Sanding/Filling - what am I doing wrong

Valiant · Post by **Valiant** » Thu Mar 14, 2013 9:14 am

Oh wise experts... where do I fail?

Steps:

1. lightblock interior
2. glue peices together
3. Prime
4. Notice gaps
5. fill gaps
6. Sand filler/glue seams using fine grit, then 3000 grit.
7. Paint
8. Notice scratches/uneven surfaces
9. attempt sanding/filling again again
10. fail again.

Any help guys? I'm really needing some techniques or something...

Rocketeer · Post by **Rocketeer** » Thu Mar 14, 2013 11:17 am

Always use a sanding block. If you just use your fingers, you get "waves" in the surface, or valleys.

Always wet sand. Keeps the paper cleaner; clogged paper causes grooves and scratches. The wet surface also makes it easier to spot irregularities, especially waves.

Probably not necessary to go all the way to 3000 grit. I rough sand with 220, then 400, then (maybe) 600 before priming.

Count on sanding away most of your first couple coats of primer; it usually takes me a couple coats before the fine scratches are filled.

View your surfaces under a slanted light, shining across the surface; that throws all the irregularities into relief (casts shadows) and they're easier to spot.

Let your glue dry thoroughly before starting the puttying. Old-fashioned tube glue, especially, tends to shrink for a long time after it's supposedly "dry".

Some putties shrink a lot. Squadron Green and Testors are especially notorious shrinkers. Squadron White doesn't shrink as much. Best of all are the two-part putties: Milliput, Aves, Evercoat auto glazing putty.

You might conceivably be having a reaction between your putty and your primer. Tamiya primer, especially, is very "hot", and there have been times when I've suspected it was eating away at lacquer-based putty (Squadron white stuff). I try to do all my bodywork in two-part putties (Milliput or Aves, or Evercoat two-part auto body glazing putty), which are more inert when cured.

Also, I should mention that most of my projects go through four or five putty-sand-repeat cycles before I'm satisfied. So don't feel bad; everyone has trouble with (and hates) filling and sanding.

Kylwell · Post by **Kylwell** » Thu Mar 14, 2013 12:59 pm

It sounds like you're not letting the grits fully take down the previous grits valleys/scratches. One of the many reason I also polish with a polishing stick to let those scratches show. Once you've primed it there's no need to start with the coarsest grit, start a few grits down from that as the primer has already filled the worse of it.

Valiant · Post by **Valiant** » Mon Mar 18, 2013 10:27 am

where could I find a small sanding block?

Kylwell · Post by **Kylwell** » Mon Mar 18, 2013 11:32 am

I usually make them. Piece of wood the size needed, some gel CA and sandpaper.

Glorfindel · Post by **Glorfindel** » Mon Mar 18, 2013 8:44 pm

Rocketeer wrote:Always use a sanding block. If you just use your fingers, you get "waves" in the surface, or valleys.

Always wet sand. Keeps the paper cleaner; clogged paper causes grooves and scratches. The wet surface also makes it easier to spot irregularities, especially waves.

Probably not necessary to go all the way to 3000 grit. I rough sand with 220, then 400, then (maybe) 600 before priming.

Count on sanding away most of your first couple coats of primer; it usually takes me a couple coats before the fine scratches are filled.

View your surfaces under a slanted light, shining across the surface; that throws all the irregularities into relief (casts shadows) and they're easier to spot.

Some putties shrink a lot. Squadron Green and Testors are especially notorious shrinkers. Squadron White doesn't shrink as much. Best of all are the two-part putties: Milliput, Aves, Evercoat auto glazing putty.

Also, I should mention that most of my projects go through four or five putty-sand-repeat cycles before I'm satisfied. So don't feel bad; everyone has trouble with (and hates) filling and sanding.

Most excellent advice. Important to remember that modeling, in any genre, is not a race. Take your time, learn patience, and your efforts will be well rewarded. You'll find you'll get better with each new build moving forward. So sand on cowboy.

Kylwell · Post by **Kylwell** » Mon Mar 18, 2013 10:05 pm

I rarely use a sanding block and wet sand even less.

But what i work on are smaller surfaces, not massive long nacelle seams.

Valiant · Post by **Valiant** » Tue Mar 26, 2013 2:12 pm

I found this article online... and I know little about grits and all (learning) but... shouldn't this be starting with 150 and working up to a 600??? or have a I missed something?

http://www.modelaces.com/_scale_model_t ... _seams.php

Kylwell · Post by **Kylwell** » Tue Mar 26, 2013 2:51 pm

Valiant wrote:I found this article online... and I know little about grits and all (learning) but... shouldn't this be starting with 150 and working up to a 600??? or have a I missed something?

http://www.modelaces.com/_scale_model_t ... _seams.php

He is, I'm guessing just to be difficult, using a different grading system.

Here's some light reading http://www.doityourself.com/stry/a-comp ... VH82Bk84gY

Valiant · Post by **Valiant** » Wed Mar 27, 2013 8:45 am

thank you guys! I went out bought something like a 320, 400, and 600 and its most definitely doing the trick! I think I was just using to low grit and to high grit to effectively do the job.

eeun · Post by **eeun** » Wed Mar 27, 2013 12:45 pm

One of the greatest tips I've come across for seam sanding was to use the fingernail sanding/polishing sticks. The finer ones have about a 320 / 400 grit.

Having hot primer shrink seams plagued me for years. Still does on occasion if I forget to lay down a couple very light coats first. Only SGT (superglue/talcum powder) seams are worry-free for me.

Tankmodeler · Post by **Tankmodeler** » Wed Mar 27, 2013 2:56 pm

Valiant wrote:I think I was just using to low grit and to high grit to effectively do the job.

Coarse grit paper will remove a lot of material, but leave huge valleys for subsequent efforts. I never use anyting coarser than 200 grit and that only for reshaping when I want to remove a lot of material. For normal seams, I tend to scrape the seam if I can with a blade or small scraper to get most of any excess material off the seam and then sand with 400 wet and a sanding block/sanding shape.

I'll put down a couple layers of filler primer and then sand them pretty much all the way back with the 400 grit and when I'm pretty happy do one more layer of normal primer and lightly touch that with 600 grit to knock off any flecks or orange peel. If I'm going for a real gloss finish (which I almost never do, so I don't have a lot of experience with this) I'll use a filler primer as the last coating and then use 600, and 800 grit over that. If I am not seeing a nice sheen with the 800 grit, then I don't have the surface smooth enough for a gloss coat and I'll do it again.

Sometimes, especially if you are kitbashing/scratchbuilding and have to blend many diferent materials together on a surface, it can take 8-10 full or partial sand/fill cycles to get things just perfect. Gloss finishes definitely require a lot more effort than matte finishes.

Tankmodeler · Post by **Tankmodeler** » Wed Mar 27, 2013 3:02 pm

Kylwell wrote:
Valiant wrote: He is, I'm guessing just to be difficult, using a different grading system.
No, I think he's got his grits backwards. I think the ALO is aluminum oxide, the grit in wet-dry paper. The SIL is silica or silicon oxide (also known as "sand") which is one of the normal dry paper grits.

He talks about starting with 600 grit and then, at the end sanding with 150 grit all over, which is exactly the reverse of what you should do.

And 150 grit is waaaay too coarse for normal model work, especially on normal seams.

Paul

Kylwell · Post by **Kylwell** » Wed Mar 27, 2013 3:11 pm

Tankmodeler wrote:
Kylwell wrote:
Valiant wrote: He is, I'm guessing just to be difficult, using a different grading system.
No, I think he's got his grits backwards. I think the ALO is aluminum oxide, the grit in wet-dry paper. The SIL is silica or silicon oxide (also known as "sand") which is one of the normal dry paper grits.

He talks about starting with 600 grit and then, at the end sanding with 150 grit all over, which is exactly the reverse of what you should do.

And 150 grit is waaaay too coarse for normal model work, especially on normal seams.

Paul
No, it's the FEPA or Federation of European Producers of Abrasives non"P" grading system.

I use 150 all the time for hogging shapes but yes for general model building it's on the coarse side. IIRC I usually start @ about 340, maybe 240.

Tankmodeler · Post by **Tankmodeler** » Wed Mar 27, 2013 11:34 pm

Kylwell wrote: No, it's the FEPA or Federation of European Producers of Abrasives non"P" grading system.

I use 150 all the time for hogging shapes but yes for general model building it's on the coarse side. IIRC I usually start @ about 340, maybe 240.

So 150 under the FEPA system is a fine grit? What does it relate to? The "normal" grit system related to the size of mesh teh abrasive particles will pass through. What does the European system relate to?

Learned something new today. Thanks!