51 BMW 1973 R75/5 Setting Up A Paint Booth & Paint Equipment

I’ve done motorcycle painting once before on the Silver Ghost project, a 1975 R75/6 that I converted into a replica R90/S. I repainted the bike using the R90/S Smoke Silver colors. I learned a lot while doing it and from the mistake that caused the paint to fail.

The reason for the failure was my ignorance about the primer. I used Glasurit (original BMW paint available from Holt BMW) but applied auto store rattle can primer (also know as 1 component, or 1K primer). I did this based on my friends advice that I could use any cheap primer as long as I sanded it nice and smooth. That was wrong as the solvent in the Glasurit paint is very aggressive and it liquified the primer and the base coat ends up floating on top instead of adhering to the primer. I had several paint peeling episodes when painting it, and easy chipping of the paint along the edges of the fenders and tank. The primer has to be a 2 component, or 2K primer, either epoxy or urethane, and it is always best to use the primer supplied by the paint manufacturer.

The Glasurit primer is mixed with a hardener, much like epoxy is mixed from two parts, and has a certain “pot life” meaning a fixed time you have to spay it before it starts to set up.  Any you don’t use is wasted. An you don’t want to delay cleaning your paint gun either.

When I painted the Silver Ghost, I borrowed the equipment (2 Hp compressor, oil/water filter, gun and hose) from my friend. I used sheet plastic to create a booth in one bay of my garage. I had no climate control and had to paint when the temperature and wind were accommodating.

I knew I would have to redo the Silver Ghost paint at some point but I got about 3 years out of the paint job. Now that I am ready to paint “Grover”, the R75/5, in Monza Blue, it’s time to paint both bikes since setting up for paint work takes time and so I might as well paint everything that needs it at the same time.

Setting Up a Temporary Paint Booth

Since doing the Silver Ghost project, I’ve added a one car garage size workshop that is insulated and has heat. So I should have better control over the temperature as long as I paint before the hot days of summer.

Plastic Sheeting

The overhead garage door leads to where we park both our modern bikes (R1150-RS and F650-GS), so it’s the best place to construct a temporary paint booth.  I use the overhead door rails to support a sheet plastic. I have a roll of it that is about 9 feet wide. I cut off a long piece that goes from the floor over both overhead rails and back to the floor on the other side. I attach it to the bottom of the rails using masking tape so the door can still be used.

Taping Plastic to Garage Door Rails

Taping Plastic to Garage Door Rails

I cut a piece for the floor and tape it down. Based on the first time I painted, I will need the booth for awhile as I apply the primer, base coat and clear coat and the inevitable “Oh Shit!” where I get to redo one or more parts. I am going to park the two bikes inside the booth when I’m not painting, so I will likely have to repair this floor plastic if it gets torn, but that’s easy.

I cut another piece of plastic sheet that I clothes pin to the inside of the overhead door and to the sheet the goes over the overhead door rails. This seals that end. Another sheet goes on the opposite end which is the entrance to the booth. I tape one side to the wall and use clothes pins to secure the other side to the end of the overhead sheet so I can enter and exit just by removing the clothes pins. If you roll the two sheets of plastic together along the seam and add a clothes pin, it seals nicely.

Romex Clothes LIne, Hangers and Plastic Covering Garage Door

Romex Clothes LIne, Hangers and Plastic Covering Garage Door

I add some scrape romex cable from wiring the workshop between the overhead door rails using existing cut outs in the side of the rail to loop it through and secure it. This gives me a place to hang parts when I paint them. I also use two saw horses and will add a piece of scrap plywood on top (not shown) covered in plastic. This is a handy stand for the Windjammer fairing and if I add some posts the plywood, I can support the gas tanks and fenders to paint the sides, and hang them up to paint the tops.

Paint Booth Saw Horses

Paint Booth Saw Horses


I need to vent the booth, but I don’t want a strong breeze moving through it. I use a box fan in the far corner of the shop and crack one the window near it.

Forced Ventilationi for Paint Booth

I use some 4×4 scrape to prop up the door so I have an exhaust opening to vent paint fumes.  The air flow from the box fan has to take a 90 degree corner which should prevent a breeze in the booth, but provide enough air movement to ventilate the booth.

Exhaust Opening When Painting

Exhaust Opening When Painting

When I tested this, the plastic side walls barely bowed in and there is positive ventilation to the outside. I don’t want to kick up dust and this seems to work well.


You can never have enought light when you paint. When I built the workshop, I didn’t put much overhead light near the overhead door. I picked up four 75 watt clamp-style lights at the Home Depot. I clamp these to the overhead door rails at the four corners of the booth. I get almost shadow free lighting in the central part of the booth.

Paint Booth Lighting With 2 of the 4 Lights

Paint Booth Lighting With 2 of the 4 Lights


I will heat the workshop for painting, but I want to be sure I keep it between 70 and 75 F. So, I hang a thermometer in the booth with “easy to read” numbers for my aging eyes 🙂

Easy to Read Thermometer at 70 F

Easy to Read Thermometer at 70 F

A Place for Parts to Dry

When I paint, I need someplace to hang the parts to dry. I use some more scrape romex and make a clothes line. I use single strands of the solid core wire and make some hangers to go on the clothes line. I need to have access to the workbench to mix paint but not bump into the parts. With two bikes worth of painted parts, it’s crowded.

Test Hanging Parts to be Sure There is Room to Work

Test Hanging Parts to be Sure There is Room to Work

Adding Hanging Wires to Parts

I make sure I can hang all the parts easily. In the case of the side covers and bikini fairing for the Silver Ghost, I add some wire so they are easy to hang on the hangers.

Wire for Hanging Side Cover

Wire for Hanging Side Cover

R75/6 Bikiini Fairing Hanging Wire

R75/6 Bikini Fairing Hanging Wire

For the gas tanks, I use short bungee cords and put the ends through the holes on the tank strap at the rear of the tank. I can pass the bungee cord over the clothes line and hang the tank for painting and drying.

A Place to Mix Paint & Clean Guns

I want a place where I can mix paint and clean up, but I won’t be near the drying parts. And, I need to have a clear path between it and the paint booth. I use the second work bench I just added this winter. It has a large enough surface that I can put the paint instructions on it and the mixing containers, filters, filter stand, paint cans, lacquer thinner for cleaing, access to paper towels and a rack to hold the paint gun. I learned the hard way from my first time painting. I had a cramped work space and knocked over mixed paint more than once.

Primer Materials, Mixing Cups, HVLP Paint Guns, Gun Rack

Primer Materials, Mixing Cups, HVLP Paint Guns, Gun Rack

Protecting Things from Stray Paint

You would be amazed where sprayed paint goes: Always on what you don’t want it to. 🙂 I am storing both the Silver Ghost and Grover in the workshop, so I cover them completely with sheets so no stray paint gets on them. I also cover windscreens with newspaper and any spare parts are in boxes or drawers.

Protecting Me While Painting

It is important to protect myself from solvents and paint while painting.I use a one piece suit with hood to keep paint off my clothes.

Painting Body Suit

Painting Body Suit-$10.00

I use a respirator mask and filter from 3M rated for solvents. I got this at my local Sherwin Williams store when I painted the Silver Ghost. Since that is three years ago, I bought a new filter as they have a definite life expectancy.

3M Respirator and Filters

3M Respirator and New Filters

The filter cartridge attaches to a fitting on the side of the mask and contains activated charcol. It has an exterior particulate filter that attaches to outside of the cartridge.

Cartridge Respirator Filter Installed (Grey Plastic)

Cartridge Respirator Filter Installed (Grey Plastic)

Particulate Filter Attached to Outside of Cartridge Filter

Particulate Filter Attached to Outside of Cartridge Filter

To test the fit of the face mask, remove the filter cartridges. Put the mask on your face, adjust the straps for a snug fit and put your thumbs over the holes where the filter cartridge mounts and suck in your breath. The mask should compress around your nose and mouth. That means it’s providing an air tight fit. When painting, you should not be able to smell the paint. If you do, you should adjust the respirator for a snug fit and/or check that the filter cartridge is tightly attached NOW, not later.

I wear eye protection and gloves when painting.

Protection Supplies for Painting (and a Tack Cloth for Cleaning Parts)

Protection Supplies for Painting (and a Tack Cloth for Cleaning Parts)

Painting requires atomizing paint and solvents with air, which is what a carburetor does. That means it’s much easier to ignite this mixture.  So, I took my fire extinguisher off the wall and have it handy just ouside the entry to the booth as insurance.

Emergency Insurance

Emergency Insurance

Paint Specifications

The paint kit Kent Holt supplied has enough material to do one bike. I have two kits, one Monza Blue and the other Smoke Silver.  The primer, base coat (color) and clear coat in a kit each have a specification sheet.

Primer Instructions

Primer Specifications & Instructions Sheet

This provides important information I need for a good paint job. It shows the ratio of material to mix (there are different materials for the primer, base and clear coats), the paint gun nozzle size, the pot life, the flash time and the dry time.

Material Mixing Ratio

The primer mixture is made from three materials: the primer, the hardner and the reducer. The specification sheet shows these are mixed in a 4:1:1 ratio meaning 4 parts primer, 1 part hardner and 1 part reducer. I use a paint mixing cup that makes this fool proof.

Paint Mixiing Container Graduated for Mixing Ratios

Paint Mixiing Container Graduated for Mixing Ratios

On the side are different ratios commonly used when painting. There are several vertical sets of bars for mixture ratio. Shown here is the 4:1:1 set of bars. Each set of three bars is labeled “1, 2, 3, 4,” etc. correspond to a different volume of finished mixture. This lets you mix a little or a lot depending on how much you think you need. The cups are available at any local autmotive paint supplier. I got mine from TCP Global, when I ordered my pin strip paint and tape and paint filters.

To mix a “6” level of primer, I pour the primer up to the first “6” line, then the hardener to the next “6” line and finally the reducer to the third “6” line. Then I mix with a wood stir stick for about a minute or so and pour the paint through a filter into the paint cup on the top of the paint gun.

Paint Filter and Stand

Paint Filter and Stand

HVLP Gravity Feed Container with Primer

HVLP Gravity Feed Paint Cup with with Primer

Pot Life

The pot life is how long the paint can stay in the gun before it sets up. This primer has an 8 hour pot life.

Flash Time

The flash time is how long you need to wait between coats. Flash refers to the evaporation of the solvent from the primer. This primer takes 60 minutes at 68 F and will be less in warmer temperatures.

Drying Time

The drying time depends on how you dry the primer. For air drying at 68 F, it takes 8 hours, but at 140 F (with a heat lamp), it takes 30 minutes while an infrared heater takes 11 mins.

Painting Equipment

I need a compressor, hoses, pressure regulator, oil/water filter, and a spray gun, or guns.

Air Compressor

This time around, I have my own compressor and I added some paint guns to the tool kit. The spray guns I finally selected I got from Eastwood and are HVLP (High Volume Low Pressure) and require 4 SCFM at 30 PSI at the inlet to the gun.  I decided to get the three gun kit including a panel, detail and air brush. This maybe overkill, but I anticipate needing a smaller detail gun to bleed the smoke color on top of the silver for the Silver Ghost while the panel gun is necessary to apply the primer. The air brush is for “fun” so I can experiment with one. 🙂

The compressor is one I found at Home Depot and is rated for 4.4 SCFM at 40 PSI. This is important since the HVLP guns require 4 SCFM at 30 PSI at the inlet to the gun.  I chose an oil less compressor to limit opportunities for oil contamination in the air. I also use an oil/water filter on the supply line to have a clean air supply.

Spray Gun & Mixing Needle Size

I chose HVLP guns which are very common. The bigger gun can use mixing nozzles and needles of 1.2, 1.4 and 1.8 mm.

Spray Gun Nozzle, Cap and Needle

Spray Gun Nozzle, Cap (with blue ring) and Needle

The “Gravity Cup” specification on the paint specification sheet shows the mixing nozzle and needle size in mm. It calls for 1.5 mm for the primer. I have a 1.4 mm and 1.8 mm so I will choose one and then test it on a test panel before I spray the parts. If one size doesn’t work well, I can change to other until I am happy before I paint any parts.

Test Panel to Adjust the Spray

I use an old piece of 1/4 inch plywood with a sheet of newspaper for testing. I just wrap another sheet onto the plywood for the next test. You can see it leaning up against the wall in the paint booth behind the saw horse.

Plywood Test Panel with Newspaper Behind Saw Horse

Plywood Test Panel with Newspaper Behind Saw Horse

Setting Up the Compressor

I have a 25 foot 3/8 inch hose for spray painting. My compressor has two outlets, so I use one for tools and the other for painting. I attach an oil/air filter to deliver clean air to the end of the hose that plugs into the compressor outlet.

Oil/Water Filter on Inlet to Hose

Oil/Water Filter on Inlet to Hose

The compressor has an outlet pressure regulator and I set the oulet pressure from the holding tank to 50 PSI. The compressor will operate when the air in the tank drops to 90 PSI and then continue pumping until it reaches 100 PSI when it automatically shuts off.

Compressor Outlet Pressure Set to 50 PSI

Compressor Outlet Pressure Regulator Set to 50 PSI

I use a second pressure regulator on the other end of the hose just before the snap fitting I attach the spray gun to so I can set and monitor the inlet pressure to the gun easily while I paint. The gun is designed for 29 PSI inlet pressure and will maintain 10 PSI pressure at the nozzle. This means the gun meets the low VOC regulations established to reduce environmental contamination from the solvent and paint.

Pressure Regulator at Paint Gun Snap on Fitting

Pressure Regulator at Paint Gun Snap on Fitting

Setting Up the Paint Gun

Each gun can be setup differently with adjustments according to the instructions. This gun has three adjustments, spray pattern, paint flow and air flow.

Spay Gun Insructions for Controls

Spay Gun Insructions for Controls

In addition, I can change out the mixing nozzle and needle to match the primer, paint and clear coat specifications. With all these adjustments, testing the gun on a test panel BEFORE you spray a part is essential. Temperature, humidity and the mixture all affect how well the material will, or won’t atomize. Every time I mix a new batch of material, I test spray and adjust the gun and then spray the part.  Even with all that, I expect to have some runs, waves and splots now and then. But, that’s what sand paper was invented for. You can always fix a paint mistake with sandpaper 🙂

5 thoughts on “51 BMW 1973 R75/5 Setting Up A Paint Booth & Paint Equipment

  1. Pingback: 1973 R75/5 Rebuild: Setting Up a Paint Booth & Paint Equipment | Motorcycles & Other Musings

  2. Hi Brook Are the black side panels on late seventies R series a gloss paint ?,they seem to me to have an almost plastic look,or is that because i have only seen old ones?.Ian

    • Hi Ian,

      The 1983 RS I am working has a matte finish on the battery covers and rear fender. My 1975 R75/6 had gloss paint on both. I suspect the kind of paint on the battery covers changes with the overall paint scheme, so there may not be a single answer to your question.

      I hope that helps.


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