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Priming F'Glass

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Old 05-16-2003, 04:12 AM
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Canuck1
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Default Priming F'Glass

I have a question regarding the first steps after my first primer coat. First of all when the entire fuse was glassed, I roughly sanded any joints and over laps to gain a fairly smooth finish. After my first primer coat, it has many uneven flaws where the glass has overlapped, as well as some low spots which I anticipated. I will wet sand with 220 grit probably within the next couple of days. I am planning on using some automotive glazing and spot putty to fill the low spots. My question is regarding the use of the spot putty. Do I apply it prior to my first sanding job? I know the wet sanding should level out the overlaps, I am hoping anyway. When I do sand will the seems become non existent? I assume I will need several coats of primer to finally fill the weave as well to achieve a smooth finish. My other concern is doing to much sanding and eventually cutting into the glass cloth. I used west systems to apply the glass to a foam fuselage. It worked very well. Is 220 grit to harsh to the 2oz cloth that I used, or should I use a finer grit of paper? I have also read some posts a while ago, and they we saying that sanding could also be done in a circular motion. I would like some opinions regarding that as well.

Enough questions for now. I am looking to achieve great results, however being my first Glassed Airplane, I do have many questions. Thanks for you time.

Craig
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Old 05-16-2003, 05:10 AM
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briankenney91
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Default Priming F'Glass

I used to do body work for a living so I will help you out as best as I can. The first thing you want to do is sand down your primer. That way the spot putty has something to stick to, I would not go any finer than 220 grit for this or you could have adhesion problems with the spot putty. Then apply your spot putty sand down again with 220 grit until its smooth and your seams are gone, if you have to put another coat or two on then do it until you feel that it looks right. You can rub your hand lightly down it and you should be able to tell if you have high or low spots in it or you can feel your seams. If you can't tell by hand take an old t-shirt and place it flat in your hand and rub it across it will help you feel the bad spots easier. After that put about 2-3 coats of primer and wet sand down with 400 grit if you are using automotive paint that way you don't leave sand scratches. Then you can put your base coat and clear coat on. I hope this answered your question for you. If you have any more questions don't be afraid to ask.
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Old 05-16-2003, 03:38 PM
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Thanks Brian.

I will give your method a try. I figured that I would have to sand prior to the putty. I will post back with the results.

Craig.
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Old 05-16-2003, 04:15 PM
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No problem Canuck I hoped that helped you out.
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Old 05-16-2003, 09:11 PM
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Default Priming F'Glass

That worked very well. I have some Grey primer remaining and you can tell that these are the low spots. I can go ahead with the putty but I have one other question. Can I sand until most of the remainder of the primer is gone? Or will this effect the glass?
I was amazed how fast the primer was removed with wet sanding. After the putty application, I will have to dry sand those areas I assume? I still have a few area's which need more primer into the weave. Should I use primer, or give it a quick once over with the putty?
Once again thanks for your help.

Craig.
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Old 05-17-2003, 05:58 AM
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Default Priming F'Glass

Ok to answer your first question I would try not to sand all the primer off, that way you don't have to worry about cutting into the fiberglass to far. As far as your next question you can either wet sand the putty back down or you can dry sand it what ever your prefernce is. If the weave is very noticable you probably should put a little putty on it rather then bury it in primer but if its not too noticable than you can throw a little primer on it.
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Old 05-18-2003, 01:06 AM
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Default Priming F'Glass

Canuck,

you are getting some good info. Would like to add that when you shoot your last round of primer/surfacer, let it cure for about 30 days or until you can't smell the thinner in the primer. That is, stick your nose next to the surface and sniff. If the thinner odor is gone, it's time to scuff with ScotchBright or 400 and paint. If you rush and shoot color before the surfacer finishes shrinking, it's a lead pipe sench that glass weave and seams will show before very long.
Also, you mentioned "putty", if you are referring to lacguer putty, you will notice a certain amount of shrinkage in that material as well. If you were referring to a polyester product such as EverCoat, then "putty"shrinkage isn't much of a problem.
If I may mention one other thing: As regards sanding through the cloth, if you sand wet and keep the surface clean by flushing with water as you work, it goes a long way toward avoiding sand-throughs. You can see what you are doing much easier is what I'm trying to say. Good luck with your project. What are you are building?
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Old 05-18-2003, 01:43 AM
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The best kind of primer to use is not a laquer primer but a primer that you have to mix in the reducer and activator, I have sanded it down a couple hours after spraying it. I would reccomend 3M Flowable finishing putty I liked that alot better than the Evercoat, but that is just my opinion.
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Old 05-18-2003, 03:07 AM
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91's right, epoxy is sort of the ultimate. A bit expensive when compared to the old lacquer standby. Also, be aware of the health concerns of using an epoxy-based product and not breath the stuff and keep it off your skin. While we are considering alternate primers, vinyl ester primers are available here and there. They are a good deal less expensive than epoxy. Catalized with polyester catalyst ( keep this stuff away from your eyes...instant blindness)and can be reduced with wash lacquer thinner. Will handle a lot like the old K&B primer but is a bit more difficult to sand: Probubly has less filler. Wouldn't use the product on open bay surfaces...just sheeted areas due to the added pressure required to sand the stuff. Health risks are a concern with anything Ester. In short, it handles about the same as epoxy, but is a good deal cheaper.
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Old 05-18-2003, 06:40 AM
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Default Priming F'Glass

The method Brian explained to me has worked very well. I am using just standard Grey automotive primer with good results. The putty I am using is Bondo, glazing and spot putty. The stuff goes on smooth, dries in half and hour. It wet sands great and feathers well. The fuse at this point is a combination of grey red and white. After I sanded with the 400 grit with water, the fuse is at a nice state, very smooth and hardly any pin holes.
I am building a 90in Lancaster bomber from Chris Gold plans. The fuse is a wood box construction with foam for the outer shape. I glassed the foam with 2oz just for some extra strength to prevent hanger rash. The remainder will be glassed with .75oz cloth using the West Systems. The West Systems is great. No measuring as the hardener and epoxy are delivered by pumps on the container. It is very then and requires no thinning. This is my first glassing job and I am pleased with the results so far. I have also been getting some great support here from fellow modeler's. I do thank all the opinions and ideas that are on this site.

Craig.
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Old 05-18-2003, 02:41 PM
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Good Canuck glad to hear that the steps I told you are working well, post some pictures so we can see what it looks like before or after its done.
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Old 05-18-2003, 06:28 PM
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Great project! The Lancaster is a super looking plane. One of our club members owns a giant scale....about 10 or 12' span. Haven't seen it fly, but understand that is a very docile plane that looks like the real thing in flight. It's painted in camo, but I can't remember what squadron markings. Likewise, hope you post some shots of the plane.
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