prep mild steel

[Jonathan Webb]

Hi,
I'll be painting my sculpture soon with Sigmacover 280 primer and Sigmadur 520 topcoat.
I can't sandblast the thing so what is the next best method I can use?
I have been using a Dronco flap disc to remove spatter etc (can't remember the spec, it's red, possibly 80grit) and started to use this to clean the steel of surface rust and grinder scuffs.
However, the bulk of the surface has a hard grey appearance - does this need to be taken off?
If so, using what? The flap wheel is not overly effective.
Many thanks.

 

[Dcal]

Where will it be displayed?
Inland or near the sea?
How long do you want it to last before repainting?
You have proposed a good paint system so I would follow the manafactures recommendations and get it blasted if at all possible.

 

[Kent]

It's better blasted and primed quickly after. You could get away with less though

 

[Jonathan Webb]

Where will it be displayed? Inland or near the sea?

About 9 miles from the sea, although the Isle of Wight's in the way too, so less exposed than other South Coast towns. Shaded under a tree and next to a 6' fence, so not so much UV either.

How long do you want it to last before repainting?

As long as possible. Won't be my problem then, but I would like as long as possible - my research showed industrial paints can be good for 10-15 years, so that's what I'm hoping.

You have proposed a good paint system so I would follow the manafactures recommendations and get it blasted if at all possible.

I asked around various suppliers. Landed with Promain. I have talked to them & he acknowledged that it was going to be prepped with hand tools, but I didn't think to dig deeper. I think I have since read on a spec sheet that 120 grit was recommended for hand tools. I agree blasting would be best, but the budget is stretched by now. I'll get an idea of price just to see. When I spoke to a powder coating firm last year, he advised that at 3mm thickness, they couldn't guarantee that there would be no distortion. Their quote was £207+vat to blast & electro-spray zinc. I can't see a blasting quote coming in much under £100?

It's better blasted and primed quickly after. You could get away with less though

I agree. PPG allow for manual prep in their blurb. So my question - the dark grey coating - has that got to come off (whether blasted or ground)?

Are the cheap blasting pots any good? I have an Abac 3hp 11.2cfm compressor - is that adequate? If so, I could buy the stuff & do it myself - even if it is a bit slow. I'm hoping to do more sculptures (and also could blast our boat hull back to gelcoat next winter) so a bit of an investment (this is only a hobby ATM) but might be worth it.
Cheers

 

[Ianb]

I have a similar sized compressor with a small homemade blasting pot, in answer to your question the compressor is adequate as long as you don't mind spending a while doing it, and in my case letting the compressor have cooling off breaks, with mine I have found cleaning up new steel with surface rust relatively quick compared to having to clean heavily rusted painted items.

How big is the statue?

 

[Jonathan Webb]

I have a similar sized compressor with a small homemade blasting pot, in answer to your question the compressor is adequate as long as you don't mind spending a while doing it, and in my case letting the compressor have cooling off breaks. How big is the statue?

Thanks, its 2m x 0.8m - a lot of it is not there as the pic shows! I'm going to make a new post about blasting I think, as this is getting interesting! More tools!

 

[Ianb]

Guess you have access to a welder, if so have you thought of making your own blasting pot, I got the idea off here iirc. Only need a gas bottle, few valves, pipe fittings, nozzles and a length of proper sand blasting hose. Here is mine, ignore the broom handle, just saves so much grit un the ears and face!!

 

[Jonathan Webb]

Thanks, Yes I have a welder. I've casually read a few bits and watched a few videos, but I don't quite know how these things work and what is needed. Normally my "why buy it if I can make it" drive would be engaged but I am short of time on this. This is compounded by the fact that my knowledge of air fittings is utter noob level - I used the compressor for the first time on Saturday, to Waxoyl the inside.

I was supposed to be painting it now, for imminent installation as I'm rather overdue and I find myself with a multi-day sidetrack of grinding the crud off the metal before I can even paint it...

 

[Dcal]

No problem making a blast pot but they are so cheap is it worth the bother? Also remember this will be a pressue vessel and rules and regulations are tighter (for good reason)
I also have one of these pots and it will do the job but you will not be paying yourself much compared to what it will cost to get it blasted by someone but that might not be the point.
If you do get a pot it is worth getting a 3mm tungsten nossel from eBay as the ceramic one that come with them are crap.
3mm won't keep up with a 3hp compressor but it will be close enough

What finish do you want on it?
If you don't want to blast, it might be better to go for a surface tolerant primer (jotun 87 or Sherwin Williams epigrip?) but I would recommend you thin it and apply more coats to get the film tickness.

Car paint - epoxy primer and 2k top coat will also probably last 10 years if it is not sitting in the wet or getting dripped.in by trees but industrial coatings might last better. It can be more to do with the thickness of the coating than anything else.
Having said that it's all in the prep and if you cut down on the prep it will not last as long but maybe good enough.
An acid etch or one of the other pre paint treatments might help but you will be on your own if it fails sooner than expected.

 

[Jonathan Webb]

No problem making a blast pot but they are so cheap is it worth the bother? Also remember this will be a pressue vessel and rules and regulations are tighter (for good reason)
I also have one of these pots and it will do the job but you will not be paying yourself much compared to what it will cost to get it blasted by someone but that might not be the point.

I understand about the time/rate for the blasting job, but getting it blasted involves also getting it to & from the blasters (careful packing, hitching the trailer & strapping it in etc and doing it all again on return), plus mileage and all this at their convenience of schedule. And I'm not necessarily earning money whilst it's not here, as this is a sort of hobby/sideline. If I get a pot, I've got it for this and any other sculptures that I may get, and I can blast our boat back to gelcoat in the winter.
[/QUOTE]
If you do get a pot it is worth getting a 3mm tungsten nossel from eBay as the ceramic one that come with them are crap.
3mm won't keep up with a 3hp compressor but it will be close enough
[/QUOTE]
Thanks for the nozzle info. What do you mean "won't keep up with a 3hp compressor?

[/QUOTE]What finish do you want on it? [/QUOTE]
The finish is semi gloss, I have the paint: Sigmacover 280 primer and Sigmadur 520 topcoat

[/QUOTE]
If you don't want to blast, it might be better to go for a surface tolerant primer (jotun 87 or Sherwin Williams epigrip?) but I would recommend you thin it and apply more coats to get the film tickness.

Car paint - epoxy primer and 2k top coat will also probably last 10 years if it is not sitting in the wet or getting dripped.in by trees but industrial coatings might last better. It can be more to do with the thickness of the coating than anything else.
Having said that it's all in the prep and if you cut down on the prep it will not last as long but maybe good enough.
An acid etch or one of the other pre paint treatments might help but you will be on your own if it fails sooner than expected.[/QUOTE]
I'm committed on the paint now and increasingly minded to get a blast pot. I have also asked a local company for a quote.
I've also got a wet film thickness guage as I want to do this properly.
Cheers.

 

[Dcal]

Jonathan, don't get me wrong I'm with you on the buying stuff and doing it your self - as you will learn more, get a better job done and the real bonus is the kit is there for all the other wee jobs that you don't even know about yet.
It's just worth considering and you should never under value your own time.
We all still need to do stuff to learn and get good at it, however sometimes it's better to pick your battles.if you find it interesting why not?

Even a quick blast will improve matters no end and if you are anything like me you could spend far more time getting it perfect which will do no harm at all. Just don't skimp on the PPE

What I mean about the 3mm nossel is a 3hp compressor wouldn't make enough to run a 3mm nossel full time (at 90psi) and you will have to stop blasting to allow the compressor to build up pressure or blast at a lower pressure (which will be wasteful of grit and your time)
Even a sweep blast - where you just give it a quick run and don't try to get every thing to clean "white" metal will be better than any other mechanical preparation (sanding, grinding and the like)
It's also good practice to radius any sharp edges / corners or rough welds (before you blast) as that is where the corrosion will start. A 3mm radius is all you need, but I see from the photos you are pretty good in that department already.

Good luck and just go for it.
If you need further advice on the blasting just ask on the blasting thread you started .
There are plenty of people on here with similar setups (including me) to help you out.

 

[Gareth J]

I echo the comments about getting someone else to do it.

A pro blasters will have enough kit to make the job bearable and will be using a compressor soooo much bigger it'll take a fraction of the time.

 

[Jonathan Webb]

I echo the comments about getting someone else to do it.

A pro blasters will have enough kit to make the job bearable and will be using a compressor soooo much bigger it'll take a fraction of the time.

I've just been quoted £150 vat wasn't mentioned. Either way, I could work for a number of hours at a passable rate and still come in less.

 

[Jonathan Webb]

Dcal, thanks for explaining stuff.
I radiused the bends as that's how it turned out... I was wondering about fairing them a bit sharper though.

Re time, you make a valid point. I couldn't earn £150 in twice the time it would take to get this blasted (he said an hour). You mentioned you had similar gear - what would be your guess as to how long it would take you? Half a day?
Cheers

 

[Gareth J]

I've just been quoted £150 vat wasn't mentioned. Either way, I could work for a number of hours at a passable rate and still come in less.

That sounds a tad steep to me but if that's your only option then fair enough!

 

[Dcal]

I would say half a day would blast that with the kit I have and leave it ready for painting.
It's way easier to remove rust and mill scale than.paint, or my pet hate plastic coating.
Now the bad news it will probably take longer to clean up unless you have some means of containing the grit blast.
I use jblast superfine as I think it lasts better than glass but either will do and if you are not recycling just go for the cheapest you can get.
I'd estimate you will use 3 or 4 bags if you can recycle you might get away with 2
Optima21's advice in the link he gave you earlier in the thread seems sound to me. I use an airfed half mask fed by a separate 2hp compressor which I already have for spraying

 

[Kent]

This 700mm disc cost me twenty quid blasted prior to prime and paint .
Galvanising can realy screw these up so it's blast off the oxide and zinc epoxy prime before painting

 

[Jonathan Webb]

This 700mm disc cost me twenty quid blasted prior to prime and paint .
Galvanising can realy screw these up so it's blast off the oxide and zinc epoxy prime before painting View attachment 146430

Cool, not RAL 5012 by any chance?

 

[Kent]

Cool, not RAL 5012 by any chance?

Without checking proper - yes!

 

[Jonathan Webb]

Without checking proper - yes!

That's the colour specified by my client.

I did a quick calc based on the assumption that blasting was coated by surface area and my sculpture by your blaster would be about £100 instead of my £150 quote.
I've now got all the blasting gear bar the air hose & fittings which I hope to sort today