Block sand after which coat of primer?

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PostPosted: Sat May 07, 2011 9:49 am
odg is always right :rotfl: :rotfl: :rotfl: :rotfl: :rotfl: :rotfl: always guide coat, whats it going to hurt. :)












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PostPosted: Fri May 13, 2011 3:29 pm
bjde0b wrote:Since I used a guide coat with the Slick Sand, do I need to use a guide coat again when sanding the 2k primer?

I do. It makes sure you don't oversand in areas so you can move on to the other areas of need in your blocking....
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PostPosted: Tue Aug 09, 2011 7:03 pm
vwbobby wrote:ODG is right. If you don't put at least 2 coats of primer down, you run the risk of sanding through too easily.
Then you end up chasing your tail putting more primer down.


this is where i'm at... lol

a little background on my project. i'm prepping some fiberglass motorcycle fairings for paint. they came with a urethane primer on them from the factory. they say you can just scuff the primer and it's ready for paint. when i took them out of the box there were a bunch of light scratches from shipping. after talking with a few people who know much more than i do, it was suggested to just go ahead and prime everything again before i paint.

a guy i know recommended the shopline jp202 primer. of course when i went to my local ppg supplier they didn't have any. they gave me some omni mp282 2k primer and said it was the same thing. i really struggled with getting the primer to spray out of the gun (that's a whole different story but i've got it worked out now).

through all this trial and error i THOUGHT i had plenty of primer on there, even though i sanded a lot of it back off when it wasn't going on the way it should. i was happy with my last attempt but it went on a little dry. it all sanded down nice and flat but there are a few spots where i broke through to the original primer.

my plan now, is to spot prime the areas i broke through and then go ahead and re-prime the whole piece. i'm sure if i don't i'll break through somewhere else. these parts have more curves than they do straight areas, so it's really tough trying to block sand but i'm getting better at it... lol

ok, sorry for all the blabbering... my main question now is, is this a good plan? can i put more primer on after i was final sanding with 400 wet or do i need to scuff it with some 220 first? the tech sheet for the primer calls for 180 - 240 grit on old finishes/body filler. it prolly doesn't matter at this point but i scuffed the factory primer with 180 dry before i hit it with my 2k primer.

tia for any help or pointers you guys can give me, i really appreciate it. i've been searching, reading and studying around here for the last few months and this is an awesome site you have here.

tom

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PostPosted: Tue Aug 09, 2011 9:57 pm
Use a guide coat. if the filler work is good and you watch those edges sand through should be no problem.Omni primer will fill the 180 scratch fine. 3 coats is what I go with before final block sanding. The Omni primer will stick to 400 grit scratch.
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PostPosted: Tue Aug 09, 2011 10:40 pm
timbo wrote:Use a guide coat. if the filler work is good and you watch those edges sand through should be no problem.Omni primer will fill the 180 scratch fine. 3 coats is what I go with before final block sanding. The Omni primer will stick to 400 grit scratch.


cool... thanks... my biggest concern was laying more primer on the 400 scratch. i pretty much knew i was ok with the 180 when i started. the pieces i'm working with are new so there isn't any "filler" other than the 2k primer i'm putting on, the problem is most of it is curves as they are sportbike fairings i'm working on.

i ran out of primer the other evening right when i was starting to get everything dialed in (gun and technique). i got pretty good coverage but it went on a little dry (prolly needed to be a little closer to the work and maybe open up the fluid knob a little more) so the surface is a little rough. i'll try to post some pics but it's hard to get a shot of the texture.

i was trying to block with a sponge and it was a bit of a pia but it came out pretty good until i got a little carried away in a few spots. today i stopped and got some more primer, some of the powder guide coat and some dura-block sanding blocks. i KNOW those blocks will make my life a little easier and i'm excited to try them.

being that the surface is a little rough, should i knock it down a little before i put the guide coat on?

any tips or tricks for blocking the edges and tight spots in the grooves of the body lines? again, lots of curves, tight spots and funky corners/angles. hope that makes sense... lol



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PostPosted: Wed Aug 10, 2011 12:31 am
here are a few pics, try not to laugh too hard... :oops:

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broke through trying to work the corner


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same thing here. i prolly could have left it b/c the seat pad would hide most of it. i was trying to flatten out some of the "dry" (?) texture


100_1007.JPG
close up of the "dryness"


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some of the angles i'm working with. you can see where it was getting thick in the middle when i was trying to get more paint on the vertical sections on either side


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this is the front of the belly pan a little dry and blotchy.


the primer seems to be drying almost as soon as it hits the surface. my non-professional opinion is i'm moving to fast (trying to avoid runs) and maybe i should open the fluid control some more.

thoughts?

try not to beat me up too bad... :knockout:



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PostPosted: Wed Aug 10, 2011 12:56 am
one more...

100_1011.JPG
side of the belly pan. still a little dry but i was starting to get a feel for it. i'm confident i can get it flat but i don't think the color is going to be consistent.


any suggestions for sanding the edges of the big hole and in the bolt hole?

i'm starting to think i should block all these other pieces with 220 and then work on getting a few nice wet coats on there before i try to do my final block with 400.

also, this is my track bike, so i'm not looking for a perfect show quality job but i do want to put the effort in to get it as nice as i can. there's always the chance it'll be sliding down the track next time i go out but i figure this is good practice for me to learn on and develop some skills for some other projects i may want to tackle.

if it matters, everything but the belly pan will be painted the same lime green you see on the bike in the back ground. the belly pan will be gloss black, i know i've got some work to do to get the black looking half way decent.

thanks again for any help/advice

tom



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PostPosted: Wed Aug 10, 2011 8:38 am
you've got a primer problem ,it should go on nice and smooth. this happens with the cheeper primers, are their differant activators for your primer? some have panel activator and overall activator, the panel aciyator is fast drying the overall is slower. you can allso reduce it a little with some slow reducer, like an ounce to a gun full of primer. there are other things that can cause your problem like your tempature their, or are you spraying outside in the sun :)
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PostPosted: Wed Aug 10, 2011 9:13 am
What size is the tip? Gun tip may be too small for the primer....try an extra splash of reducer. Also might check pressure at the gun...little too much maybe. Run the fluid tip full open and in 1/4 turn.
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PostPosted: Wed Aug 10, 2011 11:48 am
badsix wrote:you've got a primer problem ,it should go on nice and smooth. this happens with the cheeper primers, are their differant activators for your primer? some have panel activator and overall activator, the panel aciyator is fast drying the overall is slower. you can allso reduce it a little with some slow reducer, like an ounce to a gun full of primer. there are other things that can cause your problem like your tempature their, or are you spraying outside in the sun :)


outside in the shade :mrgreen: it was late afternoon/early evening, air temp was about mid 80's. primer is the omni mp282 with the mh284 hardener with dt895 reducer, mixed at 4:1:1

timbo wrote:What size is the tip? Gun tip may be too small for the primer....try an extra splash of reducer. Also might check pressure at the gun...little too much maybe. Run the fluid tip full open and in 1/4 turn.


you're all over it. tip is 1.4, specs call for 1.6 - 1.8

i do have another tip from another gun that i modified with a drill bit to 2.0. problem is when i tried to use it in this gun it doesn't give me any air when you first pull the trigger, it goes straight to paint. i've got one more tip that i could try to modify with a 1/16th drill bit which would put me at about 1.58mm.

do you think i could get away with the 1.4 tip with an extra splash of reducer? i'm prolly wrong but i feel like i can get there even without the extra reducer with a little more work on the gun set up. my test sprays came out better than the spray on the parts... :lol: gun pressure had crossed my mind too. the manual calls for 15 - 45psi. i shot for the middle of the road and was running about 29psi at the gun with the trigger pulled. the fluid tip was about 3 turns out and the fan was as wide as it would go, which was putting out about a 12 inch fan pattern.

a few more pics... not sure how well they'll show but this piece came out the best so far. still a little dry and blotchy but much better than the others.

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100_1017.JPG
you can see some faint stripes towards the bottom of this one.

100_1018.JPG

100_1019.JPG


with these parts i haven't sanded yet, i should block them with 220 (?) before i try to put any more primer on. right?
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