Casting Filler?

[Andrew TinsleyParticipant @andrewtinsley63637]

I have been filling and sanding some of the castings for the Quorn. Just as I was getting somewhere near getting the castings finally sanded down, chunks of the filler broke away from the surface. This happened with both iron and aluminium castings.

All surfaces were cleaned by ultrasonic bath and the final treatment was a wipe down with cellulose thinners. Once thoroughly dry, Isopon was knifed on to the castings. The correct ratio of hardener to filler was used and the temperature was 17 C in my workshop. The first Isopon used was the normal type. I then tried the elastic type. Same problem with adhesion!

If I fill in dents in my car, this material sticks like the proverbial to a blanket. So why it isn't working with the casting, I really don't know. I never had this problem with the old Trimite filler, long since unobtainable!

Has anyone who has done this job on castings had a similar problem or did you use another type of filler that worked for you?

Andrew.

[Andrew TinsleyParticipant @andrewtinsley63637]

[JasonBModerator @jasonb]

U-pol works for me. Was your stuff fresh?#

When you say knifed on were you putting it on very thinly if so a knifing or surfacing putty would be a better bet. Also known as glazing/spot putty

 

Edited By JasonB on 09/07/2017 20:21:03

[Andrew TinsleyParticipant @andrewtinsley63637]

Hello Jason

I have had the filler about 3 months, so I don't think it is out of date (depends how long it was in the car accessory shop!).

I knifed on a goodly layer, maybe 3 or 4 mm thick on the iron casting as it was very rough, maybe a couple of mm on the aluminium casting which was much better for surface finish. I really don't like using knifing putty, except as the merest smidgen, where you just need to finish off. I find the stuff will shrink if it is applied in anything other than a very thin layer. It seems to act like dope on model planes, it is forever shrinking, even if you use banana oil!

What bugs me, is that I filled in some dents on my old MG a couple of weeks before I used it on the castings. That filling was spot on and showed no signs of delaminating even when feather edged. Never used to bother much about prep work when I used Trimite. This time I was very fastidious about prepping the castings!

Never seen or heard of U-Pol, is it a car accessory shop job, or is it marketed for something else?

Thanks ,

Andrew.

[JasonBModerator @jasonb]

Made for car bodywork, Halfords do some of their stuff which is where I usually pic mine up.

**LINK**

Works OK as you have described

[Nick_GParticipant @nick_g]

Posted by JasonB on 09/07/2017 20:16:31:

U-pol works for me.

.

I have also used U-pol and Isopon P38 on castings with good results.

I did do a final clean 5 mins before application with acetone. 

Nick

Edited By Nick_G on 09/07/2017 20:59:00

[Rik ShawParticipant @rikshaw]

I was chatting with a lady some months ago who was exhibiting her pen turning skills. She told me that to fill holes in brass and other material she uses a proprietary method which uses brass dust and some sort of syrupy mixer. I do not remember the details but would be interested to hear from anyone who has come across this sort of "filler".

Rik

[JasonBModerator @jasonb]

Its brass powder (aluminium and bronze also available) and usually mixed in with a GP fibreglass resin though some people use an epoxy. Alex Tiranti do it a sdo some woodturning suppliers

Did this bowl with it

[mechman48Participant @mechman48]

FWIW… I have used cast iron dust/filings mixed with 2 part epoxy resin to fill in a couple of casting blow holes on my 10V some time ago & it stuck like the proverbial, it machined & cleaned up with emery nicely, I would suspect it would be fine for not so large area requirements but for very large areas I reckon Isopon P38 would be better.

​George.

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