Can You Stain and Varnish Primed Wood?
If wood has been primed, then it is ready to be painted, not stained. If your intention is to stain the wood, you should never use primer beforehand, as it will prevent the wood from absorbing the stain. Before you can stain and varnish the wood, you will have to remove the primer.
Stripping the Primer
A commercial paint stripper and a rag are all you need to remove the primer before staining. Of course, you should always work in a well-ventilated area while wearing protective goggles and gloves when using paint strippers because they give off toxic fumes and can irritate your skin and eyes. Spread the paint thinner over the surface of the wood, and allow it to sit for about 10 to 15 minutes. Scrape the primer off the wood, using a plastic putty knife.
Even if you manage to get all of the primer off the wood, you should still give it a thorough cleansing because the paint thinner may leave behind a residue that will interfere with the staining process. Mix 1/4 cup of trisodium phosphate with 1 gallon of water and use this solution with a scrub brush to scour the wood. This will neutralize the paint thinner while removing any residual primer or other stains.
You must allow the wood to dry completely before attempting to stain it. Once the wood is dry, apply a stain of your choice with an appropriate applicator tool, such as a roller, sprayer, cloth or paintbrush made of synthetic or natural hair or foam. Gel stains are recommended for wood projects with lots of vertical surfaces, such as chairs or cabinets. When you are finished applying the stain, wipe the surface of the wood with a clean cloth to soak up any excess stain.
A common practice with varnish is to thin the first coat by mixing the varnish with an equal amount of mineral spirits. This ensures that the varnish will form a hardened seal over the wood. Once the first coat is dry and cured, lightly sand it with fine-grade sandpaper and wipe it with a tack cloth before applying the second coat — use undiluted varnish for this and all subsequent coats. When applying varnish, always move your applicator with the grain of the wood.