drilling ferro cement

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lilianroyle

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I need to make a 12-15 mm hole in my ferro cement hull. In the past I have used diamond hole cutters for the transducers (v expensive, and probably can't get a small enough cutter), a ring of tiny holes and lots of patience for the sea toilet (incredibly time consuming) This time I was thinking of using a conical grinding bit.
Any thoughts from anyone with experience of this?.
Pete
 
Hi I have a ferro boat and have read a lot about the subject as we had a problem that needed repair but have never needed to drill a hole however you may know of Colin brookes web site www.ferrocement.org that has lots of good information and refers to his book on working with ferro that i have purchased and find excellent. I beleive he advocates using a small masonary drill to begin and then gradually open the hole up as needed - good luck
 
No direct experience of ferro cement but in a previous incarnation did loads of diamond drilling for machinery foundations in the car industry, so this might be relevant.

Your problem's not so much drilling the cement, it's drilling through the steel armature that will give you problems. If you're using a masonry drill as soon as you hit steel the drill will either wander off line or you'll b*gger the drill bit. Either way I can't see it giving you an accurate hole. Best results are certainly from diamond drilling. You can get diamond core bits down to 15 mm no problem, in fact I've still got a couple of 10mm dia ones. Oh if you're using diamond core drills, spray with water periodically to keep the drill bit cool and act as a lubricant
 
Diamond drill, cheapest are at Topps the tile place or ebay.
Tip for starting the hole, make a template, drill the same size hole in a piece of scrap plywood and tack it on with silicone or other GP adhesive, it will stop the drill from skating round. If the thickness you're drilling is greater than the drill, drill part way and chisel out then continue.
 
This is a bit unrelated but I think that I want to take my rudder off so that I can check the prop shaft[the way the rudder is means that the rudder has to be taken off to do this]. But the rudder has been on for the past 27 years and it will mean taking bolts out and then putting them back. How does that work? Would it be possible do you think? I mean, those nuts and bolts have been in the cement for years!
I'll post a pic of the rudder on my blog just in case anyone wants to pop over to give me an opinion.
 
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