A number of softwoods, as well as some of the more porous hardwoods such as maple, aren't conducive to stained finishes. This is because wood density and porosity varies, causing some areas to absorb a lot of stain, with other areas absorbing very little. Because of this, many people find that this results in a finish that is splotchy and unattractive. In addition to maple, other problematic woods include pine, fir, alder, and birch.
Using a Pre-Stain Wood Conditioner
To help even out the color when working with bare woods, you can try using a pre-stain wood conditioner. The conditioner works by penetrating and temporarily sealing the wood to even out the rate of absorption, thereby creating a much more uniform stain coat.
Some woodworkers claim that brush-on pre-stain conditioners are necessary whenever using brush-on or rub-on stains with certain woods, but that gel stains are much less prone to splotching and can be used without the pre-stain conditioning. There is some debate about this, but many experienced woodworkers believe that standard liquid stains will produce the best results on pine, fir, alder, maple, birch and similar woods if the surfaces are first treated with a conditioner.
Pre-stain conditioners are available in both water-based and oil-based forms, and the general recommendation is to match the conditioner to the stain you plan to use: a water-based conditioner for a water-based stain, and an oil-based conditioner if you plan to use an oil-based stain.
Before applying the pre-stain wood conditioner, be certain that all blemishes have been addressed and all surfaces have been properly sanded. Gouges or scratches should be filled, and it's important to make sure any glue residue has been removed. You should also finish preparation with a light hand sanding for a perfect final touch.
Then, remove all sawdust with a shop vacuum and wipe the project with a dry cloth. Finally, use a tack cloth or clean cloth moistened with mineral spirits to clean off any remaining sawdust. A perfectly clean surface is critical to the success of the conditioner and the application of stain.
Use a brush or cloth to apply a liberal coat of the pre-stain conditioner to all surfaces of your woodworking project. As with the stain you will soon apply, always work in the same direction as the wood grain when applying the wood conditioner. Allow the conditioner to penetrate the wood for 5 to 15 minutes, and then wipe off any excess. As per the instructions on the can, you'll likely be advised to apply the stain within two hours of the application of the conditioner. If the wood appears to be excessively absorbent, a second coat of conditioner may be advisable. Then, clean up with mineral spirits or paint thinner.
It's fairly important to apply the stain within the recommended window of time—from 15 minutes to about two hours of application of the conditioner. Woodworkers who allow the conditioner to dry beyond the two-hour window report that the conditioner loses all effectiveness, and some even claim that the stained results can be even worse than if no conditioner was applied at all. This time limitation can pose a problem when working with very large furniture pieces, where stain application can take quite a while. In these cases, it may be best to try and break up the job into smaller segments.
Finally, using a pre-stain wood conditioner will likely lighten the color of your stain to some degree, since the role of the conditioner is to slightly hinder the absorption of the stain. Be sure to test the stain on an inconspicuous spot on the project before starting. You may find it necessary to apply a second coat of stain to reach the desired color, but the stain's color will be much more uniform than if you had skipped the conditioner altogether.