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Painting cast iron - What have I done wrong?

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Hollowpoint25/04/2020 21:48:35
474 forum posts
58 photos

So I recently painted an xy table of mine and im having some strange problems.

The table is cast iron and was powder coated before I stripped it back to bare metal. I then filled the imperfections with body filler (which stuck like sh*t to a blanket btw) smoothed it off, cleaned it thoroughly with panal wipe and painted it with hammerite.

I know some of you will groan about hammerite but it's what I could get hold of in these uncertain times. And the finish doesn't need to be brilliant.

I gave it 2 coats and waited a day between each. I then waited another week for the paint to harden up before removing the masking tape. This is when the problems started. The paint seems to be flakey and chips at the smallest bump? Ive used Hammerite for years and it doesn't usually act like this? This was a brand new fresh can btw.

I couldn't be bothered to re do it so I thought I will just have to put up with it.

Next job. I bought some self adhesive scales to stick to the table which are basically very thin stainless steel rulers attached with strong double sided tape. I stuck them down only to find them hanging of an hour later? They simply will not stick to the painted surface? And its not because they aren't sticky, I stuck an off cut to a piece of unpainted metal with no problems whatsoever?

So my question is, has the hammerite formula changed recently? Or is it the cast iron surface? What am I missing here?

Steviegtr25/04/2020 21:59:01
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2436 forum posts
336 photos

Not sure , I recently refurbed a cast vice. After cleaning with acetone I then painted with etch primer just to be sure . Then used the paint. It has stayed on so far with no problems.

I am just wondering if some cast iron has a greasy type coat to it. It is funny stuff. Maybe an etch 1st would have helped. Never really had any trouble with Hammerite paints & they do say no primer needed. Hope someone else has a better idea.

Steve.

not done it yet25/04/2020 22:07:43
6812 forum posts
20 photos

Dunno what you mean by ‘recently’. The formula most certainly changed when it was no longer produced by Huntings Paints. Likely a cost or chemical reason for the change, but certainly not the original formulation. The smoothrite I have says do not re-coat within six weeks if the current coat has hardened. These days one can add a further coat at any time.

Hollowpoint25/04/2020 22:25:51
474 forum posts
58 photos

By recently I mean 2 weeks ago.

I did wonder if the cast iron had absorbed some oil or something but I did clean it and the filler stuck very well indeed.

pgk pgk25/04/2020 22:25:52
2563 forum posts
293 photos

Certain the new hammerite is nothing like the old. I did paint some steel with the new while ago and it all went well. Your exerience makes me wonder if the current hammerite solvent pulled contamination out of the cast and it's failing to dry completely? Looking at hammerites site link

And at their solvent data sheet suggests that their solvent is a complex mix (pehaps something like a turps substitute???) and may well ahve soem extended dryng time in cetain situations...?

pgk

Martin Kyte25/04/2020 22:38:28
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2756 forum posts
48 photos

Is it the paint thats chipping or has the hammerite reacted with the filler and the filler has degraded.?

regards Martin

Hollowpoint25/04/2020 23:09:52
474 forum posts
58 photos

The paint seems to have stuck better to the filler than it has to the bare metal. Interestingly it also seems to have stuck better to the rough underside where I couldn't remove the old powder coated finish completely.

This makes me think it's the cast iron rather than the paint. But then why won't the adhesive double sided tape stick to the paint either?

Hopper26/04/2020 00:01:51
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6412 forum posts
334 photos

Did you use primer?

Nick Clarke 326/04/2020 09:02:38
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1427 forum posts
63 photos

I always understood that the hammered look of Hammerite was caused by silicone in the paint causing the effect - which might explain why your scales did not stick, but usually the paint sticks to the object like glue.

Bo'sun26/04/2020 10:20:39
609 forum posts
2 photos

Hammerite has certainly changed. The previous formula never used to skin in the tin. Now, I throw away a fair amount when removing a thick skin.

vintage engineer26/04/2020 10:29:46
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258 forum posts
1 photos

New Hammerite is crap as the EU banned the use of chlorinated hydrocarbons which was the solvent used in the original mix.

Hollowpoint26/04/2020 10:48:29
474 forum posts
58 photos

To answer a few questions

1.I didn't use primer, says you don't need to. I've never bothered in the past.

2.I used smoothrite not the hammered finish.

3.When I opened the can I was supprised at the lack of smell so maybe that explains the absence of the banned solvents?

4.Dont get me started on the EU. 😠

Bo'sun26/04/2020 11:08:20
609 forum posts
2 photos

Sounds like the sooner we dump the EU the better. Bring it on!

SillyOldDuffer26/04/2020 11:16:39
Moderator
8698 forum posts
1967 photos

Have a read of this website, it starts: 'Bare cast iron is nonporous and too slick to support long-lasting painted finishes. If you try to paint directly over the top of bare, untreated cast iron, rampant finish failure will result.'

With glue and paint I've found the hard way that reading the small print can be vital. Preparation is often more important than the product. Scrupulous cleanliness is typical and many surfaces need to be keyed or primed before painting. I had one or two bad experiences where paint and filler refused to marry. (Car filler and wood paint, if memory hasn't let me down again!)

'Hammerite' isn't a single particular paint. At least 4 different types of paint are sold under the Hammerite brand for different purposes. Maybe one of the others in their range might be more suitable?

Dave

Steviegtr26/04/2020 11:18:37
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2436 forum posts
336 photos
Posted by Bo'sun on 26/04/2020 11:08:20:

Sounds like the sooner we dump the EU the better. Bring it on!

Can't see it doing much good. The whole Industry has had to move over to water based paints. Stupid thing is, You say paint a car or anything else.

You give it coats of water based primer, various colour base coats. Then a clear coat. The clear coat is still 2 pack, which is isocyanate based or includes it.

Son in law has a garage. Car bodywork & classics. He hates the stuff, but is forced to use it now.

Steve.

Andrew Johnston26/04/2020 11:35:23
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6603 forum posts
701 photos
Posted by SillyOldDuffer on 26/04/2020 11:16:39:

Have a read of this website,..............

Don't think I'll bother, they'll be advocating burning 5G basestations next. smile

I've painted a lot of bare cast iron with smooth Hammerite in the past. All the tooling/machines are in regular use and have chips and scratches, but the paint has never flaked of it's own accord.

Andrew

SillyOldDuffer26/04/2020 12:29:42
Moderator
8698 forum posts
1967 photos
Posted by Andrew Johnston on 26/04/2020 11:35:23:
Posted by SillyOldDuffer on 26/04/2020 11:16:39:

Have a read of this website,..............

Don't think I'll bother, they'll be advocating burning 5G basestations next. smile

I've painted a lot of bare cast iron with smooth Hammerite in the past. All the tooling/machines are in regular use and have chips and scratches, but the paint has never flaked of it's own accord.

Andrew

Point taken, but what's causing Hollowpoint's problem then? I like the idea it's 5G! devil

Paint / filler incompatibility? Dirty cast-iron? Old paint? Failure to stir? I doubt it's because all new Hammerite is crap.

I foolishly bought a small cheap cast-iron vice at an Exhibition without opening the box. Perfect paint job, shame everything else about it is nasty!

Dave

Hollowpoint26/04/2020 12:53:13
474 forum posts
58 photos

Ive just read the article in the link and some of it rings true. I did clean the cast iron thoroughly but the surface was very smooth and I didn't use primer so maybe it is too non-porus for the paint to stick properly.

.. And maybe the old formula had some etching properties?

The adhesive scales might be a separate problem. I might try some epoxy glue. Unless the EU has ruined that too?

Grindstone Cowboy26/04/2020 13:19:14
859 forum posts
64 photos

FWIW I've found that the Smoothrite range, which the OP used, does tend to chip far more easily than the hammered finish ones.

duncan webster26/04/2020 14:32:24
3990 forum posts
65 photos
Posted by Bo'sun on 26/04/2020 11:08:20:

Sounds like the sooner we dump the EU the better. Bring it on!

So we can go back to poisoning the environment. I was never impressed with Hammerite anyway, OK it dried quickly, but as it got old it chipped off easily as well

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