Primers come in various levels of firepower and when you have stains, you need a stain blocking primer with a lot of power, like our top choice here. 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:
- Prime Lock Plus 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.
- Aqua Lock Plus. 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’.
- BIN, a shellac-based primer 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!
- 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 150 grit sandpaper)…then…
The best and first choice should be an oil-based primer (yes, you can put latex paint over it). We use Prime Lock Plus 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
Aqua Lock Plus, 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, a shellac-based primer. Shellac cleans with rubbing alcohol or denatured alcohol. IMPORTANT: you need a respirator! First you pick the mask (we recommend this), which comes without filters…and this filter for vapors. Read above about filters just for dust, pollen etc. The BIN spray can 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 primerOderless Kilz 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 ProblemsRust Scat an oil-based, fast drying metal primer. We were surprised how fast it dries on a warm day (outside).
Rust converter 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 a Mildewcide, and then Mold Killing Primer: just buy a small quantity for where the mold really grows. Use the above primers for the rest. Finally, add Paint-Guard a mold-inhibiting additive 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 PrimerBen Moore's Block Out, 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 Cover Stain oil primer 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.
- Learn how to convert stained wood (trim, cabinets) to paint
- What paint you will use? We like Advance and we explain why, and how to apply it in our post on the best paint for trim and cabinets.
- How to paint trim is a common question, and it’s easier than you think: read the short how-to paint trim.
Spraying primer? Sure. Go for it. We have written all about sprayers here. Graco is the brand we know and trust.
* 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 dollar-store 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?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.
- Pick the best paint for your cabinets or trim —-Best Paint for Trim In Every Case
- If you are converting from the wood look to paint, read the essential extra steps you must take to not have a disaster.
- Learn how to paint your trim or cabinets whether you are just repainting or converting from stain. —–Painting Trim (Painting Wood Trim, Cabinets in Any Condition)
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.