FlatSpin

not sure if this is the place to put this or not. but my parents friend had like a 1/5th scale spit fire. like ten years old. basically all done. just needs a motor and to be covered. but the question is. do you think the balsa is any good still. he thinks it maybe all dried out and to brittle.

if this is true is there a way to rehydrate the balsa?


thanks
JAY

Sky Sharkster

Hello Jay,
I haven't experienced any problems with balsa drying out, even after several years. The main problem I've seen with older planes is the glue drying out, and this was mainly on models that were decades old, when the celluose glues (like Ambroid, Testors, DuCo) were popular.
Now if the model was treated with butryate dope and sat for a long time, it might crack. But unfinished balsa, not so far. I have sheets of balsa that (I believe) are at least 10 years old-I have a LOT of balsa! and it's all fine.
I guess you could try light pressure on a non-critical part of the plane, or a part that is easily replaced. Say the bottom of the rear fuselage or wing sheeting that's normally inside the fuselage. Or maybe a "Twist" test of the wing, holding it by the tips and warping it slowly.
Perhaps others have had different experiences, but so far, my balsa "Lifespan" seems pretty long!
Good Luck,
Ron

FlatSpin

thanks. ill be sure to forward the info. to my parents friend. so hopefully ill take it over and finish it.

i would love to see this thing in the air.

Bill G

I've built several kits from 40 year old balsa that seems fine. I did inherit a partially built 40 year old Sig kit, where the balsa had obviously become very crack prone, assumingly due to drying out. I think what killed it was that it had been in a basement, where it went though countless damp/dry cycles, and had mold residue from being very damp at times.

Saucerguy2

One of the processes I use with what I build in the non rc world requires treating the wood that comprizes the trim. This wood needs to bend and is a porus form of mohagony. Once it's in place, it gets treated with fiberglass resin. This soaks in and makes it very strong. If you find the balsa to be needing some extra support, I highly suggest treating it in the same manner, be it, using thinned down PVA instead since fiberglass resin will weight it down too much.

E-Challenged

I have encountered "punky" wood in really old model kits that splits, breaks, and crushes easily as if it were dehydrated. If you are building from a really old kit , test some of the sheet wood by attempting to cut small pieces from it. If it handles as described above, consider tracing the parts onto onion skin paper and cutting new parts from fresh balsa from the hobby shop. I also substitute new basswood stringers and longerons for old "punky" balsa for electric R/C conversions. It may be worthwhile to make new spars and wing leading and trailing edge pieces too.

carlosponti

the wood does continue to dry out which is problematic for building however a plane that is already built the problem is with the adhesives being brittle with age. now if you have a kit you wish to build that is really old you can rehydrate a bit by taking a really hot shower with the kit in the bathroom with you(not in the shower) the humidity will rehydrate it. then you acclimatize it for a week or so to your building area and start building. now if the plane is already built if you can determine when it was built that would be nice in the last 20 years the wood glues are phenomenal if that's what they used. Epoxy will become brittle with age as well. in that case just look the airframe over and check the glue joints most likely you will have a good flying airplane.

salat

what is suggested humidity in percent? I recently discovered that we have only ~20% now due to use of electric heater. I guess it is too low and I'm afraid of loosing my big stocks of balsa wood from overdrying..
Thank you,
Kostya

carlosponti

i would say more that its about length of time than the percentage of humidity. wood no matter what kind unless its sealed keeps drying out. I am a hobbyist wood worker and wood drying is something you have to first deal with and second be aware of because you cant build from green wood because the drying process will continue and cause shrinkage etc. the main thing is you have it acclimatized to your shop before doing work with it. now it works the same way with model kits the wood continues over time. one quick way to tell if the balsa is too dry is if you cant get CA to dry on balsa.

now there is a better way to tell if you have the money to buy one a moisture meter is nice to have. now in woodworking around 10% Moisture Content in the wood is fine more not good less not good either. in balsa i am not sure what the 'MC' should be.

salat

Can you tell me what would be good room humidity for wood storage?
Yes, I have experienced CA failures some times. I noticed that I need to blow it with my breath to kick CA. Otherwise it tends to stay fluid quite long. For several minutes. Do I have overdryed wood then? BAAAD . I have about 15kg of it in stock...

carlosponti

it might be dried out but you can add moisture back to the wood. if you follow the tip about putting the wood in the bathroom and take hot steamy shower with the wood exposed to the air. could build a steam box as well. might get a humidifier for your shop, I guess try to maintain around 40% humidity in the room. the wood is not junk yet so don't throw it out.

michaely

I know this is a very old thread........but the notion that old balsa should be rehydrated is not typically correct.

The balsa that we use (and was used in the past) is initially kiln dried to perhaps 6-7% moisture content and then acclimatizes the relative humidity of the environment it (as sheets or in built up models) is lives in, along with seasonal changes in RH of its living environment.
It does not uniformly "continue to dry out" over time without regard to its environment.
Seasonal changes in relative humidity typically result in only a couple of percentage points in moisture content of any wood and this is typically not enough to affect balsa wood in the (relatively small) sizes of applications in model airplanes. In my climate area - north of Toronto, seasonal changes in relative humidity can be from 30% in late winter to 80% in late summer, yet the seasonal 'acclimatized' moisture content of wood stays within a range of 8 to 10%.

Yes, any wood can deteriorate if stored poorly - alternately wetted, dried without proper airing can cause sheets to warp, attract mould, etc.

But no, that balsa wood in that kit stored in the hot attic or dry cool basement for 40 years, along with built up models, should be fine and not need to be artificially 'rehydrated'.

Probably the most extreme wood movement would be a balsa model built in humid conditions - say Florida - and then be sent to live in a dry state like Arizona..... the width of the balsa sheets in a fully sheeted wing of very large model might contract sufficiently that splits may open along the glue joints.....

good luck,

Michael