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Stain Blocking Primer (Cover Any Stained Wood, Walls, etc)

A coat rack without stain blocking primer shows a stain bleeding into paint
In this photo of a coat hanger, the painter did not use a stain blocking primer. Below we explain what product to use for different kinds of stains, including stained wood trim, and why.
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Primers come in various levels of firepower and when you have stains, you need a stain blocking primer with a lot of power, like . If you put just any average primer on stained wood, on walls with water stains, or on wood with ‘knots’…and then paint it…the stains will bleed through every of paint and you will have to start over—square one.

Why? The resins and tannins in wood stains such as knots and many other kinds of stains will bleed through if not stopped with a stain blocking primer. Primers without stain blocking components merely make different surfaces with un-alike porosity all the same: they do not block tannins and resins. This is oversimplified but true.

If you want the short list here at the top,

For blocking severe stains (like changing wood trim/cabinets to paint) use:

  1.  Benjamin Moore’s best blocker: (interior)   and Block Out (exterior—see below). We have never had any tree sap, or tannin or any water stain or tree knot stain bleed through this top-notch primer. These stains can take a long time to bleed up into the top coats which makes us look bad.
  2.  When you don’t want to mess with oil-based blockers, go with   This and the two just above are all Ben Moore’s best and it’s almost all we use: our time is money. We don’t get ‘call-backs’.
  3.  The ultimate nuclear-option in is the very best stain blocking primer is,   with white pigment. Nasty, but very effective. Cleans up with rubbing alcohol, and comes in a spray (discussed below). It is the #1 stain blocking primer on the market.

It gets complicated, but below we make it digestible. You’ll be the judge of that!

Prevent a nightmare: get the right one!
wood need stain blocking primer
Pine boards lack stain blocking primer so knots bleed into paint
  • Primers without blockers: Like with new drywall, different surfaces have different pore densities, and a primer fills and seals them all equally and creates an even surface so your paint will not be shiny here and flatter there. We call this ‘flashing’.
  • Blockers come in the more expensive primers—these stop resins, tannins and other bad guys like tree sap, that will bleed through into your top coats of paint.

Do you always need a primer with stain blockers?

No, not unless you see stains or have new wood.

Sometimes it takes a year for some wood knots to bleed through, so you need to be sure now.

Choosing a Stain Blocking Primer

You want to block all the stain in one step. You should really never need 2 coats of any primer. (Exterior primers are at the bottom.)

As always, using poorly engineered primers (and paints) is more expensive in the end. Spending more up front saves money in the long run.

Choice #1: Simply the best

Whether you just have a few stains or even if are you converting wood trim or cabinets to paint: Lightly sand every square inch (just enough to scratch it up for better bonding—we use  )…then… 

The best and first choice should be an oil-based primer (yes, you can put latex paint over it). We use   from Benjamin Moore: we have never had a problem with stains coming through. Important: wear a respirator (we simplified the complex world of filters here), and open windows or somehow ventilate the area. This off-gasses fast, so after a few hours, you’re safe to be around it with no respirator.

Prime Lock blocks crayon, smoke damage, odors, and all the other stains already mentioned. (See Ben Moore’s spec sheet).

Converting wood trim or cabinets to paint? Jump to this info.


Choice #2: Best stain blocking primer—water based

 If you don’t like oil-based goop, (and who does?), use  , a water-based primer almost as powerful as Prime Block.

After that, if there are any nasty stains bleeding through (rare with these products), we go nuclear with BIN,  . Shellac cleans with rubbing alcohol or denatured alcohol. IMPORTANT: you need a respirator! First you pick the mask  , which comes without filters…and this filter   Read above about filters just for dust, pollen etc. The   is good for any small extras you did not get the first time, but you have to be careful with overspray: it does not come off! (Tip on BIN at the bottom*).

Choice #3: Odorless oil-based stain blocking primer

   oil-based gets you the stain blockers that cannot be mixed in water-based solutions but without the stink. We only used this one time, for a very sensitive customer who just bought a smoker’s old condo. Yick. But it worked. Popcorn ceiling and all. It’s not totally odorless, but close. NEED KEYWORD FOR PEOPOLE WITH ALLERGIES AND SENSITIVE NOSES HERE

Choice #4: Taking a risk with whatever

If you have some random primer leftover from some project, or if you want to avoid the level of toxicity of the big boys above (Aqua Lock is not that bad), go ahead and use your primer. After a short time, you will see some stains bleeding through. Remember that some stains may take a year or more to bleed up through the top coat.

At that point, just spot prime with BIN (link above). NOTHING gets through this nastiest of nasty, but the best stain blocking primer.

Special Problems

 For rust and other metals, seal it with   an oil-based, fast drying metal primer. We were surprised how fast it dries on a warm day (outside).

  also acts as a primer after changing the rust by chemical reaction. We would prime with Rust Scat (just above) after using it as well before painting. 

For mold, first, of course, you need to whack it Mr. De Nero, using  , and then  : just buy a small quantity for where the mold really grows. Use the above primers for the rest. Finally, add Paint-Guard a   to your top coats of paint.

For interiors, there is nothing else in our arsenal of stain blocking primers. We don’t mess around with things on sale as they end up costing us time and money.

Exterior Stain Blocking Primer

 Oil-based primers are always preferred, and with  , you can prime your whole house and get great protection and bonding.

If you want a water-based primer and stain blocker, use the old standard: Rustoleum’s   when painting outdoors. We’ve gone through a gallon or a thousand.

Now, how to do convert wood trim and cabinets to paint…we have it all covered for you, not literally, duh.

Spraying primer? Sure. Go for it. We have written all about sprayers here. Graco is the brand we know and trust.

painting with stain blocking primer
* Tip on primers used for spot priming. BIN, in particular, is nasty stuff and as soon as you put a brush in it, that brush will never be useable for anything else. We buy   for this, even though the bristles fall out! Here is what we do: before dipping the brush, cut off the handle so the brush will fit inside the can with the lid closed. After you’re done priming, seal the brush in the can! Yes, it’s messy when you go to get it out (rubber gloves, man), but you only ruin one brush per can. BIN needs to be stirred or shaken after sitting only a few hours. Watch the video below as I make a fool of myself showing how to shake a paint can without taking it to a paint store.


Paint and Primer in One?

 We don’t love them. In the early days they, well, sucked. But nowadays, ok, better, we talk more about paint and primer here. The technology now is that tiny particles come together to form a seal and act as a sealer/primer, but not necessarily a stain blocker. If they fail, we look bad, not the paint makers. Even if the customer does not see it, we do and have to do touch-ups. But it is a faster and less expensive way to go and it’s used in many rental properties.

That’s our look at how to block stains with primer. Have any comments? Let us know below.

Related posts:

Here we just need to seal a stain from a wood knot that bled through the primer and top coats of paint:

How to shake a paint can: always do this for stain blocking primers to mix the solids into the solution.

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6 thoughts on “Stain Blocking Primer (Cover Any Stained Wood, Walls, etc)”

  1. I am painting over a knotty pine tongue and groove ceiling. It is stained a medium yellow and has a thin coat of varnish on top. Do I need to do any surface prep for a ceiling? Or can I just put on a coat of primer followed by two coats of paint? I was thinking I was going to have to use BIN, but now I am wondering if you think the Prime Lock would be enough? Also, should I wait until winter, when the wood is shrunk b back a bit, before painting? Thanks!

    • Hi. Interesting question. Since the ceiling will never be touched, I think you are lucky that you don’t have to sand it for touch reasons, but it would not hurt for long-term bonding. If you have a ‘pole sander’ scuff it up with some 100 grit or about that…not so important what grit. Then, since the knots are probably sealed, I don’t think you need a real strong stain blocker. I’d likely end up using STIX for the bonding factor since you won’t be needing much de-glossing. But Stix will not block knots if they want to bleed thru. But the varnish should be your stain blocker. My approach would be to buy a small can of Stix, apply to knots, dry, then ceiling paint on your test spots (1 or 2 coats, whatever you will do for real) and wait a while to see if the knot bleeds through. Sometimes knots show in the primer, but are in fact sealed and won’t bleed up anymore. If they do, go Prime Lock. Good luck! Send me pics and I’ll post before and after if you like: it will really help future readers. Most of all, have fun… sure brad.

  2. Thank you so much for your response! It might be a month or two yet bc we are tearing out a wall first, but I will send pics! Thanks!

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