To achieve a flawless paint job on a car involves meticulous attention to detail at every step in the process. One such element that often separates amateur work from true craftsmanship is the technique used in masking body jambs. These recessed areas around the vehicle’s doors, hood, trunk, or tailgate present a unique challenge during the painting process. Improper masking can lead to visible hard edges, uneven transitions, and overspray issues that compromise the overall aesthetic of the vehicle. 

There are several ways to mask these areas to prevent unsightly results. And, like many processes in the shop, each craftsman believes their method is best. In this article, we’ll demonstrate three of the most common and effective ways to get a clean edge. Whether you’re a seasoned painter or a first-time DIYer, you can’t go wrong with either approach.

Foam Tape

If you’re looking for a quick, safe, and fairly easy approach to getting clean transitions, look at what the professional shops use. Designed with body shops in mind, soft-edge foam tape looks like a continuous roll of foam packing peanuts. But unlike packing foam, this material features an adhesive strip and is compatible with both water- and solvent-based paints. It also holds up to the heat of low-temp curing ovens and lights.

Masking with foam tape is straightforward. Just unroll a length of the masking foam, peel back the edge of the adhesive backing paper, and start sticking down the foam following the contour of the jamb. The foam takes moderate curves with no issues. Tight corners can be masked in sections by easily tearing or cutting it to the desired lengths.

With the foam’s 3/4-inch diameter, the paint edge will gently fade underneath it well before hitting the hard edge of the adhesive strip. Leave the foam in place between coats and when you’re done simply pull the foam off. The adhesive is mild and should leave no residue. Any texture where the paint edge fades can be blended with fine sanding (400-grit or finer) and buffing.

Back Taping 

Not everyone prefers foam tape. It is, after all, yet another shop supply to purchase, and a single-use product at that. One thing that’s relatively cheap and always around is masking tape. Of course you can always just use the trimmed edges of masking tape in your jambs. However, that method will almost always leave you with hard edges. A better way is to create a soft edge with back taping.

This method is quite versatile, especially in places where thick foam may present challenges. We find 3/4-inch wide masking tape works best for back taping, offering a good balance between coverage and flexibility. 

In its simplest form, the process requires little more than laying down the center of the masking tape over the edge to be masked. Once in place, roll the exposed edge of the tape back on itself to create a soft edge similar to the foam tape. When you close the door, the tape will act as a seal, closing the gap between the panels to prevent paint from blowing too far into the jamb.

Double Taping

Not everyone gets perfect results with this type of masking. Sometimes the tape sticks to the jamb or pulls away if the door gets opened. Some extreme body lines may also make it difficult for the tape to lay flat when close. Other times the tape may not close the door gap completely. In any of these cases, there’s a second step you can take to ensure a good seal called double taping.

Double taping is exactly as it sounds. A second application of tape after the initial soft roll tacks the live edge securely in place. You can do this in localized trouble spots, or for good measure double tape the entire opening. 

Remember, always practice these techniques on a small, inconspicuous area before tackling the entire door jamb. Each method has its own advantages and drawbacks. Ultimately, the choice may depend on personal preferences and the requirements of the job.