Seam Fill Failure: Next Step, Sand Prime Coat?

strangelove · Post by **strangelove** » Sun Jul 26, 2009 1:21 pm

My first attempt at seam filling with putty was an abject failure. Sanded most of the putty off and the seam showed through the prime coat.

Question:

Do I need to sand off the prime coat (of Krylon Fusion spray) before reapplying a new layer of putty to cover the seams?

See video and pictures here.

Thank you for your time,

Post by **TER-OR** » Sun Jul 26, 2009 1:58 pm

Don't try to sand all the primer away - leave a layer on the area and sand it smooth. I don't know if the spray-primer is your best bet for this. If you have a more conventional filler you should brush that on fairly thickly on the seam area - overcoat well, cover the whole bevel. Then you can sand the area smooth. You don't want to see the seam ever again, just a smooth layer of filler.

Another option would have been to cement some thin styrene strip over the seam - or into it - and then buff the area smooth. Use a hot cement like Tenax, you want to literally dissolve the interface.

You don't need to remove the primer, you could decant some primer and brush it on thickly if you want. That way you don't have lots of primer built up over the entire model.

photoguy · Post by **photoguy** » Sun Jul 26, 2009 2:30 pm

When I putty, I use a small painter's pallet knife as a mini-putty knife and get the putty as smooth as I can BEFORE I start sanding.

I used to have the same problem when I would use my finger to more or less "glob" the putty onto the seam and try to sand everything smooth.

Get it as smooth as you can while the putty is still workable, and use finer sand paper to even out the surface without removing too much of the dry putty.

#2 Get a better respirator mask. I had used those fiber dust masks for quite a while, and could never figure out why my Kleenex turned rainbow colors...

I started using an MSA Advantage 200 this year, and LOVE it. No pretty boogers, and absolutely no paint smell of any kind while I'm working. And I kinda look like Darth Vader while I'm working

kenlilly106 · Post by **kenlilly106** » Sun Jul 26, 2009 2:50 pm

What putty did you use?

How long did you let it dry?

Ken

strangelove · Post by **strangelove** » Sun Jul 26, 2009 10:13 pm

Thank you all for your helpful replies. I went ahead and sanded the seam with a 80 grit, which took out most of my errors and eliminated the worst of the seam. I probably should have then reapplied putty, but wanted to see how things would turn out.

Results proved ok for my present purposes.

Lt. Z0mBe · Post by **Lt. Z0mBe** » Mon Jul 27, 2009 4:51 am

strangelove wrote: ...I went ahead and sanded the seam with a 80 grit, which took out most of my errors and eliminated the worst of the seam. ....

That may be part of your problem too. Grits that coarse don't allow putty or primer of any type to feather easily. They're taking off huge chunks of plastic and paint and putty with each pass. Get thee to Wal-Mart or the equivalent in the fair country to the north and get one of the 3M bulk packs. It will have three or four of each of 220, 320, and 420 grits. They are wet-dry papers. Use them wet; cut off little three/quarter by about two-inch strips for easy handling. You, sir, will be amazed. Start off with the 220, work down to to 420. Then, you can use the really high grits - 600 and up for polishing prior to priming and painting.

I hope this helps.

Kenny

photoguy · Post by **photoguy** » Mon Jul 27, 2009 8:10 am

Yep. I try to think about "scale" paint effects too. 80 grit would be like rubbing the surface of the ship with boulders.

Typically, I start at around 400 grit, and finish at 2000 - just a little coarser than notebook paper.

You can get variety packs that fine in any automotive supply store - they keep it near the paint racks.

seam-filler · Post by **seam-filler** » Mon Jul 27, 2009 8:17 am

And use it wet!! The paper will clog less and there will be less friction. I also add a few drops of dishwasher rinse-aid to the water, further reducing friction.

I don't know what you're using for paper, but do NOT use sandpaper - this is meant only for wood and wood products and is not suitable for plastics & resin - if you have been using "sandpaper" this may also explain some of your problems. Use the stuff intended for metals & plastics (in the UK we call it Wet and Dry paper.

Sandpapers are usually light tan or red in colour whereas W&D paper are most often shades of gray or green.

Post by **TER-OR** » Mon Jul 27, 2009 9:58 pm

3M black sandpaper is built for wet-sanding. Get some spraymount adhesive and glue it to various things...

A $5 12" square of marble tile is great for flat-sanding.

seam-filler · Post by **seam-filler** » Tue Jul 28, 2009 1:20 am

In the UK, if it's "Wet & Dry" then it doesn't get called sandpaper ('cos the grit isn't sand). And yes, the £M Wet & Dry is excellent stuff, but pricey (here at least) compared to other brands.

As well as Ter-or's idea for using a tile, you can make your own sanding sticks cheaply and in any grade you like.

Get some of the stiff, self adhesive compressed felt for protecting laminate & wood floors (we can get loads of this for £1 GBP). Peel off the backing & stick your wet & dry paper to it. You can then cut it to any size or shape you want. They don't last as long as some sanding sticks, but, hey, they also cost next to nothing!

Post by **TER-OR** » Tue Jul 28, 2009 8:25 pm

you can get the 2-sided mounting tape, it's a thin layer of foam with adhesive. You can stick it to anything - wood, plastic etc... It's a great way to make oddly shaped sanding surfaces for specific tasks. The foam gives it a bit of softness, but it's still stiffer than your finger etc.

Pandaphil · Post by **Pandaphil** » Mon Aug 24, 2009 9:13 pm

I know a lot of people are disdainful of Testors white tube putty. But what I love about it is it can be thinned with plain rubbing alcohol. So I glop it on, let it dry, then basically just smooth it out with an alcohol dipped Q-tip before I do any sanding.

Currently starting a Revell Cylon Raider. so yeah, I'm gonna have to become an expert of filling seams real quick.