Hi Nerijus,
Sure, I'll be happy to talk you through this.
It's not quite clear how badly broken the board is at that point. If it's pretty much failed completely and there is little holding it together then it would be good to know if the board is solid carbon fibre or uses some sort of core. If it does use a core then it might be a good idea to take out some of the core, either side of the break so that you have a cavity. Into that cavity you could bond (using epoxy resin) some material which could 'bridge' the gap. Something like plywood might sound quite low-tech but could be ideal for this application; it's easy to get hold of, easy to shape, has good compressive strength and epoxy bonds really well to it. By adding more strength at this point 'inside' the board, it would mean that you don't need to build up too much extra thickness on the outside of the board, in order to equal or surpass the strength the board original had in in this area.
If it's not badly broken enough to justify 'opening it up' and adding some strength into the core at this point then we're limited to a repair on the outside of the deck. A good rule-of-thumb when dealing with a repair is that you'll need to add ass much new reinforcement thickness as the damaged part previously had. That means that if the deck used 2mm of carbon fibre in the skin (either side of some sort of core) then your repair will need to add 2mm of thickness onto the outside of this area. Clearly this rule assumes that the material underneath is fully broken and effectively not contributing anything. If it's not and it is still reasonably in tact then you can 'adjust' the rule accordingly.
For the repair itself, as you suggest you will need to tidy up any fibres/material which are out of line. Anything that's still in line should be left in place, loose strands and splinters can all help to 'knit' the repair together. Key the whole area with coarse
120 grit abrasive paper to give the epoxy something to bond onto. Use alcohol or a solvent like
acetone to ensure the area is fully de-greased.
The best resin to use for this repair would be our
EL2 Epoxy Laminating Resin. It's easy to use, has fantastic mechanical properties and comes in at the right price. For a relatively small repair like this in normal ambient temperatures, you could go with either FAST hardener or choose FAST and SLOW and mix them together to make a medium. You wouldn't need the SLOW.
The carbon to use would be the standard 2/2 twill 3k carbon fibre. We have our premium 210g material which uses a high strength TR30S fibre;
Carbon Fibre Cloth 2/2 Twill 3k 210g 1000mm or our budget '
Black Stuff Carbon Fibre 2/2 Twill 3k 200g 1000mm' which is more of a commercial grade product at comes it an around half the price of the premium grade. In terms of difference, the mechanical properties are about 20% better on the premium grade, the quality control is super tight and the product has full traceability/certification supplied. For a repair job though, our Black Stuff may well be the way to go!
My suggestion would be to repair the bottom side of the board first, let that fully cure, tidy up the repair and then flip it over and repair the top side. This will make the project much more manageable and less messy than trying to do the top and bottom at the same time. After doing your hand laminating it would suggest consolodating the laminate mechanically (i.e. squashing it down with something) whilst it cures. Nothing as sophisticated as a vacuum bad would be required but maybe some
perforated release film onto the wet carbon, then some
breather cloth and then a metal plate with some clamps on. This will basically give you the same effect as a vacuum bag (for a small repair area) for a fraction of the cost.
I hope this helps and look forward to seeing how you get on with the project.
Matt StathamEasy Composites / Carbon Mods - Technical Sales