Monday, March 4, 2013

Exterior Floor Seam Sealing Take 1: One for the Blooper Reel

Have you ever walked in your freshly mowed grass barefoot, savoring ever cool, comfortable step, only to rudely discover your favorite family pet or neighborhood menace has left you a warm, creamy surprise that is now gently squeezing between your toes?  ALL of your toes????  Yep, that’s where I’m at……..including the smell.

Fact is……I blew it.  I blew it and it’s my own fault for the mess I’m in and now I am pondering what to do to get myself back on the porch and close enough to the water hose to rid myself of this embellishment so I can feel “clean” about my state of affairs again.  And right about now, the “porch” is way the hell over there!
When we last left off, the interior floor had been completely seam sealed and the comfort level with the 3M urethane sealer was high.  With momentum on our side, we drove straight into seam sealing the exterior floor with enthusiasm.  We began by carefully taping each side of the seams on ½ of the exterior floor to begin applying the 3M urethane seam sealer and smoothing the edges as planned.  Only this time, I would be using the grey version of the sealer (3M Part # 08361) as it would more closely match the primer color and I happened to fall into a good deal I couldn’t pass up on 4 fresh tubes of the stuff.

In theory, this should have been a cake-walk job as all we needed to do was follow the same techniques we used on the interior floor and we would be golden.  In fact, everything about the “technique” side worked exactly as planned………with one tiny little exception.  For some unknown reason, I had a mental misfire and decided to use old fashioned big-box store lacquer thinner as the solvent to smooth the seams as we put them down.  After all, I had a fresh gallon of the stuff handy and I quickly discovered it worked phenomenally well in smoothing the seams to a glass-smooth finish……..and that’s where the wheels fell off the wagon.
I’m telling ya…..we were making smoke!  This stuff was laying down smoooooth and we were moving through the project like poop through a goose.  As we approached having the first half done, it was time for the requisite potty break, so in the house I went for a slight pause in the used beer department (ok, used coffee ‘cuz I HATE beer, but you get the idea).  On my return, I decided to check the first few sealed areas to see how things were coming along.  I might have mentioned this stuff cures rather quickly……..most times……..if you do everything right…….and you give it a little time…….it USUALLY cures quickly.

Well, my discovery was of the warm, squishy variety mentioned in the first paragraph.  Not only was the sealer just as sticky and creamy as the moment I put it on, it still smelled like it came fresh out of the tube.  SH*T!  What the…..
Immediately, all manner of progress came to a screeching halt, my restoration “man-card” was on the brink of revocation and the entire operation was packed up for the night.  I decided the best position to adopt was to stop where I was and see what happened after a solid 24hr drying period.  Normally, this would be plenty of time to have the sealer cure quite nicely.

24 hours came and went.  Then 36. Then 48 hours passed until I had the courage to go back out into the shop and see what had transpired.  With severe anxiety, I extended my stubby digit into the thickest section of sealer and………..damn near pulled back a stump!  SH*T! SH*T! SH*T!  My greatest fears were immediately realized in one simple motion.  Like a fresh, industrial-strength rubber booger, the sealer was just as raw and fluid as the moment I put it on.  Not a hint of curing anywhere, on any seam.  And then……..depression set in.
What now?  How do you get uncured urethane sealer out of the seams with any hope of having them clean enough to reseal later on?  Moreover, why the hell didn’t it cure!?

And then, like a punch in the gut, it started to come to me.  I changed something in the system.  I changed something out of convenience and it bit me in the butt.  The lacquer thinner!  That was the ONE thing I changed and that HAD to be the culprit!  But WHY?
So the research and noodling began.  What about the lacquer thinner trashed the party and how was I going to correct this error so we could get back on track?  So…..I started with basics:  read the product info for the sealer.  Blah, blah, blah……tools easily……moisture curing…….use no solvents containing alcohol……stops the curing process…….wha?  Come again?  Stops the curing process?  Alcohol huh?  But I used lacquer thinner and that……….(read the ENGLISH side of the can)…….HAS ALCOHOL IN IT!  Methanol to be exact.  Suddenly, my love affair with this awesome form of racing fuel has become tarnished forever!  The entire operation was undone by the very thing 3M tells you to avoid – alcohol.

So now I knew the cause of my dilemma, but what of the solution?  More noodling.  Days of it in fact before I reasoned through the solution (and monitored the state of the urethane sealant over time).  After a week, the goo was still goo, so I started digging at the thicker sections to see how hard it would be to scrape out.  What I discovered was an unexpected and welcome surprise.  Beneath the uncured surface of the urethane was nicely cured sealer!  Almost immediately, I realized the substance that was at the root of my grief was now going to deliver me from this evil if I was patient and careful.  So, it was time for a test!
Using a cheap paint brush I cut down to make the bristles short and stiff, I poured some fresh lacquer thinner in a bowl and proceeded to scrub the crap out of a one-foot long section of uncured urethane sealer to see what would happen.  To my utter amazement, the uncured sealer washed cleanly away leaving only the cured urethane behind, which as luck would have it, is quite impervious to the lacquer thinner when fully cured.  That’s it!  After an overnight drying stint, I came back the next day with my fingers crossed and discovered that the cleaned section was free of uncured sealer and although I would have to scuff and re-prime the areas to cover the small areas of exposed bare metal, I had a solution to the problem that worked!

Essentially, what I had discovered was that only the sealer that had come into direct contact with the thinner was prevented from curing.  But, the sealer deep into the seams and crevices that did not come into contact with the thinner cured normally by simple exposure to the moisture in the ambient air.  How lucky can you get?
So, with a solution developed, Ted and I set about three tedious days of scrubbing every last hint of uncured urethane seam sealer out of every seam we applied it to using our bobbed paint brushes and lots of lacquer thinner and paper towels.  It was messy, nasty and sticky work, but in the end, what we were left with was cleaned seams (again) and many areas that required fresh scuffing and primer to get back to level on the dial and start back in a positive direction.

With our clean-up work complete, we prepped and primed the suspect areas with two coats of DP40LF primer and let everything cure for a few days before sizing things up for our next seam sealing adventure………without all the drama.  I promised I’d show the good and the bad in this build and there ya go!  I sure hope this helps someone avoid making the same mistake I made!
What a beautiful place to start a seam sealing job, eh?  Nicely scuffed and cleaned exterior floor.

Taping the seams is a technique that allows me to geth the finish on the seam sealer that I want.  After applying the sealer, we peel the tape off and smooth over the sealer once again for a nice clean look.

And here is where things went off the rails!  Though those seams look nice and smooth, the sealer would not cure because I sued lacquer thinner as the solvent and the methanol contained in it stopped the urethane curing process DEAD!

Yep.  Thant pretty much sums it up.

After three days of scrubbing the uncured seam sealer off the car, what was left was thin traces of the cured sealer and a lot scuffing required to get the surfaces ready for primer.

Here, the thin (almost white) traces of seamk sealer are all that is left after the serious scrubbing they got to remove the uncured sealer.  What was left behind was solid, fully cured sealer.  Yay!

Here Ted is swabbing everything down with wax and grease remover in preparation for re-priming the seams we had to clean up.

Here is the floor after two medium coats of DP40LF primer.  The shinier traces around the lower seams is the fresh primer.  Thanksfully, we had only done about 1/3 of the lower floor pan before the wheels fell off the wagon.

Re-primed axle tunnel area.

Re-primed trans cross brace and shifter area.


  1. Man, that's unfortunate. I'm a bit surprised that the lacquer thinner caused such a problem as I used it on every bead of NAPA brand black firm urethane sealer that I laid down and it set up completely every time. Must be a "formulation" thing.

    1. Oh yeah. This was my own fault, but like you, I have used lacquer thinner on other urethane sealers before with no problem at all. Not this time!

  2. Sven!!!!!

    Man, THAT, is just not right.... Arghhhhh.....Well, at least it sounds like you have solved the riddle and recovered. Ugh, how frustrating. We feel your pain. I was reading your previous post and came across this:

    "It’s worth noting that the interior was a perfect place to experiment with smoothing techniques since I wanted to make sure we had the technique down before moving on to the “cosmetic” seams on the exterior floor later on."

    It's just never easy is it :) Recently, we were putting together these company signs we make using our waterjet and follow-up with powder coating. We nailed the powder coat on this one particular sign. It looked like a wet piece of glass without a hint of dust in it. I told my intern to wipe it off with cleaner to remove any fingerprints and to wrap it for shipment. Sitting at my desk, I suddenly had this sick feeling that he would think that alcohol and acetone are interchangeable here. As I rushed out to the shop - I met him 1/2 way there and knew from the look on his face that he had grabbed the acetone and not the alcohol. So yes - I feel your pain :/


    1. RJ, I can't blame it on anything or anybody but myself. I have used lacquer thinner on so many other sealers that I never thought to consider they are not all created equal. It bit me good!

      Oh man! That powder coat story is soooooo familiar! As a closet custom powder coater, I KNOW what that sick feeling in the pit of your stomach is all about! ALWAYS on one of the most perfect pieces you do too! And the stuff is soooo much fun to strip and re-coat too (NOT!). I guess it's these tests that make us wiser in the end......but they still suck!

  3. Lot of extra work, but certainly something that may save the rest of us. Just another reminder to thoroughly read the directions. At least it wasn't the whole car.

    1. I sure hope it helps someone avoid the same mistake for sure! Just goes to show what can happen when you take your eye off the ball for even a second. We'll be good to go shortly!

  4. I never would have guessed that there would be a difference in Lacquer thinner, let alone alcohol in it. You tackled the problem professionally and methodically, as usual Sven. That has to be some consolation. I'm not familiar with the DP40 but it can obviously be sprayed over the sealer. Actually, with the sealer in the joints, and the primer on it, it looks pretty good. Keep sojourning on. It's going to look great!!!

    1. Howdy Dennis and thanks! By any chance did you post this from the air? LOL! You are correct that DP40LF can be sprayed over cured sealer (it's paintable) and does a nice job of it as well. Once the seams actually get filled and smoothed, things will start looking downright tidy.