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-   -   Do I need primer after skim coat (http://www.houserepairtalk.com/f109/do-i-need-primer-after-skim-coat-8415/)

tractng 01-17-2010 04:34 PM

Do I need primer after skim coat
 
Hey,

Just spent the last 2 weeks skim coating my ceiling after the popcorn removal.

Do I need to primer before paint. It looks like the ceiling is smooth enough that I don't need to texture it (but I like to keep the option open). I prefer smooth ceiling :).


Tony

Nestor_Kelebay 01-17-2010 08:49 PM

I would prime before painting.

But, before you do that, you should check the ceiling by shining a bright light on it at a sharp angle to the ceiling. The sharp lighting angle will make any little bumps and ridges stand out like mountains, making them easy to find. Scrape them off with a tungsten carbide paint scraper (which are sharp enough to easily scrape off texture, but not sharp enough to damage plaster or drywall unintentionally).

PS: (you don't need to know the rest)

Most latex and oil based primers will call themselves "Primer/Sealer"s. The reason why is because in your case, you don't really need a primer, you need a sealer. A primer is a coating that not only sticks well to the substrate, but improves the adhesion of the top coat. A sealer is something that prevents fluid (gas or liquid) movement into or out of the substrate. In paints, both of these functions are accomplished by "extender pigments" which are huge rocks that are almost large enough to see with the naked eye. As the primer is drawn into the porous surface of the substrate by capillary action, it's those huge rocks that plug up the porous surface of the substrate (sealing). Those very same rocks are what cause the primer to dry to a rough surface, thereby providing "tooth" for better adhesion of the top coat (priming).

Since those huge rocks do both jobs in both latex and oil based primers, most primers call themselves "Primer/Sealer"s. Grout sealers, for example, don't have big rocks in them that cause them to dry to a matte finish unless they are advertised as Matte Sealers. If they are advertised as drying to a matte finish, it's because they do have those big rocks in them. They're still not primers because the purpose of them rocks causing the sealer to dry rough is NOT to improve adhesion of a subsequent top coat, it's purely esthetic. There's no top coat in the game plan.

Hope this helps.

tractng 01-17-2010 11:03 PM

Quote:

Originally Posted by Nestor_Kelebay (Post 39103)
I would prime before painting.

But, before you do that, you should check the ceiling by shining a bright light on it at a sharp angle to the ceiling. The sharp lighting angle will make any little bumps and ridges stand out like mountains, making them easy to find. Scrape them off with a tungsten carbide paint scraper (which are sharp enough to easily scrape off texture, but not sharp enough to damage plaster or drywall unintentionally).

PS: (you don't need to know the rest)

Most latex and oil based primers will call themselves "Primer/Sealer"s. The reason why is because in your case, you don't really need a primer, you need a sealer. A primer is a coating that not only sticks well to the substrate, but improves the adhesion of the top coat. A sealer is something that prevents fluid (gas or liquid) movement into or out of the substrate. In paints, both of these functions are accomplished by "extender pigments" which are huge rocks that are almost large enough to see with the naked eye. As the primer is drawn into the porous surface of the substrate by capillary action, it's those huge rocks that plug up the porous surface of the substrate (sealing). Those very same rocks are what cause the primer to dry to a rough surface, thereby providing "tooth" for better adhesion of the top coat (priming).

Since those huge rocks do both jobs in both latex and oil based primers, most primers call themselves "Primer/Sealer"s. Grout sealers, for example, don't have big rocks in them that cause them to dry to a matte finish unless they are advertised as Matte Sealers. If they are advertised as drying to a matte finish, it's because they do have those big rocks in them. They're still not primers because the purpose of them rocks causing the sealer to dry rough is NOT to improve adhesion of a subsequent top coat, it's purely esthetic. There's no top coat in the game plan.

Hope this helps.


Man do you have a PhD on this topic :).

I bought the Killz2
Shop KILZ 5 Gal. White Pigmented Interior/Exterior Water-Based Sealer-Primer-Stainblocker at Lowes.com


I normally don't use primer but since I have put so much effort into this job, I figure I might as well.




Tony

Nestor_Kelebay 01-18-2010 12:41 PM

Tony:

I've heard some people that used KILZ 2 weren't too happy with it, but I've never used the stuff myself, so I don't want to dis it.

For a job like this, you don't need anything special. Any general purpose (also called "PVA") latex primer would be fine.

bret 01-18-2010 05:39 PM

I use USG First Coat on my jobs.

SHEETROCK Brand First Coat Primer - USG Corporation

GBR 01-19-2010 03:16 PM

A.2.3 A drywall primer compatible with the texture material
shall be applied prior to the application of any water-based
texture.
A.4.3 Gypsum panel product surfaces shall be primed prior
to decoration.
A.4.3.1 Gypsum panel product surfaces to be painted or textured
shall be primed with a drywall primer compatible with
the final decoration.
A.4.3.2 Where paint materials are to be applied with an airless
sprayer, the sprayer manufacturer's and paint product
manufacturer's specifications for proper spray tip, application,
etc., shall be followed. Sprayed surfaces shall be back-rolled
for best results.
A.4.3.3 Wall covering shall not be applied to gypsum panel
products without first sealing the surface and allowing the
sealant to dry completely.
From: http://www.gypsum.org/pdf/GA-216-07.pdf

Be safe, Gary


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