Grinding FG surface for new attachment and tabbing

[Sven]

The Cape Horn is getting closer to reality ...

One question for those who have done new FG attachments to old surfaces ... how deep do you have to grind down the old surface to get a good new bond ? I know you have to first clean the old surface or you'll just keep smearing the surface contaminants onto the newly exposed surface as you grind, but assuming that you have cleaned the surface, do you only need to take off the top layer ?

As the attachments for the Cape Horn control line blocks are all below decks I do not look forward to doing any grinding at all, even in a tyvek suit with a mouth filter, but I also don't want to do too little and have the control line blocks rip off the interior hull surfaces at the wrong time.

Thanks,



-Sven

 

[vanfuego]

new lay up over old

Hi Sven
I usually just scuff the surface then wipe it down with acetone. Im not sure on the type of resin used for your boat sometimes polyester types are used and other times vinylester and then again epoxy resin. poly and vinyl wont stick well to epoxy. id use vinylester below the water line. Hope this helps....let me know...

 

[Loren Beach]

80 grit is a waste of time....

You need to provide good "tooth" for the epoxy to bond to. I use 40 grit or even rougher, on a disc sander. Put the vacumm inlet right in line with the out-fly from the disk.
The idea is not so much to remove x amount of surface, but to roughen up the surface to better bond to it.
Even 16 grit works fine .... you don't have to put too much pressure on it; just let it do the work. For close quarters a Stanley Surform tool is very helpful also.
I do a final cleanup of the surface with acetone, also.


Loren

 

[exoduse35]

Seriously scuff up the area. Depth ts not as important as getting a good and clean area to bond to. I use a 36 grit paper on a sander/ buffer. Or for a smaller area, a cut off wheel on a die grinder works well. Neatness at this point is not a good thing as the rougher surface will have the same effect as Velcro on the new laminate. Use epoxy! Just remember that you can never put polyester over that area. Epoxy sticks to polestar but not the other way around. In fact it is probably best to just switch to epoxy for everything and be done with polyester, it's smell and trying to remember what is made of what. Edd

 

[toddster]

Hmm... I'm stopping by HF disposable tool store tomorrow for a rotary sander to use on my boat. You guys have any preference for the 10,000 RPM air "sander" vs the 3000 RPM electric "polisher/sander?" I'm thinking that the grinder I use for welding would be a bit too aggressive, and also hard to cover a large area effectively...

(After the haul-out, it turned out that my boat has an embarrassing pox all over the keel :0 )

 

[exoduse35]

I like the air power better... But it is OFTEN the case that air is unavailable. At my shop at work it is all and only air. At home and on the boat it is electric all the way. Quality tools can be had either way. The air is nicer when it works but it eats up a bunch of air and a portable compressor WILL NOT feed it more than a few minutes, also it is prone to freezing up if there is moisture in the air, and will freeze your hands on a cold day. I guess I just decided that if you have to ask, the only answer is:go electric and be done! Edd

 

[Emerald]

When I did my blister repair, I used a combination of a 4" angle grinder and a Dremel for small stuff. Spare yourself cheap tool agony and forget HB and buy a real tool that will last more than 10 minutes. You can get something decent even from Home Depot for a pretty good price:

http://www.homedepot.com/Tools-Hard...&storeId=10051&catalogId=10053&searchNav=true

 

[toddster]

Not to increasingly hijack the thread... but I already have little angle grinders like that. My thought is that trying to strip several square feet with one of those would cause a lot of gouges and an uneven surface. I'm looking for something to apply 80-grit on a flat face. That is, there are several dozen blisters on my keel - I suspect I'm going to have to sand down the whole thing.

(HF is a little like a casino... sometimes you get a tool that lasts forever. Once in a while you get stuck with something that falls in the "dispose before using" category. More and more, I see the exact same tools with "big brand" labels sold elsewhere for more.)

 

[bigd14]

Toddster, sounds like you need the Porter Cable 7335 DA sander. The preferred tool for all manner of sanding and material removal on boats.

Sven you should have no trouble if you rough up the surface with 40 grit or less. If there is any gel coat be sure to remove it. Otherwise rough it up enough to remove any shiny surfaces and expose fresh material. Vacuum it clean and wash with acetone and it's ready for epoxy. I had some areas in my boat that I could not sand so I just scrubbed with acetone and I still got a great bond so you should be fine. It's a nasty job for sure! Doug

 

[Mike Tinder]

fiberglass work

Sven,

The 36 grit sanding disk is what I put on my grinder for roughing up the glass. I think they are the best way to go. It is all I use. If I am doing fine fairing I will use the 50 grit disk, so I do not take to much off.

Good luck.

Mike

 

[Lucky Dog]

Couldn't agree more with the Porter Cable 7335 DA sander. I use it for everything from hogging off material to second to final power sanding. Buy a extra pad. Remeber to remove abrasive right away while it's still warm or spend 10 times time.mark