Re-coring question

[CHANCE1234]

Do I need to sand/grind this down more to remove all the unwetted strands from the original layup? I removed the original core but remaining is very uneven.

[CoreyTrx]

I would grind all those dry strands and get down to solid glass. Then trowel on some thickened epoxy or polyester then the core.

[erebus]

I recored all the hatches on my 1975 18 and on my friends 1972 23.
Trying to remove all the "dry strands" is almost impossible without grinding the existing glass to nothing. It gets so thin so fast.
The glass on my 18 was a little thicker than the 23. The hatches on the 23 ground away to nothing so fast, I burned through in a couple of spots.

What I did was remove as much loose stuff as possible with, I think a 60 grit on a grinder.
Got it mostly flat, then wetted it all out with un-thickened vinylester.
Let that kick for a little while, and while it was still green, backbuttered and bedded down my core with vinylester hull and deck putty.
I put some weights on top (batteries I think) and troweled and filleted the edges where it squeezed out and let it kick again for a little while.
While still green but not wet, I wetted out templated and pre-cut 1708 and laid that over the top smooshing it into the corners and edges and getting all the air out.
Then let it all kick.
Worked out great.
Just remember to bevel or fillet the edges of your core, as the 1708 will not wrap around a 90 degree corner. And when you get to the "add weight" part of it, put the hatch on a nice hard FLAT floor, garage, basement, whatever.
I did one hatch on my 18 that I left up on a wonky workbench and it got a weird little twist in it.

[CHANCE1234]

Good info. Thanks Zak. That's what I'll do.

[FishStretcher]

I have a few pics of my recore.

I (think I ) didn't use thickened VE resin. I used un thickened. I didn't grind much. I did sandblast and put a layer of mat between the skin and foam.

http://www.classicseacraft.com/commu...pictureid=1449

Starting here, halfway down has more details than I can remember. Other than the backache.

http://www.classicseacraft.com/commu...t=25405&page=7

[pelican]

in this situation:

I attempt to fair the surface,before coring it.this will assure you have an even surface,with full core contact...

coring to a dimpled/rough surface - this can and will create a few low/high spots in the fiberglass skin

[erebus]

Originally Posted by FishStretcher

put a layer of mat between the skin and foam.

Doh!
I did this too. Totally forgot about it and didnt put it in my description above.
I templated and wet out a piece of 1708 with unthickened VE, and put that right into the lid. Let that kick for a bit, then installed the core with thickened VE on top of it, then went to the last piece of 1708.
It's true the extra layer of glass helps smooth out the internal surface of the original glass while also adding a little strength.

Thanks for reminding me! I knew I had forgotten something...

[FAS]

that will add tons of strength,also weight...try not to use too many 1708's.. great fiber and strength.but do not need too many layers....try this,.grind out the dry weaves,the skin cant be that thin,BUT,be carefull..put thickened resin(your choice)on the skin side and the core side, and put together with weight to force the excess out.clean up the edges and when dry put 1 layer 1708..use a hard roller to even it out.If you have access to a vacuum system, its a different process.It will all work out in the end !

[CHANCE1234]

So this is what I've done so far. Removed wood core, cleaned with acetone, mixed some poly resin and applied to the whole underside to saturate the un wetted strands. When dry I roughed it up with 60 grit, wiped with acetone again and applied system three fairing compound to make it as even as possible. Tomorrow I will sand that down and apply more fairing compound as necessary and sand to get it damn close.

After that I will cut to fit the Nida core leaving a one inch perimeter all the way around. Then I will cut a piece of mat wet it out and put it on the under side. Before it fully kicks I'll put down some hull and deck putty then the Nida core with weight applied. Once cured I'll cover the core with one layer of mat followed by one layer of woven since I don't have any 1708 on hand. Does that sound sufficient?

[otterhound]

It sounds like your using epoxy products (System Three) and if so it might not be compatible with straight mat that has the binder. The epoxy doesn't dissolve the binder well, if it's a sewn mat or biply then no problem.
Rod