any reason to remove excess old fiberglass while grinding your hull?

Smeag

Seaman
Joined
Apr 11, 2009
Messages
64
my plan was to leave the excess there and just glass it in as if it was the hull. i have already ground away all the glass that was in the channel for the new stringers and a little extra to make sure nothing gets in the way of the new stringers. is there a reason to remove this or am i making the right choice? sorry for the poor pic, if you look at the top left you can kinda see what i'm talking about. there is also a rise in the center aprrox 1/2" think as well. they aren't in the way at all.

P4240005.jpg
 

drewpster

Commander
Joined
Oct 17, 2006
Messages
2,059
Re: any reason to remove excess old fiberglass while grinding your hull?

You want clean, smooth glass to promote adhesion. Grind away enough so that the new glass will not "bridge" low spots and the surface is completely clean. Gelcoat on the surface can cover up problems underneath it. I would recommend removing enough of the surface pigment so that you can verify that there is no voids or dark spots in the laminate. If you lay glass over what is already there without checking you risk laying new glass over bad glass.
Delaminated, or poorly laid glass, will show up as a white areas in the glass. Glass that has been contaminated or possibly holding moisture will show as dark discolored areas.
My boat had allot of these bad spots in it. I was grinding for days. But at least now I know the new glass will stick and I am not worried about trapping water in the hull. (causes freeze cracking) Fiberglass is not impervious to water.
Make sure you are satisfied that you are laying new glass on a clean, undamaged, uncontaminated surface. Even epoxy wont stick to dirt. And of course you never want to lay glass on top of paint.
 

Smeag

Seaman
Joined
Apr 11, 2009
Messages
64
Re: any reason to remove excess old fiberglass while grinding your hull?

yeah i've ground away any bubbles i saw and i plan on making peanut butter to bridge any gaps and make it a smooth flat surface to work with. but the only place the excess glass will be is far below the deck, so i'm not worried about what it looks like, just the structural integretry. thanx for the tips :)
 

F14CRAZY

Ensign
Joined
Aug 12, 2008
Messages
945
Re: any reason to remove excess old fiberglass while grinding your hull?

I would also suggest grinding away most all the old glass. You might leave a little to use as a reference for the new stuff but as mentioned, bonding is better with a clean surface
 

Smeag

Seaman
Joined
Apr 11, 2009
Messages
64
Re: any reason to remove excess old fiberglass while grinding your hull?

the excess glass is factory, so i'm pretty sure it's the same clean surface there as it would be it i were to grind it down to the hull. keep in mind i'm talking about areas that were 1 and 1/2 inches thick or more that i have already ground away approx 1/2" or more of the surface of these areas.
 

PiratePast40

Lieutenant Commander
Joined
Mar 21, 2009
Messages
1,734
Re: any reason to remove excess old fiberglass while grinding your hull?

I found it very difficult to get good adhesion around the old glass. These were only 3/8 to 1/2 inch tall lines left on each side of the old stringers. What you end up with is a double angle to try to lay mat and cloth into. The result is that the material lifts and you have bubbles (voids) in areas that are critical for strength. You could fill in with filler (peanut buter) or construction adhesive to form a smooth joint but you're talking additional material and it must cure before you lay in more material. I can tell you from personal experience that the work of grinding out your own mistakes is pretty rough. It's even worse if you've allready done a super job of vacuuming and washing out the entire hull to get rid of the dust - thinking you're done with that part.
 

F14CRAZY

Ensign
Joined
Aug 12, 2008
Messages
945
Re: any reason to remove excess old fiberglass while grinding your hull?

A few times I had felt that I did enough grinding of the old glass but I ended up going back to grinding and rewashing it out like twice
 

Smeag

Seaman
Joined
Apr 11, 2009
Messages
64
Re: any reason to remove excess old fiberglass while grinding your hull?

here is what i plan to do.

red is the new stinger
light blue is the peanut butter i planned on seating the stringer down into
dark blue is my new glass--fully covering the stringer
purple is the hull
black is the excess glass, assuming a former peanut butter the factory used to glass in the old stringers.

so the point is to leave the old glass, use the peanut butter to make a nice angle to work with, and then glass in my stringers. sound like a good idea?

stringerplan.jpg
 

PiratePast40

Lieutenant Commander
Joined
Mar 21, 2009
Messages
1,734
Re: any reason to remove excess old fiberglass while grinding your hull?

Personally, I don't see why it would not work. Make sure that it's perfectly clean and then scrub the area again with a scrub brush and soap, rinse well, and then clean it again. Make sure your joints are smooth and the material is cured before tabbing in or laying the full lenght of mat. And again, make sure you also give the area a good acetone wash before you even think of laying in any mat. The extra material is making it necessary to bend the glass in 2 - 90 degree angles in close proximity to each other so reducing the angles is critical - make sure that joint is strong and cured before the mat or cloth goes on. I'm telling you this from someone who's been there.
 

Smeag

Seaman
Joined
Apr 11, 2009
Messages
64
Re: any reason to remove excess old fiberglass while grinding your hull?

it's so much easier to explain with a diagram lol. thanx pirate for the extra tips. i'm sure i'll have an update whenever i finally get to glassing. it seems this grinding never ends though.......
 

film495

Petty Officer 1st Class
Joined
Apr 8, 2009
Messages
285
Re: any reason to remove excess old fiberglass while grinding your hull?

put some type of fillet on the seams of the stringer to hull - fiberglass does not like sharp angles - so you need to build that up enough so the glass isn't bubbled and weak at the joint; I've heard of a quarter used as a guideline as how much bend you need to get a good seam and be strong.

the only advantage I see of removing the old glass is weight - but, what did that old glass do? are you replacing all the strength of that old material? with new?
 

capri1600

Petty Officer 2nd Class
Joined
Apr 20, 2009
Messages
150
Re: any reason to remove excess old fiberglass while grinding your hull?

As the others have said, the most important part is to make sure you are ground down to strong, good fiberglass. I spent yesterday grinding more out of my 1983 Bayliner Capri 1600 and EVERY seam that was part of glassing in the wood internal structure had many many dry spots and had a pretty weak bond to the hull. I have been taking the time to grind the bulk of the excess glass off and alwasy hidden inside there have been defects. Now, to be fair, the solid looking stuff was bonded well enough to use and I probably will not grind every bit of it out but really watch for those dry or rotted spots. Fiberglass does rot and can trap moisture. Those spots have to go even if you have to dig for them.
 
Top