Q: I am currently working on a project that has old, untaped drywall that was never finished and has turned yellow. What is the proper procedure for texturing and finishing over drywall in this condition?

A: Myron Ferguson, a drywall contractor in Middle Grove, N.Y., and a presenter at JLC Live, responds: A few years ago, I taped and finished a cathedral ceiling that had remained untouched for a whole summer. The drywall had yellowed quite a bit, but I really didn’t think that it would be a problem. I taped the seams and primed the ceiling with regular latex primer, and then applied the texture over that.

When the texture dried, I was surprised to see that yellow was bleeding through everywhere on the ceiling except where the seams had been taped. I figure that because the texture went on very wet and then took a while to dry, it must have drawn the yellow through the primer.

So, in your case, I’d start by taping the drywall seams. Then, depending on how badly the drywall has yellowed, choose what type of stain-blocking primer to use. If the yellow bleeds completely through the joint compound on the taped seams, I would seal it with an oil-based stain-blocking primer. But if the compound has covered up the yellow, you could probably get away with a water-based stain-blocking primer. When the primer has dried completely, apply the texture.

I always prime after applying a texture, so you will need to apply a second coat of primer anyway. If the yellow continues to bleed through after the texture is applied, I’d use a stain-blocking primer a second time; at this point, the latex version would most likely be fine. Just make sure the primer is totally dry before applying the finish paint.