keel sandblasting

tgalea

tgalea

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Dear forumites,

In preparing my boat for next season, one or two people at the yard mentioned that i should sandblast the keel and apply 5 coats of interprotect after filling in.

Another guy said not to bother with the hefty expense of sandblasting and just sanding it down using an electric orbital sander with 40 or 60 grit sandpaper and then painting it.

Can someone please help as to what they think best or what should be the deciding factors for me as to which opion to chose.

thanks in advance for your comments

Regards
Tyrone Galea
Malta.
 
No question. Grit-blasting (rather than sand blasting) is by far the best way. With the correct grit and a competent operator, the surface will be prepared to the proper standard. Epoxy paint immediately behind the operator to reduce the risk of flash rusting, then apply the other coats as soon as possible thereafter.

I did this system about a year ago on my keel and so far it's perfect (so it should be too!) but when, I used an angle-grinder etc a few years ago, followed by epoxy, the rust returned during the second season!

IMHO if you're going to spend big money on epoxy paint, at least give it the best chance of succeeding!
 
Hi
There have been a quite few postings on this in the past.
I usually just clean back any local rust, put on some phosphoric acid based gunge, then prime the area and hope. Others speak well of Hammerite paint (It works well on my gate) but I have not tried it on the boat but I will. We lift out every winter so a quick fix is ok but I guess if you leave your boat afloat for a few seasons a more robust job would pay in the long run. Such people in our club have done the full Primocon treatment and have had good results. I think it is just a matter of how much you want to spend in money and time.
 
Problem Solved

Paint the bottom and keel with red antifouling. Unless you are racing a few bits of rust wont matter.

You'll just have to do it again in a couple of years when the rust spots reappear.

Donald
 
Hi,

Had a look at this site. Product looks quite impressive. Do you have an indication of how much one of those discs would cost ?

Thanks
Tyrone
 
G'day thalassa'

If the action is as described then it would be much the same a needle gun but I suspect faster. However needle guns do not work on cast steel as the action does not remove all rust, but drives small particles back in. Do you thing the disc would have a similar action?

I have always blasted cast iron to class 2.5 and had no problems, the trick is to be just behind the nozzle and get some epoxy resin on in seconds to avoid the flash rusting that is common on cast iron.

Avagoodweekend......
 
Had a look in a 2005 catalogue. A single row disk is listed as 34.75 EUR, double row 67,50 EUR , triple row disk works out 95,5 EUR (sorry, continent-based). Two brothers in my club started out a "business-on-the-side" by perago-ing other member's boats! They told me you can do about three 30 ft steel motorboathulls with one double-layer disk. And yes, it's a bit like a needle gun, but faster; the stuff comes off a bit flakey, so less dust . You do need adequate ear protection, though.
 
For your information.



Many thanks for your enquiry from our web site. Prices as follows:

Perago Scraper
Soft, medium or hard £22.50 inclusive of delivery and VAT

Perago Blaster
Single £22.00 inclusive
Twin £40.50 inclusive
Triple £60.63 inclusive

Perago Blaster Multi
230v or 110v £499.08 inclusive
Air powered £374.59 inclusive

Please contact me if you need any additional information.

Regards
Mike Cribley

B.C. Aviation Ltd
Old Lamb House
Marnhull
Dorset DT10 1QG
UK
Tel: +44 (0)1258 820491 Fax: +44 (0)1258 821464
Web: www.paint-stripper.co.uk
 
I think that there is an argument between doing it propery once and continually keeping just on top of things.
With my old boat I try to do one (major) job properly each season otherwise I would not make progress.
With the keel you could just chip off the really bad bits and use 'red lead' or hammerite type products to keep the rust at bay till you can afford time or money to attack it completly.
Good luck.
 
Having seen this advise a couple of times and as I am building up to doing it myself - how to you follow behind the blasting without getting grit over everything you are trying to paint?

Or is it a lot cleaner than I think?
 
To get you coating on as soon as possible after blasting I do the following:

Safety first. Respirator, eye and ear protection as well as protection for your painting hand ii using a short brush or roller(I don't), the best alternative is an 80 mm roller on a long handle.

1. make sure the blasting starts at the windward end of the keel

2. Always work from top to bottom in strips about 4 to 6 inches wide

3. do the leading or trailing edge depending on wind direction first

4. As soon as the nozzle is 6 inches away, start applying you coating

Notes:

Don't worry if you get runs, they can be sanded out before you add the next coat.

Fill any low areas with epoxy resin and closed cell balloons.

Top coat filled areas with epoxy resin after sanding.

Prior to adding an undercoat give the epoxy a light sand with 200 or 250 grit, just enough to remove the high gloss only and do this with a block and paper.

This is the method I use and have had no problems.

Avagoodweekend......
 
Last question to Mr Old Salt (well, on this subject!!)

When you said there was a need to follow up quickly with the epoxy I thought that you meant in an hour not a minute!!
Question.... Doesn't the epoxy go off while you are blasting?
Regards
 
Humidity below 74%, temperature above 18*C, mix only small amounts (about a cup and a half) in a wide shallow container and it will be fine for a least 30 minutes, by that time most if not all of the keel will be finished.

Blasting should be to class 2 and a half, that means the steel will look almost white with no shadows. Flash rusting will visible in under a minute.

More resin can be added wet on tacky, don't push down too hard. Cured resin must be washed prior to sanding to remove residue left by the curing process; just have a hose running and scrub with a plastic kitchen scourer, the little yellow cube of sponge with the green strip on side is good, it only takes a few minutes, work from the top down and rub till the water no longer forms beads.

Clean up with white vinegar, this will remove the bulk and reduce exposure to acetone used for the final rinse. Epoxy resin is soluble in water before it hardens, so soap and water will also work but not as well.

Avagoodweekend......
 
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