51 BMW 1973 R75/5 Repair Clear Coat Sand Through

While I was sanding out the clear coat on the fairing, I sanded through in several places on flat surfaces; the front under the windscreen, on one panel on the side and several spots inside the headlight shell. ūüôĀ ¬†The clear coat was thin and went on too rough due to poor atomization.

NOTE: I fixed the problem causing poor atomization. It was caused by the air line fittings having small internal diameters. I bought some Devilbliss High Flow fittings. You can see the difference in the write-up on how I painted the parts in “LESSONS LEARNED: Replace Fittings with High Flow Fittings“.¬†I installed the High Flow fittings before I shot the clear coat for the repair. As you will see later, the clear coat went on like glass. ūüôā

Why You Can’t Blend Clear Coat Into Existing Clear Coat

Unlike the old days with lacquer, where you could blend in a patch since the solvents would melt the old paint and integrate the new paint with the old (it’s thermoplastic paint) you can’t really apply new¬†clear coat on top of old and blend it in. It cures via a chemical reaction (it’s thermosetting) so the new clear coat can¬†not blend in, but only sit on top adhering through a mechnical bond via the sanding scratches¬†in the old clear coat. Therefore, there will be an edge where the new clear coat is very thin and this¬†will eventually start to delaminate and peel.

Okay, so the correct solution is to¬†sand the entire fairing with¬†1000¬†grit to rough it up and then respray it again with clear coat. But, I learned you can make a repair using the natural body lines of¬†a part to limit how much of the part you have to spray with clear coat. ¬†As I have limited clear coat left, I’m going to try this to repair my mistake. But, this repair will eventually fail and the entire part will need to be clear coated again.

Here is where the sand through areas are. They are in very visible areas. I took these pictures after I had masked the parts.

Hazy Areas are Sand Through Spots

Hazy Areas are Sand Through Spots

Sand Through Spots (White Spots at Bottom)

Sand Through Spots (White Spots at Bottom)

“How To Do It” YouTube Videos

On YouTube, I found some helpful videos about repairing clear coat to avoid recoating an entire part.

Repair Procedure

Based on what I learned, this is the procedure I use.

  1. Sand the areas to be recoated lightly with 1000 wet paper to roughen it.
  2. Mask off the rest of the part to protect from overspray leaving a small gap next to the sections being repaired.
  3. Back tape along a trim line and over the tape used to mask the rest of the part.
  4. Set the gun for small fan and light coat.
  5. 1st base coat is away from the edge and light. Blend a bit toward the back taped edge.
  6. Peel tape back a bit.
  7. 2nd base coat should cover and be a bit larger area that 1st coat.
  8. Peel tape back a bit.
  9. 1st clear coat is light, tack coat. Keep very light at trim line.
  10. 2nd clear coat for coverage and gloss and covers entire panel.
  11. Peal tape off trim line and then lightly spray blender at the trim line edge to reduce height of clear coat edge.
  12. If blend line is rough, use 2000 grit to smooth out the transition between the new clear and existing.
  13. Buff at low speed on the blend to avoid removing the thin clear coat.  Coarse buff then fine buff as on original clear coat.

The sand through areas on along the front of the fairing under the windscreen, on a small side panel and on the inside of the head light well. I mask off two different repair areas on the fairing using a technique called back taping.

Back taping forms the masking tape into a curve folded back on itself which you can see in the pictures above. When the paint hits the tape, it bounces back toward the repair area creating a gradual reduction in the amount of clear coat that tapers off as it gets closer to the tape. The edge is thin and can be blended into the existing clear coat without being visible.

I used painter’s plastic to wrap the sections of the fairing I am not working on¬†to protect them for any clear coat overspray.

To prevent potential peeling of the soft clear coat, I “whet” the tape before applying it. I stick the small pieces to my jeans a few times and burnish the longer pieces across my pant leg¬†to remove some adhesive and to reduce it’s stickiness.

Wheting the Tape To Reduce Stickiness

Wheting the Tape To Reduce Stickiness

Here are the masked off areas ready to shoot the clear coat.

Masked off Front for Clear Coat Repaint

Masked off Front for Clear Coat Repaint

Masked Off Side Panel Section

Masked Off Side Panel Section

I masked the¬†side panel mto take advantage of hard edges and body breaks to help hide the edge of the new clear coat. I masked this section two times before I got what I thought was good back taping. It’s harder¬†to do with curved body breaks.

Repainting the Base Coat

In some places I had sanded throught the base coat and of course it got scuffed when I sanded through the clear coat. I need to reapply more base coat so it will look like the original base coat. The Kevin Tetz videos show how to adjust an HVLP spray gun to get a small pattern and light paint application. But I decided to try out my new airbrush and use it for applying the base coat.

Air Brush Kit, Hose and Eye Droppers

Air Brush Kit, Hose and Eye Droppers

I use some of the left over Monza Blue paint that is mixed 2:1 with reducer that I saved just in case I screwed up and needed to patch the paint. I bought some eye droppers from Hobby Lobby so it is easy to fill the paint cup. I bought a hose that has a 1/4 inch coupling on one end and a Shrader (bycycle tire fitting) on the other that screws into the bottom of the airbrush. I added a quick connect fitting to the 1/4 inch coupling so I can snap the airbrush hose into the air line I use for painting.

I put a couple of eye dropper full amounts of paint into the airbrush cup. I don’t have a holder for the airbrush, but the spray gun holder worked okay as long as I put the airbrush in a slot¬†near its¬†balance point. I need an airbrush holder if I do air brush work.

I have not used an airbrush before. The one I bought is dual acting. I push down on the button to behind the paint cup to get air flowing and toggle it back to add paint to the air flow. The airbrush has a screw at the back that limits how far back I can move the button to reduce the amount of paint. I shoot some tests on a small piece of white note paper. I got some splats at first until I adjusted the screw in the back to get a light coat of paint.

Adjusting Spray Pattern

Adjusting Spray Pattern

I was concerned about putting too much paint on the sand through areas and it was hard to see how where the paint was going and how much was being applied. I took a small piece of white paper and put that in front of the sand through area. Then I sprayed on the paper to align the airbrush and adjust the spray so it was light and then removed the paper to put the paint on the spot I wanted it. I made small sweeps over the sand through sections to blend the edges. I sprayed 3 or 4 light coats until the new paint looked like the existing paint. This is the side panel and head light shell after touching up the paint.

Airbrushed Paint On Sand Through in Side Panel

Airbrushed Paint On Sand Through in Side Panel

Airbrush Repair in Headlight Shell

Airbrush Painted Repair in Headlight Shell

After I finish¬†touching up the base coat, I clean the air brush. It has very tiny parts and the needle is very sharp and thin. Be careful when¬†you take it apart and reassemble it as it’s very easy to damage the needle. ¬†And small parts instinctively fall into the darkest, hardest to reach places under the work bench, DAMHIK ūüôā

Cleaning the Air Brush: Lots of Tiny Parts

Cleaning the Air Brush: Lots of Tiny Parts

Spraying the Clear Coat

I hadn’t taken down the paint booth. I figured I’d end up fixing a mistake (how well I know myself ūüôā ).

I used my detail gun and mixed a small amount of clear coat. When I adjusted the gun I could hear and see the difference the new High Flow fittings made; the atomization was much improved.

Clear Coat Repair on Fairing

Clear Coat Repair on Fairing

I sprayed a light first coat and kept it away from the back taped edges. I let it flash for 10 minutes by the clock. The second coat I sprayed medium wet on the entire masked sections getting as smooth a surface as I could.

As soon as I finished spraying the 2nd coat, I sprayed some blender to help thin the edge of the new clear coat so it will not be as visible on the the old.

Clear Coat Blender

Clear Coat Blender

I sprayed it very lightly, or so I thought, but I got some sags. I sprayed a second light coat but¬†one quick light coat is all it takes. Live and Learn. ¬†No worries as I’ve gotten good at sanding out sags and runs on this paint job.

Blender Sag Needs Light Sanding

Blender Sag Needs Light Sanding

Drying the Clear Coat

Kent Holt mentioned he has used halogen shop lights to bake his paint. I have two 500 watt lights on a light bar and decided to see much they would heat the repaired areas.  I measured the surface temperature with my infrared thermometer. I could get 140 F or more with the lights about a foot away from the part. I baked each repaired section for 15-20 mins.

Baking the Fairing Clear Coat Repair

Baking the Fairing Clear Coat Repair

Here is the nose of the fairing where I had back taped it. The new clear coat is shiny and the rest of the fairing is dull as it’s wet sanded with 2500 grit.

Blended Edge Before Buffing

Blended Edge Before Buffing

Below, you can see below well the clear coat went on with the new High Flow fittings. It is very close to glass smooth with very minor orange peel.

Glass Smooth Clear Coat :-)

Glass Smooth Clear Coat ūüôā

For comparison, this is the result I got with the stock air line fittings. You can see how wavy the surface is and how coarse the orange peel.

Original Clear Coated Fairing Using Stock Air Line Fittings

Original Clear Coated Fairing Using Stock Air Line Fittings

Sanding and Buffing

I sanded the blender sags with wet 1500 grit until they were smooth. I lightly sanded the minor orange peel and sags with 2000 and then 2500 wet grit. On the edge of the new clear coat, I very lightly sanded with 2500 wet paper until I couldn’t feel any roughness or an edge.

I buffed out the repaired sections using Griot’s polish. I used the “2” setting on the 3 inch random orbital polisher so I wouldn’t take very much clear coat off near the blended areas.

Here is the fairing after buffing and polishing and painting the pinstripes on it.  It is looking nice.  It is not perfect, but it will work for awhile.

Clear Coat Repair on Side Panel After Sand, Buff & Polish

Clear Coat Repair on Side Panel After Sand, Buff & Polish

Clear Coat Repair on Side Panel After Sand, Buff & Polish

Clear Coat Repair on Side Panel After Sand, Buff & Polish

Clear Coat Repair on Fairing Nose After Sand, Buff & Clear

Clear Coat Repair on Fairing Nose After Sand, Buff & Polish

4 thoughts on “51 BMW 1973 R75/5 Repair Clear Coat Sand Through

  1. A couple of questions, Duane:

    – My R75/6 came w/ Lester aluminum alloy wheels. I have sand-blasted (w/ very thin medium) them for I like the unpainted look. Should I clear coat them…? The bike stays in the garage, and will be ridden very occasionally. Wheels look GREAT unpainted…

    – Want to install an electronic tach (the MotoMeter–or is it “MonsterMeter”…?– is too expensive to repair…). How do I wire it…? It’s originally a mechanical system, but I heard it can be done.

    – If I choose a mechanical tach (cable driven), do you know the thread dimensions…? I know the ratio is 2:1

    Thanks again!

    –Luis

    • Hi Luis,

      I wasn’t sure if you meant to post this on this page? Anyway, I can’t answer your questions, but maybe someone else will be able to.

      Best.
      Brook.

  2. Good Morning Brook. I recently had a newly acquired toaster tank repainted Monza blue. I now see some toaster tanks with pinstriping around the chrome accent and others with no pinstriping on the tank. Do you know what is “correct” for a monza blue toaster tank ? I posted this question on the /5 United site but don’t recall seeing a response.
    From reading your blog I learned about the blue accents on the chrome side covers.
    Good stuff. Larry in Jax, FL
    [email protected]

    • Hi Larry,

      Thanks for stopping by. I don’t have an answer for you. In looking around at pictures of toaster tanks bikes, I find some with white pin stripes around the chrome side cover (red tanks) and some without (gold tanks, black tanks). I didn’t find any pictures of the Monza Blue toaster tank.

      I looked at Phil Hawksely’s site for some clues, [http://www.bmbikes.co.uk/pinstripes/501-550.htm] but so far I only find the generic listing of Monza Blue with white pin stripes listed. That certainly was the case with the non-toaster tanks, but I can’t find explicit information with the toaster panels.

      Sorry I don’t have the answer.

      Best.
      Brook.

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