Decks, Patios, Porches and Docks - Knot Bleed Through

Since the problem is with my newly screened in porch I will post here, however this may be the wrong forum. Please correct me if I have posted to the incorrect forum.

Last summer I screened in my front porch, 8' x32'. The portion under the large screened "windows" is about 18" high, made from tongue & groove pine from a box store. I applied 3 coats of white shellac to the knots before applying 3 coats of solid white oil based stain. Later in the summer, I noticed that some knots were showing through the stain, so I applied 2 more coats of shellac and 2 more coats of stain. I have now noticed that just about all of the knots are showing through again, more on the inside of this "wall" than the outside. The porch faces east, and these wall sections don't really get very much direct sun. Is there something I missed during construction? More importantly, what can I do now to permanently cover the knots so they don't bleed through again?
Thanks for all replies.

Was the pigmented shellac mixed well before you applied it? the solids like to settle to the bottom of the can.

If the knots have cracks in them - caulking might help.

I don't know that I've ever run across a situation where a stain would bleed thru after a couple coats of pigmented shellac primer. What brand did you use?

Thanks marksr for your reply. I will have to check the brand, but I know it was a new bottle, but I don't think it was a brand name. It was well mixed before I used it. Maybe not using a brand name was where I went wrong. If I apply a good brand now, and then apply more stain, will that stop or seriously slow down the bleed trough?

With the exception of some type of an ink stain on a metal post at a YWCA almost 40 yrs ago, I've never had any problem with any brand of pigmented shellac. Occasionally a stubborn stain will require 2 coats of primer. That's why it's mystifing that you are having such a problem. Pigmented shellacs often settle to the bottom and if the solids weren't mixed back in - there can be issues..... but you would have noticed the primer being runny.

Zinnser's BIN is one of the better brands of pigmented shellac primer, it's also the easiest one to find. Not every store stocks pigmented shellac primer.

Thanks again marksr. If I apply the suggested shellac over the shellaced and stained knots now, will that work, or do I have to sand to bare wood?
Thanks.