PDA

View Full Version : Sandblasting using a pressure washer & wet blast kit- anyone?



Kev Williams
04-30-2017, 1:03 AM
I have 600 sq ft of steel houseboat hull I need to sandblast, dry blasting with a basic 100# pressure pot and 60 gallon compressor just ain't doing the job, and I'm not really into the roughly $1000 per hour rates for someone else to do it...

--I've been attacking this hull many different ways, none all that great-- angle grinders, wire brush wheels work great on rust and loose paint, and get into the rust pits ok to so-so, but they barely touch several layers of bottom paint, and they only work well for a few minutes... once the wires take on a bend, they do more skidding around than cutting. Sandpaper wheels cut thru the paint like gangbusters, but don't work well on rough rusty areas. And they clog up quick. Tried a wheel with carbide chips, it's great for cutting thru paint but I wore it out quick, and it wasn't cheap. Plain sandblasting is frustrating- it works great on the rust and pitted areas, but it's slow. And it's real slow to remove the paint. And even with a 60 and 30 gallon compressors tied together, it takes a couple of minutes to do a square foot, and then then I'm below 100psi and using air faster than the compressors will replace it. Have to wait on the compressors. And messy, my gawd!

So after searching out dust-free sandblasting services, I found out there's wet blasting attachments for pressure washers! Watched a few videos- not quite as efficient as the big wet units, but they do seem to work, provided you have enough pressure washer to draw the sand. Some looked ok-ish, the one by Power Eagle worked quite well on an old painted and rusty steel tank, it ran off a square foot a lot faster than my sandblaster will.

HD has some reviews on one they sell, mostly bad, but mostly because the user's pressure washer is inadequate. Mine is 2800 psi, and it's probably inadequate too, BUT- I'm not against buying or even renting one with enough grunt, and also, I DO have the luxury of already having a sand delivery system, which it seems to me would be no big deal to set a pressurized flow rate that would work...

So just wondering if anyone's used one, and if you like it?

Wayne Lomman
04-30-2017, 1:45 AM
Kev, I have been blasting and painting for a fair bit of the last 20 years - between woodworking - and there are some basics. DONT USE SAND! Use some other abrasive so we don't hear about your demise from silicosis.

First, any blasting is messy. Dry you sweep it up, wet you hose it down. Your choice but it is messy. However, dry you blast until 2pm, dust it down and paint the clean area before it flash rusts. Wet, you watch it flash rust as you blast and you have to let it dry etc etc. You end up with a compromised job.

Dry blasting is the quickest and easiest unless you have access to a very high pressure water blaster in 20,000psi+. The units you are looking at will not help your problem.

Your main problem is air supply. You don't have enough. Hire a decent compressor for the job. 60 gallon is a measure of the tank. You need more cubic feet per minute - cfm. Check your blast pot to see what cfm it needs to run at 100psi and hire a compressor at least 25% bigger.

Your productivity of 2 minutes per square foot is a bit low. If my guys can do 100 square feet per hour I am happy. You are getting 30 square feet per hour. To fix this, first fix the compressor problem. That will help a lot. Next, blast at a 45 degree angle to the surface pushing against the paint and leaving bare steel behind. Do it once like you are colouring in at primary school. Remember when messy colouring in got your knuckles whacked? Welcome to blasting!

The paint on the surface makes a difference too. Is it shattering off or peeling back like plastic? Most likely the second option in which case you have to be patient. Too many boats use thermoplastic paints and they are always a mongrel to get off.

They guys wanting to charge you a grand per hour are on a good paddock. That's more than double what it should be worth, even allowing for higher Australian wages. Should be one days work for a half decent contractor. Plenty more advice if you need it. Cheers

Jerome Stanek
04-30-2017, 8:34 AM
I have a 3500 psi pressure washer with a sand injector that works great on stuff like paint on concrete. I used it to remove gum off sidewalks for a drug store chain. But it will rust steel real quick.

Dave Lehnert
04-30-2017, 11:16 AM
Just toss this in for sake of discussion. I have no experience using this kind of blaster. Only became aware of this type of blaster because a company, Coldjet, is local here.
Looks like Dry Ice solves the mess problem????


https://www.youtube.com/watch?v=l_9nITRz--0

Kev Williams
04-30-2017, 2:00 PM
I know you shouldn't use sand to sandblast with due to health issues, but that leads me to a dumb question: Why do we buy the stuff for our kids to play in?

That said-- where the boat is, wet blasting will be preferable to dry, although a few HF tarps could contain the cloud from dry blasting. The other issue with dry blasting is the suit of armor needed. And I'd be happy to get 50 sq. ft an hour, that would make it only a weekend job!

I've been looking to buy ground glass, but I can't find a local supplier, at least online, and $30 a bag ($8 plus $22 shipping) (Northern Tool) is a bit steep...

My 2 compressors together move around 14 SCFM at 90 psi. I have a friend who may still have a his big diesel screw compressor, but having fallen on hard times I'm thinking he's sold it. Phone call is in order!

Lon Crosby
04-30-2017, 9:27 PM
Do a better search on Google - say 40/70 Grit Ground Glass Media. Lots of manufacturers so depending on where you live, there should one or more local manufacturers (for local pick-up) since it is just ground bottle glass. You may want to specifically search for a mfg that grinds recycled plate glass as it is harder and may work better for your app.

Wayne Lomman
05-01-2017, 2:13 AM
Yes, 14 cfm won't do it. Get something like your friends compressor and it will make a world of difference.

Sand is hazardous when broken down extremely fine. You can live on the beach and not get silicosis. Sandblasters used to routinely die in their 50's if they were lucky.

Dry ice is very specialised and very expensive. Best used where clean up is impossible. The down side is you don't get a surface profile for paint adhesion. Cheers

John C Cox
05-01-2017, 9:46 AM
I think when you total up all the materials and supplies - you may find $500-$1,000/hr is not all that bad...
Especially when you consider the specialty media that cuts fast, tarps, masking, respirators, filters, bringing it all with them, setup/cleanup, and all the rest....

If those guys are doing 100+ sq-ft per hour - they are going through a LOT of media - thats probably a pallet or 3 of media in your 600sq-ft boat hull... And thats all part of your cost...

Jerome Stanek
05-01-2017, 10:53 AM
Have you thought about a scaler

https://www.amazon.com/Nitto-Kohki-EJC-32A-Electric-Needle/dp/B00NV7IV8W/ref=sr_1_1?s=industrial&ie=UTF8&qid=1493650204&sr=1-1&keywords=electric+needle+scaler

Ruperto Mendiones
05-01-2017, 12:23 PM
Could you rent a big diesel compressor and/or a complete sandblast outfit?

Kev Williams
05-02-2017, 6:46 PM
thanks for the advice everyone-- :)

needle scalers, never heard of them. Looks like they would do a good job really, was trying to locate a video of one being used on something bigger than an old drill press base to see how fast they work. I have to wonder how well the $985 version Jerome linked to works vs. the $80 types.

According to a certain website that sells sandblasting equipment, they're using six $10 bags of ground glass media per hour of blasting. That's plenty reasonable as far as media goes, IF i can find it for that price...

To give you an idea of the task at hand-- this is just about half the bottom, maybe a snick more...

359484

Stray current corrosion caused it...

Wayne Lomman
05-03-2017, 5:49 AM
Kev, abrasive blasting is your only option to get anything like a job that you won't have to do over again in a couple of years. It gets you a white metal surface which is essential for full submersion and it gives you the surface roughness you need for paint adhesion. Your power tool options are not going to do the job. Talk to your paint supplier about a correct coating system and procedures as you need to monitor relative humidity, temperatures of air and steel and calculate dew points. Don't cut corners. It just shortens coating life. Cheers