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Quick Tip: The Unifying Coat of Primer

The Importance of Priming Even Pre-Primed Moldings

how to paint moldings

After applying a unifying coat of primer on our half bathroom moldings. Before and after pictures below.

[This is part of our How to Paint Moldings series.]

Even if all of the flat-stock and moldings you installed come from the factory coated in primer, you still need to apply a final, unifying coat of sandable primer before you apply your first finish coat of paint.

Here are my four reasons why.

1.  To Cover Bare Wood or MDF

This one is obvious, but you need to cover bare material before brushing on a finish coat of paint.

before and after molding pictures

Primer will: cover bare wood, bare mdf, spackling on gaps and nail holes.

2.  To Cover Spackling or Glue

The spackling you used to cover all of those nail holes, gaps and gouges, will show through your two finish coats of paint as a rough or dull spot.  So they have to be covered with primer.

how to paint large baseboard moldings

Before: A cope joint gone bad that I filled with spackling.

Likewise, any glues that seeped between your moldings or were smeared on their surface, need to be covered with primer, otherwise those spots may show through your finish coats of paint.

how to prime moldings

After: The same cope joint covered in spackling. With a little more attention, you’ll never see the filled joint after I’ve painted it.

Below  All of the nail holes you filled with spackling and then sanded will need to be covered with primer.

Rather than trying to spot-prime only the nail holes on pre-primed moldings, just cover the whole thing with a fresh coat of primer.

how to fill nail holes in moldings

Before: Spackling over nail holes will be sanded and then primed over to create a unified surface.

how to prime diy mdf moldings

After: The same nail hole after being sanded and then primed over. Can you see the hole now?

Eye-Level Flaws Need Extra Attention

The two before and after pictures below show a nail hole in the wall frames that appears right at eye level as you exit the room.  It’s hard not look at this spot.

So this nail hole and others like it should get a little extra attention.

how to prime mouldings

Before: Nail hole that has been filled and sanded.

Below  See how the nail hole is still just barely visible after I’ve covered it in primer?

It’s just possible that after sanding the primer and then applying two finish coats of paint that divot may still show through.

And I can’t take that chance.  Not when it’s right at eye level.

So I will apply a spot coat of primer here and then sand it again.  That should take care of it.

how to prepare mouldings for paint

After: The same nail hole now barely visible. It may need a little more work before it’s perfect.

3.  To Fill Small Gaps

Most seams between wall and molding or between two moldings will need at least some caulk to fill them after your primer coat is applied.  But not all of them.

how to prime mdf moldings

There was a very small gap here between wall and molding before I primed it. Now it is filled with primer.

Those really fine gaps will fill with primer, eliminating the need to caulk them.  And that can save you a lot of work.

4.  To Unify the Quality of Finish

This is the most important reason for applying a coat of primer over your entire molding installation.

Because each of your installed material surfaces will have slightly different textures to them.  And each of those textures may show differently after your two finish coats of paint have been applied.

And you don’t want that.  So you apply an even coat of primer over all of the moldings you installed.

how to prepare molding for paint

Before: The intersection where door trim, ceiling and wall moldings intersect.

how to prime bathroom moldings

After: The same molding intersection with a unifying coat of primer applied.

Note 1:  Use only Sandable Primers

You want to be able to sand your primed moldings with fine grit sandpaper, like 120 or 220 grit, for a silky-smooth surface.

Many primers are designed only to cover a surface that you don’t want bleeding through the finish coat, and so they cure with a plastic-like coating.

That’s the wrong kind of primer to use on your moldings.  Kilz2 is that kind of primer — good for covering stains but not for sanding.

Use a primer that is designed for covering bare wood and mdf.

A sandable primer leaves you with a smooth, uniform surface texture.  When dry, these primers feel chalky.  That’s the one you want.

We’ve been using a Sherwin Williams brand that we really like (details about this primer here), but Benjamin Moore and other paint companies have good primers as well.

Note 2:  A Second Coat of Primer

Sometimes you’ll find some imperfection on your moldings that requires you to sand down to bare material again.

sherwin williams wood and wall primer

Before priming: Seeing all of the moldings as separate parts.

You’ll need to cover that bare spot with primer again, but you don’t have to re-prime the entire molding pattern.  Just make sure you feather-out the primer away from the re-primed area.  You don’t want to leave a visible line of freshly applied primer.

When the re-primed area is dry, sand as usual, blending the newly primed and original primed areas together until smooth.

how to paint large baseboard moldings

After: Finally you can see your moldings as a complete pattern, and that can be very motivating!

The Primer Coat and New Motivation

A great benefit to applying the unifying coat of primer is that you’ll get to see your moldings become the thing you had envisioned.

The primer allows you to see the complete pattern as a unit, rather than as individual materials nailed to the wall.

And seeing that always breathes new life into my motivation to dive back into a long, drawn-out installation.

The Next Step

Sanding all of your primed moldings to a very fine surface is the next step after priming.

If you have any questions about priming moldings, use the comment section below.

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2 Responses to Quick Tip: The Unifying Coat of Primer

  1. Corey Graham January 9, 2013 at 10:35 PM #

    Great post and a really nice primer. After using it I’m sold for life that it’s worth every drop.

    Question on using this on unfinished bare wood. I like working with solid wood so I use that a lot to make my own flat stock, back band, build my own pieces and other elements of trim I use around windows, doors etc. I like making up my own ideas – giving me an excuse to haul out my woodworking tools rather than just buying pre-made pieces.

    So I usually end up with a healthy mix of pre-primed pine, unfinished hemlock and fir, primed MDF, etc. So when the primer goes on it obviously looks great over the pre-primed material but what was the unfinished wood looks like it could use a 2nd coat. After a light sanding, vacuum and wipe-down can I get away with doing this on just those areas or should I plan on giving everything a 2nd coat?

    • Ken January 10, 2013 at 11:28 AM #

      Kudos to you for making your own moldings, Corey. I’ve done it a few times, and it takes a lot of skill and planning. More than I’m usually willing to do.

      I sometimes apply a second coat of primer on bare wood. And yes, you can apply it on just the places you need — just be sure to feather-out your wet edge really good. And to do it really good you’ll have to work pretty fast before it dries, because it drys rather quickly, especially on those thin feathered sections.

      But it’s not hard to do. In fact, the fact that this primer feathers so well, allowing you to do spot touch-ups without leaving a line of dried primer, is one of the main reasons I love this brand of primer.

      Thanks for commenting Corey.

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