Blocking and Finish Sanding

[Fishcop]

Okay experts...

I've got my project to the point where I'm happy the car is close to smooth and has perfect profile, I've been using several of the "Durablock" brand blocks for wetsanding to 400 grit. However I'm not happy with a few blocking marks I can't seem to smooth out, and I think 400 is too course. The area I'm most worried about is the rear "hips" of the car which are arguably the prettiest and most noticable areas of a flaired 911 with their complex convex and concave curves. I have Upol "Dolphin Glaze" for filling minor imperfections and have so far used very little filler anywhere.

So far I have not hand sanded (I know not to use fingers, only soft heel of my palm and let the paper do the work) but I think this is what I need to do as a final step. I also think I should step to 600 grit - is this too fine for single stage solid colour? The tech sheet I have talks about 800-1000, but can't help but think that's too 'shiny'?

I also have two very small places where I hit metal - should I shoot a spot coat of primer back over these areas an blend back in, or can modern 2-pak cope with small direct to metal areas?

I've worked too hard and long to screw this stage up so I'm happy to keep doing it over and over to get it right!

Thanks in advance!

[962porsche]

your right the 800 to 1000 grit paper is not going to work . there is not enough sanding scratch for the top coats to stick to . what paint system are you going to use ? are you going to spray a coat of sealer 1st before you spray your top coat (color) ? glasurit 22 line you want to wet sand with 400 to 800 paper . if your not using a sealer you want to sand using grits 600 to 800 if your going to seal the car then use 400 or 500 grit paper . the thing is if its taking more than 24 hours to prep sand the car . thats from the time you started sanding the 1st panel then you should seal the car . the reason why you would want to use a sealer after that amount of time is because the primer will start to close up the sanding scratches you sand in . when the sanding scratchs closes up there is not much for the color coat to bite into . your other choose is to not use a sealer and to gray pad the hole car right before you blow it off and wipe it down for paint . i don't do the gray pad thing . it makes a mess that gets into the masking paper and just blows out when you paint giving you a dirty paint job . if you want to take a look at the glasurit tech sheets i have pm me your email and i will get them right to you .

[Fishcop]

Thanks again 962

Yes Line22 - I'll PM you my home email, the tech sheets would be great!

I wasn't going to use a sealer as the colour (Ossi Blue) is a high solid mid to dark blue, but I didn't realise there was window in which the scratches close. I'm pretty sure I can mask and paint in a timely manner and not have to use a grey pad. I will pick up some 600-800 grit tonight.

What's your opinion on the two small sand throughs (to bare metal) should I primer back over them?

[962porsche]

you should spray a primer over the brake throughs . you could also spot seal them and just top coat . that way you don't have to go back and sand again . if your using glasurits 285-60 primer that can also be mixed as a sealer . the sand line you were talking about should sand out ? just spray a very light coat of guide coat over were the line is and resand . if your thinking you could get some finger marks from your hand then take some 1.5 inch masking tape and rap it twice around all 4 of your fingers . this will keep your fingers together and that way you can't sand lines in the primer . if your going to do any spot glazing over the primer to fill chips or so on you should spot prime or seal them too . what could happend if you don't a year or two down the road you will start to see the spot coming back . this happends after the finish cures and srinks in .

[Fishcop]

Awesome thanks again.

[village idiot]

I always use a 3M scotchbrite pad cut in half then folded into thirds with the paper wrapped around that. Makes it hard to put finger marks into the surface. Make sure you use lots of water to keep the paper clean, turning it often.

[962porsche]

using a scotch pad is not always the best idea . say you are rapping a peice of 400 paper around a red pad . as the red pads sanding grit is = to a peice of 220 grit paper as the red pad starts to brake down from the sand paper moving around on it the red pads grit will get between the 400 paper and the surface (substraight) and you will be sanding the grit of the pad right into the panel . the same will hold true with a gray pad and its = sanding grit .

[village idiot]

Originally Posted by 962porsche

using a scotch pad is not always the best idea . say you are rapping a peice of 400 paper around a red pad . as the red pads sanding grit is = to a peice of 220 grit paper as the red pad starts to brake down from the sand paper moving around on it the red pads grit will get between the 400 paper and the surface (substraight) and you will be sanding the grit of the pad right into the panel . the same will hold true with a gray pad and its = sanding grit .

Ttue.Which is why I keep a constant stream of water going over the surface to flush it clean.

[Fishcop]

Thanks guys. I ended up picking up a very soft pad with dual density layers (one side is very squishy) which appears to have done the trick on some practice panels. Over the weekend I layed up another coat of primer and some filler which I'll let cure through the week and go at it with #600.

[962porsche]

the motor guard block # AL-1 is a good soft block . i my self like to hand sand using no block on things like the wheel opening on porsches . another thing to do is pre soak your sand paper for 15 minutes to a half hour before you use it . this softens the papers backing so it will not fold with a sharp edge . some people say use soap in the water . thats a big no no ! don't do it .

[DaddyGlenn]

Originally Posted by 962porsche

{snip}.... if you want to take a look at the glasurit tech sheets i have pm me your email and i will get them right to you .

Any chance you can send those my way, too? I'm getting close to the paint portion of my project. And will be using Glasruit 22 also.

glenn861@aol.com