Comparion of Coated Tissues

[Piecost]

This thread summarises some experiments performed on different types of tissue sealed with acrylic and with wallpaper paste. It is inspired by Anyun's build thread, which I was starting to hijack :

Rieseler R III scale 1/25
https://hpa.aeromodelling.gr/index.php?topic=394.0

Anyun described using a type of Japanese tissue which is lighter than that available from aeromodelling suppliers. It is obtainable from fine art or book restoration specialists and can be very expensive. It is known as Tengujo Kashmir. I have obtained "Kozo Shika", which I hope is the same stuff. Either way, it was the only type that I could obtain the the UK. The postage was significant; a third of the cost. I was too frightened to even find out international postage rates for overseas suppliers.

The Czech aeromodelling forum is a constant source of inspiration and information, but Google translate struggles with hobby specific words. So, my understanding remained rather sketchy. I had actually bought samples of the tissue and the Czech wallpaper paste, a few years ago, but didn't know what to do with them! Anyun's thread has motivated me into action.

Link to Robert Pajas page describing different tissues:
https://www.minimakety.cz/howto/2009/Potah/index.php

Anyun is following Czech practice of using a very porous tissue and applying multiple coats of wallpaper paste to form an inpervious skin.

I bought two different mass of "Conservation Kozo Shika" and attached samples to 100mm x 100mm balsa frames.

The "9gsm" tissue measured  9.1gsm
The "4gsm" tissue meadured  3.5gsm

I sprayed 1 coat of unthinned Pledge Multi-Surface (acrylic) wax, instead of dope. This was nessesary to bind the fibres together before applying the wallpaper paste. Despite this; the fibres of the lightest sample started to pull appart when the paste was being brushed on.

I applied 5 coats of Metylan wallpaper paste, starting in a ratio of 0.57g of powder to 20ml of water. This was following the stronger mix ratio stated on the packet. As Anyun advised; more water was added to the mixture for subsequent coats to retain the consistancy. It's consistancy was slightly more runny than liquid honey. Liberal coats were applied with the softest brush that I could find.

A careful inspection of the surface was required to ensure that all the pores were filled. Perhaps further dabs of paste should be applied over pourous regions, rather than coating the whole surface.

Conclusions

The 3.5gsm tissue was easy to handle and to glue to the frame when dry. But is very delicate when damp and would be challenging in covering double curvature areas such as wingtips. It resembles a mesh/net more than a solid surface and 5 coats of paste sealed in some areas, but was not enough in others. The fibres are easily pulled apart when brushing and have caused slackness in some areas.  It is not practical for my skill level.

The 9gsm was really easy to use dry. Care would be needed when damp. I have not tried it on curved surfaces such as  wingtips. The paste coating worked well. The covering is drum tight and resembles doped Esaki. However, in my limoted experience, it does not offer a weight saving over other aeromodelling tissues.

[Piecost]

Unfortunately; I could not obtain the 6gsm version of Kozo Shika. I anticipate that when filled that it will be significanty lighter than the aeromodelling tissues without the drawbacks of the 4gsm sample.

It has been successfully used by Jirka Pavlicek on his fanstastic Zlin build:
https://hpa.aeromodelling.gr/index.php?topic=273.15

I was intriged by the finished mass per area of these tissues compared to more readily available, lightweight, aeromodelling tissues.

So, I made further samples of different tissues from my stocks.

I attach a table giving the mass/area of the untreated and treated tissues. They are ordered from lightest to heaviest of the finished samples.

I water sprayed the samples to taughten, then sprayed a single coat of Pledge.
This was applied to all samples at the same time using an airbrush. Each sample was then, in-turn, and sprayed induvidually until it was sufficently wetted.

Conclusion

The following only considers mass and a cursory look at the surface porousity and smoothnes. Other critical items such as, wet strength and shrinkage are not considered.

The table of weights of the coated tissue should be taken with some skeptasism. I do not know how repeatable the results are. So, the results should be taken to indicate general trends only. Other poeple might get different results.

The 4gsm Kozo was the lightest, but not useable . The tissue disintegrated in places; slack and porous. Other areas quite useable.

I was supprised that thr 9gsm Kozo was one of the lightest tissues but that the wallpaper paste, needed to seal its pores, pushed the total weight up to more than many conventional aeromodelling tissues. Perhaps, I am applying the coats too heavily.  Do more numerous, thinner, coats seal it better? My conclusion has to be that the 9gsm Kozo offers no advantage in finished weight. It is nice though and I may use it on my next model. This increases my desire to obtain some 6gsm Kozo, which I feel will be lighter.

The Dilly tissue was similar in uncoated mass to Esaki, but was significantly lighter after 1 coat of Pledge. It's surface is very smooth.

I think of Esaki as the benchmark. It doesn't really need coating to produce an air-tight surface. It took a little more mass of Pledge than the Dilly. Perhaps, I over-did it.

The Lense Tissue (the stuff used for cleaning glasses) was too porous and really needs some coats of wallpaper paste to seal it. This would increase its mass. I don't consider it useful for our purposes.

The Gampi was very similar to Esaki, a good sustitute. But, I have not tried it on curved surfaces.

The yellow Asuka was a little heavier than Easki and took more Pledge. But, again, felt like a good substitute. It is slighty heavier than Dilly and Gampi, but comes in a limited selection of colours.

The Balsa Cabin tissue was heavier and took more Pledge. Whilst it was sealed; it's surface was still blotchy, like it had not been sufficently wetted. The increased mass would be more suitable to models larger than peanuts. Again, it.comes in colourz.

Using Solvite wallpaper border adhesive was quite heavy at about 0.2g. It was not accounted for in the weight comparion table. This is heavy relative to coating on the tissue. Dope and thinners might be lighter.