Fiberglass Cloth

[PSBreen]

My wife and I have been collecting materials for our trailer and are getting close to starting to build. Weather/waterproofing is one of our concerns. Steve Frederick's book recommends fiberglass and epoxy for this but doesn't mention what weight cloth to use. So I have to ask, what weight of fiberglass cloth is sufficient to make a trailer waterproof or is it need? Any suggestions?

I'm just guessing here so hopefully more experienced builders will chime in and offer some suggestions. My thoughts are based on what I've done with model aircraft so they may not really apply.

1 to 3 oz cloth - It doesn't add much strength but the tight weave gives a very smooth finish with little or no filler required.

6 and up oz - Drastic increase in strength but requires fillers or multiple coats to get a smooth finish.

[Juneaudave]

Right or not, I used a 3.5 oz plain weave on my trailer. Plain weave is easier to wet out, but when you use lighter weight cloth (such as a 3oz cloth), you need to be careful when you handle it not to snag it. You certainly don't need anything heavier. I typically stay away from tight weaves due to wet out problems....

[asianflava]

If waterproofing is what you're concerned about, just about any weight will work. The resin is what makes it waterproof, the cloth is just the matrix that holds the resin. Coating with resin and no cloth will also help in waterproofing. As you posted, the weight of the cloth will determine strength.

If unsure, split the difference and use something like 4oz?

[PSBreen]

A lot of our concern is about leakage around the roof/side joint. One of our thoughts is to use 2" fiberglass along that seam and then 4-5 coats of spar varnish over the entire trailer. Any thoughts?

[starleen2]

If you do use the 2' around the edges - go with the firberglass tape pre cut - it comes with a selvage edge that keeps it for coming unraveled.A real time saver. I've Cut 3 Inch strips before out of cloth and it was PITA to work with. Never again.

[afreegreek]

A lot of our concern is about leakage around the roof/side joint. One of our thoughts is to use 2" fiberglass along that seam and then 4-5 coats of spar varnish over the entire trailer. Any thoughts?

if you are brushing on unthinned varnish, 3 coats is more than plenty.. biggest mistake people make is thinking more is better.. more is what causes finishes like varnish to craze.. long oil varnish is supposed to be a supple finish so it can move with the wood.. if you put too thick a coating on it will be rigid and crack..

specs for finished film thickness are on the can..

[hoytedow]

Epoxy will last longer than varnish. Sanding varnish impregnated fiberglass is a PITA. Epoxy is less permeable than polyester resin and has less smell. It costs more but the final result is worth it.

[Jim Edgerly]

I used 3 coats of epoxy resin, without cloth, then followed up with 3 coats of spar varnish.

[Larry C]

If you do use the 2' around the edges - go with the firberglass tape pre cut - it comes with a selvage edge that keeps it for coming unraveled.A real time saver. I've Cut 3 Inch strips before out of cloth and it was PITA to work with. Never again.

As for me, never again will I use selvage edge tape on anything. I cut all my "Tape" from cloth. It has to be cut on a bias (45degree). The cut edge will not fray if cut on a bias, and it will follow a compound curve. The tape won't.

$.02
Larry C

[Larry C]

I typically stay away from tight weaves due to wet out problems....

Dave,
I use 3.25 oz tight weave cloth exclusively now, and haven't had any wet out problems. Maybe the 5 oz is tougher to wet out, but 3.25oz is very easy. In fact it's easier than 6 oz plain weave. Also, I have read that a single layer 3.25 oz. tight weave is almost as strong as 6oz. plain weave. I do use thin epoxies such as Raka. I have even wet out 2 layers at the same time with no issues. I only use rollers for applying epoxy. I no longer use brush or the pour & Squeegee methods.

What I really like about this cloth is the glass to resin ratio. It takes a lot less epoxy resin to bury the cloth. Wet out, and one fill coat usually is enough. That's whole lot of $, time, and weight savings without sacrificing strength.

These are the methods that have worked for me after many years of using epoxy/glass. You will find many opinions on this subject. There are many many types of Epoxy and fiberglass cloths to chose from. Also, there several methods used to apply the cloth/epoxy. They all work, but the one that works for you is the "best one"



Larry C

[afreegreek]

until you have significant experience using epoxy as a base for bright finish on wood you are much better off sealing the wood with a coat of thinned epoxy first.. there is noting that will show sanding scratches and bruises on wood better than epoxy will.. the softer the wood the more this will be apparent.. woods like pine and cedar are the worst but even harder woods like cherry and walnut are suspect.. epoxy is a 20x magnifying glass for imperfections in the prep job..

that little spot you bumped, the spot where your clamp block crushed the wood a little, the one you THOUGH you sanded out.. ya, that will show up like a spotlight on a dark night the moment epoxy hits it.. this means you live with it or pull the cloth and throw it in the garbage.. it's much better to find these first then fix them before you blow $300 in glass and resin.. plus you will avoid other problems like insufficient wetting and off gassing..

ya ya, I know... you and Joe down the street do it without sealing first and have good results but the pros in the shop across town don't take the risk.. that's why they're the pros and you are not..

[hoytedow]

You can avoid out-gassing by applying epoxy to warm surface. As the surface cools it the gases in the wood cool too and actually contracts, sucking the epoxy in with no out-gassing at all.

[hoytedow]

I fiberglass in the late afternoon sun when all is warm.

[PSBreen]

"I fiberglass in the late afternoon sun when all is warm" HaHaHa That ain't happening here. Today was foggy and damp (80% humidity) with a blistering 32°F for the high. I'll be using a heater in the garage and waiting for dry days. The goal over the holidays is getting the walls built. Basically try to get everything into a kit so we can assemble it when the we have a few good days.

[hoytedow]

First, make sure working temp is adequate. Make sure the wood is warmer than the resin, but make sure the resin is warm enough to work with. After glassing, don't let the room get warmer than it was before glassing, but still warm enough not to unduly slow reaction time. As the room cools slightly the gases in the wood will contract and pull in the epoxy.