MasterSeries Silver, SPI Epoxy, and a head to head adhesion test

[Evil_Fiz]

The adhesion test data starts in section 3 below.
This post is intended to provide information to users who are not familiar with the products or are new to the restoration hobby.

REALLY Long post ahead; get confortable

Here are some of the things I learned the hard way:

Reference material
- Karmann Ghia chassis and floor pan measured drawing (Metric): https://www.thesamba.com/vw/gallery/pix/1491678.jpg
- Ghia body hoist frame - for use with a comealong: https://www.thesamba.com/vw/gallery/pix/1494719.jpg
- Ghia Body dolly - measured drawing and materials list: https://www.thesamba.com/vw/gallery/pix/1494718.jpg
- 180* under-car - Type I rotisserie (Measured Drawings): https://www.thesamba.com/vw/forum/viewtopic.php?p=9000133#9000133


Paint removal and metal prep
- If you plan to take the whole car to bare metal you may want to look into building a body dolly or a rotisserie.
- If you plan to strip paint from hard-to-reach areas, make sure it "really" is necessary. Hard to reach = hard to paint. If there is no rust under the paint and it is well bonded to the metal, scuff it with 180# sandpaper or a Maroon Scoth-Brite pad, if you plan to paint over it, and move on. otherwile, leave it alone.
- Decide ahead of time what product you will be applying as your first layer onto bare metal. That will determine how you prep the metal.
--- MasterSeries Silver = OK to use phosphoric acid
--- Epoxy = NO PHOSPHORIC ACID, EVER
- The options for stripping and prepping the metal for primer are, in order from best to least best:
--- Sand/Glass Bead/Coal Slag blasting = expensive if contracted out but puts the best profile (tooth) on the metal for paint adhesion. You can Blast, blow off thoroughly with compressed air, and paint all in the same day. Budget permitting, this is the route I recommend and will take on my next project. Factor in between $1200 to $2000 to have it done. Ask for references and make sure they know how to blast a car to prevent the warping of large panels. A rotisserie will save money by saving blasting time. If done in sections at home the same process applies. For home blasting, a 100 Lbs. capacity pressure pot blaster is the better option.
--- Chemical stripping = Cost-effective but time-consuming. You will need paint stripper, different size metal putty knives, and coarse steel wool. You can get to every last bit of the car this way but your fingers, hands, and arms will want to call in an air strike on you. I speak from experience. This is the route I took. It poses no threat of warping the metal but will need to be thoroughly neutralized and washed off after applying. You will also need to sand the metal with 80# sandper by hand or machine to provide a good "tooth" for the primer to bond with.
--- Mechanical stripping = Cost-effective, time-consuming, but only suitable for exterior surfaces. You will need coarse sandpaper (80# and lower), a Dual Action sander and suitable sanding discs (PSA interface pad and discs are better for this process), a grinder with wire brush attachments, 5" fiber stripping discs, and a small sanding block. You will also need these tools if you chemical-strip the car.


Primer options and Testing
I performed comparative adhesion testing on MasterSeries Silver (MSS) and Southern Polyurethane Inc (SPI) Epoxy. These products have completely different chemistry but perform the same function, i.e. they are moisture-proof primers and are intended to be applied directly onto adequately prepared bare metal. MSS is a Smaba favorite and is sold by Smaba member Chuck P/"VWSplitMan". SPI is as good or better than the "Big Name" epoxy brands and is a small, family-owned business. Both companies have great customer service and tech support. Both products are far less expensive than the "Big" brands and perform on par with them.

|| Primer properties ||
- MasterSeries Silver
--- Color = Silver/Aluminum
--- Chemistry = High solids Moisture Cure Urethane with a high concentration of fine aluminum/aluminium powder
--- Mix ratio = 1-part product; ready to spray out of the can
--- Environmental conditions = Above 35*F and below 60% relative humidity
--- Application = Can be sprayed or brushed on
--- Flash time between coats = 2 - 3 Hrs.
--- Recoat window for chemical adhesion = 48 Hrs. Max. After 48 Hrs, the MSS must be wiped with MS reducer and sanded with 320# sandpaper. MSS or epoxy must be resprayed to renew the chemical adhesion recoat window.
--- Recommended Minimum Panel prep = Remove loose rust and treat with phosphoric acid. Smooth bare metal should be sanded with 80# sandpaper or sand-blasted. All panels should be cleaned with waterborne wax & grease remover until fully clean.

- SPI Epoxy
--- Color = White, Black, or Grey
--- Chemistry = High solids 2-part epoxy
--- Mix ratio = 1:1 epoxy/activator
--- Environmental conditions = Above 65*F (strict )and below 90% relative humidity (recommended). Must be kept above 65*F for 24 Hrs. after application
--- Application = Can be sprayed or brushed on
--- Induction time after mixing = 30 Min. to 24 Hrs. in a covered container
--- Flash time between coats = 30 Min.
--- Recoat window for chemical adhesion = 7 days Max. After 7 days the epoxy must be sanded with 180# sandpaper. A single coat of unreduced epoxy must be resprayed to renew the chemical adhesion recoat window.
--- Recommended Minimum Panel prep = Remove ALL rust. Smooth bare metal must be sanded with 80# sandpaper or sand-blasted. All panels must be cleaned with waterborne wax & grease remover until fully clean.

|| Test Conditions ||
- Air Temerature = 65*F
- Overnight Temperature = 45*F
- Home 2-car garage spray both with 2 3500 CFM axial drum fans to remove fumes and overspray
- Panel NOT KEPT above 65*F for 24 Hrs. after application

|| Test methodology ||
- test panel = Karman Ghia hood
- Purpose = A test to determine the performance and adhesion of both products under less than ideal or recommended conditions. Temperature, Humidity, and metal prep were all outside the recommended parameters.

// Panel prep \\
- Chemical paint stripping with Citri-Strip paint remover
- Washed with Dawn/water solution and rinsed with running water
- Wiped metal with a phosphoric acid solution - 2 passes (Eastwood After Blast) brushed on then wiped off
- Allowed acid to fully dry to confirm the absence of any white, powdery residue.
- Hand and DA sanded the left side of the hood with 80# sandpaper to remove the phosphoric acid coating and provide proper tooth
- Divided the hood into quadrants with 2" painter's tape and taped off 1" around the perimeter
----- Upper Left = Q1 (Acid then sanded)
----- Upper Right = Q2 (Acid only)
----- Lower Left = Q3 (Acid then sanded)
----- Lower Right = Q4 (Acid only)
- Cleaned the panel with waterborne wax & grease remover; 2 passes

// Primer application \\
- Paint gun = Vevor R500 LVLP (6 CFM max air consumption)
- Paint gun settings = 26 PSI, 1.4 Tip, Fan and fluid wide open
- Compressor - 3 HP/60 Gal./135 PSI/12 SCFM @ 90 PSI
- Sprayed 2 thin coats of MSS on Q1 and Q2. Flash time between coats was 3 Hrs.
- Allowed 24 Hrs dry time
- Sprayed 2 thin coats SPI Epoxy over MSS on Q1 and Q2. Flash time between coats was 30 Min.
- Adhesion between coats was chemical only.
- Sprayed 2 thin coats of SPI Epoxy on Q3 and Q4. Flash time between coats was 30 Min.
- Allowed 48 Hrs. dry time after the last application

// Adhesion Test \\
- Removed tape after 48 Hrs.
- Stored hood in an enclosed garage for 7 days
- Sanded with 80# sandpaoer on a DA sander
- Sanded quadrants until there was a feathered edge all around
- Scratched panel with a flat screwdriver and 1/2" wood chisel until bare metal was reached
- Stripped panel of all paint with fiber-mesh stripping disks and 80# sandpaoer with DA sander and by hand

// Results and Observations \\
- Both products had exceptional adhesion on all four quadrants of the panel
- The lack of sandpaper scratches did not have any noticeable effect on MSS adhesion to bare metal
- The lack of sandpaper scratches or the possibility of acid film contamination did not have any noticeable effect on epoxy adhesion to bare metal
- The MSS appeared to have a slightly stronger bond on all 4 quadrants
- It took a fair bit of effort to scratch the epoxy-over-MSS quadrants
- It took slightly less effort to scratch the epoxy-only quadrants


EDIT: Detailed Results

|| Q1 - Acid treatment then sanded to bare metal ||
// Expected Results \\
- Excellent mechanical adhesion of MSS to bare metal
- Excellent chemical adhesion of SPI Epoxy to MSS
- Smooth feathered edge transition between Epoxy and MSS
- Smooth feathered edge transition between MSS and bare metal
- Elevated effort needed to completely remove coatings from metal

// Observed Results \\
- Excellent mechanical adhesion of MSS to bare metal
- Excellent chemical adhesion of SPI Epoxy to NSS
- Smooth feathered edge transition between Epoxy and MSS
- Smooth feathered edge transition between MSS and bare metal
- Elevated effort needed to completely remove coatings from metal


|| Q2 - Acid treatment-only over smooth OEM metal finish ||
// Expected Results \\
- Reduced mechanical adhesion of MSS to bare metal
- Excellent chemical adhesion of SPI Epoxy to MSS
- Smooth feathered edge transition between Epoxy and MSS
- Compromised feathered edge transition between MSS and bare metal
- Reduced effort needed to completely remove coatings from metal

// Observed Results \\
- Excellent mechanical adhesion of MSS to bare metal
- Excellent chemical adhesion of SPI Epoxy to MSS
- Smooth feathered edge transition between Epoxy and MSS
- Smooth feathered edge transition between MSS and bare metal
- Elevated effort needed to completely remove coatings from metal


|| Q3 - Acid treatment then sanded to bare metal ||
// Expected Results \\
- Excellent mechanical adhesion of SPI Epoxy to bare metal
- Smooth feathered edge transition between SPI Epoxy and bare metal
- Elevated effort needed to completely remove coatings from metal

// Observed Results \\
- Excellent mechanical adhesion of SPI Epoxy to bare metal
- Smooth feathered edge transition between SPI Epoxy and bare metal
- Elevated effort needed to completely remove coatings from metal


|| Q4 - Acid treatment-only over smooth OEM metal finish ||
- Compromised mechanical adhesion of SPI Epoxy to bare metal (Delamination expected)
-Compromised feathered edge transition between SPI Epoxy and bare metal
- Reduced effort needed to completely remove coatings from metal

// Observed Results \\
- Normal mechanical adhesion of SPI Epoxy to bare metal (No delamination)
- Smooth feathered edge transition between SPI Epoxy and bare metal
- Normal effort needed to completely remove coatings from metal


|| Observations ||
- Both products met expectations when applied following ideal/recommended preparation procedures
- Both products met expectations when applied following LESS THAN ideal/recommended preparation procedures
- MSS appeared to have a slightly stronger mechanical bond to bare metal than SPI Epoxy under ideal and non-ideal conditions
- SPI Epoxy did not delaminate as expected over the non-sanded acid-treated metal. This application method is not recommended and was done only as a test.
- Both products required the use of fiber mesh stripping discs to completely remove them from all 4 quadrants of the test panel. The use of 80# sandpaper alone was not enough to efficiently remove the products from the test panel
- MSS required slightly more effort to remove from the test panel than the SPI Epoxy

- - - End edit - - -

- DO NOT USE MICROFIBER TOWELS to apply phosphoric acid onto bare metal, to clean metal or paint with either solvent-based or water-borne wax & grease remover, or to wipe metal or paint with any other solvents. This can lead to paint adhesion problems and delamination.
- Either primer will work well to protect bare metal and detur future rust
- If acid was used to prep bare metal the best option is to sand with 80#, apply 2 coats of MSS followed by 3 coats of epoxy, and finally any filler that may be needed, within the recoat widows
- If acid was not used to prep bare metal the best option is to apply 3 coats of epoxy followed by any filler that may be needed, within the recoat window
- Epoxy is more flexible than MSS and equally tough. It can be used on the body as well as the chassis and pans
- Epoxy provides superior chemical adhesion with filler and should be used below and above filler to provide a moisture-proof barrier
- MSS is sensitive to ambient humidity. Care should be taken to minimize open can exposure to the environment. Do not paint straight from the can if brushing it on. Pour out small amounts and reseal the can immediately.
- Epoxy is sensitive to low temperatures but not to humidity. It can be used for several days after mixing as long as it is stored tightly covered in a climate-controlled area.
- Filler will bond to epoxy within the recoat window without the need for sanding. The filler's chemical adhesion to the epoxy is superior to its adhesion to sanded bare metal. The epoxy-under-filler process prevents rust from forming under the filler
- Neither product is truly UV resistant and should be top-coated with Base/Clear or Single-stage paint.
- Search The Samba for more information on MSS
- Visit/Search the SPI forum for information on their products as well as a wealth of painting advice from Pros and amateurs alike: http://www.spiuserforum.com/index.php

I can't think of anything else at the moment. If you have made it this far in the post, feel free to contribute any wisdom you may have acquired.

We're all in this together,
Emil
_________________
“…It's not just about what's interesting. It's also about what's helpful, and it's helpful even if it helps just one other guy working on a Ghia.”
kiwighia68

See my build on TheSamba at:
The K_R_A_K_E_N_N : a 70 Ghia Convertible reinterpreted

[RLFD213]

When I did my bug, I took it all down to bare metal and brushed 2 coats of MSS. Then did my filler work and covered my filler work 2 more coats of MSS. Then we did high build primer and skim coated filler. And finished with 2-3 coats of sealer. Then paint…… so far so good after 2.5 years

[Evil_Fiz]

I edited the original post to include a detailed results section.

-----
Emil
_________________
“…It's not just about what's interesting. It's also about what's helpful, and it's helpful even if it helps just one other guy working on a Ghia.”
kiwighia68

See my build on TheSamba at:
The K_R_A_K_E_N_N : a 70 Ghia Convertible reinterpreted

[Evil_Fiz]

[RLFD213]

Well I used aircraft stripper, wire wheels and sandpaper to get to bare metal. MSS, then scuffed it. The second time, high build and sealer I used wax and grease remover

[Kafer_Mike]

Thanks for the detailed analysis. I haven't used MSS, but have sprayed SPI (black and white) numerous times without issue. And as you mention, their support is fantastic.
_________________
Kafer_Mike
Build 'em fast...or let 'em sit.

[chrisflstf]

Cool info, thx

[74 Thing]

Very informative! Thanks

[Doumacamatic]

I may be getting myself mixed up with these names so I apologize.

What was the optimal mixing time you used for the epoxy/master series? I didn't see how long you prepped either thing (or i could of missed it reading, so again, I apologize.) for this experiment? I do not know if mixing for longer would yield different results than, for example, mixing for the minimum amount of time.
_________________
"It's Okay To Do Things A Little Differently"

[Evil_Fiz]