"This would give back the same mast hight.
hope I make myself clear with this explanation.
Still have problems to explain myself in english
No need to worry about your English, it is certainly better than my Italian.
Yes, actually you would be making two splices, and splicing in a new section. Masts are often too long to ship in one piece and sometimes you'll see a boat with one splice in the mast because of this. That is always where one section has been placed inside the two halves of the mast, and then both halves are riveted up to it. In order to replace a missing section, you will need to match the missing section, and then insert two sleves, one at the top and the other at the bottom, making two splices. That certainly can be done but I've never seen one repaired that way. I would think that trying to match the missing section would be very difficult unless you had a plain mast extrusion, not tapered, nothing fancy.
"the part with the 500 us. I dont understand why I should spent 500 us for material to repair a part of a FC boat with a resin mix if it could be done otherwise."
And that is the question. There are many many different concrete mixtures, all with different properties, and many additives, all with different properties. If you make it yourself, you need to be sure you are making the right mix. Part of what you pay someone else is the cost of resin (which is usually expensive) and part is the cost of shipping
. Especially if they are shipping
a mixed material and not just selling you additives. But then you are also paying for their expertise and reputation. If you can be sure of what you are making, and you can make it yourself locally, then there is no need to pay them for that. The question is, how certain will you be that your mixture is as good as a professionally made mixture?
Encore, if you have used white glue as a binder, that's great. But in the masonry business I've only seen latex (or fancier) additives, never one from casein, never a mention of white glue. Except from boatbuilding sources, which all say never to use white glue where water
or moisture resistance is a problem, because it will fail. I can't see how it would perform in cement unless something unexpected happens in the cure. Given the cost of an additive designed to do the job? I'd use the additive and not gamble on something coming apart five or ten years down the line. Or twenty.