Apron Seam Sealing & Undercoating with U-Pol Raptor

As Fall weather began imposing itself on Southeast Michigan, I began keeping an eye on the sky and the calendar to maintain momentum getting the front apron work completed and to find a window of opportunity in the forecast to complete this, my last “outdoor” project for the year.

With the car now solidly sitting on the body cart, the process of masking the exterior apron seams in preparation for seam sealing was a rather easy, albeit time consuming process.  Using the same techniques that were used on the floor pan, the seam sealer was applied on each masked seam and smoothed with a finger wet with xylene.  This smooths the sealer very nicely and makes the seams almost disappear when finally coated in bed liner material.  A few evenings dedicated to the job and the entire exterior apron area was fully seam sealed and scuffed for the final preparations before coating with spray bed liner material to match the floor.  However, before that could be undertaken, I had one small bit of repair work to complete.

Specifically, I needed to rebuild the left front lower valence mounting location that was torn away during one of the cars archival mishaps decades ago.  I reasoned this job would be a good one to tackle at the same time I cleaned up the areas of the front frame horns once concealed by the front rotisserie mounting arms now that they were perfectly accessible with the car on the body cart.

With a small swatch of clean sheet metal in hand, I simply traced the shape of the right side frame tab on the sheet and cut out the profile with material to spare on the back side to allow the parent material to be trimmed and perfectly fit to the new repair part.  Then it was a simple matter of fitting the repair to the prepared spot and tacking it up.  With a few small adjustments to the position and shape, I carefully TIG welded the mounting tab in place and dressed the welds smooth.  The final step was to drill and lightly chamfer the mounting hole and we were off to the next adventure.

Next up, was a thorough cleaning of the surfaces once masked by the rotisserie mounts and treatment with “prep & etch” to prepare the surfaces for a few coats of PPG DP40LF epoxy primer.  I like to let the DPLF cure for several days before topping it with any coating that is not designed for a “wet-on-wet” application over it.  This allowed plenty of time to begin masking the entire engine bay and aprons for application of the U-POL Raptor bed liner.

The final process before the bed liner application was several days’ worth of careful masking of the inside and outside engine bay, lower frame rails and front radiator support.  For this kind of work, the masking process is a “top down” operation.  In other words, I started by masking the upper surfaces of the inner and outer aprons, radiator support and firewall and methodically moving down until the entire complex was masked.  As always, I started by defining the sharp paint lines with tape and them coming back and masking the large, uncoated areas with more tape and masking paper.  As the process moved lower on the chassis, I made sure to overlap the masking paper such that all of the seams faced toward the ground to help prevent them from blowing open when the bed liner was sprayed as it is sprayed at a rather high pressure of 45psi and is very heavy-bodied so it’s impact force is rather high as well.

As the process continued to progress, the masking formed a very nice “road map” of sorts that allowed me to start focusing on the areas that required coating with little distraction.  This makes it much easier to visualize the end result in my minds’ eye and starts to tease out a hint of what it will look like when completed.

The final masking was a simple application of plastic drop cloth as an easy means of covering a lot of area in a simple and economical way that works well and quick to apply.  Then……we wait…….with a “weather eye”.

After several days waiting on Mother Nature to decide freezing temps and/or rain were deserving of a short break, we saw our opportunity and were ready to capitalize.  In short order, the car was in the drive and in position for the application of the U-POL Raptor bed liner material to begin.  The plan, as was predetermined days before, was to apply two solid coats of material with a third “texture coat” used to achieve the desired finish and touch up any “holidays” in the job we may have missed.

With my dad’s sharp eye and helping hands, the application of the Raptor went just about as textbook as it could have.  With weather cooperating perfectly, the first coat was concentrated on the areas we had predetermined to be problematic to coat and then we simply filled in the blanks between these areas.  This established a nice base coat that we allowed to flash for one hour before the second coat was applied.

The second coat was a purposefully even application over all of the surfaces with more attention paid to achieving the finer grained texture I prefer.  This coat was also intended to fill in any obviously thin areas as well and was again allowed to flash for an hour before the final “texture” coat was applied.  This was a light, “dusting-coat” applied from a greater distance to firmly establish the finer grained finish I prefer.

After about a 15 minute flash time on the final coat of bed liner, we immediately began remove the masking very carefully to ensure the sharpest masked edges and prevent the masking from becoming glued to the surfaces forever as the Raptor is some of the stickiest, most tenacious coatings you will ever run into.

And with that, I can comfortably declare the entire underside of the chassis finished and the work will now progress to more cosmetic challenges ahead.  Back to the firewall work first, then on to “real” bodywork!

Masking for neat seam sealer application is no less work than masking for paint.  The end result is well worth the effort.

Clean and smooth seam sealed joints are a favorite of mine and look great under spray bed liner materials.

I took a little extra time to seal up the areas around the lower control arm mounts to ensure a clean look under the car.

Outer firewall seams often require a fair amount of seam sealer to get them sealed properly.  By using the masking technique, even these seams are very tidy.

This is the final chassis repair I needed to make before primer and bed liner application.  This corner of the front left frame rail was torn away at some point in the past.  This is the repair just after smoothing up the weld.

The final step in this repair was to drill the new mounting hole for the lower front valence brace.

After brushing the front frame sections that were hidden by the rotisserie mounts, each side was treated with Prep & Etch and primed with PPG DP40LF epoxy.

Even after decades in a very harsh climate, these front subframe sections are very solid and straight and look quite nifty in fresh primer.  The mounting tab repair is virtually undetectable in this shot.

The really BIG job in this phase was masking the entire front of the car in preparation for the Raptor bed liner application to the outer aprons, radiator support and lower frame rails.  I start from the top and clearly define every tape line that will be seen to ensure clean and crisp tape edges.

As the process moves down the panels, the intricate masking details soak up lots of time.

The front radiator support is a bit tricky to mask.  I planned to have the forward surfaces coated in Raptor, but the interior surfaces in paint in such a way that the bed liner will not be seen when examining the engine bay.

Front the front, you can now get an idea what surfaces on the radiator support will be coated in Raptor.

Along the top edges of each apron, I leave a small 1/8" reveal to ensure the edges of the sheet metal are completely coated in Raptor.  This edge will be hidden completely by the fender when the car is assembled.

At the front of the radiator support, I mask down 5/16" from the top to ensure there is no Raptor visible above the gap cover that will hide this area from above.

Here, the front of the engine bay is completely masked.

Work now begins in the rear of the engine bay and firewall.

The driver side firewall and cowl are completely masked off.  You can also see how far back into the transmission tunnel the masking is carried.

With the passenger side firewall and cowl fully masked, it's time to finish up the prep work and head to spraying the bed liner material!

The windshield and front part of the roof and door openings is covered with plastic drop cloth material for an easy way to cover a large area.

Go time!  A quick review of the U-POL Raptor application instructions and we were ready to spray!

To make it easier to spray the underside surfaces, we jacked up the front of the body cart and placed it on stands.

First coat is concentrated on the hard-to-reach areas and then what's left in the gun is evenly applied to all of the other surfaces.  Full coverage is not the goal on this coat as it is more directed at the details.

After an hour of flash time on the first coat, the second coat is applied with a more even hand over all of the surfaces.  This establishes a nice even color and coverage.  Another hour of flash time and a much lighter third coat is applied to establish the final texture desired.

After the third coat has flashed for about 15 minutes, we begin to carefully remove all of the masking to ensure all of the taped edges are crisp and nothing sticks under a coating of bed liner.  This stuff is some of the most sticky poop you can find and will glue ANYTHING permanently in place if you let it.

Left side apron coated and looking very nice!

Right side apron completed as well.  I wonder if anyone will notice the relocated upper control arm holes????