Glasing question
 

All right,
this may be a dumb question, but why do we need the fiberglass cloth in the first place? In other words, why not a couple of layers of sandable lacquer + 6 or 7 layers of polycrilic + primer? I understand the fiberglass adds strength, but
after all the same airframe cpould be covered in monokote, the strength coming from the balsa structure... So if I do not need the extra strength, why do I need to use the cloth?

Thanks

RE: Glasing question
 

The Monokote gives you strength in tension the same as the glass does. However, the glass is much stronger than the Monokote and it can be painted more easily than the Monokote making it easier to achieve a more realistic finish.

RE: Glasing question
 

It is a finishing issue not a solely structural matter.

With plastic coverings the range of colours is determined by what is available from the manufacturers. With paint, the range and effects of colours is determined by ones endless imagination. E.G "Shading/Blending," finishing around compound curves.

Ed S

RE: Glasing question
 

Think in term of "ding" resistance. You can scar the surface under Monokote, with a fingernnail. That is NOT true of a glassed surface.

Les

RE: Glasing question
 

SO in other words, if I wanted to just have a model that's going to hang from a ceiling rafter, no fiberglass would do it, but if I want something that will be exposed to the inevitable hardship of a working model (and I am thinking about car trunk mishaps mostly) fiberglass
is necessary. Is that so?

RE: Glasing question
 

The wood grain will come back through unless you add something to stabilize the surface under the paint. 'Glass cloth, tissue, carbon veil, silk, silkspan, etc is used to bridge and seal the grain.

RE: Glasing question
 

Hello,

I use glass and polycrylic all the time but you can also use silkspan with polycrylic. I give the whole airframe two coats of minwax sealer which is getting harder to find. You can also seal with hairspray. I buy the large cans for about 2 dollars a can. Two coats sand between coats. You can also use this for glass with epoxy or polyester. Stops the resin from soaking into the wood.

You have to seal with polycrylic, After sealing put the silkspan on damp and then hit it with polycrylic. Two coats sand between coats. After drying hit it with your favorite primer. I use lacquer without any problem. The finish with what ever paint you use.

On an open bay wing I cover it with doculam then ruff it up with steel wool and cover it silkspan and polycrylic. Sticks like glue. Then primer and paint as above. I use the doculam under silkspan to give the silkspan strenght it uses less polycrylic to fill. Also keeps little fingers from going through. Over 10 years and no delams with the silkspan and doculam using this method.

Rick

RE: Glasing question
 

Just about any model that you would consider using fiberglass to finish is going to be built strong enough to withstand flight loads even without any covering at all so it's not a case of strength. It is a case of durability and, as stated by JeffH, a necessity to stabilize the wood. I have not tried every type of finish out there but I have tried many and where no substrate is used (glass cloth, tissue, silkspan, etc.) the finish tends to develop hair line cracks (or worse) over time. That's my experience anyway.

RE: Glasing question
 

I have decided to experiment on a 6''x6'' panel made with a stick frame covered on both sides with 1/16 sheeting. I finished it with 220 sandpaper and applied two coats of deft sandable lacquer. Did not sand between coats, but I will sand before starting applying the
poly over the fiberglass. I am giving the lacquer a solid week to vent any residual solvent, as I read about problems with blisters forming under intense sun. The idea of the mock-up panel is to practice the technique (and see if I like it). Given how much I have come to hate monokote, I do not think it will be a problem at all...

RE: Glasing question
 

You could also use liquid sheeting. It is a polymer 2 part mix that you just brush on or you could use an old credit card or the like to apply it. Takes about a week to fully cure like latex and becomes a hard shell. No glassing, or prepping balsa surface necessary. However you need to do this outside because the fumes are bad and should be left outside for at least 3 days for the fumes to ware off. After cure, sand, fill and defects. prime and paint. If using latex no need to prime.

RE: Glasing question
 

Definitely not the case. Here are three models I built where the wings will fold during normal manouvres if the surface is not skinned with glass.

The first is a 12th scale TA152 used in combat where the blue foam wing was skinned directly with 1oz cloth and epoxy. The second a very high aspect ratio scale glider an ASW 27 where the glass finish was applied over the usual veneer and moved from 2oz at the root to 0.6oz at the tip. Both flew well and survived some high G manouvres. The glider wings would arc during loops though. The third was a F 104, now the wings are so short they might have survived but as it was capable of over 200 mph [ clocked more than once on a radar gun on a high speed pass ] I would not want find that out. N.B. The kit included instructions that specified glassing the wing for strength.

RE: Glasing question
 

Hnmm... a coat of fiberglass and resin, and a couple layers of primer (that'll be completely sanded off nearly) or 10+ layers of laquer, polycrilic and primer before color..

yep, i'll go with the fiberglass!

RE: Glasing question
 

if its a 80 inch span plus warbird , over 20 pounds , your going to need the glass for strength , especially on the wing.

its alot more work , but thats the price you have to pay

RE: Glasing question
 

not necessarily. Their are many warbirds back in the day that flew around with monokoted surfaces

RE: Glasing question
 

I am working on a 1/8 Corsair, hope to keep it at or below 12 lbs. I have started working on the panel I mentioned earlier. I have applied the lacquer base, gave it 6 days to dry, sanded it and now I have applied .7oz fiberglass cloth with two coats of WB Polycrilic (Tom Pierce's method). So far so good. Planning to add 4 more coats with sanding in the next few days. The panel started at 16g. After applying the lacquer based went up to 19 grams, will weight it again when I done with the WBPU and the primer. Aside from the fact that it is going to take some time, it does not seem an overly difficult job. By then, if I watned quick results I'd get an ARF...

RE: Glasing question
 

Notice I said "just about any model". There are exceptions and your three models may be among them. (And I'd bet the F-104 actually isn't an exception.) I stand by my statement that the vast majority of fully sheeted RC models are designed such that the covering is not necessary to withstand flight loads.

RE: Glasing question
 

And, "just about any modeler" understood your point. :D I've seen lots of planes with paint straight over balsa and knew a guy that built beautiful planes painting epoxy paint straight over balsa then sanding and re-coating until it was flawless. None of them had structural issues.

RE: Glasing question
 

There are plenty of sailplanes that aren't glassed that survive just fine. I have a 4m Roebers Discus that is Obeche over white foam, no glass. The wings bend greatly, but they have held up for at least 20 years thus far.
Once again, .6 oz cloth is NOT adding much strength to the airframe, it is providing a stabilized surfrace to paint. glass a piece of 1/16" balsa, then try to break it. Sure it gains some strength, but not enough to consider it structural. If you could glass bloth sides with .6oz cloth, then you will gain some measurable strength. If the design depends on glassing the skin with .6 oz cloth, the design is lacking in my opinion. One ding in the wrong spot could spell disaster.

RE: Glasing question
 

i agree on brushing thinned epoxy over balsa, then painting, it does make for a really nice finnish.

RE: Glasing question
 

My P-51 wing is 1/16th balsa and is spec'd out to be monokoted, but the skin is so thin that even if I did cover it I would surely put holes in it picking it up. In this case glassing makes for a better skin.  Structurally not needed, but for toughness, recommended by me at least.

RE: Glasing question
 

In the UK it was rare to see a sailplane over 4 m where the wings were not glassed. This was needed to survive winch launches and flights with ballast on windy days.

In some cases the glass/epoxy skin was applied UNDER the veneer to glue the veneer to the foam and add extra strength. This was quite common in small scale kit production as it avoided the need for sanding the glass layer.

Although I do accept there were some flying with just a film over veneer finish, usually with a degree of care though. Glassing adds considerable strength and ding resistance.

RE: Glasing question
 

J.D.
You make a interesting point.
Years ago I was working on a big Chipmunk that I got from 3W in Germany. The plane came with balsa sheeted wings. When I went to cut into the wing to install hardware and servos, I was amazed to find that the foam cores had been glassed before they were sheeted. The wings were incredibly strong and light. Al the glassing I had ever done had been over the balsa sheeting.
Live and learn I guess.
paul

RE: Glasing question
 

This has been a most interesting thread to read, and I thank you all for providing expertise. Earlier I mentioned that I was going to experiment on a small panel.
The panel was made sheeting on both side a 6''x6'' stick frame with 1/16 balsa. I applied 2 coats of DEFT sandable sealer, sanded after the second coat, 6 coats of minwax polycrylic over .7 oz glass cloth, sanding between each coat after the second, followed by two coats of primer/filler sanded down plus a final coat. I waited 6 days after the last application of sansable sealer before applying the glass/polycrylic. The latter was applied over a period of a week. Up to the primer, everything went well. I was surprised how easy it was to work with this stuff, and how good it looked by the end. HOWEVER, I decided to make a last test, and after waiting for the primer to dry over several days, I placed the panel in a convection over set at 150F. The idea was to simulate the inside of a car left in the sun on a hot summer day (I live in North Carolina). After about 1/2 hour in the oven, blisters started to develop! They appeared randomly over both sides. This problem has been reported in other posts, and my test confirms it. The working hypothesis, is that there are adhesion problems between minwax polycrylic and te lacquer based sealer that show up when the temperature goes up. Some people suggested it is due to solvent in the lacquer being trapped under the polycrylic. Note that I waited 6 days for the sealer to dry, during which the max daily temp reached ~80F and the min ~55F. So beware, if you operate in warm climates...
I want to make an experiment mow using hairspray as a sealer. Any suggestion on brands?

RE: Glasing question
 

I've used Final Net hairspray for years before I do any glassing.
It seems to cut down on the absorption of the resin into the bare wood.

paul

RE: Glasing question
 

Is this the non-aerosol (no propellant)?

Alberto

RE: Glasing question
 

Alberto,
I've only used the aerosol with propellant.

paul

RE: Glasing question
 

I've read many times about sealing the balsa before laying down the polycrylic to prevent absorption.

I'm thinking out loud here as I've never used poly and fabric. HEY, no smart remarks from the peanut gallery:D

How about spraying a mist coat of the polycrylic on first to seal the wood? It could go on pretty dry if you just "dust" it on. On the other hand if you put the poly directly on, most of it will evaporate.... right???? so not much weight to be gained anyway????? I have also read some will "seal" the wood before using epoxy. It seams a bit counter productive to seal the surface instead of letting the bonding agent (epoxy or poly) not soak in a bit for the best bond.

So with he above said.... If you chose to seal the wood to prevent absorption, I would find a way to use the same product to seal, as what will be used to bond the fabric of choice to the wood. I think you will solve any issues from dissimilar materials bonding (or not) to each other.

IMO, you have only one chance to bond the fabric to the wood as securely as possible to gain the most strength and that is the first coat of what ever product that touches the wood and cloth at the same time with nothing between them.


OK... My flame suit is on:D:D

Ken

RE: Glasing question
 

Ken,
I have read about people suggesting the same thing (using the poly as a sealer). I am concerned about the water soaking into the wood and causing warping issues. I think that is the reason it is recommended to use a non water based sealer as a first layer. Of course, I could use a lacquer based polyurethane, which would not require a sealer, but I'd like to avoid dealing with fumes, plus I like
being able to clean up stuff with water. I got a can of hairspray and will experiment with that. BTW, there were several types to choose from, most of them listed water as the first ingredient, so I stayed away from them. I picked one that has alcohol as first ingredient and no water at all. I will build another panel and experiment with hairspray+water based poly and report back the results.
Alberto

RE: Glasing question
 

Alberto,
I too would be hesitant to use anything water base on bare wood for fear of raising the grain. That's why I have used the hairspray first with good success. If you can't find a lacquer based hairspray, juts go get a can of Deft sanding sealer and use that instead. I'm doing a plane now that I used the Deft product first, then used the Polycrylic water base product right over it to apply my 3/4oz cloth. I have yet to have an issue with delamination. All that dissimilar material/ adhesion discussion is exactly that.... Discussion. I'm sure there's a chemistry lesson in here somewhere but I can tell you using the two products together won't fail you. I have used the Deft product throughout the glassing process too, but using the Polycrylic sure cuts down on the fumes and eases clean up. You won't have any problems with delamination as long as the Deft sealer is fully cured.

Hope this helps,
paul

RE: Glasing question
 

Paul,
It is not just discussion. As I mentioned in post 22 above,
using deft under poly resulted in blisters forming when heated to 150F.
You may argue that 150F is extreme, but it is not unheard of in a car
in direct sunlight. Once I left a heli canopy in the car. It basically melted down...
Alberto

RE: Glasing question
 

Alberto,
I'll keep the 150 degree issue in mind. Usually though, I try not to keep anything of value in 150 degree heat. Here in Buffalo, New York, that's something I would never worry about as hell might freeze over before that happens. I know of several Top Gun builders in south Florida however who routinely use the method I have described. Additionally, I've had sun/heat damage done to Monocoated,"Solartexed" and fiberglassed models before in heat, a lot less oppressive that 150 degrees. I'm gonna continue to use these two products together as it's easy,it works and produce beautiful durable results for my planes. To each his own I guess

Good flying,
paul

RE: Glasing question
 

What about removing monokote from an arf and glassing? What problems would you run into doing this?

RE: Glasing question
 

None,

Just remove the stuff then glass. I'm doing that now!

Charles

RE: Glasing question
 

I've used the light weight spackle quite a few times as a "leveler" on balsa. I thinned it with water to make a light slurry and painted it on. I've never had a warping issue. It dries fairly fast, like a WBPU does. I guess my only concern, using a wood sealer, is not having the first coat of product soak into the wood providing the best bond possible with the glass cloth.

I guess it comes down to what ever works for you.

carry on:D

Ken

RE: Glasing question
 

I did some experiments with alcohol based hairspray. 2 coats of hairspray, 6 coats of WBPU + fiberglass cloth. Baked at 150F for 1/2 hour, no bubbles/blisters.
I did noticed though some warping at the end. Not sure when it started. It may have been there from the beginning, though I noticed only after a couple of coats of WBPU.
So now I am doing a final experiment
with just a sheet of 1/6'' balsa (no frame). So far the first coat of hairspray went on without warping. The second is drying right now. Will then do the usual
WBPU. I reckon that if warping occurs, a plain sheet of balsa should show it. Will check after each coat.

My only gripe is that the only hairspray I could find that is alcohol based is scented. What happened to the old cheap hairspray?

Alberto

RE: Glasing question
 

Ok,
it seems that if I do not apply the hairspray liberally the warping occurs after applying the WBPU, while if I apply the hairspray liberally warping occurs right away. Either way, no good. Probably the harispray is not the right one.
Pacoflyer suggested a lacquer based one. Will look into it.
At this point, if I can't find it I am inclined to go with the DEFT sealer and make sure I do not leave the ship in a hot car...

Alberto

RE: Glasing question
 

Hi!
No hairspray is necessary!!!!!!!!

RE: Glasing question
 

I agree, I never used any pre treatment, just epoxy onto bare balsa or veneer.