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Wood Knots Bleeding Through Paint: Seal Them Up

Here’s an short post on how to seal up those nasty tree knots. There is only one kind of primer that you should use and the others fail.

I made a video that explains all this: jump to the bottom to watch. Also, see the last section labeled “Caution”.

Don’t use just any primer or you will be sorry!

Tree knots are full of resin that bleeds through low-budget primers and all paints. They simply don’t have the solids that block wood resin stains.

Not sure? Here is a post on every kind of stain and the primer you need.

The ONLY primer that works here has a “shellac base”, and that means alcohol is the solvent. Even oil-based will allow knots to bleed through.

White-pigmented shellac is what you want.

The correct primer in this case

You need to spend a bit more, (quite a bit) but you don’t need to use a lot of primer.

I use two products interchangeably. They are both great for nasty stains. They both stink, literally.

1. BIN, shellac base. Comes in two sizes. For DIY painting, a quart is probably best.

Because a gallon can go bad if you don’t seal the lid perfectly, I buy a gallon with some empty quart or gallon cans. Ha! (don’t use plastic or glass … don’t ask)

DO NOT BUY the “synthetic shellac”. It’s water-based and it will not work on tree knot stains. (Learned this the hard way).

2. Kilz, shellac base is the same as BIN.

If you can find it grab it. It’s often out of stock. I see it nowhere online right now.


Again, you don’t use much so it really lasts a long time, UNLESS you don’t seal the can well. So I buy a gallon and 3 empty quart cans.

Tip for these nasty primers

These primers’ solids settle fast so after the initial shaking you will need to re-shake or stir well (and stirring this is nasty).

How to seal tree knots

  • Shake well (a paint store will shake it for free)
  • Open your quart or gallon
  • Pour off what you need in your work bucket and close the lid
  • Keep the lid tight when you are not pouring and your supply will last
  • Leave an air gap and your primer will be solid in no time

Read the label to find the solvent. If it “cleans up with water”… avoid it. That’s ok for other types of stains, but not the nasties.

Look for ‘denatured alcohol’ or just ‘alcohol’. I use rubbing alchol to clean up. Bing. Done.

(Water stains are almost as tough so I use shellac on them too.)

Caution #1

Careful: there are water-based types.

Don’t get “SYNTHETIC SHELLAC”. It won’t work for nasty knots.

Caution #2

Wear a respirator and ventilate around these products. They are toxic. Not nuclear dump toxic, but toxic.

Here is the final paint job:

 

and here is the bottom of the bottom with an unsealed knot. In a year I’ll re-photograph this and we’ll see how the stain bleeds through!

 

 

 

Any questions? I’ll be watching.

2 thoughts on “Wood Knots Bleeding Through Paint: Seal Them Up”

  1. What if the board is painted and the knot bled through? Do I have to sand the knot before applying bin? Am I risking bleed thru if I don’t sand before applying bin?

    Reply
    • Not a big problem. Sanding optional probably but I cannot see it! Just spot prime with the Bin… Shellac based bin, not water based will seal any knot. The other stuff is good for most things and much less smelly
      Good luck!

      Reply

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