English Electric

I have just covered the aircraft I am constructing with fibreglass and the associated polyester resin and hardener. I now need to create a smooth surface, due to the set fibreglass is course. The back of the package which the fibreglass and the complement products came in, suggests filler (plastic padding), which can be glasspapered smooth. I cannot help thinking that this will consume a great deal of time and money. Is it possible to just sand down the fibreglass as it is, without having to add any further material?

davidfee

Yes, you can sand the lumps down. Basically, you'll be reducing the strength by cutting up all the glass fibers into short pieces, but it's quite likely the structure is already strong enough. You can also use one of the lightweight fillers, often sold at home DIY centers as "lightweight spackle" for fixing holes in walls. You can spread this on with a broad spatula and then sand it smooth after it has dried. Then prime and paint as desired.

-David

3dd

My Feedback: (6)

you don't say how many coats of resin you put on but i like to put my cloth on with one thinned layer of resin then put on one coat of unthinned resin and sand this with 300 wet and dry paper to get a smooth surface that is not to heavy.then fill any little dings with a patch of resin only with micro ballons in it and sand that to a glass like finish

English Electric

Thank you for your replies. They are most useful. I will probably apply a standard paste, regardless of the time it will take.

RCHYFLYER

My Feedback: (1)

I'm getting ready to glass my cessna with West System resin and .75oz cloth. I am looking at doing one coat to hold the cloth down and then finish with evercoate top coat filler. Do you think this will work or will it be too hvy?

Jetman007

My Feedback: (6)

Here's one tried and true way

http://artshobby.com/fiberglassing.htm

CAPtain232

My Feedback: (40)

Hey guys,

i have used the technique as described in ART's article with good results. After a good paint job, the surfaces are a slick as glass

English Electric

It is fine for those who are using the mysterious 'Z-Poxy Finishing Resin', but for those of us who are not, it does not help. Furthermore, there is absolutely no way the instructions are substantial enough to undertake the task in hand. If I even attempted to follow them, I would have one project ready for a scrapping order.

I will just have to use car filler paste over the rough fibreglass surface and sand it to a smooth finish, regardless of how much time it will really take.

davidfee

Z-Poxy is nothing more than a reasonably good low viscosity epoxy, similar to most laminating epoxy resins. It just happens to be sold to modellers in a convenient small package, unlike most good epoxies (which are sold by the gallon).

As for the sanding and filling, what weight of fiberglass did you use? It should be a light glass with a fine weave, so there should not be much filling or sanding to do really. A lot of guys seem to like applying a wet coat of resin to fill the weave, but resin is fairly heavy and it's not particularly strong... so in my mind it's wasted weight. But whatever. If the glass is fine then my suggestion would be to sand it smooth and if there are any dry spots or deep wood grain, fill those with spot putty or lightweight wall spackle as needed. There should be no "Bondo" car body filler on your airplane (very heavy)! After the largest bumps have been sanded down, then spray on a high bulk "sandable" primer... and when dry, sand back down to the glass so the primer just fills the low spots remaining in the weave. Repeat until satisfied with surface, then paint as desired.

One of the best tips anyone can give is to try any new technique or material on a piece of scrap... not on your pride and joy. Patience here will really pay off.

-David

English Electric

Purely out of interest, may I ask which fibreglass is generally stronger - fine weave or course weave? Personally I would have thought the latter was the stronger (myself having used it on several vehicle tasks).

davidfee

If the fiberglass cloths you're comparing are essentially the same weight (oz/yard^2 or grams/m^2) then there should be only a small difference, if any, in the relative strengths of the two. The coarser weave will have larger yarns, so it might have greater bending stiffness in a flat piece, but the finer weave will result in a torsionally stiffer finished panel because the fibers are more straight... curving less around the other yarns. If you're comparing different weights of glass, then the heavier one will obviously be stronger.

-David

newbiepilot

Hi guys,
Just reading the posts here, and I was wondering, what is spackle?
Thanks for the info.

newbiepilot

Oh yeah,
And does anybody know where you can get "Z-Poxy" ?
Thanks.

davidfee

Spackle is the putty you fill pinholes in your walls with (in your house) before painting. Lightweight spackle usually has microbaloons (tiny glass bubbles) in it and it is very light. Bondo, by contrast, is filled with solid glass bits... and is relatively heavy. They use it on cars to fix dents.

Z-poxy should be available at most hobby shops, or from Tower Hobbies, etc.

-David

hnesitd1

davidfee - great info. What ratio of microballoons/epoxy would you recommend for filling 3/4 oz cloth (if necessary). What ratio for forming fillets. Thanks.

hnesitd1

Davidfee - I've always assumed that Poly Resin has a very strong smell, ie, not good for covering glass fiber in a basement enviroment, eh? Isn't Z-Poxy, poly resin? Has the smell been removed; can this stuff be used indoors or should a person invest in epoxy resins? Your reply would be appreciated.........thanks.

davidfee

I don't want to give you the wrong impression about strong odor relating directly to health hazards. Epoxy also has fumes and they are likewise not good to breathe. It's just that epoxy resins smell sweet and epoxy hardeners have a faint ammonia smell, whereas polyester resin is mostly styrene monomer which is very aromatic and has a high vapor pressure (and really stinks). The polyester odor is very strong, so I will only use it outdoors... or in a garage with the door open. Epoxy is ok in the basement if you have an open window (or door) and having a fan for air circulation is good.

Z-poxy is epoxy, not polyester. It's fine for use indoors, with proper ventilation. You really shouldn't use any adhesive or paint (including CA) without good airflow.

I don't have fixed ratios for microballoons... I basically keep adding more until the thickness is right. If I want to be able to spread it over some glass to fill the weave I'd make it like the consistency of ketchup or a little thicker. For filleting I'll make it really thick... like whipped cream or peanut butter. If you pull your mixing stick out, you should see a little peak. Depending on how thick it is, the peak will either fall over or stay up. For fillets, it should stay up.

Good luck,
-David

FLYBOY

My Feedback: (11)

I use red devil spackle from ACe hardware. I thin it with water after the surface glass has dried, paint it on with a brush, sand it smooth, prime and paint. Adds zero weight, fills the holes and looks awsome. Works pretty well and you can buy it in various sizes of containers. You will know it when you pick it up. Some fillers weigh a ton, this stuff weighs nothing.

B Vial

I use good old sandable primer and microballons. Dip a 2 inch or so brush into a jar of sandable primer then dip it into a jar of micro ballons. Use the primer as the glue and the microballons as the filler. Load on just about as much as the wet brush will take of the microballoons. Then just brush it on all over. It sure looks like heck until you sand it down but it sands real easy and is light also.

KC-135

My Feedback: (3)

When I glass my wings I spray a little 3M 77 and it allows you to postion and smooth out the glass cloth and it holds it in place.Then I pour on enough resin and using a squeege spead it out till you just about have the weave filled,let dry,you should just see the weave. Now you can do a second coat and add micro ballons and do the process over.This will allow you to sand down the surface easier.Then if theres any imperfection spray primer, sand almost all of it off, spray, sand ,spray, sand till you get a glass like finish. remember that your only trying to achive the finish.Not strenght.

hnesitd1

Thanks for the info guys. The other question is, can micro-balloon be mixed with wood glues for filleting, etc? Would the weight be a consideration? Thanks again.

davidfee

What type of wood glues are you thinking of? When I think "wood glue," I'm thinking yellow carpenter's glue... which is water-based aliphatic resin. This stuff is fantastic for gluing wood, but it shrinks a lot as it dries... since the water evaporates away. A fillet would shrink a lot and take forever to dry (no air can get to the glue inside). But yes, you could certainly add microballoons to wood glue without any odd side reactions. There are better ways to make a fillet though.

-David

hnesitd1

Davidfee - Yes, I did have aliphatic resin in mind. You raise some interesting points though. Keeping in mind that there are other methods, would you recommend using micro-balloons for fillets - it would appear to be very easy to work. I would like to glass my fuse with 3/4 oz cloth and then use micro-balloons for the fillet. I think I can appreciate the advantages of fibreglass on those models where detail is a factor, ie, paint schemes, panel lines, etc.

davidfee

Ok, so here is what I would suggest for the fillets (wing-fuselage and/or tail-fuselage). For the wings, make a piece of very thin plywood (1/64" is fine) or thin balsa which represents the shape of the fillet as projected onto the wing. Sandwich a piece of waxed paper between the wing and fuse, glue this wood former/template in place, then mix up some really thick and fluffly microballoons and epoxy. Slather the stuff in position to make the fillet and rough shape as desired... sand smooth when cured. If the model is large, it will be lighter and probably a little easier to make a rough shape out of foam and then use light fiberglass and a epoxy/microballoons slurry. For the tail fillets just use the epoxy/microballoons slurry. It's not a bad idea to make a test article before you try this on your actual model.

-David

hnesitd1

Thanks again for the info. Searching the FORUM re: fibreglassing, I've discovered a lot of USERs advising caution when using glues, resins, etc. I don't believe that this info is stressed enough and I appreciate people being candid in this manner. Anyway, I think I've been convinced on several things re: fiberglassing. My plan will be to use water based polyurethane for applying the 3/4 oz cloth to the fuse and epoxy resin and heavier cloth for fabrication.