This section covers
Flash Line Removal, Flatting, Gelcoat Repairing,
Compounding, Waxing & Polishing
Surfing the web to learn about sanding, compounds, polishers, polisher speeds, different types of foam pads, lubrication, grit factors and gelcoat properties was very boring and boggling. But after a while, and after watching many YouTube videos, it became clear what I needed to do and how to do it. But I had to sift through an awful lot or bumf to piece together my strategy.
The advice on forums and blogs ranged from "You can never get rid of flash lines completely" and "I just used wet & dry and some T-Cut," to the more elaborate and in-depth blow-by-blow accounts of how to de-flash, repair, compound, wax and/or polish to achieve a mirror finish.
I also spent many hours on compounding and finishing websites looking at their videos which supported their products. All were very good and all achieved a perfect finish. I also learnt loads from yacht repair sites. They too were very useful sources of information.
I also discovered when surfing for inspiration, a very common way of achieving a perfect finish was to use 400 or 600 wet & dry to start, and then 800, then 1200 and maybe 1500, then 2000 and then 2500 and 3000 grit size before compounding.
After much deliberation and indecision I decided to err on the side of caution and start with 800, then go to 1200 and 1500, then 2000 and 2500, then finally 3000. Then I'll give the body a good going over with G3 and G10 (before possibly anti-swirling) and then a good polishing and waxing. I've no idea what polish or wax to use yet as these areas are internet minefields that I don't need to cross yet.
So Down To Business and Here Goes
Flash Line Removal
One of the things that attracted me to GD was the quality of their gelcoat finish. And as the gelcoat on my car was really quite blemish free and shiny, my strategy was to not mess it up more than necessary.
So, having my procedures, tools, and products at the ready, I experimented on the flash-line going across the diameter of the headlight (I haven't cut the hole yet.) This trial area being perfect to verify my research and untried bodywork skills.
A couple of hours later, and with no major issues to write home about, I was ready for the big time i.e. to tackle a real flash-line. I started out very gingerly, picking away with a Stanley blade thinking the whole body would fall apart like some circus jalopy. But after an hour or so, everything was still in one piece so I moved on to tackle a chunk of sharp under-wing GRP with my new file. By this time I was well into my stride, scratching and sculpting away like a good'un with the enthusiasm and vigour of a sculptor creating a curvy masterpiece.
As I am restricted for space i.e. having only a single garage, I decided to take off all the flash lines from one side, the back, and the front of the car before turning it around to tackle the other side.
A few days later, and with all the flash lines reduced to a gentle discontinuity, it was time to tackle the no less traumatic task of intentionally damaging the surface of the gelcoat with wet & dry to get rid of the rest. And in this theme I bought one of those [generic] rubber sanding blocks, the type that fit in the palm of your hand, thinking that was the way to go. But as the residual flash-lines stubs are quite small, and as the block is quite long and wide (125 mm x 67 mm) I was not comfortable using it because it would cause unnecessary damage to quite a large area. So 'Plan B' was invoked and I reverted to my trusty 7x4x2 cm piece of wood with a piece of rubber glued to it. I've used this method of smoothing when DIY'ing around the home so I knew I would have more control over a smaller area.
- A Stanley blade: Used to shave away the majority of a flash line
- A Stanley blade with electrical insulating tape over each end of the blade: A variation of the above method and very effective when shaving to just above the surface i.e. for getting the flash lines to within one tape depth of the surface
- A modified Stanley blade: I ground down each end of the blade leaving an ~5mm raised section of blade in the centre. This created the necessary room to get into areas that were slightly concave
- A variety of files: These were good for removing chunks of GRP. However, this is a very aggressive method and I did have to be careful as the GRP disintegrated like a digestive biscuit dipped in hot tea
- Sanding Block: As stated, I used a small piece of wood with a piece of rubber glued to it. It was big enough to get the job done with the delicacy and firmness required. But this method is no good on concave areas
- A Piece of Copper or Rubber Pipe: I had an issue with some convex and concave areas. The sanding block being too flat for anything concave and not ideal for convex: the Stanley blade techniques could grab in awkward areas and a file is long and usually too flat to be of any use. And in some cases, plain old hand held wet & dry was too fiddly. So I wrapped a piece of wet & dry around a 15 x 50 mm piece of pipe and used it like a spoke-shave. This provided a firm but flexible sanding edge which contoured to the body thus providing the control I required
- Just plain old wet & Dry: Used during most methods and was very effective. Tacitly, this was very good as the flatting surface contoured with what needed doing.
Freshly Hatched In The GD Loft
Untouched flash line and gelcoat default shine.
(The white bits are sticky-tape glue stuck to the body)
Work in Progress
The above picture is with the flash line removed and the area sanded with 800, 1200, 1500 then 2000 grit wet & dry. Notice the shiny vertical area through the scuffing. I tried a little G3 and then G10 and buffed it up with a clean rag as an experiment, and I was pleasantly pleased -and relieved- with the result. The white tape glue was removed with a squirt of WD-40. I rubbed some on with a paper towel and let it soak in for a few minutes. It then peeled off easily.
I used the camera flash for this photograph as the intense light accentuated the scuffing. So it looks worse than it really is. But running my hand over it I couldn't detect any ridges, only a change in resistance due to the scuffing. Job well in hand and I can't wait to get buffing with the electric polisher.
Five long afternoons later, all flash lines are gone and the body is as smooth as the gurgle of a V8 gargling cough mixture. Now I have to learn about gelcoat repairing, compounding and then polishing & waxing.
I'm pleasantly pleased I don't have to do too many gelcoat repairs... And not able to put it off any longer I decided to bite-the-bullet and get on with it. But first I needed to practice and do a couple of experiments.
For this, I used the centre [waste] GRP disk piece from the headlight. First I created some damage with my Dremel and a Stanley knife, then I made up a small amount of gelcoat repair mixture. One tablespoon of gelcoat to a smidgen of catalyst. I agonized how to measure 3% of catalyst, the percentage being dependent on the outside temperature (so I've been lead to believe.) But... having lost the plot many times on how to measure this accurately -and- to supposedly allow for the ambient air temperature, I decided to guesstimate the 3% smidgen of the catalyst using a plastic teaspoon and ignore the temperature factor. ( * More on the temperature factor later in this article.)
Having mixed the brew, I spatulared the dark gloop (RAL9005) onto and into the damaged areas with a cocktail stick, trying to be careful not to get it too proud of the undamaged surrounding areas. Then I covered the repairs with cling-film. Apparently, gelcoat might not go off if exposed to the air. I also made a similar test area using the scrap bit of GRP from the front oval vent. This to be my "non-covered" experimental test piece.
So far so good, and I noticed I had about 10 minutes before the brew "went off" and became unusable. I was also quite pleased that it was easy to apply and that it didn't run much.
Note to self: Wear gloves next time.
The next day I reviewed my experiments and was very pleased with the outcome. The cling-film did, however, stick to the gel coat, but it came off with light sanding. And the uncovered experiment similarly hardened, which surprised me. I also peeled off the residual hardened brew from the inside of the mixing pot to see how it had dried, and it was reassuringly hard but flexible. So tomorrow, it's gelcoat repair day...... Result!
But... I now have "Plan B" to consider..... Got talking to Keith Akerman and he suggested I take a look at Mark T's website (which I did.) Some excellent information on gelcoat repairs there, and I have modified my repair procedure, that being I will be covering the wet gelcoat with PVA -not Clingfilm. Mark T' also made reference to an acetone finishing technique, but I don't intend to do this as there is a risk of the acetone damaging the GRP unless you really know what you're doing... which I sorta' don't... More details on Mark's website
So the next day I applied a brew of goo to the damaged areas and covered them with PVA. I then waited for 24 hours before starting the next phase. This being sanding and finishing.
The following day I tried to remove the PVA scabs. And what a kerfuffle that was... After wetting the PVA and waiting for it to go white, I tried to peel it off. The smaller scabs came off quite easily but the bigger scabs stuck to the new gelcoat like a limpet on a rock in a storm. I tried drenching the areas with water-soaked kitchen paper, but to little avail. So I spent all morning picking away to get to my gelcoat repair. I also had to use my scribe to pick and prise the PVA out of the deeper indentations. Here is a short video of my PVC Removal efforts...
Really not a good day. I'm not going to use the PVA method on the larger areas, I've decided to just let the repairs cure "al-fresco."
Comment: When you think about it, the final surface of gelcoat that will be seen is, in effect, beneath the surface of the new gelcoat surface, so when it's sanded down and finished all should be good.
General Gelcoat Repair Procedure:
- Opened up the damaged areas to provide a keyed surface with my trusty Dremel and a 2 mm Diamond Point bit.
- Made 1-2 mm indentations on the larger areas thus provide a well-keyed surface for the bonding process
- Mixed no more than a couple of tablespoons of repair elixir for each session
- Used a wooden cocktail stick and/or a modified paint brush [I'll explain later] to apply the mixture
My main repair areas and the areas that concerned me most were the ridge along the top of the doors and the joint at the back of the engine bay just below the bonnet lip. These are very messy and bumpy areas and they looks awful. The doors having a 1-2 cm wide damage line along the top and of which is peppered with little pin pricks and indentations and the bad bits in the engine bay looking very scrappy.
Procedures for these repairs:
- Engine Bay Area: I keyed the surface with my Dremel and the 2 mm diamond drill bit. Then I slapped on a generous coating of the shiny black brew.
- Top of Door: Keyed the surface with a round file (as it's a convex area.) Then I slapped on a generous coating of my black brew with my [modified] paint brush applicator. Not happy with my repair on this area but it'll have to wait until spring. It's too cold now (Oct.)
* Note... I noticed my gelcoat repair mixture was not 'going-off' as easily for the doors (Oct.) And when I did my windscreen spindle fitting by using some gelcoat to create a smooth surface for the spindle to sit on the GRP (Nov,) it didn't go off at all until I heated it up gently with a heat gun. Then all was good... So it appears the temperature factor is very important. I'm not doing anymore gelcoat repairs until next summer. It's not worth the hassle -and the IVA tester doesn't care how good my gelcoat repair skills are.
Modified Paint Brush Details: The cocktail stick method of goo application was good for the smaller areas, but on larger areas this type of applicator was no good because I could not produce a flat'ish surface. Moreover, this is a very slow method of applying the mixture, and, as time is always against the repairer, I needed to apply it fairly quickly... But with what!!! A standard ¼ inch paint brush was too big, and the smaller artist type brush was too floppy -and if I'm honest- too expensive to use for this kind of job. Each brush being a one time deal.
So I took a 50p two-inch brush that had quite tough nylon bristles and some small tie-wraps and I made a number of littler brushes from the big one. This was the perfect solution as the brush area was small enough to be manageable but large enough to provide good coverage. The bristles were also long and firm enough to provide positive control, and it held enough of the gloop to be able to produce a flat'ish repair surface quickly. Bottom line: one 50p brush made about 12 small brushes.
What an internet minefield this is. Some products being ridiculously expensive and come in quantities the majority of which would be sitting on the garage shelf congealing for the next 20 years. So, at this stage, and as I don't want to pay an inordinate amount of money for essentially shelf jewelry, I opted for a couple of bottles of Farécla G3 and G10 as my starter-for-10 (excuse the pun.) The decision clinchers' being, Farécla has a very good reputation, it's been around for years, it's not expensive and the advertising bumph told me exactly what it was meant to do.
1st Try with the G3: I fired up my new electric polisher using a moist, firm density compounding pad, a squirt of G3 and some water. Result.... Pants to say the least.
I did eventually have some success on the side panel but I couldn't remove some slightly deeper scratches or some niggley imperfections. Moreover, the pad totally disintegrated after a couple of hours of gentle use. I was not impressed in any way shape or form... The pad was supposedly a decent one and advertised as being for course compounding use. But, having had three disintegrate in quick succession, I really was getting a bit pissed off.
So I had a decision to make, that being to buy more of the same type and carry on regardless; to buy more and reduced the polisher speed, or taking the risk of ordering a different make and density and start again from scratch. But, not being ready to commit to any option I did some more research. My conclusion being the pads I were using were too soft and generally rubbish.
And in that theme, I discovered that pad technology is a very complex subject and the definition of "firm" being relative and open to interpretation. So thinking somewhat logically, I opted for some 'firm' 50 x 150 mm Velcro backed pads from The Polishing Shop. Essentially I bought two very firm compounding pads, two medium density polishing pads, and an M14 backing plate for less than 30 quid. My rationale being, Velcro pads are less expensive than the M14 molded on type and I'll have a backing plate for anything else I want to do in the future. The gelcoat finishing rep' I spoke to also confirmed my findings that the pads I had were of the cheapish import type and are not what I should be using for what I wanted to achieve (to put it politely.) So a couple of days later I was back in the garage with renewed enthusiasm, buffing away with a pad that stayed in one piece.
Compounding Procedure Used:
- Got rid of any imperfections with 2000 grit wet & dry, but I did use 1200 and 1500 grit where necessary
- Washed the car with clean water and a new sponge
- Mopped the body over with a new microfiber cloth (which was very therapeutic)
- Compounded with G3 over the whole body, polisher set at about 1800 rpm. Clean water was used as the lubricant and heat dissipater. And I don't think I was being overly cautious by using a new spray bottle, therefore avoiding unintentional chemical contamination from a cleaned out spray bottle from the kitchen
- Washed the car with clean water to removed the residual G3 compound
- Mopped the body with a new microfiber cloth
As you can see from the below pictures, the camera flash accentuates the fine lines that the G3 won't [as yet] get rid of. I expected it to be flatter than that... Maybe I just need to continue!
Inside the garage - Camera flash on
The reflection shows the overhead storage platform and my sparsely populated tool board
Niggly little lines that need to go - not good so far
And the swirl lines that need to go
(and a 50p as a point of reference)
Got talking to a [different] professional GRP finisher about the fine lines that I can't shift, and he informed me that if the temperature in the working environment [the garage] is too low, flatting cold gelcoat can be like using a damp doughnut to polish granite. I have to admit, I was flatting [on-and-off] between Jan-March, and the air temperature in the garage was about 8-10 degrees centigrade, and that was with the wall heater going. Moreover, the gelcoat was very cold all the time I was working on it -and- I was using cold water to lubricate the pad.
Retrospectively it appears I did everything wrong for the time of year. He suggested when flatting in winter, the garage will need to be at least 15 degrees and he recommended I also slightly warm up the gelcoat with a hair dryer or heat gun....Not my first course of action Kemosabe. But as this is all new to me, and to minimize the risk, but to try to recreate the conditions, I compromised and waited for a lovely spring day (May) and let the car sit in direct sunlight to warm up. I also used warm water as the lubricant. Conditions were 18 degrees in the shade and about 30-33 degrees in direct sunlight.
Success... The gelcoat responded better to the wet & dry, and the G3 with the polisher was much more effective. I did, however, have to be much more careful as I realized that even a creased piece of wet and dry could mark the surface. I also went over the scuffing with 2500 and 3000 grit wet & dry before using the polisher.
So armed with this new awareness I'm encouraged that I've reached the point where I want to be with the reams of varying degrees of wet & dry and G3.
2nd Try with G3
(with my extra 2500 & 3000 handiwork)
I'm really am not this short and dumpy but I could do with losing a few pounds (of the weight type...!) I'm quite used to losing a few pounds of the "Sterling" type as I haven't finished my build yet.
Hmmm..... let me correct myself. When building a Cobra, you will not looosse anything. The pounds are just tied up in the car until you sell. So in effect, and with the banking interest rates being virtually non-existent, it's a no-cost exercise in asset management. (That's my interpretation of a no-risk investment strategy and I'm sticking to that story-line.)
The scuffing I need to get rid of is just left of centre of the air intake.
(The other things that look like scuffing are cloud reflections)
(Not tooooo bad!...!!! I think I'm ready to try some G10)
Did a couple of passes with G10 and one going over with Meguire's "Ultimate Compound"...
Very impressed with the result
And with some polish and wax -and it's first Christening.... Am very impressed
Front Oil Cooler And Oval Side Vents
I wasn't sure where to put my information on my body piercing activities as they are apparent in many of my build activities. Nothing too dramatic about this only to say the Dremel, a bunch of files and a lot of courage was all that was needed to get the front end in shape.
The front oil cooler vent I did using the Dremel and the spiral cutting bit. It had been scribed but I verified using Keith Akerman's marking gauge technique. Happy with this. And not wanting to mess up the GRP by cutting too close too soon I decided to cut ~5 mm inside the line and work out gradually. Having cut the hole I had much better access to the inner rim and of which I trimmed to within ~2 mm of the scribed line using the Dremel "Speed click" cutting wheel. The final dressing being with 40 grit sandpaper and a variety of files.
A similar technique was used for the two outer oval vents except I had to eyeball where to cut the hole. No factory scribed markings. The final sanding being done with a round and a flat file.