Replies

1. 
   calvin | Mar 30, 2012 06:57am | #1

   Good luck

   I don't believe you'll find a primer that will stop the knot sap movement in pine when the sun or heat contributes to the process.

   But I guess it's worth a try.

2. 
   DanH | Mar 30, 2012 07:43am | #2

   Seems like this is a question for the Nots Forum.

3. 
   aaron_agosto | Mar 30, 2012 09:12am | #3

   Ive had some problems with efflorescence in the past and my painter friend recommended using a white pigmented shellac. I imagine that would you help you there as well. I've also used that gripper primer in the past.

1. 
   IdahoDon | Mar 30, 2012 11:47pm | #4

   I'd second a shellac or shellac based primer for interior applications.

4. 
   Piffin | Mar 31, 2012 08:48am | #5

   Calvin is right that if there is sap bleeding, there iss little you can do, but if this is just shadowing showing where the knots are, you need a shellace based sealer to hide, sometimes 2-3 coats for bad ones, then your fininsh paint over. You only need to spot prime on the bad spots.

   Shellace based dries fast, and you use denatured alcohol to clean the brush - or use a disposable brush and leave it in the can between coats.

    or you can get a spray can if there are only a ouple of small spots.

5. 
   MarkH | Mar 31, 2012 09:21am | #6

   I use a heat gun to heat the knots first so they release some of the gum.  Then clean up with acetone before priming.

6. 
   hammer1 | Apr 01, 2012 11:06am | #7

   The traditional method has been to scrape then wipe off excess sap with a solvent, such as mineral spirits. Apply a minimum of two spot coats of pigmented shellac, apply an over all coat of an oil based primer, then paint. How well this works will depend on the amount of sap in knot. Generally it will work well for a number of years. When it's time to repaint, sand the knots and repeat the process. It's the properties of shellac that seal the sap but the spot primes will flash through paint, therefore, the overall primer after spot priming.