Primer, the Cure All for sealing balsa?
 

Here is a link to my latest build using primer only to seal the balsa.
http://forums.rocketshoppe.com/showthread.php?t=9815

When it is all said and done, I cannot believe the results I received without using balsa sealer. I have used Balsa Sealer and filler ever since I started building rockets to seal and fill the balsa. For the most part I have had great success, but that is because after the balsa sealer is dried and sanded I spray 2 to 3 coats of primer with more sanding for a smooth finish. Now in the beginning all the rocket directions and rocket books mention using balsa filler or sealer then spraying the rocket with Enamel top coats. Never in the literature did it say anything about using primer after the sealer and before the top coats so that is what I used to do.....For the most part the rocket would come looking ok but obviously without primer some imperfections would show. Also the balsa fins would be smooth but some grain would show unless I used 7 to 8 coats. Now that everyone is using primers, you can see by itself it works great as a filler and does not add much weight as long as you sand most of it off and I think most of us do that anyway. The biggest advantage I see with the primer only is that you only sand twice vs 4 to 8 times as with sealers and primers together. I sprayed 3 coats of primer with no sanding in between coats and let it dry for one day. The next day I sanded it smooth and added 2 more coats. Now I think the only thing I might do different is after sanding the first time I would look to see if I have any major imperfections and correct with putty or wood filler, on this build there were no issues. After filling the major imperfections I would only sand the filler and begin spraying my next 2 to 3 coats of primer. I have seen others on these forums use primers only and also the new Estes directions now mention to use primers to fill the balsa so why would we still use fillers or sealers? I have only built one rocket with this method so I have not made up my mind if I am going to do this with all my builds but I will post my results and like to hear what others think.

Because we are old school model builders. Yes sir :D

I have pretty much always used primer. I've used balsa sealer a few times and for your afore mentioned reasons, I've all but abandoned the practice. I get great results with just using primer. I use primarily gray for starters usually 2 coats (then sand) and then another coat (more sanding). I'll shoot a last coat of white (with a final sand) if the rocket is not going to be white in it's final color. I do sand the balsa sheets several times using different grits before removing/cutting the fins, which kinda helps to lessen the grain somewhat.
I occasionally fill spirals with Fill and Finish (or whatever it's called today) but the sprials have to be "big". FNF generates way too much dust for my likes.

Occasionally there's a grain or two that peeks through, but I'm good with that. After a flight or two there's usually going to be couple of dings anyway. OTH, with your showroom finishes that may not be acceptable to you.

I guess everyone is different and it boils down to how much time you want to spend sealing, priming, and sanding. It is supposed to be a hobby.

I agree with that Leo, but like I said I didn't start priming rockets until I came back into the hobby 6 years ago. Before that it was sealer and top coat and that would be true old school. Part of me would miss good ole Aerogloss so I am thinking about still using it on my vintage builds and using primer on my new models.

Balsa Fillercoat and Sanding Sealer "toughen" the balsa; the fillercoat fills and penetrates making the balsa "denser" which prevents easy denting, and the Sanding Sealer gives a tough "plastic like" top coat further toughening the balsa.
Primers do virtually nothing to toughen balsa.
For Basswood or ply, primer is actually plenty.
Not so for balsa unless you want easy dentability.

I was thinking that but then remembered that when applying filler or sealer we sand it back down to the balsa so there is not top coat. What makes it seem stronger is the fact that the grain is filled and that is also done with primer. I used test pieces of balsa and there was no difference in strength or dentability....if that is a word....nope it is not a word.

I'm thinking you are sanding the filler and sealer far too deep.

I've been using Rustoleum "High Build" automotive primer since my second BAR build, and the results have been fantastic even with only the most minimal treatment with Elmer's FnF underneath.

I do notice that it tends to add a little more weight to the bird.

I just built Sunward's Explorer, and the instructions do not mention using a sanding sealer on the balsa at all, just primer. This was surprising to me. I don't ever remember any instuctions that do not mention using sealer.

I only use primer on wood as a paint base for the topcoat. I do all of my sealing and grain filling with other products. I have tried many different techniques and this works the best for me. On tubes I use a light coat of primer as a base before I fill spirals because it helps to prevent scuffing when I sand down the spiral filler. Once all of the surfaces are smooth, I hit the entire model with one coat of primer. I very lightly sand that coat and after toweling off the dust I proceed with top coats. I try to limit my use of spray primer and paint because of the cost. Aside from spraying a thin coat onto paper tubes prior to filling, I only use primer for its main purpose, which is to help the paint adhere to the surface. Using it for such things as sealing and filling wood grain and filling tube spirals quickly becomes expensive. I have tried using it for those other tasks, and I was appalled at how quickly I ran through cans of it.

I am not disputing your conclusions about the technique, but for me it is just not economical to do it that way.