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  #31  
Old 12-18-2008, 07:56 AM
micromeister micromeister is offline
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[QUOTE=Mark II]I recently got some Aerogloss Balsa Filler, so I'll give it a try. As for the Ceramcoat being hard to sand, that's why I wet-sand it. Dry-sanding quickly heats up the surface of the filler too much, making it soft and gummy, and the sanded dust melts and reforms into gummy crumbs that quickly load up the sandpaper. Sanding it with an aluminum oxide sandpaper (the black stuff) that has been run under the faucet for a couple of seconds right before you sand, and then periodically re-wetted, helps to avoid this problem. The water helps to keep the surface cooler and it helps to float the sanded particles away, preventing them from building up and melting right under your pressure point. Aluminum oxide paper seems to shed fewer grit particles during use, which also helps to lessen the build-up. Finally, as you re-wet the paper, you rinse off some of the slurry that is accumulating on it, which helps to delay the eventual load-up of the paper.

I usually start with 400-grit aluminum oxide paper. This grade (grit count)



Mark:
No I'm not necessarally using "Hi build" Primers. Remember the idea is to use the Cheapest primer we can get my hands on so some are hi build others are not. It doesn't seem to matter as Hi build or not 3 coats are always applied before the first sanding.
The .87 Walmart grey or brown auto primers are not high build. some I've pick up at Pep-boy for a bit over a buck are, K-marts "Fresh & Easy" Grey, Black and Brown preimers are not.
In all cases I DO NOT wet sand primers. Premiers by nature are porus. That's one of the ways they flash off and dry so quickly. but that also allows mositure to migrate through the material to the base material. Raw metal on cars.. Paper or wood on our models. IN any of these cases this can cause damage to the underlaying material and/or beark the bond between the base material and primer...the one real reason for priming in the first place.
I know some of the spary primer cans have instructions that seem to indicate they can be wet sanded but i've been told by two of the manufacturers that this is a "generic" lable insturction that really shouldn't be on their primer cans. This was S&W (Dutchboy, Fresh & Easy K-Mart brand) and others.

It sounds like the Delta Ceramcoat is more sealer then primer which is why your able to wet sand it without screwing up the underlaying material.
I'd have to really use this stuff before making any kind of judgement on it.

Just so you guys know "Wet Sanding" is a very useful technique used on FINISHED Color and top coats.

Basic prep work for those tops coats include primer and dry sanding to smooth the surface but even on my MICROs it's rarely necessary to use any paper finer then 320 to obtain a babies but smooth finish. Yes I have and use 400, 600 and papers up to 4000 grit but they are reserved for very fine finishing of final color coats and/or clear tops coats. It's quite true one COULD do all the sanding necessary on a model with 600grit sandpaper and if you have that much time your welcome to do that. but sandpapers are like every other tool in your box, each has a specific purpose. Learn to use them as they are ment to be used and you'll greatly inhance your modeling experience.

Its been my experience that once you realize you've been spending way to many hours sanding by using far to fine a paper you'll see your finishing improve while taking far less time in the process.


As mentioned in the earlier post after the 3 unsanded coats of primer have dried. start with 120 grit to knock down any major high spots then go to 220 to remove most of the primer. when all grain is been eliminated or nearly so, switch up 320 or 360 whip with a tac-rag often and holding the model up to a light source to get a good look at the area.

When your happy with the surface apply a coat or two of white. some folks like to use matte white or white primer which has the finest "solids". if you see a flaw you can't live with in the white coat. sand it out and reapply. then it's on to color coats.

Which reminds me!
Why are there different color Automotive Primers? Because they have different Grades (sized) solids content.
General use: Black, Brown, Grey: these are the heaviest largest particles.
Red Oxide: fine particles (normally a spot filler)
White: finest particles ( a finishing primer) NOTE this does NOT include KILZ which really is NOT a preimer in the first place its a stain killing overcoat for Latex paints.

but all this is sooooo far off topic I almost forgot is thread started about not warpping 1/16" balsa fins.
To that end I'll add I use 1/20th, 1/32" balsa on fins and other details as well as 1/32", 3/64" and 1/64" basswood and 3-ply birch ply on some compeititon models. rarely to I get warps with either sprayed Primer method or in laminating with Tracing vellum weighted with books.
Just to get us a little back on track LOL!!!!
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Last edited by micromeister : 12-18-2008 at 02:31 PM.
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  #32  
Old 12-18-2008, 12:04 PM
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Mark II Mark II is offline
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I am not disputing your methods, John. The procedure I described applies if you are using the Delta product (or the Pine-Pro as well). It is specific to those products, and I don't have any experience with using it in any other situation. All I can say is that I have been very pleased with the results that I have gotten. Using Delta Ceramcoat APS (All Purpose Sealer) is not the only option out there for getting a smooth base layer on balsa, but if someone wanted to use it, then I would suggest that they try the procedure that I outlined. The same things apply if you are using Pine-Pro Sanding Sealer (if you can fnd it), although with this product, you can get away with doing some light dry-sanding on it.

I don't spend any more time sanding nose cones now than I did with previous methods. Wet-sanding this stuff actually goes quite fast, because it is so effective. Yes, APS seals the wood grain along with filling it, so that the water doesn't affect the base material - it only acts on the layer of APS. OK, I should have mentioned that you could wet-sand it with 320 or 240 grit as well, especially if you put on a couple of coats of sealer first, instead of just one coat. (What I had described was my own procedure, which may reflect a touch of OCD, as well as an obsession with getting a super smooth base layer. ) As I mentioned, the reason that you would do better to wet-sand this particular product rather than dry-sanding it is because wet-sanding avoids overheating the sealer and it makes the sanding go much easier (and quicker, too). I tried sanding it in the usual way at first, but I kept experiencing the softening and gumming problems that I described, so I switched to wet-sanding it, which worked much better.

I do agree you with in that I would not recommend that anyone wet-sand base coat primer that has been applied to unsealed wood, for the reasons that you said. In order to do any wet-sanding at any step in the process, the wood grain has to be sealed. Normally, wet-sanding is reserved for the final phase and is done on the topcoat of paint. By that time, you have applied multiple layers of primer and at least one coat of paint, and so the wood is effectively sealed. But even then, if you left the water on long enough, it would eventually penetrate to the base material, and you never want to see that happen. When I wet-sand topcoats of paint, I frequently stop and wipe the area dry for that very reason, and after a few sanding intervals, I let the area rest while I move on to another section. I described doing the same thing when I talked about wet-sanding the APS or the Pine-Pro.

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