Stain-Blocking Primer Tips

Advice on a sealing prime coat for maple casework. January 13, 2006

I use soft maple exclusively for my paint grade casework. I've used several primers over the years. This past year I started using MLC Polystar WB primer/undercoater. This last batch of soft maple had the brownest color I've ever bought. I absolutely love the Polystar, however the soft maple is bleeding right through. Should I use a first sealer coat of BIN shellac before I undercoat with the Polystar?

Forum Responses
(Finishing Forum)
From Paul Snyder, forum technical advisor:
You do need a stain blocking primer, but you'll have to check with the manufacturer to make sure there's no compatibility issue. Zinsser BIN works very well and would be a good choice. Do you really need two primers? If one does the job, why use another over it? Or is there a compatibility issue with the BIN and topcoat?

From the original questioner:
The Polystar is supposed to be tannin blocking. The stuff is the best sanding primer I've ever used. BIN sands like crap and just clogs sandpaper like that was its purpose.

From Paul Snyder, forum technical advisor:
Spray very thin coats of the BIN. It works surprisingly well with such thin coats and sands nicely. Thicker coats are a pain to sand even after drying overnight. 1-2 thin coats should be all you need.

A clear shellac sealer like Zinsser is another way to go. The shellac will seal in the discoloration. For primer only jobs, I use one thin coat of Zinsser BIN and leave it unsanded. I used to use Chemcraft Optiprime, but had a complaint one time from the onsite painter that his paint wouldn't stick. The BIN took care of the problem. I've used the Polystar on one job, refinishing the base cabinets on a large kitchen. The paint was failing and needed to be redone. Polystar was used originally, so I needed to use the same thing since I wasn't doing the upper cabinets and it needed to all match. The primer worked well.