i don't rightly know. If I were to guess I would say that asking the finish paint to physically and chemically bond to the substrate, have good coverage, contain favorable additive like mildewicide, be (mostly) non-toxic, be affordable, look beautiful, and be durable is simply too much to expect from a single resin, so they offload part of the function to a primer.

This is a pretty good summary. The reality is there is only so much you can get into a gallon of paint or primer. The goal of paint is to impart color and have a certain sheen. This must be accomplished with a variety of pigments. To prime as well, the coating should have a high resin content. At some point it just gets to be too much. You see today though that there are self priming paints out there, but to get a true self priming paint, you'll probably want to spend the good money on it.

ccarlisle 11-11-2010 09:16 AM

The OP is probably one of several millions of people who, like several millions of people not too long ago, bought the marketing hype and became of the opinion that laundry detergents and fabric softeners should really be converted into one time-saving product...one cleans while the other softens.

A classic. Nowadays, marketing guys are coming up with something similar in putting out a product that paints and primes at the same time. And oddly, it comes out of the same genius stable known for their inferior paints albeit marketing successes. And I'm not talking BM or SW here...

Sure it's possible - but like the laundry detergent+softener fiasco, it is not chemically feasible unless you compromise on quality of both aspects: ie you can put a bad paint with a sort-of primer and get a $40/gallon paint-and-primer-in-one for the occasional DIY homeowner - you'll make a few bucks at it - but you'll never see pro painters line up for it at HD...

Right now, the state of the art of chemically formulating a 'paint' as we know it, is not conducive to putting lots of dense fillers (ie a primer) in the same can with lots of resins, carriers, pigments and additives (ie a paint) and have the product give you quality results on both accounts.

However, you can if you compromise and go for low-solids on the paint side - and low-solids on the filler side - of the equation...but 'low solids' is practically the definition of low quality isn't it?
:yes:

Matthewt1970 11-11-2010 04:48 PM

The paint with the primer mixed is is marketing BS. DIYHelper hit the nail right on the head "The reality is there is only so much you can get into a gallon of paint or primer." The stuff you need to put into paint to make it bind/seal the way it is supposed to leaves little room for color and sheen. Also a true primer should leave a somewhat porous surface for the top coat to bind to.

The reason they can get away with it is that 9 times out of 10 you don't need a primer anyways. Latex paint will stick to latex paint all day long. Where it will fail is on new drywall and glossy surfaces.


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