1/16" Balsa

[tbzep]

Next time you guys use 1/16" balsa for large fins, don't use thinned F-n-F to fill the grain. I made it thick as I could and still brush it on and it still warped the fins. I got them straight after the first application and I will after this one, but it is a pain in the butt to fool with. Just thought I'd vent a bit.

http://i7.photobucket.com/albums/y283/tbzep/Rockets/dsc_0008-1.jpg

[Ltvscout]

Cool! A home made wacky wiggler. Someone should build a rocket using the 1/16" balsa and purposely warp the fins to see how it wobbles going up.

[tbzep]

Cool! A home made wacky wiggler. Someone should build a rocket using the 1/16" balsa and purposely warp the fins to see how it wobbles going up.

:p

It would be easy to wet the wood and make some interesting fin designs. :cool:

And to think I had everything so well aligned before I started filling. I told Kody that the Apogee fins were closer to perfect than any fins I had done before. :rolleyes:



.

[kurtschachner]

:p

It would be easy to wet the wood and make some interesting fin designs. :cool:

And to think I had everything so well aligned before I started filling. I told Kody that the Apogee fins were closer to perfect than any fins I had done before. :rolleyes:


Apogee II? And you used balsa? 1/16" fins are a poster child for basswood. The only time I would consider using balsa is in a glider.

[STRMan]

Apogee II? And you used balsa? 1/16" fins are a poster child for basswood. The only time I would consider using balsa is in a glider.

I used 1/16" balsa for my EAC Viper clone. I papered them with Avery Labels. They are super strong and have been holding up quite well.

[tbzep]

Apogee II? And you used balsa? 1/16" fins are a poster child for basswood. The only time I would consider using balsa is in a glider.

I had to. :rolleyes: It's a re-build of my best friend's rocket. ;)

He gave me all his old stuff when he got out of rocketry and the original nosecone and payload section was still in there including the lead weights. Yep, I could call it a clone, but I'm going to call it a restoration. Heck, those guys replace most of the metal with fresh stuff in those classic car restorations. :eek: :p


.

[tbzep]

I used 1/16" balsa for my EAC Viper clone. I papered them with Avery Labels. They are super strong and have been holding up quite well.

I didn't have any trouble with warping at all with my EAC Viper rebuild. Those fins were smaller and the balsa was a little more dense to boot.

[kurtschachner]

I had to. :rolleyes: It's a re-build of my best friend's rocket. ;)

He gave me all his old stuff when he got out of rocketry and the original nosecone and payload section was still in there including the lead weights. Yep, I could call it a clone, but I'm going to call it a restoration. Heck, those guys replace most of the metal with fresh stuff in those classic car restorations. :eek: :p



I was mostly just yanking your chain. But I did recently complete an Apogee II clone and I used basswood for those fins. It worked out very well.

I'm pretty much a total basswood convert, purging my stock of the evil balsa whenever I can :)

[tbzep]

I was mostly just yanking your chain. But I did recently complete an Apogee II clone and I used basswood for those fins. It worked out very well.

I'm pretty much a total basswood convert, purging my stock of the evil balsa whenever I can :)

I've never tried basswood. How does it cut and sand relative to balsa?

[Doug Sams]

I didn't have any trouble with warping at all with my EAC Viper rebuild. Those fins were smaller and the balsa was a little more dense to boot.I imagine the density was a key factor. It likely limited the absorption and thus minimized the warping.

I rarely use 1/16" preferring to instead upgrade most of my clones to 3/32" for the sake of durability. That said, I still use it on occasion and don't see many problems. I normally lay down a coat of Zinnser primer first, and I wonder if that averts the warping by limiting the absorption of the thinned FnF.

Doug...thinking out loud...

.

[DaveR]

I've never tried basswood. How does it cut and sand relative to balsa?
Personally I like basswood. Some may argue that it's brittle but I haven't run into any problems with it.
It's a little harder to cut (especially on thicker pieces) but nothing a good sharp blade can't handle. I find it's very easy to sand (and somewhat more forgiving than balsa) and most of the grain can be filled with just primer. :cool:

[LeeR]

I've never tried basswood. How does it cut and sand relative to balsa?

Trickier to cut, since it is denser (heavier, of course). I buy scalpel blades to replece a #11 Xacto blade, which helps. I have also used my tabletop bandsaw to cut a stack of 3 or 4 fins, and then take them down to the pencil outlines with a small Dremel belt/disk sander.

For smaller rockets, the basswood in 1/16" may be heavier, but it is such a small amount. I've used basswood on a upscale Orbital Transport, and you definitely feel the weight gain. I only did this for the main wings, and not the glider wings.

Basswood fills really fast, too, because of its tight grain. I only use sanding sealer these days, but on some basswood, you could almost go straight to primer with good sanding between coats.

[Eagle3]

I find basswood much easier to work with than balsa. I'd never use it on a competition model, but for sport models it's great. It's slightly harder to cut and sand, but when I'm sanding basswood I feel I have a lot more control over the shape. You can sand a mistake into balsa a lot faster than bass. Bass has a finer grain, is much easier to fill n finish, and as mentioned earlier won't warp as easily as balsa. In the past when using 1/16 balsa I used tissue and dope to finish the surface, but I'm old skool. ;)

[micromeister]

I'm with most of the other posters on this point: Bassswood is almost always preferred over balsa for my sport flying models. Particularly in 1/16" or less in thickness. the very small penelty in added weight is always overshadowed by the increased strength, stiffness and ease of finishing.

[Royatl]

Next time you guys use 1/16" balsa for large fins, don't use thinned F-n-F to fill the grain. I made it thick as I could and still brush it on and it still warped the fins. I got them straight after the first application and I will after this one, but it is a pain in the butt to fool with. Just thought I'd vent a bit.



I use it on 1/16" balsa all the time.

before... Choose hard C-grain balsa if possible. A-grain is just asking for trouble anyway.
1. apply it BEFORE attaching to rocket
2. use it full strength and apply it with your finger (vinyl or nitrile glove recommended). rub it in.
3. apply it on both sides at roughly the same time (i.e. not one side and let dry, then other side)


from what I can tell in the picture, your fins were close to A-grain, and your F'n'F had a much higher water content than it needed to be.

[SecretSquirrel]

I imagine the density was a key factor. It likely limited the absorption and thus minimized the warping.

I rarely use 1/16" preferring to instead upgrade most of my clones to 3/32" for the sake of durability. That said, I still use it on occasion and don't see many problems. I normally lay down a coat of Zinnser primer first, and I wonder if that averts the warping by limiting the absorption of the thinned FnF.

Doug...thinking out loud...

.


Could be, I usually brush on a coat of clear dope to limit absorption and it seems to work fairly well.

[scigs30]

I am finishing my Apogee II right now and it is an original so I used the balsa stock that came with the kit. I used Aerogloss balsa sealer, 4 coats and no warps. After 1 coat of grey primer the grain was all filled. Since I am building the original, I don't have the luxury of using basswood.
http://i89.photobucket.com/albums/k211/scigs30/reee.jpg

[Mark II]

I still mostly use balsa, but I pick the sheets with the hardest C-grain that I can find. I also use basswood on occasion, especially on larger rockets, but I'm thinking about using it more often. Thick basswood, like 1/4" or thicker, is A LOT of work to sand. (I use a a palm sander, and even then, it takes awhile.) Yeah, basswood is more forgiving than balsa to sand, in a sense, but that is because you have to make many, many more strokes (and go through much more sandpaper) to remove the same amount of stock. When you are making, say, 200 or more strokes to round one edge of a fin, as opposed to, say, making 30, it is easier to make subtle adjustments to correct minor errors. :rolleyes:

I have used this stuff (see attached image) to fill the grain in balsa fins, and I have not seen any warping. Once the Delta Ceramcoat filler is completely dry, you can give it a light wet-sanding with 400-grit sandpaper to get a nice smooth surface. It may require 2-3 coats, depending on how coarse the grain is. I also use it on nose cones. You can find it in the crafts section at Walmart, and at Joanne's Fabrics and Michael's.

One other filler that has worked well for me is Pine-Pro (http://www.pinepro.com/products_parts.shtml) Sanding Sealer, which I have only seen at my local hobby shop (in with the pinecar derby supplies), but you might be able to find it at Michael's, too. It is thicker and it fills faster than the Delta product, and it also wet-sands smoother. Unfortunately, I can only find it in small bottles, and it goes fast. (I used almost an entire 2 oz. bottle on my Golden Scout. :eek: ) Because of that, I mainly just use it on nose cones. But this stuff is truly great, and it is what I would use all the time, if I could get it in larger bottles. The Delta Ceramcoat filler and Pine-Pro are both water-based, but I have never had either one cause fin warping. They both just clean off my brushes with soap and water. Before you wet-sand either one, though, make sure that the coat has completely dried.

http://www.hofcraft.com/images/deltaprep.jpghttp://www.pinepro.com/images/stock/10059.jpg

Mark \\.

[Mark II]

BTW, I also think that FSI might have been on to something when they used 1/16" aircraft plywood for the fins in many of their kits. It is very hard, and if the fins aren't too big, there isn't much of a weight penalty. Tack the stuff on with gel CA, then give it some thin epoxy fillets, and the fins are bullet-proof! The birch aircraft ply that I have used was finished much smoother than regular plywood. It still needed to be sealed, but it usually just needed one light coat of filler to completely fill the grain. The downside? It was almost as hard to sand as basswood (almost) ;) . I haven't tried make fins from 1/32" birch plywood yet, but it might work out that the slight extra weight would be offset by the much thinner aerodynamic cross-section.

Mark \\.

[MKP]

I also use the Delta Cream Coat, and really like it. I've tried both it and Aerogloss, and the Delta product seems to work just as well and isn't nearly as toxic and stinky. (When I use Aerogloss everyone in the house gives me grief.)

[micromeister]

Seems that 3 coats are the Charm regardless of the "filler material" being used.

Sigs30 used sanding sealer, some use (myself included) have or are using Balsa filler containing much higher solids, other are using waterbased sealer/fillers.
I've all but stopped using these "fillers" long ago.

Since i'm going to be priming and sanding the model anyway thats were i've learned to start.
Indstead of wasting a bunch of time with fillers I Start with whatever el-cheap-O rattle can primer I can find on the raw wood and bodytubes. As with all the other methods... open grain balsa fins, cones and transitions generally takes 3 coats to fill the grain. Basswood I've found can generally get away with two coats. DRY sand with 120 to 320girt papers to a babies but smooth surface ready for whatever base or color I choose. Recently I've been using a Walmart .89 grey auto primer with excellant results under Krylon (old formula) and rustoleum color coats .

Drawbacks: * Sometimes takes an entire can to fill a large model (like the E-interceptor).
*Should use a spraybooth or box to contain a bit of overspary.
* if spraying indoors you'll want to exhaust the smell outside with a blower.

Advantages: * Less smell than Pactra or other brand Lacquer based fillers.
* No brushing or trowel applying messy fillers.
* Much Quicker filling.
* generally less expensive (depending on primer used).
* Fills Bodytube seams and grain at the same time.
* Fewer steps to the completed model.
Hope this helps.

[tbzep]

Drawbacks: * Sometimes takes an entire can to fill a large model (like the E-interceptor).
*Should use a spraybooth or box to contain a bit of overspary.
* if spraying indoors you'll want to exhaust the smell outside with a blower.



Those reasons are part of why I use Fill-n-Finish. The biggest reason is that I can sand the stuff in 10 minutes. The only primer that comes that close is lacquer primer, and the only lacquer I can get here is very expensive, so I only use it after slicking up all the balsa with F-n-F.

I hate sanding, so when I finally get in the mood, I need to get on it quick and get it over with. :p

[cas2047]

I hate sanding, so when I finally get in the mood, I need to get on it quick and get it over with. :p

I'm with you there.

How will you, or how did you fix the warped fin? It looks like it would need to be sanded, wet down and clamped in between two flat pieces of wood or metal...

[Mark II]

I can't argue with your results, Micromeister, but I'm a bit squeamish about sanding raw balsa nose cones, even if they have a coat or two of primer on them. I used to do that, but too many times I ended up with misshaped nose cones!

Your method is exactly what I used to do when I started building rockets again a few years ago. Eventually I started using fillers and sealers before priming because they gave me much better results!

A bottle of Delta Ceramcoat All-Purpose Sealer also lasts a whole lot longer than many cans of spray primer. Two years ago, I bought two 8 oz. bottles of it at Walmart. I'm still on the first bottle.

I do agree that the extra steps are a bit of a pain, though. I'm always in favor of finding, simpler, easier methods to accomplish the same thing.

Also, as I mentioned in a thread awhile ago on finishing techniques (or was it on Krylon paint?), I suspect that what methods work best for an individual builder may depend, in part, on what part of the country (or world) that he or she lives in, and what the predominant climate is like in the area. I don't know that this is true, but I suspect that it might play some role.

I do all of my spraying outdoors and out in the open on warm, dry days when there is little or no wind. (Where I live, that limits me to doing all of my painting during a few weeks in high summer.) To avoid blushing the paint, I do not do the spraying out in my yard, because the area over the grass, and in the vicinity of shrubs, etc., has higher humidity than elsewhere. I take my rockets down to the end of my driveway, or even out to the street in front of my house, to lay on coats of spray paint. The air is always drier in those places. (In addition to the general climate of a local area, there are little micro-climates over and around everything, especially living things like plant foliage.) If I had a large slab of concrete (not asphalt) to go to that was out in the sun for part of the day (and would therefore be well-dried) and that was free of dust and wind, that's where I would do all of my spray painting.

Or else a well-designed and well-ventilated spray booth... ;)

Mark \\.

[tbzep]

I'm with you there.

How will you, or how did you fix the warped fin? It looks like it would need to be sanded, wet down and clamped in between two flat pieces of wood or metal...

I just moistened spots here and there and let it warp itself back straight on its own.

[micromeister]

Those reasons are part of why I use Fill-n-Finish. The biggest reason is that I can sand the stuff in 10 minutes. The only primer that comes that close is lacquer primer, and the only lacquer I can get here is very expensive, so I only use it after slicking up all the balsa with F-n-F.

I hate sanding, so when I finally get in the mood, I need to get on it quick and get it over with. :p


Absolutely with you there !!! I hate sanding as well. but if we're going to get a decent finish we have to bite the bullet and sand on something. I've just eliminated most of the in between stuff.
Depending on were you live and the humidity level at the time your priming one can be sanding in less then an hour. I usually try to let each of the three coats set up for about 5 to 10 minutes, then wait about a half hour after the 3rd coat is applied. If the primer starts building up to quickly on the papers, I let it set awhile longer, or even let it go overnight if the humidity is high in the house:)

I'm not sure I follow you Mark? sanding on RAW balsa??? it's got at least 3 heavy coats of sandable primer... Not hard as nails but at least as hard as balsa filler/ sanding sealer and surely harder then f-N-f.
I can't remember the last time I really screwed up a nosecone or transition during sanding. If you start to see wood ya just add another coat before continuing.
yeah! I guess i'm pretty lucky I live in a Very high humidity area but have outfitted the rocket lab with two spray booths so I can spary anytime I want.
I will give the Delta ceramcoat a try in the future, I'm always looking for products and techniques to update my Tech-tip articles series.

[Mark II]

[...]
I'm not sure I follow you Mark? sanding on RAW balsa??? it's got at least 3 heavy coats of sandable primer... Not hard as nails but at least as hard as balsa filler/ sanding sealer and surely harder then f-N-f.
I can't remember the last time I really screwed up a nosecone or transition during sanding. If you start to see wood ya just add another coat before continuing.
yeah! I guess i'm pretty lucky I live in a Very high humidity area but have outfitted the rocket lab with two spray booths so I can spary anytime I want.
I will give the Delta ceramcoat a try in the future, I'm always looking for products and techniques to update my Tech-tip articles series.
OK, maybe I misunderstood - I thought that you were talking about sanding in between each of those first coats of primer. Also, were you talking about using high-build primer?

Maybe I have gotten gun-shy from my earlier experiences, but I am very reluctant to touch sandpaper to a nose cone until I have, at a minimum, sealed the surface. I want to be sure that I am just sanding the surface grain, and not the cone itself. It may just be me, but ever since I started taking that precaution, I haven't messed up any more nose cones.

When I sand the filler/sealer coat, I wet-sand with 400 to 600 grit sandpaper. I am not really sanding the stuff off, but rather, it is more like I am smoothing it out. I try whenever possible to use the approach of building up a smooth surface through the application of many thin layers, rather than flooding the surface of the object and then sanding it down to something smooth.

As for sanding in general, I don't mind it at all myself, as long as it is producing good results. I like the look of a smooth paint job better than a rough one, and so I will do the work that is needed to get that look. I get great satisfaction when I can see that the surface is looking better and better as I sand it. But I haven't shown very many of my builds to anyone else yet; the reason I put so much care into the finish of them is purely for personal satisfaction.

Mark \\.

[tbzep]

Maybe I have gotten gun-shy from my earlier experiences, but I am very reluctant to touch sandpaper to a nose cone until I have, at a minimum, sealed the surface. I want to be sure that I am just sanding the surface grain, and not the cone itself. It may just be me, but ever since I started taking that precaution, I haven't messed up any more nose cones.

Use what works for you. That's the beauty of reading all the different methods and materials. It all ends up looking good in the end, but different techniques and materials work better for different folks.

One thing I haven't done, but have read about here and thought it had merit is to use a different color primer for the first coat so that you see when you are getting down near the wood. You could then use a different color primer over it, or Fill-n-Finish, or any other type of filler. That might be what you are doing when you use a sealer first.

There's one thing I have figured out over the years, and believe me, I've tried to prove it wrong. No matter what method or materials I use, I'm gonna have to do a lot of sanding to get a good looking finish. :rolleyes: :p

[scigs30]

I have experimented with Aerogloss sealer and filler. Multiple coats of primer no sealer. Ceramcote and FNF. I will agree they all worked but each had advantages and disadvantages. For me Aerogloss sealer fits my building style so that is what I use. Also all the above techniques still require proper application and sanding technique. If you are sloppy with sanding, well the finished product will look sloppy. With Aerogloss sealer, I am able to sand after 1/2 hour and 3 to 4 coats is plenty. I am using old balsa wood from vintage kits. I apply the sealer the same way I apply filler when building wood projects. I make a conscious effort to brush the sealer into the grain using a stiff brush. I noticed in the beginning when I just half hazardly brushed the sealer on, the grain would not fill. But now that I am using a stiffer brush the sealer makes it into the grain. So basically it is 2 coats of sealer, sand, one coat sand and possibly one last coat and sand. I sand with 320 to 400 gritt. If I was unable to use Aerogloss, I would probably use Ceramcote. There is no oder and clean up is easy. I did find it tougher to sand, almost like sanding Elmers glue.

[Mark II]

I have experimented with Aerogloss sealer and filler. Multiple coats of primer no sealer. Ceramcote and FNF. I will agree they all worked but each had advantages and disadvantages. For me Aerogloss sealer fits my building style so that is what I use. Also all the above techniques still require proper application and sanding technique. If you are sloppy with sanding, well the finished product will look sloppy. With Aerogloss sealer, I am able to sand after 1/2 hour and 3 to 4 coats is plenty. I am using old balsa wood from vintage kits. I apply the sealer the same way I apply filler when building wood projects. I make a conscious effort to brush the sealer into the grain using a stiff brush. I noticed in the beginning when I just half hazardly brushed the sealer on, the grain would not fill. But now that I am using a stiffer brush the sealer makes it into the grain. So basically it is 2 coats of sealer, sand, one coat sand and possibly one last coat and sand. I sand with 320 to 400 gritt. If I was unable to use Aerogloss, I would probably use Ceramcote. There is no oder and clean up is easy. I did find it tougher to sand, almost like sanding Elmers glue.
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) of paper is usually reserved for the final stages of sanding, but I find that it works really well for this particular purpose too. The idea is not to really sand the coating down, but more to smooth it off. I find that I get the best results when there is enough water on the paper to create a bit of very loose slurry on the surface as I sand. After anywhere from 30 seconds to a minute of sanding, I stop and wipe the cone dry with a paper towel, and check my progress. Usually, two or three coats of Ceramcoat, with wet-sanding between coats, is enough. Since I am usually going for a mirror finish, though, I tend to keep on applying thin coats and wet-sanding until I reach a point of diminishing returns. This extra work is a bit of a pain, but I am almost always pleased with the results, so for me it is worth the additional effort. Your mileage and your priorities may vary, though. One thing that I learned from reading Micromeister's Tech Tips a long time ago was that the smoother you get the base layer, the smoother your topcoat will be.

Better than Delta Ceramcoat APS by a mile is Pine-Pro Sanding Sealer, as I mentioned in an earlier post. It looks similar, but it is thicker and it fills the grain faster, it dries harder, and it wet-sands smoother than the Delta product. The only size that I can find it in is a 2 oz. bottle at my "local" hobby shop, which is 52 miles away. The LHS usually has only one bottle in stock (sometimes two), so that's all I can get per trip. Sadly, a single 2 oz. bottle doesn't last long. If only I could stock up on the stuff, I would be using it for all of my wood surface prep.

Mark \\.

[micromeister]

[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!!!!

[Mark II]

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. :rolleyes: ) 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.

Mark \\.