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Hammerite drying times??

Moonshane

By Moonshane
in DIY Astronomer

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Moonshane

Moonshane

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hi all

I have just brush painted my mirror cell with two coats of hammerite and 24 hours later the paint is touch dry but soft and easily takes a fingernail mark.

does anyone know how long hammerite usually takes to cure properly and go 'properly' hard?

cheers

Shane

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Psychobilly

Psychobilly

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Put it somewhere warm to help it cure to depth... some sites are saying anything up to a month to fully cure

"Reading the specifications from the Hammerite site, there are two stages of drying (obviously!) the first is around a few hours and the cure takes TWO WEEKS"...

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Moonshane

Moonshane

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oh no. not what I wanted to hear!

maybe I should get it all shot blasted off and start again with an acrylic spray can.

I'll put it all in the boiler cupboard for now and see what happens. annoying I need to be adding some teflon pads with impact adhesive which is not going to work very well with soft paint!

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JamesF

JamesF

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AFAIR the curing times are different for "smooth" hammerite and "original" hammerite. I do seem to recall that for "original" that it's weeks until it's really properly hard, though I've not used it for a while. I used some spray-on black smooth hammerite when I made a solar wax melter a couple of years ago and that definitely took a couple of days to cure, though I actually left it a month or more before using it in anger (a thermocouple in the top of the melter suggests the internal temperatures get up to 95C+, so it's probably just as well).

James

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Psychobilly

Psychobilly

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I have been known to "cook" metal parts that I paint in the oven...

It doesn't make me to popular with the rest of the household but am I bothered....

I sometimes preheat the metal before painting as well...

A Normal hair drier should help kick of the curing...

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Moonshane

Moonshane

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quality - cheers guys. oven baking might be just the job. as you say though - first thing in the morning, all windows open etc etc.

personally, I would strongly not recommend Hammerite for anything ever again (unless the spray on stuff is a lot better). I certainly won't be using it unless for e.g. a garden fence or similar.

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AstroGnome

AstroGnome

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Two things I've found that help with Hammerite paint, from personal experience.

1) Use very thin coats and allow a few hours between coats, don't try to do it in one thick coat.

That's the obvious suggestion, now the less practical option...

2) Heat the metal to about 800C with a gas axe before applying. Paint sticks quick and the solvent evaporates instantly (learned this from painting Landrover chassis and suspension parts, may not be applicable to more delicate telescope components, but it works)

M....

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ollypenrice

ollypenrice

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This is very odd. It has always worked a treat for me. Very thorough stirring is usually critical with paint - several minutes. Heat certainly helps. I suspect either not enough stirring or something on the original surface. It was really clean?

Olly

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Moonshane

Moonshane

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cheers Olly

the cell was shot blasted so it was well cleaned.

maybe it is stirring as I did a little but the tin said not too much or too vigorously.

I'll try the oven technique on Tuesday when I have the house to myself.

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Gina

Gina

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Oil or grease could be the problem. I've used Hammerite on lots of things and never had any trouble. Mostly the smooth type. In fact I can't remember when I last used the hammered finish - I would expect that to take longer to harden. Small items I've often put on top of the Rayburn (when going) with a piece (or pieces) of wood between. I let it dry/harden for 24 hours before handling. We also use it for most of our farm machinery.

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Moonshane

Moonshane

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mine has had almost 48 hours and it's still almost as soft as after it was touch dry.

everything was either shot blasted or coated with special metals primer and the only possible oil on it was off my fingers (clean) as I carried it out.

one possible explanation is that the paint shop added a tint to make it blacker. maybe this contained something weird.

I'll try the oven technique tomorrow and report back. I won't be using it again even if it's not really at fault. it seems a lot more hassle than a spray can and I wish I'd gone down that route originally now. if I had, I'd already be on with the base.

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todd8137

todd8137

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its great paint but if the part you are painting as not been sanded or rubbed down with sand paper, and left at least 4/5 days between coats, then trouble will come your way i have used it and it cures after 2/3 weeks to a solid finish

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Gina

Gina

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mine has had almost 48 hours and it's still almost as soft as after it was touch dry.

everything was either shot blasted or coated with special metals primer and the only possible oil on it was off my fingers (clean) as I carried it out.

Hammerite must be applied directly to the steel - it will NOT mix with other paint, even if that has already cured. The solvent is different and will dissolve other paints. Rust doesn't matter, though any loose rust must be removed or that plus paint may drop off. Shot blasting is not necessary but removing all grease, including finger grease, is. Grease may be removed easily with Hammerite thinners, after which don't handle with bare fingers. The thinners dry off very quickly. Use in a very well ventilated place or outdoors. Beware the thinners and paint is highly inflammable.

I have always applied Hammerite with a brush. I've always stirred it well and sometimes thinned it down a bit with a small amount of it's special thinners, especially in winter - it doesn't want to be too thick.

It could be that either the paint or the surface has been "contaminated" with another paint or solvent (thinners) - this may well prevent the Hammerite from hardening.

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Astrokev

Astrokev

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Hi Shane

Not what you really want to hear I guess but I've never had a problem with hammered finish. Couple of thin coats rather than one thick has worked for me with plenty of gentle stirring, nothing too vigorous.

Could you remove the paint from just the areas where you want to put the teflon?

Hope you get it sorted.

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George

George

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Shane Ive only ever used the spray cans, I used a spray hammered finish a couple of years ago on some counter weights and a side by side plate I made...took around an hour to be touch dry. Last time was a couple of weeks ago on that pier extention I showed you, this was also spray but smooth finish this time....that took 3 or 4 hours to dry stood in front of a hot air blower at work.

Im wondering if they have changed the formulation as there was a good 3 hours between the first and last time I used this product.

Still once its cured nothing beats it IMHO

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