Laser v dry ice cleaning

[silverthorn2151]

A quick question for anyone who has experience of either in a building fabric context, not automotive.

I'm advising on some external dec's to a mansion block. There are cast iron railings to balconies that could do with stripping back. I don't really want pressure washing as it might not do the job and I don't want too much water.

The client has suggested laser, I suggested dry ice for comparison.

Specific questions.

1. Is heat produced during laser?
2. Will dry ice strip layers of paint from steel and vast iron?

I'm researching elsewhere but the the PH collective mind is vast.

[MG-Steve]

I have had a couple of cars dry ice blasted underneath, it will certainly strip paint and corrosion back to bare metal if the air pressure is high enough. If its on site they will need to bring a massive compressor, even in our workshop with a top of the line pro compressor used for paint spraying and air tools its nowhere near enough.

[dhutch]

In for that watch!

[silverthorn2151]

MG-Steve said:

I have had a couple of cars dry ice blasted underneath, it will certainly strip paint and corrosion back to bare metal if the air pressure is high enough. If its on site they will need to bring a massive compressor, even in our workshop with a top of the line pro compressor used for paint spraying and air tools its nowhere near enough.

That's interesting thanks. I've seen it used a number of times on the various YouTube channels I watch which is what sparked my interest.

I don't think having a large compressor will be an issue and the areas involved are fiddly rather than large.

As an example of the issues. The posts for the guarding are set within an asphalt roof covering. The point of penetration doesn't leak at present but such joints are always susceptible. Reducing the volume of water would be very useful.

Similarly, if there is heat generated by laser (how can there not be?) the issue around hot works could be significant.

[Cow Corner]

I have never specified either, but I did a similar project a few years ago on a mansion block in London - sadly we found that by the time the original cast iron railings had been exposed, they had corroded at the base, where they entered the slab (and had been effectively sleeved by the asphalt, trapping moisture). Repair was theoretically possible, but was not cost effective, nor would anybody take responsibility for their long term safety.

So while I can’t advise on those methods, I would want to use the least aggressive option that you can to clean them up, and if you can, do a very detailed survey of their current condition - the issue we had was that despite our best attempts, we couldn’t get access to all the areas until we got the scaffold up, due to tenant access and huge amounts of junk being stored on the balconies….

[RustyNissanPrairie]

I have a CO2 blaster at work - we occasionally use it for cleaning our mixing heads/production equipment.

I have a pair of massive Ingersol Sierra compressors that meet the airflow demands but pressure is limited to 8bar.

We found that it only works if the Co2 pellet projectiles can find an 'edge' if you just blast direct onto a smooth surface film or coating then the pellet's just skim off.

Running it with a large 16bar towed mobile compressor was better but........


.......the noise levels are bad/very high at 8bar, at 16bar it is not option anywhere in a domestic environment.

[silverthorn2151]

Interesting comments and observations guys.

I've chatted to a colleague who has used the ice method on internal painted beams to great effect. Almost dry after stripping and just swept up the risings.

Investigations ongoing.

[Aluminati]

Cow Corner said:

I have never specified either, but I did a similar project a few years ago on a mansion block in London - sadly we found that by the time the original cast iron railings had been exposed, they had corroded at the base, where they entered the slab (and had been effectively sleeved by the asphalt, trapping moisture). Repair was theoretically possible, but was not cost effective, nor would anybody take responsibility for their long term safety.

So while I can t advise on those methods, I would want to use the least aggressive option that you can to clean them up, and if you can, do a very detailed survey of their current condition - the issue we had was that despite our best attempts, we couldn t get access to all the areas until we got the scaffold up, due to tenant access and huge amounts of junk being stored on the balconies .

Bane of my life !

[hidetheelephants]

Given there's going to be a lot of detritus produced anyway why not economise and use soda, walnut shells or even good old-fashioned grit?

[LooneyTunes]

Both of those are directional: consider the likes of https://peelaway.co.uk/131/peelaway-7

[dhutch]

hidetheelephants said:

Given there's going to be a lot of detritus produced anyway why not economise... ... good old-fashioned grit?

It works well, but is messy i guess. Dusty.

[.:ian:.]

Theres a video here comparing sand blasting vs laser vs grinder vs needle gun

https://youtu.be/TNykX7X0n58

They did eventually settle on laser cleaning, though more to do with not having to ship out tonnes of media to a lighthouse in the middle ofbthe sea

In the latest video they have a modified cnc cutter fitted with fricking laser beams to automate it!

For railings the tight focal point of the laser will probably make things even slower.

Edited by .:ian:. on Saturday 18th October 16:16

[ATG]

(complete layman in this area, but I have a little experience with high power pulse lasers. I would be surprised if they heated the iron significantly ... as in even measurably. They'll be spitting out an enormously powerful but very short pulse, so that the total amount of energy in the pulse is fairly modest. The power is enough to blow the electrons out of the surface of the target, turning it into a plasma. That'll produce a pop, a flash of light and remove the top layer of crap. But the laser will then be off for many times the length of the pulse before it fires again. So the power of the light pulse might be megawatts, but the actual average power of the laser light might be maybe 100W. So it'll heat the rusty crud to several thousand degrees, but the post itself will hardly warm at all.)

[silverthorn2151]

That's really interesting and helpful.

I guess I had imagined a continual.....er.....beam, but of course your commentary makes much more sense.

I'll have a look at that video too.

Interesting though isn't it. 😃