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Using Ammonia.

Auster J1.

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David Barker 228/11/2018 09:52:09
22 forum posts
14 photos

I have read somewhere that using Ammonia on balsa-wood makes it easy to bend. Is this true?. And if so is it used neat or watered down. I have bought an 87" wingspan Auster J1 kit from DB Sport, ready to start in the warmer months. As the first stage of the build is bending fuselage longerons. Thanks for any help.

Mowerman28/11/2018 10:06:05
1561 forum posts
105 photos

Diluted to about the strength of window cleaner(or you could use window cleaning stuff) If you try it with neat ammonia the fumes will be a bit much so would need to do it out doors.

Edited By Mowerman on 28/11/2018 10:08:35

Alan Gorham_28/11/2018 10:35:24
1336 forum posts
146 photos

If you have a look through some of the build threads on the PSSA Hurricane mass build from earlier this year you can see lots of us used Ammonia to allow the fuselage sides to take up compound curves.

FWIW I use Ammonia neat and I don't like wetting balsa with water as it swells too much.

Hurricane build threads here:


Bob Cotsford28/11/2018 10:38:24
8791 forum posts
494 photos

I used it diluted to about 5%, but mainly to mould sheet rather than strip.

Harry Twist28/11/2018 10:39:29
357 forum posts
270 photos

Have a look at the PSSA mass build Hurricane thread, ammonia is used very successfully to achieve some of the shapes in balsa sheet and in longerons.

Here are some things I would recommend:

Wear disposable gloves and use in a well ventilated area, or create an airflow using an electric fan

The fumes are powerfully strong - especially directly above any container the ammonia is in, if available wear a face mask/ or painting style respirator, keeping your nose out of the vapours!

Use neat and brush liberally over the area required.

Whilst wet- jig or clamp the material into the final shape required

Allow to dry thoroughly ( typically 30 mins plus, depending on surrounding air temperature)

Glue into situ, brushes etc can be cleaned as normal

Once dried, where the ammonia has been brushed in will be indicated by a faint yellow stain in the balsa

Sounds complex but its quite straightforward and you can get the balsa to comply to surprisingly contorted shapes.

Hope this helps.




Edited By Harry Twist on 28/11/2018 10:42:34

Geoff S28/11/2018 12:04:59
3818 forum posts
49 photos

I've never tried ammonia for helping to shape balsa but I thought I'd try it. I tried all the pharmacies in my immediate area (2 small market towns) and none sold ammonia. So where do people buy it?

When I was at school back in the 1950s the chemistry labs had bottles of all sorts of chemicals ranged on shelves all round the room completely accessible to all of us (we used to dare each other to take a sniff of the stuff that smells like rotten eggs - ammonium sulphide?), including ammonia. It doesn't seem to be available generally now.


Alan Gorham_28/11/2018 12:08:50
1336 forum posts
146 photos

I got mine from Amazon.

Former Member28/11/2018 12:17:03
1322 forum posts

[This posting has been removed]

Andy Sephton 128/11/2018 12:22:29
157 forum posts
395 photos

I've successfully used ammonia on indoor models, especially the props. It allows the balsa to take up a compound curve and hold the bend for some time afterwards. I soak the wood in a solution of 15 - 25% ammonia diluted in hot water mixed in a container filled to the brim. I introduce the balsa to the container and fit the lid so that the balsa is suitably covered in the solution. I then leave it for a couple of hours or so to be thoroughly wetted, then remove it from the container, set the bend or twist and leave it overnight to dry.

However, for simple bends in longerons, etc, I prefer steaming. You need to keep your hands out of the way of the steam...or wear heat proof gloves! Hold the item in the steam while introducing a bending load. Take the item out of the steam and regularly check the shape, then use the item as required.

Don Fry28/11/2018 12:36:01
4557 forum posts
54 photos

Meths/ water mixed 50/50 does the job, for smaller sections. Brush onto the outside face of the curve.

But big stuff, steam. No coincidence that the bent trees used in the old sailing ships were steamed/ clamped to shape, not cut.

kc28/11/2018 12:36:48
6709 forum posts
173 photos

In the past lots of people have said it's not really safe to use ammonia and so i would avoid it!

Some designs that need a sharp bend in the fuselage longerons specify kerfing -multiple cuts part through- the longeron on the inside of the bend, then filling cuts with epoxy when bending to shape. Example of this was Peter Miller's Turbulent design for RCModelWorld decades ago - worked well for me. The cut area could also have thin ply braces top and bottom to reinforce. Could be worth experimenting on a scrap balsa part if you have any doubts. Another design I saw recently   ( Ron Moulton's Workmaster - a similar Auster )  cut the longeron at a shallow angle - like a scarf joint - and joined it onto the straight front part then reinforcing by lapping with balsa inside. Either way would be better than using a hazardous substance and forcing the wood into an un-natural bend,

Edited By kc on 28/11/2018 12:47:39

Former Member28/11/2018 12:36:55
1322 forum posts

[This posting has been removed]

Craig Carr28/11/2018 14:19:08
734 forum posts
519 photos

I use it neat... works amazingyes

Just don’t hang around the fumes to long .... ideally do it outside

kc30/11/2018 11:28:43
6709 forum posts
173 photos

David. Interesting optical illusion in the photos - is your steel rule actually not flat on the bench or is it an optical problem with camera etc? Quite extreme barrel distortion perhaps at wide angle?

I have to say David's lamination method is superior to trying to bend wood with ammonia - but a little more work than kerfing or splicing the longerons.

Martin McIntosh30/11/2018 20:07:46
3572 forum posts
1231 photos

About £3 a bottle from Homebase. I have posted this elsewhere on here. Brush it on neat then run like hell. It works.

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