Saturday, October 25, 2008

Hull preparation - my best techniques summary

This post is mean't to be a notes to myself for that time 'hopefully' in the not to distant future, when I am preparing the main hull.  It's also a post for others with the following label.  'Every amatuer builder is different and the best techniques for one builder will not be a good fit for another.'  

1) Lay up the foam as fair as possible.  Use the polyurethane construction glue (the stuff that does not expand that much) so that the outer hull can be immediately sanded without any hard spots.
2) Always wet out the foam before laying any laminate.  I have found that this is absolutely required with the fine weave aerospace cloth that I am using.   
3) Always use peel ply when doing any hand lamination.  Using plastic sheet over the peel ply is a good way to ensure a good result.  When squeegeed the plastic creates a local vacuum (for good adhesion) and allows you to remove the excess resin.  I may be at the point of not bothering with vacuum bagging as I fail to see any major benefit for all the extra trouble and cost.
4) Apply fairing compound sparingly and sand most of it off.  Good results were obtained with Quickfair.  Sand, sand and sand with the long board (60 grit) until there are no low spots left.  Where possible make sure the bare laminate serves as the local high spot for the long board.  
5) Apply skim coats of epoxy resin to seal up the fairing compond and fill the pinholes.  Sand with the orbital sander (no more hand sanding, except for the hard to get at places), with 120 grit until the hull is smooth.  Smooth is when the surface is all smooth and dull with no shiny spots.  It's okay to apply more fairing compond at this point, this is the last chance.  The thin first primer coat will seal it.
6) Apply the bottom paint.  Thinking ahead, do a good job with a manometer or laser to get the designed waterline right on the main hull.  VC Performance Epoxy can be rolled on.   At least 3 coats.  The  surface can be wet sanded as smooth as required.
7) Apply the topcoat finishing primer with a foam roller.  With Endura EP-2C primer sealer thinned 15% air bubbles are not a huge problem.   I have been waiting till it is fully cured then sand with the orbital sander with 220 grit until the hull is smooth. 
8) Unless an excellent method for applying the topcoat is found, take the hull to a paint shop for topcoat spraying.  

1 comment:

Rod said...

Excellent comments. Thank you. You have reinforced the tack that I was going to take.