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Body filler on brass?

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Simon Collier27/06/2018 11:32:15
338 forum posts
55 photos

i've been filling seams and divots in my brass tender with soft solder but I'm not finding it easy and I'm at the stage of dismissing returns, pulling as much solder out as I'm adding ( borrowed 250W iron). How does body filler go on brass? I'm sure in theory it is unsuitable but how about actual experience?

mechman4827/06/2018 11:59:10
2634 forum posts
408 photos

How about you trying this... save your/any brass filings, mix up with 2 part epoxy resin, deep scratch/etch/degrease your tender surface devil​, or drill through with mini drills < than 1mm, to make a key for the resin leave to set, rub down prior to finishing ? I have used this method on a couple of faults in my efforts, plus used Cast Iron filings & epoxy for similar faults on my S10V / S50H castings. Works for me. face 20


Ian S C27/06/2018 13:32:19
7468 forum posts
230 photos

Filling with solder can be difficult if you don't have the right grade, you need the stuff used by panel beaters(used to be), it has more tin, and stays pastey longer, also used for wiped joints in subterranium cabbles, power and telephone.

Ian S C

John Rudd27/06/2018 14:57:04
1368 forum posts
66 photos

Ian is correct....

Lead loaded joints were often used on car body shells where joints were hidden ( roof panel to pillar section springs to mind..), as for wiped joints, lead piping joining to copper was another use ( my first house had lead pipes for the cold water supply, when I replumbed the house in copper, I had to join the 15mm copper to the lead incomer...)

Maybe using a supplementary heat source such as a hot air gun will help to flow the solder?

richardandtracy27/06/2018 15:42:04
938 forum posts
10 photos

It's on a tender & doesn't get hot? If so, and it's painted.. how about car body filler like P38?



Mike Poole27/06/2018 15:55:33
2545 forum posts
60 photos

Around 100lbs of lead loading used to go onto a Rolls Royce body shell to hide all the joints and give the appearance of a one piece moulding. The lead after it was applied to the body with a blowtorch and sticks of lead would be moulded with a fluxed wooden spatula and finally be disced to a finish. The guys discing the lead wore air fed hoods and total coverage overalls in a special booth to control the distribution of the lead dust. The lead compound as mentioned above had a wide zone where it was pasty and could be worked without running or being solid. Electrical solder has next to no pasty range as you want it to solidify as soon as you remove the iron. Lead loading in the car industry was finally phased out in the 1980s. The new Mini had one seam that would have been leaded in the old days but was brazed and disced to a finish, on the lastest version even that has been designed out. If you are not using a suitable material it is going to make life harder and more difficult to acquire a new skill. A useful tool is a curved tooth body file, they have a planing type cut and leave a smooth finish and cut quickly.


Edited By Mike Poole on 27/06/2018 15:55:55

Bob Stevenson27/06/2018 17:38:37
386 forum posts
6 photos

the best way to fill brass, provided you don't want a polished brass finish, is to use epoxy putty, namely 'Milliput' in either black or white...... moistening the brass seems to help the epoxy grip nicely and also to smooth off. This works very well fo rthe backs of clock dials and faces so the only drawback for you is size as Milliput has a significant (but not prohibitive) cost....

Nick Clarke 327/06/2018 18:27:57
686 forum posts
21 photos

A long time ago I used to work in a motor factors selling to the body trade. Bodylead came in sticks about 1" by 1/4" by a foot long ( or thereabouts) The idea was to use a blowlamp to put knobs of solder in the area where it was needed and then use a wooden stick dipped in tallow to smooth out the lead using a soft oxy acetylene flame (usually the only source of heat in a workshop) - ideally from behind so the metal was warmed up gently. Bakers fluid was the flux of choice. Any roughness was sorted with a bodyfile. As well as the Rolls, FX3 and to a lesser extent FX4 taxis used a lot of lead to hide seams.

Down at the 'fag end' of the motor trade the process was modified and the wooden stick was sometimes the top six inches sawn off the top of the yard broom - it had a nice rounded end, and resin flux in a tin like shoe polish. I have even seen multicore solder or the thin plumbers solder in sticks about 3/16 wide used to tin the area first.

Visiting a customer/friend once I tried to use body lead. Just the once. What didn't end up on the floor ended up in and on my (non safety) trainers - painful!!.


Simon Collier27/06/2018 22:43:44
338 forum posts
55 photos

Thanks for the interesting replies. The use in car manufacture sound fascinating. Buying lead solder is now rather difficult as lead free plumbers solder has taken over, and what you can get in rosin cored mostly. I have been using 50/50 1 mm solid wire. I found on line some bronze impregnated filler in the U.K. for castings but as I only need very shallow skim over hammer dimples around rivets etc., I will use the body filler I have, cleaning and scratching it up first. I bought the well recommended 3 part petrol tank sealer kit to seal the inside seams. I'm glad it is only 5" gauge as I am finding it very heavy to slosh about with some water inside!

richard king 928/06/2018 04:55:26
1 forum posts

Add some lead to the solder. I think you want 75:25, 80:20 or even 85:15.

I tried to lead fill years ago, when brown brothers still sold body lead, with no success. Then I caught a few minutes of american hot rod, When I had some bike tin work to do, needed loading on edges that were not really suitable for plastic, I tried lead filling and it was a bit slow but I managed it OK. The thing I was missing out when I tried it in the 70's was tinning the surface first, I bet there are some vides on youtube.

People buy 40 quid kit's, I used what I had knocking about. Made some tallow, used plumbers flux, used plumbers solder with added lead and wooden bit's were just that, some scraps of wood.

If you look in machinerys handbook it gives the solder ratios and solidus temps.

Simon Collier28/06/2018 09:19:56
338 forum posts
55 photos

Richard, I just looked it up. It is available, 70/30 body lead. I had no idea about this old method so I have learned something. It is obviously still used.

JasonB28/06/2018 10:34:53
17856 forum posts
1954 photos
1 articles

If you are only filling small hammer marks then a surfacing putty would be better than a filler as it will feather out well and set better. There are some body fillers that have etching agents in them which would suit deeper jobs.

JBWeld would be another option but takes a lot more work to rub down and a bit OTT as you don't need it's high temp range.

Ian S C28/06/2018 10:38:29
7468 forum posts
230 photos

Sorry I got my tin and lead mixed up in my previous post.

Ian S C

Gordon W28/06/2018 12:00:44
2011 forum posts

Lead solder in various grades are easily bought of the net. I just bought some "lead plumbers solder" comes in sticks about 4-5 mm thick, seems it will do for body filling ok. Use bakers fluid and a blowlamp. Sorry but can't find a ref.

Dave Smith 1428/06/2018 14:35:15
91 forum posts
8 photos


If it is a painted surface, etch primer suitable for brass, then filler primer, then cellulose putty or similar same as a car body, finally top primer and top coat. That is what I do on 4mm scale etched brass loco kits.

I am also interested in the fuel tank sealer you are using for my tender?


Richard S228/06/2018 18:41:29
177 forum posts
109 photos

A suitable sealer and filler I found some years ago here in UK is 'Leak Fix' by Plastic Padding. Usual disclaimer, but I found it bonds really well to prepared brass. It is still well bonded after 30 years. A bit fast on setting time, but will flat easily with various grades of abrasive paper and primes well. Old tube of it is still usable.

On the Plumber's Solder subject, I have a few Old bars of Frys Belfry grade which (was) had general purpose use originally. It is the same grade as Body Lead Solder with up to 34% Tin. Melts at around 252c and solid at 185c. Has the benefit of the longer plastic state for 'wiping' like in the old jointing method using a Moleskin wipe.

Tinman's Solder grades would not be suitable if required to remain plastic,as it has a higher ratio of Tin + Antimony.and lower Melt and Solid temps.

Good luck with which ever method you use. I'll have some blending work to do, but I think I'll get away with shallow Etch/Primer build up prior to paint.

Simon Collier28/06/2018 22:05:38
338 forum posts
55 photos

Dave, just search motorcycle fuel tank sealer and the kits will come up. I think the three solutions are 1. Cleaner/ rust remover 2. Etch 3. Sealer. Not sure what polymer the sealer is but I suspect polyurethane. I was talking to a member who is a respected expert loco builder and he uses steel and brass angle for tenders and seals by sloshing around 2 pack polyurethane paint, as used on the outside.

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