rxAxilleas

hi guys,
i just primered my surfases on a sbd 85 in by Bates.there are small pinholes all over the area.
the surfases is covered with koverall and a gave them 5 coats of nitrate dope.the primer is automotive with 20% flexible additive.
what is the reason for these holes?
this flexible additive is realy needed?
thanks
achilles

LesUyeda

You don't say how you applied the nitrate, but if you tried to spray: the air pressure will blow holes through the fabric in the thinned nitrate. I have always brushed the nitrate filler, then, occasionally used auto primer with no real problems. More currently, I fill with nitrate, then spray silver butyrate, and refill any problem aeras with brushed butyrate.

Les

rxAxilleas

thanks Les,
that was the problem. i made a test piece and the primer had no holes. the only diference with my surfases is that i sprayed the final coat of nitrate. althought the test piece had only two coats of nitrate instead of five it came perfect with thw primer and the other pieces ful of holes.anyway now it is too late. do you thinkn i will have any problem?
thanks achilles

TomCrump

Sand the airframe. Fill the pinholes with automotive spot putty. Sand. Respray. This may take a few tries, before you get all the pinholes.

I like to use high build primer.

From your description, I don't see anything abnormal.

chashint

I use Koverall and dope too, sometimes I will get pin holes, they are usually isolated to a specific area (right on top of course where they are impossible to ignore) instead of being all over the plane. I do not know what causes them because the nitrate does not appear to have pinholes in it. What ever causes it, the pinholes are hard to get rid of, I have sanded down to the covering and then built it back up with nitrate dope only to have the pin hole come back in the same spot. It must be contamination of some kind, but I am careful to clean everything between coats so I don't know what it would be.
Since you are using automotive primer the suggestion to sand it, fill it with putty, sand, and prime it again seems like the best (only) course of action to me.
I have been painting my planes with dope only so the pinholes are showing up in what I intend to be the top coat, I think it will be easier to deal with in the primer stage since it is still sandable.

rxAxilleas

Charlie and Tom,
thanks for the reply.a more serius problem is that the flexible additive i put in the primer made it very difficult to sand it. it turned like a ruber.it is imposible to sand it on the fabrik!
DO I REALY NEED THIS ADDITIVE on my future projects?
it seams that everything would be easier if i didn t used it.
also i want to build some details with this high build primer (rib stich, tape) . but i am afraid to add this flexible additive again since it turn in an unsandable rubber.can i simply use the high build automotive primer???
i know that i must built these details before primer with tapes of koveral over the ribs . initialy i thought that these details are slightly noticeable on the sbd so i shoot the primer and intented to build these with more coats of primer. now as i study more pictures i think i made a mistake and didn t build them beneathe the primer.
thanks ..

TomCrump

I've never used the flex additive in the primer.

I have used flex additive in the color coats, but these were on civilian models.

I've been using WarbirdColors on military subjects, with good results.

rxAxilleas

hi Tom,
the warbird collors is a very good idea . i am thinking of painting with latex or warbirds collors.
when you say that you never used the additive in the primer , you mean that you also had fabrik surfases and shoot primer without problems?
i was afraid of cracking of the primer...
thanks

TomCrump

My painted, fabric covered models are open bay, civilian subjects. One has a small amount of cracking at a wing/fuselage joint. The top coat did have flex additive.

Before I tried glassing, I built one fully sheeted warbird, covered in "tex" fabric. The weave was filled with high build, no additive. No problems, either. The control surfaces were not sheeted, just covered. Still no problems.

I now glass my sheeted models, but I still use the high build to fill the weave, and add some details.

chashint

The first plane I did in fabric had automitive primer (high build spray can type not flexible) applied directly over the nitrate dope. The finish coat is Krylon exterior grade enamel (John Deere green and yellow) from the spray can also.
The paint is very hard and there are a couple of places on the bottom of the wing in open bay area where pieces as big as a quarter have chipped out.
I always thought that if I were to use "paint" again I would get the flexible type of paint to hopefully prevent this from happening.
I was talking to one of my fellow club members about this and his thoughts on the subject was for me to try landing on the runway instead of out in the weeds and any ol' paint will be fine.

chashint

As a follow up to my last post, I don't know if the flex additive is needed or not, I have used dope for the last models and they do not have enough age on them to know what the long term durability will be.
On hard surfaces like aluminum landing gear the dope is easier to scrape off than paint is.
Once I work through all the dope I have on hand I am going to try the Stits Poly-Lite products.
http://www.stits.com/store/index.html

rxAxilleas

Hi Charlie,
thanks for the help and the link. i will search it.
achilles

chashint

Hi Achilles,
I just now noticed you are in Greece, I think this is wonderful that I get to converse with people around the world.
If you have time post some pictures of your model, I am sure there are plenty of us out here that would like to see it.

SoCalSal

My Feedback: (16)

Hi. I can tell you from my own models I have used the "Stits" system and it is by far the best out there. Useing different types of coatings on the same project will almost always cause some type of problems, if it is not because the coatings don't work togeather it is because you may forget how much and how lite or heavy to apply the coatings. The "Stits" system is not that much more in cost then most of the "model" coverings out there. The only problem is if you are building a smaller model. Then you will have way more than enough paint or polybrush than you will need on one model. You can only buy the paint by the quart in the smallest amount. The Ploy paints do have much more solids in the color coats than most other paints. You don't need to apply it very heavy at all to get a pro looking job. It is easy to work with as well. Just remember to use some type of spray mask because the fumes are really strong and you may get high on them not to mention all the other bad things they can do to your lungs,

Most of the Stits products come already thinned and flexitive added for you. Once you get the fabric applied it will never sag. I can send you some photos of my Waco that I used the Stits on.
I'm now covering a 30% Stearman with this product. You will be very happy once you try it.
http://www.stits.com/ This is were I get all my supplies. They are just good people to work with.

rxAxilleas

hi guys,
thanks again for the info.
Charlie , i dont know how to post pictures. i am sending a link : http://www.rcscalebuilder.com/forum/...109&PN=1&TPN=1