I suppose it was only going to be a matter of time before I stuck my head
up - and threw in my 2 cents worth as well.
I have to say firstly that having read the whole thread, I am still having a bit of difficulty picturing exactly what you're trying to do. You said you wanted to raise the deck level to give yourself more headroom
in the aft cabin
- and I was wondering if you could tell me:
- are you trying to cut around the hull
itself - or the existing cabin
top, or the horizontal deck?
- what are you intending to rebuild
and in what material?
- can you provide any photos so that we can see just what we are dealing with?
Just a couple of observations on previous comments - it's well known from my thread comments on the cutting of this yacht that I do not favour trying to 'chip back the cement' to expose the existing mesh and rods - and then attempting to cut this and weave in new areas of mesh and steel
- and then re-plaster it all. I believe the time and effort involved and the difficulty in trying this, is not justified. And this is from someone who has meshed, tied and cemented (for more than 4 years) more than most of us would ever want to see in a lifetime. (Unlike a 60' Ferro
that was here recently that legend has it - was completely cemented in 1 DAY
using 15 plasterers and 80 helpers).
It can certainly be done - and the new wet mortar can be satisfactorily bonded to the old by using a 'hydrophylic' (water friendly) epoxy resin. My entire 75' ferro
yacht was cemented by me alone - in large sections - over several years - using a straightforward method of both inside and out - overlaps of cementing, through the many layers of mesh - and copious quantities of this special resin - splashed and painted over the rough moonscape surface of the old meshed concrete edge. The resulting join which was sometimes done 6 months later - as the sections cemented were alternated from side to side and front to back (for weight and curing reasons) was trowelled so that the final joined area was more than a foot wide and this resin blends perfectly with both fully wet new mortar - and soaks in to the old dry.
I honestly believe that the sections of these joins - are stonger than the normal cemented areas. It is not possible for any crack to ever develop - because of the very nature of the jagged nippled moonscape surfaces involved - over such a wide area - with multiple layers of mesh - and there is just nowhere for a crack to form or follow.
It's hard to describe - and I will see if somewhere I can find a photo
that shows it.
But, if you are going to remesh and rejoin new to old cement - then I would suggest you talk to a local epoxy manufacturer and tell them precisely that - and see if they have a similar product. The resin I used I obtained from a local manufacturer and friend Les Baker at Norglass Laboratories (NORGLASS LABORATORIES - | Marine Paints | Specialty Finishes |
) - it had no specific trade
name - and was specially provided to me for the wet on dry method of construction - and I found it just amazing how it would perfectly blend and work with both being trowelled together. I suppose it could be similar to an underwater curing epoxy.
I have no experience in using the PVA based product that Alan mentions so will not comment.
Truly though - I would recommend that if possible - you cut the section of deck or cabin top - and either raise it higher using steel
plates, bonded and bolted to the 2 sections. Or, that you cut off the cabin top and rebuild
it in glassed ply - bonded to the remaining deck. Although, every bit of my hull
and superstructure is ferro-cement - and there has been no problem - I think if I was doing it again - I would end the decking at the cabin edge lip and build the cabins and superstructure in wood or similar - both for lightness in weight up top - and ease of working. It is a simple matter to bond and bolt to the deck and build from there.
Many a ferro-cement hull is actually built this way - with only the outer hull - and part of the deck being built in ferro - and then all the deck and top sections in timber or ply. Ferro-cement bulkheads below providing the cross hull bracing strength.
Again I say - can you please provide some more specific details of what you are actually doing to the hull?
The 3M scourer discs Alan mentions are just excellent - and I have been using them for several years - but primarily to polish stainless steel - all the railing, fabricated fittings - and now the 316 ss plates going around the hull - are 'polished' using them - they give a very attractive, finely brushed shiny finish. They are also excellent for stripping back any type of paint - and I have recently lent my grinder and discs - to a few people in the shipyard who were stripping back bottom paint
- using other types and methods - and they have been astounded at the efficiency and ease of these woven black scourer discs.
They must be used on a variable speed grinder - and cannot be run at more than 3-4000 rpm
otherwise they will just fly apart - DO NOT attempt to run them on normal grinders at high speed - as they will disintegrate instantly and could cause harm. I use a Ryobi variable speed (only a cheapie) I've had for many years - and it's been worked into the ground - and still going - a great ad for them really.
Here is a photo
of mine taken a few minutes ago - these are 150mm discs - the one on the left is a different brand - stiffer and more suited to stripping - it's a 3M one on the grinder now - that I've been using to clean up the SS hull plates I'm putting on. They cost about $20 each here. I was actually first introduced to them by a stainless steel Polisher tradesman.
They will not melt themselves or the paint or job - if you only run them at the recommended speed or slower - you will soon see what is the optimum - and using them too fast will cause them to heat and leave a black smear - but if used correctly will have no trouble stripping paint from the deck or timber back to bare.
Like all grinding or scouring discs - if you are going to use them on stainless - you should only use SS grinding discs - and do not use these scourers on both ordinary steel and then SS - you will contaminate the SS surface with minute ferrous particles that will cause the SS to show rust spots. Keep one aside - just for SS.
Can you send us - or me (at firstname.lastname@example.org
) - any photos of what you are doing at present with the 'chiselling' of the deck?? It sounds like an 'ugly' scene to me.
As I've often said in the past 'I threw in my 2 cents worth - and it was thrown back out - for what it was worth'. But at least it was given in good faith - it's up to you always - to still decide what you want to do.