I did not have to "grind out my seams" on my MKIII. I sanded close to flat my seams were clear of gelcoat. I shaped with Rage Gold and went about the rest of the body work. Check your seams before you go grinding down deep and creating work.
There are people with more expertise than me on this board, but this is the advice I got on the MKIII and it worked great for me.
Some of the MK III bodies are very good, some are very bad. You need to grind the seams to take a look. Also go to search function and type in "seam grinding". This is just one thread on the subject. HTH Mac
Dremmel will work but takes awhile. I used a 3/8 rotory file in a die grinder to remove the gel coat from the seams on my Mark3, some use a angle grinder held side ways to grind out the seams.Some places needed to be ground 3/8" deep to get the gel coat out. Sand the seams flat since they are uneven to begin with and once the gelcoat is sanded off you will be able to see if any gel coat line is present in the seam.I used a disc sander with 80 grit to knock down the ridge. Some m3's were good,some bad but you need to check. If you do find some seams that need grinding once done fill with the 3M hs filler. All you want to do with the filler is replace what you ground out,no real shapeing or contouring as that gets done with the Rage or whatever brand of body filler.
Here is what I used. Finished the whole car in only a couple of hours. Works great for the seams and getting the car blocked and ready for paint. This is my third one I have owned. I wore the other two out. I love them. They make short work of bondo and other sanding and blocking needs. Got mine from Grainger for about $100. Best rough body work tool in the tool box.
I used my dremel tool with the router attachment. I was able to set the depth and not worry about going in too deep. I used one of the pointy grinding stones. Then you can use a different attachment to angle the edge so you can fill it the right way.
Just make sure you don't use ordinary filler to fill the seam after grinding...A really good glass-filled product is needed (like 3M)...Evercoat also makes a short-strand glass-impregnated seam filler , as does Bondo.
I used a 1/4" round nose burr in a die grinder. Grind about 1/2 of the depth of the mold seam out. Fill the ground out seam with West Marine polyvinyl resin stiffened up with their silica filler. This is the same resin that the body is made of. Sand the seams down and then shape with Rage gold. This way the seams will expand and shrink the same as the body and will not come back to haunt you. Good Luck!
FFR bodies are made with ""Vinyl Ester" resin. No "Poly" that I know of. 3M HSRF is the only "Vinyl Ester" filler that I've heard of. From their label; "3M Marine High Strength Repair Filler is a uniquely modified vinyl ester structural filler formulated with short strand fiberglass for non-fairing applications. Sanding of this high strength filler is difficult". Keep it low and finish with "Rage Gold". Your life will be a lot easier.
If anyone wants the sander Lowcountry was talking about you can find it here http://www.aircompressorsdirect.com/catalog/product_info.php?products_id=649
I took a look at Mr Macs site but didn't see it there. The only question I have is with all the compund curves we have on this body, I'm not so sure this is the right tool. Quick and easy usally means low quality. That's just my 2 cents
It's not the tool but the users hands that make the difference in quality with the straight line sander. It works exactly like blocking the car with a long board but a lot faster. Making up to 3000 strokes a minute takes a lot of elbow grease out of the equation. If you don't use it right it will flat spot the car in a hurry but if you use the 45 degree cross pattern and roll the curves correctly it will make short work of the seams and give you a beautiful job in the process.
Here are some pics of my car.
Here you can see the vertical seam only half done.
First coat of FeatherFil.
Here are the specs on the sander:
Description: Twin piston prevents stalling and provides smooth, reliable power. Automatic trigger release with positive-stop action. 3,000 reciprocating 1-inch strokes per minute for efficient performance. Excellent for Smoothing Down Body Filler or Shaping and Leveling Large Flat Areas. Average use 8 CFM. Requires 90 psi.
Always get the right tool for the job. I think it makes all the difference in the world.
Air file like pictured above can and will make short work of sanding the body filler. You will still need to do the final blocking by hand and unless you have the experience useing a air file you may not want to use it unless you plan on doing a few bodys. Probally the toughest part of getting the seams to come out smooth a straight is how you apply the rage. Putting on the rage or body filler evenly and thinnly so it follows the fenders contour is the biggest help in getting them to turn out looking good. Someone mentioned useing a hack saw blade useing the dull side to apply and smooth the filler over the fenders countour. It does work, same as a large size plastic squeegy does. Applying the filler so it has the basic shape of how you want the finish contour to look is one of the easyest ways to make less work out of snading and blocking the fenders. Also don't add little spots of filler here and there to try and make thing even but apply a thin smooth skim coat over the entire area. This helps blend and keep low,high spots form comming thru as you block thru different layers of filler.
Hind Sight is right. My finial primer pic is after about 1/2 gal of Rage applied with a wide plastic squeegy in wide thin coats several times. This was then sanded again with the air file or straight line sander to get the rough shape. After several coats of Rage, several sanding sessions and more Rage and as the finish got closer to the finial appearance I switched to hand blocking only. To get to my finial primer coat three more coats of FeatherFil G2 were applied and hand blocked for the paint ready finish. The sander just speeds the process up alot. Taking a job that has taken some weeks to complete and making it a weekend task. Getting the body finially paint ready is still a long process but you have to let the right tools help you to speed along the process.
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