Kevlar cloth help

D

don novicki

Active member
I am in the process of building another open water layout and had a question about using Kevlar cloth in place of fiberglass mat. I typically use 1.5 oz. fiberglass mat on the bottom of the boat (outside) along with the basic fiberglass resin/hardener to seal it up and it has always worked well. I thought I might get a little fancy this time and use Kevlar cloth in place of the F.G. mat. My question is can I just use regular resin/hardener like I always do or does Kevlar require some special product to make it adhere? Also how do you cut the Kevlar cloth ? the cloth I am looking at is rated as :ballistic grade. Thanks for any help. Don
 
Good morning, Don~

A basic question: Is your boat made of 'glass - or would you be using the 'glass as a covering/sheathing material over wood (presumably plywood) ?

BTW: I believe you need special scissors for cutting Kevlar

All the best,

SJS
 
I dont' know what "ballistic grade" is. For boat building it would typically be labeled with ounces (per yard) and a description of the weave, so you know what you are working with. I can believe that there are types of Kevlar that would be unsuitable for building.

As far as putting Kevlar down (if what you have will work) it is just like putting glass down with epoxy. One thin to consider is that the Kevlar is usually put down with a layer of glass on top because it does not like to be sanded (fuzzes worse the more you sand). So... you are talking 2 lavers (Kevlar AND glass to cover it) - which is more weight.

There are special scissors, but they are just very sharp scissors, I'd get some rather than messing around.

A layer of Kevlar is several steps up from 1.5 matt. An intermediate would be woven glass in a 5-6 ounce weight.
 
Don, I have been putting Kevlar into my 60 to 85 ft sportfish boats for 30 plus years. Kevlar has its place, but unless you really need it, I would just use an extra layer of glass. We use diamond dust scissors to cut it {very expensive}. You really need to use peel ply on the edges, unless you are burying it under a layer of cloth simultanously. As Todd said this stuff wont grind, it just fuzzes up when you hit it with a grinder. As to being bullet proof, back in the eighties we were building a 56 ft cold moulded wood and epoxy sportfish. This was our first experience with kevlar. The bottom of this boat was triple diagonal ocume ply with kevlar between the layers, a kevlar under 12 oz biax on the outside and inside. all set in epoxy. Our customer was all pumped up about having a bulletproof boat. I took a cutout, laid it on the ground and shot it with a 22 short. The slug went thru the sample and traveled so deep into the ground that we couldnt find it. Rich
 
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Don~

For sheathing a plywood hull, I would use 6 ounce 'glass cloth in epoxy resin. Epoxy is far superior to polyester in terms of both adhesion and waterproofing. I would double the cloth over high-wear areas like the keel and chines.

Chopped strand mat (CSM) is primarily used in molding hulls etc in conjunction with woven roving and polyester resin. Most mat is chemically incompatible with epoxy resin.

Kevlar is best for weight savings - as in canoes, kayaks, etc. It might be useful for abrasion resistance - but note Tod's thoughts about the fuzzing.

BTW: I have been very satisfied with all the materials I have gotten from U S Composites. They have everything you would need.

Hope this helps,

SJS
 
Dynel cloth yields very good abrasion resistance as well as being compatible with polyester resins and epoxy resin.

Rich, Kevlar 49 is the cloth used for abrasion and blunt trauma crush offset in boat building applications. Kevlar 29 is the ballistic grade weave- an entirely different beasty not compatible with boat building applications!

A short chopping cut with a top quality pair of fabric scissors cuts Kevlar 49 well enough. Tape your cut line. You can also purchase Kevlar 49 as a tape in widths up to 6" from several vendors. Store it out of sunlight and lay a layer of fabric over it or paint it to help protect it from UV degradation over time. It wets out quite well and is actually pretty easy to work with and yields superior strength and abrasion/crush resistance when compared on a per weight basis with various fiberglass cloth weaves.
 
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Good morning, RL~

Great information - thanks!

U S Composites has the Kevlar 49 in tapes and cloth.

All the best,

SJS
 
Just wanted to say thanks to everyone on here that replied. Lots of good information which points me in the direction I want to go. Thanks again.....Don
 
Good morning, RL~

Great information - thanks!

U S Composites has the Kevlar 49 in tapes and cloth.

All the best,

SJS
Click to expand...
Steve, thanks for your earlier positive comments on US Composites epoxy resin use. Yes, I bought my biaxial, Kevlar 5 Oz. cloth and 6" Kevlar tape, along with two gallons of resin from them. Just finished sanding the decoy compartments bare in preparation for application on Bill Clarks TDB 17' Classic. I am putting a six inch wide layer of Kevlar tape along the interior chine, overlain with 1708 biaxial cloth. If anyone is wondering, there is a 14" wide layer of Kevlar cloth that runs down the keel line to the origin of the in-deck drain. There are two overlapping Kevlar layers in the foredeck that extend back about four inches past the snaps line for the bow blind panel.
 
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