Sandblasting keels

[capt_courageous]

Santa brought me a Karcher pressure washer for Christmas. A sandblasting kit a available for it. Has anyone out there used this sandblaser. It looks ok for use on cast iron keels but how would it perform for stripping old antifouling from the GRP hull? Can it be controlled enough to get the paint of without damaging the gel coat?
Happy Christmas to everyone - Spring is coming.

 

[Appleyard]

Hi Capt' merry whatsit.. good pressie!. I have a large diesel engined pressure washer which is used for washing stonework prior to repainting etc. Also have a sandblasting kit which we have used for cleaning rusty railings metalwork and other stuff. It is a beast ,very powerful ,but takes a bit of time to clean back to bare metal.,however will do a brill. job. Metal keel should be fairly straightforward, but may take a long time with a small kit like the Karcher.A lot depends on what type of grit you use. The stuff sold by Karcher will be very expensive. Go to a supplier of foundry supplies and you will be able to get the right type of grit at a very much cheaper rate.(approx £3.00) per 25 KG if I recall.
As regards the hull, you will have to be careful to get the grit size,pressure and distance correct. Try it out first on the rudder to see how it goes. You can also try using the type of sand which is sold by builders merchants for filling the joints in monoblock paviors. This is fairly fine and is sold in sealed bags,which must be dry. (If the blasting medium gets wet,it is useless of course) You will have to mask off the bits which you don't want touched by the process. Also cover all the rest of the boat very thoroughly and also all nearby windows, cars, etc. I speak from experience.having seen a patio door glass ruined by an over enthusiastic muppet. The grit will get everywhere and is a bug*er to clean up. Have fun.!!!!

 

[cliff]

Been down that road and IMHO these DIY sand blast kits for the pressure washers are a waste of time and money. They are very heavy on grit consumption, the grit must be dry - very dry as if it is even slightly damp it will not flow. The over spray gets everywhere - wet grit.

Check the grit spec before buying. If I remember correctly these "hobby" blasters use max 2mm AlOx grit which is expensive even from grit suppliers.

Sand, even sharp builders sand as used for monoblocking is a waste of time - the sand is too soft.

I found a recycling air blast much more efficient, cleaner and cheaper.

 

[Appleyard]

Thanks for repeating what I said Cliff,especially the cost of the grit... However I have used monoblocking sand for delicate surfaces and found it satisfactory. I use pressure washers in my business and know what I am on about. If he only has a small machine then he will have to use what he has. Remember the old saying"you can only pi*s with the pr*ck you have got",so it is at least worth a try. Cheers and have a good one!!!

 

[celandine]

Strictly speaking you are not talking about sandblasting, but slurry-blasting. This has certain advantages over sandblasting in that you can use silica sand (illegal for sandblasting due to health hazard) You should be able to use the dry, bagged silica sand that is usually marketed for block paving etc. try local aggregates merchants.
I have done a lot of this but not using a hobby pressure washer. My observations for what they are worth would be as follows:

*If the keel has an epoxy coating you will not get back to bright metal - even a proffessional compressor (atleast 60hp motor) has to work hard to achieve this.

*If you do get back to bright metal, an iron keel will bloom with rust in a few hours, so you need to be ready to get it to dry, and epoxy prime the same day if possible.

* Come prepared to fill voids in the original casting. These are often quite crudely cast, the manufactures tend to just fare these off with polyester filler.

Good luck with it and happy new year,

Mick

 

[snowleopard]

i was quoted £400 for a half-day to sandblast a fireplace and ceiling beams in my cottage. i then went out and bought sand blaster and compressor for under £200. i am about to start work and have dried off a load of building sand in the oven but would welcome advice on 'proper' stuff to use. the instructions say my machine will use 60 lb per hour and it won't be recoverable.

 

[castaway]

I have been investigating the Farrow System having used conventional slurry blasting on Fairweather's lower hull to clean of 30yrs worth of old a/fouling a few years back.. This was a highly messy and difficult to control process and I would be cautious about recomending anyone to experiment on their own boat with a sand or slurry blaster.

I was looking at the Farrow System as I am considering using it to strip the old polyurethane from the topsides and certainly the conventional system would be unsuitable for this...The Farrow System only uses about a litre of water per minute( which is hot) and the medium is volcanic ash (pumice)rather than sand... I understand that this gives controlability and very little mess, I guess this would be an advantage in your cottage!!

Regards Nick

www.yachtsite.co.uk/fairweather

 

[Talbot]

Unless you have a commercial version of the karcher with at least 150bar pressure. dont bother. Even then you are wasting your time, cause the metal will rust very quickly cause you are putting water on it. A lot of these will also clog very quickly. I have tried it, and quickly learnt what a waste of time it was.

However, if you have a decent air compressor (prefferably 3hp) a sand blast from one of these (using silver sand and keeping it dry) will quickly strip paint and everything else of the metal. I have used one on a tractor wheel that even had some concrete on it. For home use on metal, it is the dogs whatsists.
If you are considering use on GRP, then use the dry ice system cause that will explode out any osmosis and save any gel peeling.

 

[robind]

*If you do get back to bright metal, an iron keel will bloom with rust in a few hours, so you need to be ready to get it to dry, and epoxy prime the same day if possible*

when I had my old De Groot blasted the guy used an additive in the water and the boat stayed bright for a while until I could get it Primed which was at least over night.
Rob

 

[andyroo]

As Robind mentions if you do get the keel back to iron, suggest you paint the keel with some blast primer first. Red oxide is recommended for this. I have been told in the past this gives the epoxy a better key.

Good luck!!

 

[Joe_Cole]

I wouldn't recommend that. Epoxy will be disastrous if it's put over most red oxide primers.
Stick to the manufacturers recommendations.

 

[philip_stevens]

Capt. C.
I wish you a Happy New Year.

Instead of re-writing a post I submitted many moons ago, click on the links. They are to do with a ScrewfixDirect product similar to Neutrarust 662.

http://www.ybw.com/forums/showflat.php?C...true#Post465593

and

http://www.ybw.com/forums/showflat.php?C...true#Post456838

My Konsort Duo keels are in the process of being slurry blasted, and I will be applying the Neutrarust as soon as there is a sufficient rust covering on them. The Konsort I sold last year is still in this area, and the keels are as good as when I put the Neutrarust on them 7 years ago.

regards,
Philip.

 

[amberville]

i used southern cleaners. done great job £60 with a fully adjustable presure slurry system. give them a try not worth doing youself for this price. http://www.southern-cleaners.co.uk/shot_blasting.html

 

[amberville]

Sorry Forgot to say they used soda. No damage to gel coat and cleaned 2 kilns in 40 min. start to finish no dust or mess,

 

[amberville]

Very interesting, is it all worth it when i paid A1 Bead and Grit in Portsmouth 65 to slurry blast my one for me, first class job and no mess,