Waterproofing paint – 33B/596 or K4/10612

Nicko. Today I was looking through the content page of a 1939 edition of AP 1208 – Airworthiness Handbook for Civil Aircraft. Volume 1, “Design”, has a leaflet G-3 – Plywood Edges within it. It was I think a new item added that year. It could be of interest, but unfortunately I don’t have a copy of the actual document. 

I suspect the leaflet may also feature in the AID leaflets as they (I think) were the tablets from which AP 1208 took its source of information.

Thanks TonyT and Antoni. More reading to do!

I received AP1086 section 33B bought on ebay. It is from 1958 and it seems that 33B/596 has already been deleted. It does not appear in the body of the listing or in the list of replacing ref numbers.

Could it be “banana oil”. If you do not know what banana oil is, it is a solution pyroxylin in amyl acetate. Pyroxylin is partially nitrated nitrocellulose used for making lacquers and dopes. It is highly inflammable but does not explode. Amyl acetate is slightly oily and smells of bananas, hence the name. Amyl acetate is very resistant to blushing in very humid environments.

In the very earliest days of aviation banana oil was the first protective finish used on fabric to waterproof it, before more sophisticated nitrocellulose had been invented. When I was a lad back in the 1960s you could buy it from the model shops to use on tissue/balsa models.

If you want to find out more about pyroxylin and what goes into nitrocellulose dopes this book explains a lot.  

https://babel.hathitrust.org/cgi/pt?id=uc1.$b576564&view=1up&seq=5

http://raanz.org.nz/techproject/ac4313b.html

http://raanz.org.nz/techproject/

http://journal.sciencemuseum.ac.uk/browse/issue-06/doping-at-the-scienc…

As usual, distracted by other things. I was actually hoping to find a copy of the AP.1464 chapter in a friend’s library, but no luck there.

BTW, Oracal, I’m afraid those NAA links don’t have any permanence. I have however had a look there and am part of the way through the digital copies that are available. There is a BALM specific one not available digitised, but this is probably too early anyway (1940). It seems so far that the RAAF stores number is probably either late-war or post-war. Although that doesn’t mean the BALM product didn’t already exist. I may request a digital copy anyway.

I did come across some entries in the MOTAT collection. Not sure that the BALM specific entries will help, but there was an RAAF entry that helped me with my NAA search.

Based on specific technical advice, it may well be that the lacquer is actually essentially the same as the taughtening dope but with a much lower solvent content.

Pretty sure I have seen a BALM catalogue at either MOTAT or RAAF museum.

Nicko – there are number of items in the Australian National Archives that may be of interest;

https://recordsearch.naa.gov.au/SearchNRetrieve/Interface/ListingReport…

I have learnt something about the Australian call-out. Handy google search looked up my own copy of RAAF mods for me: RAAF mod 317 – Tropic Proofing Lacquer, K4/10612 is BALM S2027. I found that BALM was British Australian Lead Manufacturers and eventually became Dulux. Would I be lucky enough to find some kind of brochure?! TDS or MSDS?!

https://www.key.aero/forum/historic-aviation/ap1464-chapter-painting-and-doping-aircraft

Haven’t been able to get a copy of the AP.1464 chapter so far, but did manage to find AP.1086 section 33B on eBay.

Request for particular AP.1464 chapter transferred to separate topic.

Still looking through other sources.

Thanks Oracal for your notes. I leafed through AP.1464 last night and my copy is fairly incomplete. I saw the section you refer to in the old/new cross-reference table, and sent a request to someone on ebay who used to have a CD of many AP.1464 sections available in their store. I am not sure if I have the other references you noted, however I do have quite a few I have yet to have a look at.

Cheers.

This is a fascinating subject.

I have seen shellac used on a 1930s light aircraft for protecting internal wood surfaces that were not going to be fabric covered. The aircraft concerned was still in its original condition and not subject to modern refurbishment.

The Americans used ‘spar varnish’ during WW2. No idea of the makeup of this, although it is certainly not the same as the polyurethane product used today.

There is an interesting piece in the American publication Wood in Aircraft Construction (aircraft design data note no. 12) publication. You should be able to find an ‘e’ copy of it online. Go to page 140 were you will find ‘Treatments for preventing changes in moisture’. Lots of test data of interest.

Another publication you may like to look at is Materials of Aircraft Construction by E T Hill – Pitman 1944. Chapter X ‘Varnish and Protective Coverings’, it gives DTD 912 as an Air Ministry Process and Specification reference for wooden parts of aircraft except airscrews and windmills.

A late 1930s copy of Inspection of Aircraft After Overhaul for the ‘B’ licence suggests the reference BS Spec 3X7 ‘varnish for internal woodwork’ as the specification.

Until at least the 1960s the German gliding industry was using ‘coloured spirit varnish or cellulose paint (oil-free)’ to protect the wooden interior surfaces. Today there is product available, the name of which escapes me (possibly due to too much sniffing of the fumes) that does a great job of protecting wood.

ISTR that AP 2662A once had a recommendation to use bituminous paint on cut plywood edge – certainly not mentioned in my 1944/6 copies.

Perhaps a copy of AP 1464D that includes the section, Protective Treatment for Airframes, could be of help?

Thanks Oracal. Lacquers elsewhere on the aircraft are nitrocellulose. These are waterproof and I understand that nitrocellulose had in a general paint finish sense replaced shellac long before. Is it better than nitrocellulose lacquer?

The investigation began because we were trying to figure out what ‘repellor’ meant in the section cuts that show the application of fabric edging on the fuselage. I have attached one of these cuts. There is nothing in the text of the repair manual that actually  defines what ‘repellor’ is. I think that it is this ‘waterproofing paint’ that is mentioned elsewhere.

The Australian manual says ‘reduced 30% with Thinners K3/174 for spray’, so that would give an indication of the type of system anyway.

Sounds like shellac.