[Twister]

OK, so I'm painting a small closet with some wood baseboards. I need to prime the baseboards before I topcoat them. My primer is "Sherwin-Williams Premium Wall & Wood Primer".

The primer instructions on the can says, and I quote: "Premium Wall & Wood Primer is designed to sand quickly to a powder, in 2 hours. Use medium to fine sandpaper and lightly sand. Little effort is required for a smooth finish."

Question: this stuff goes on fairly smooth, so why would I need to sand it? In fact, do I "need" to sand it at all???

Do other primers say they should be lightly sanded before topcoating?

 

[SeniorSitizen]

It's thought latex base primers raise the grain on wood. Some wood seems to be more susceptible than others. SW is in a very competitive market and want their painted projects to look their very best to compete.

 

[Gymschu]

It's standard operating procedure for us painters. You DON'T have to if you're satisfied that it's smooth enough for your tastes. Most customers I work for want their wood work to be "baby butt" smooth so sanding is of the utmost importance, not only the primer, but between topcoats. So, having a primer that sands easily (and soon after drying) is of great importance.......if you want to get paid.

 

[Twister]

It's standard operating procedure for us painters. You DON'T have to if you're satisfied that it's smooth enough for your tastes. Most customers I work for want their wood work to be "baby butt" smooth so sanding is of the utmost importance, not only the primer, but between topcoats. So, having a primer that sands easily (and soon after drying) is of great importance.......if you want to get paid.

Thank you very much for the explanation.

Question: So how long is the window of "soon after drying"?

What happens if I were to wait something like 24 hrs?

Just curious...

Also, what grit sandpaper? Something in the 150-220 range?

 

[Nestor_Kelebay]

Thank you very much for the explanation.

Question: So how long is the window of "soon after drying"?

What happens if I were to wait something like 24 hrs?

Just curious...

Also, what grit sandpaper? Something in the 150-220 range?

There's no problem waiting a day, a week or even a month after priming before you sand. The only problem is not waiting long enough and having the still soft primer gum up your sand paper.

We've had this discussion on this board more than once. A primer will dry to a rough surface so that the top coat of paint sticks better. Sanding the primer might result in your top coat of paint drying to a smoother coat, but it's not going to result in the top coat of paint sticking to the primer any better.

The reason for that is that primers make the top coat of paint stick better by drying to a rough surface. That rough surface has greater surface area than a smooth surface, and it's that larger surface area that results in the top coat of paint sticking better. The paint has the same adhesive strength per square inch, but more square inches of primer to stick to results in a greater "apparent adhesion" of the paint.

Sanding the primer is going to make the surface rougher, but won't increase the surface area the paint has to stick to, and so the paint won't stick any better to sanded primer than it will to unsanded primer.

That is:

This surface:
/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\

is rougher than this surface:

wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww

but they both have the same surface area, so a paint will stick to both surfaces equally well.

 

[Gymschu]

"There's no problem waiting a day, a week or even a month after priming before you sand. The only problem is not waiting long enough and having the still soft primer gum up your sand paper."

+1 with a nod to Nestor

 

[Twister]

And 150 - 220 grit is OK?

Maybe I should go 180-220?

 

[Gymschu]

I like 220 just because it is a little finer and less likely to scratch the wood. 150 works too, but I just feel more comfortable with 220 with new wood.

 

[ToolSeeker]

+1 just the 220

 

[Twister]

OK, 220 it is!

Thanks, guys, for kindly getting me smarter on this! I'm off to go work in the closet!

 

[Twister]

Update: Primed the wood and then lightly sanded it. You can definitely feel the difference after sanding. Unsanded, it feels like the texture of a standard grocery story brown paper bag. Sanded, it feels as smooth as glass. Never would have thought I needed to sand primer before reading the label on this stuff.

So here's another question: I'm priming oak or ash (?)....lot of open grain and portions of the doorway wood trim are needing multiple coats of primer. I've already applied 2 coats of primer and I DID sand in between the 2 coats of primer. My question is, did I need to sand in between the multiple coats of primer or not?

I can definitely see sanding whatever is your top layer of primer, but what about in between?

 

[cdaniels]

Why 2 coats of primer?

 

[Twister]

Why 2 coats of primer?

Because the wood (think it's either oak or ash?) is very open grain and it soaks in the primer unevenly....lot of blotchiness/splotches in the primer. I can apply the primer smoothly and it looks nice when I'm done brushing on the primer in a certain area but then as the primer dries it developed the unevenness as the open grain soaked in the primer. This wood trim is like a giant hard wood sponge.

FYI, the un-evenness became less/looked better after the second coat of primer.

 

[ToolSeeker]

Primer is the wrong product. You need a grain filler it is not expensive and easy to use.

 

[Twister]

Primer is the wrong product. You need a grain filler it is not expensive and easy to use.

Hmmm....2 coats of primer is already on there. Heck, actually 3.....a sprayed primer many years ago by a contractor and now my 2 coats of primer applied via brush in the last week. What kind of adhesion should I expect with the primer? After my 2 coats it did fill the grain rather well.

And, in an attempt to get smarter, if one uses the "grain filler" instead, would your project then have to be primed after using the grain filler? I'm guessing the answer is "no"?

 

[Gymschu]

Twister, the primer is fine, especially if you are content with the look. As Toolseeker pointed out, grain filler is the right product to use IF you really want to ensure that you hide all of that grain. I've done it with one coat of primer and THREE coats of finish. You could still see hints of the grain, but it was barely noticeable. And, some people actually like some of that grain showing through. It's just a matter of taste. Wish I had some pics of some recent projects. Don't overthink this. You will be fine doing it as you are doing it now.

 

[Twister]

Gymschu -

Thanks for letting me know the primer will be ok. I purposely chose to not use the grain filler because I actually wanted a little grain texture showing. (When I get to my kitchen cabinets, that's a different story.)

Did you see my earlier question about the necessity of sanding in between coats of primer?

I will post pix later this afternoon of the 2 coats of my brushed primer compared with just the one coat applied via airless sprayer years ago.