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-   -   Primer vs. Flat paint (http://www.diychatroom.com/f4/primer-vs-flat-paint-25565/)

lovetrading 08-21-2008 08:08 PM

Primer vs. Flat paint
 
I have been reading the forum for few days now, It's very informative and was able to find answers for many questions I had in mind. Just to give you a little background about the project that I am involved in, I newly finished the basement of my 5 years old house. The drywall are up, mudding, tapping and sanding are done. Now I am in the stage of painting and hanging doors. From my reading it seems like SW is a good paint to use, and actually they are offering $10 off any purchase over $50 so, It's really no difference in price with other "Box" brand paint. I wanted to give it a single coat of primer and I read some where that using a Flat paint for first coat is actually better than using primer since the flat paint is better in hiding tape seems and other drywall flaws.

1) Is there any truth to that, shall I use latex flat instead of all purpose primer?

2) I do have a full bath room in the basement, do you recommend any specific type of primer or paint to use in there, I used regular drywall in the ceiling and walls, and cement boards on the walls of the stand-up shower, which I will cover with ceramic.

Thanking you in advance for your help.

Nestor_Kelebay 08-21-2008 08:55 PM

A flat paint can be used as your primer.

Flat white paint would hide an underlying colour better than a lot of primers, but I really don't see that it would hide tape seams and drywall flaws any better. You see, when you don't have sufficient hide in a paint, what's actually happening is that you're seeing the light that has travelled through the paint film, reflected off the substrate and traveled back through the paint film to reach your eye. So, you're actually seeing light reflected off the substrate.

When it comes to tape seams and drywall flaws, you're not actually seeing any colour. When you put a flat paint or primer on a wall, the extender pigments in both product will:
a) plug up the porous surface of the joint compound and drywall, and
b) make the product dry to a rough (or matte) film

You're eye doesn't actually see drywall glitches in a smooth surface like walls or ceilings painted with a satin or smoother paint. What your eye sees are differences in the way light reflects off that smooth surface, and your brain realizes that if light reflects differently there, there must be something different there. To prevent people from "seeing" that difference in reflection, building contractors will typically choose flat paints instead of glossier ones cuz flat paints scatter the light they reflect, thereby camoflaging any glitch or problem. So, if the customer doesn't see as many problems, he doesn't complain about the ones he doesn't see, and that means fewer problems for the contractor to fix.

So, I can see paint hiding an underlying colour better, but not hiding taping seams or imperfections better.

Since primer and flat paint will both dry to a matte finish, neither one should hide drywall problems any better than the other. Both have plenty of coarse extender pigment in them to plug up the porous surface of the substrate, so both should hide tape seams about equally well.

If it wuz me, I'd stick with a primer simply because when choosing a binder to use for a primer, the manufacturer will choose the binder that sticks well to bare construction materials like bare wood, bare joint compound and bare drywall. When choosing the binder to use for a flat paint, the manufacturer will also consider other things (like how hard it is to provide better scrubbability), which isn't something that's considered for a primer.

So, you can certainly use a flat paint as your own primer, but a separate primer is likely to stick better to the substrate than a flat paint would. On the other hand, paint has pigments in it, and is likely to hide the white colour of the substrate with fewer coats if you use paint as your primer. So far as tape seams and drywall problems go, I think they'd be about equal.

If it were me, I'd opt for the separate primer, but there is good logic in using a flat paint as the primer in the hope of having to put one less coat of paint on to hide the white colour of the drywall.

BAthrooms:
There's no special primer to use in a bathroom. Some people think oil based primers help keep the humidity in a bathroom from spreading through the house and fogging up windows and such, but that's really what ceiling fans are for.
Zinsser's make a really good bathroom paint called "Permawhite". It can also be used as it's own primer. (I've been told that directly by the sales agents for Zinsser in Canada; Mumby & Associates of Mississaugua, Ontario).
There really is no right or wrong. You can use a seperate primer in your bathroom. If you use a separate primer it can be latex or alkyd. Or, you can opt for using the Zinsser's PermaWhite as it's own primer. All will work. I suppose using the PermaWhite as it's own primer has the advantage of providing a larger reserve of mildewcide on the wall to keep the paint mildew free longer, but that would only hold true if you put on two additional coats of Permawhite. If you put on the same number of coats of Permawhite, the paint will remain mildew free for the same length of time with or without a primer under it.

lovetrading 08-21-2008 09:48 PM

Thanks for the detailed explanation, know I certainly have full knowledge to chose with confidence. Thank you again for your time and help with this questions. God bless your heart!

slickshift 08-22-2008 09:13 PM

Quote:

Originally Posted by lovetrading
1) Is there any truth to that, shall I use latex flat instead of all purpose primer?

No
Paints and primers have their specific jobs, and neither does well attempting each others purpose
Primers main functions are to seal and adhere
Paints are to color and protect
Although you can technically use a primer as a top coat (technically meaning you physically can, it won't explode or anything), it makes a very poor top coat
Same with using paints as primers
Technically you might "get away with it"...for a while
In a bathroom, the worst room of all for paints, it would be a very short while
Quote:

Originally Posted by lovetrading
2) I do have a full bath room in the basement, do you recommend any specific type of primer or paint to use in there, I used regular drywall in the ceiling and walls, and cement boards on the walls of the stand-up shower, which I will cover with ceramic.

A good premium acrylic primer, Fresh Start, Prep Rite, 1-2-3, and then a self priming bath paint, Moore's/Sherwin's K&B, Zinsser's Perma-White, or Aura, and you'll have the best bath paint job possible


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