Fiberglassing Question

[dmarkvid2]

I want to fiberglass a stringer, and three new bulkheads. I was told to "rough up" the exsisting fiberglass so the the new glass I lay down adheares to the old. I used an 80 grit paper to do this, but I noticed the more I sanded the more shiney and smooth the fiberglass got. Is this normal? will the new fiberglass bond to this smooth surface? Or is there another way to actually "rough up" the surface? Also there is about an eighth inch gap between the hull's bilge and the new stringer. is this a problem? I was thinking of running a bead of 5200 marine caulk along both sides of the stringer and the fiberglass hull. Would this be ok? Thanks

 

[fishingdan]

Re: Fiberglassing Question

You can find a lot of specific how-to information on the major epoxy vendor's websites. They discuss many typical repairs including those that you mentioned. <br /><br /> http://www.westsystem.com/ <br /> http://www.systemthree.com/

 

[troutlet]

Re: Fiberglassing Question

Roughing up the existing epoxy is to get past the skin of the original epoxy that has been exposed to air and whatever else. This helps ensure that you are bonding epoxy to epoxy and not epoxy to dirt, oil or other contaminates. You want a chemical bond. It doesn't have to be nicked up to stick well.<br /><br />Some boat designs absolutely require gaps this is to evenly distribute the force. I wouldn't use caulk, not even 5200. Take epoxy and mix in a good supply of wood flour (saw dust) to form a peanut butter consistancy. This will be solid as a rock. My opinion anyway.<br />Almost forgot to mention: Always wear a respirator rated for epoxy dust when sanding epoxy! seriously.

 

[dmarkvid2]

Re: Fiberglassing Question

thanks for your reply troutet, every bit of knowlege i learn is great, and get more confidence. thanks

 

[ondarvr]

Re: Fiberglassing Question

You need to use a power sander if you want a good bond, 36 grit on a 4.5" grinder will work and it's cheap. Are you going to use epoxy or polyester for the repairs, either one will work fine, but there are a few differences in how they are used.

 

[dmarkvid2]

Re: Fiberglassing Question

I'm going to use epoxy. What are the differences between the two? I also used an electric palm sander.

 

[18rabbit]

Re: Fiberglassing Question

Ondarvr has it. You need a more aggressive abrasive. I use only synthetic abrasives, 3M, but Norton also makes similar products. You’re not just taking off the surface of the existing material, you are actually cutting a ‘tooth’ into it that the new epoxy can grab onto.<br /><br />One of the best all-around tools I have found for working with fiberglass is the ($110 at Home Depot) 3/8-in angle drill made by Milwaukee (called a ‘Close Quarter Drill’). It has a variable speed control you will want for working with fiberglass, light weight, easy to control, fits into tight areas. I use either a 2-in (stiffer, more aggressive) or 3-in 3M RoLoc holder ($15/ea) that allows me to change abrasive pads with 1/2 twist. You can get by with just the 3-in Roloc holder. Unfortunately, the pads are the cheap part, around $1.50/each. You’ll want a 36 and a 50 grit. They won’t wear out in your life time.<br /><br />Also, I think what Ttroutlet is talking about is that boats require a distance between the rigid supports (stringers, bulkheads) to allow the hull to flex. It’s like the wing of an airplane, if it didn’t flex it would break off. With boats it becomes more important the bigger the boat is. Smaller boats aren’t flexing as much anyway, not really an issue.<br /><br />Epoxy has a long term negative effect to uv light. You need to either mix uv inhibitors with it (can effect its ‘cure’) or coat it with something to block the light, i.e. polyester resin (w/uv inhibitors)/get coat or paint, etc. Epoxy is easier to work with, adheres to just about anything/everything, more expensive than polyester resin or vinyl ester. Epoxy will adhere to cured polyester resin, polyester resin will not adhere nearly as well to cured epoxy. Epoxy tends to easy into hardening, while polyester resins seem to harden more abruptly.<br /><br />If you will be using epoxy be sure to get matt/woven material that is made specifically for use with epoxy. A lot (most?) of the material out there is made for polyester resin and contains ‘binders’ that will not affect the cure of polyester resin, but those binders can muck around with epoxy.

 

[dmarkvid2]

Re: Fiberglassing Question

Thanks 18Rabbit. I'll be useing fiberglass resin and woven mat that i bought a home depot. not sure of the brand, but its for fiberglass boats, and its the only brand they carry.

 

[JasonJ]

Re: Fiberglassing Question

I use my angle grinder with grinding wheel when I am roughing up. Gives a lot of texture and increases surface area for a better bond. Are you sure it is epoxy that you are geting?

 

[Bondo]

Re: Fiberglassing Question

I'll be useing fiberglass resin and woven mat that i bought a home depot. not sure of the brand, but its for fiberglass boats, and its the only brand they carry.

That's Polyester.........

 

[imported_bjs]

Re: Fiberglassing Question

do they have any automotive paint stores were you are from?i would buy that resin from them try evercoat products there good i think 3 m makes resin to but your going to pay for it since the got there name on nascar.there prices went sky fiberglass mat will work to but i would like to see use the long strand mat i think its stronger.riff up area good with 36 grit but dont take off to much lay your mat in the resin them take mat out lie on area to be repaired a good stiff paint brush poke the resin into the mat real good.applay more if needed make thick if you have to i hope this may help.

 

[2manyboats]

Re: Fiberglassing Question

West Systems epoxy rules. They have great tutorial manuals, if you're of a mind to read directions...<br /><br />ditto on the clean surface and rough surface notes, clean between coats also. Light sanding won't hurt either.