Fiberglass seams of wall/roof

[TomW]

I am considering putting a 4" wide fiberglass cloth seam over the roof/wall joints to seal.

Any suggestions/recommendations??

Thanks.

[Ralf]

That is a common plywood boat building method. If you are going with a clear natural wood finish the seam or edge of the tape will show somewhat but wont detract. You can sand (fair ) the edge of the tape and then recoat with epoxy to minimize the edge. If you are painting you can fair the edge with thickened epoxy and sand smooth. If you are clading with aluminum than you are good to go without any further prep.

the glass tape will tie the roof and sides together and add strength. Whether extra strength is needed I dont know but it cant hurt. My build is underway and I have erected the 3/4 inch mahogeny ply walls coated both sides with 4 coats of epoxy. I am not going to glass the sides but I may tape the wall/roof seam as you are considering.

Be sure to round over the edge with router or sanding so the fiberglass will hold. Sharp edges dont work with glass. Even the sharp bow of a boat is rounded over before glassing.

[toypusher]

....................
Be sure to round over the edge with router or sanding so the fiberglass will hold. Sharp edges dont work with glass. Even the sharp bow of a boat is rounded over before glassing.

A roundover bit in a router will make a very even and smooth edge for you. Just pick the size you need.

[GPW]

...and remember if you're going around a curve (such as the roof /side of a TD) you must pull the tape (tension) to have it conform easily without wrinkles...

[TomW]

I am builging a Generic Benroy. I would like skin the outside in metal but right now, metal is not in the budget. I am planning on painting the ouside. The fiberglass was mainly for sealing not strength. I am using 2 layers of 1/8 plywood for the top with 1/2" walls (sandwich).

What weight fiberglass is recommended? How much radius on the corner rounding?

Thanks again for the suggestions and direction.

[Steve Frederick]

All good info!
If you want the joint to be less visible, try to get light weight cloth, say 3-oz.
It's thinner, smoother, holds less epoxy, and will be easier to blend away. I just use cloth, cut on the bias (45-deg). Bias cut cloth will conform to curves very well. Also, to minimize work, run blue painter's tape along both edges of your proposed tape area. Run the tape (rough edges or a hem) onto (over) the painter's tape a bit, and wet it out. Don't cover all of the painter's tape with cloth/epoxy, or you'l have a nice blue racing stripe!
When green-cured, you can dent it with your thumbnail, pick up the outer edge of the painter's tape, and trim away the ragged threads with the tape.
You should be left with a nice edge that will be easier to blend away.

[Mentor58]

All good info!
If you want the joint to be less visible, try to get light weight cloth, say 3-oz.
<<<snip>>>
You should be left with a nice edge that will be easier to blend away.

You've got some super techniques there. This thread has me thinking that I'm going to do a fiberglass seam on the roof/wall line. I've built a fiberglass canoe from a kit before, and this should be easy enough to do.

One of the things I LOVE about this forum is that whatever somebody has a question about, in a day or two there will be at least a couple of folks sharing their techniques, tips and proven results. I never would have thought of cutting on the bias, or using some tape to help get a nice clean edge.

TD & TTT Forum ROCKS.

Steve W.

[Wimperdink]

this is a must see for glass taping an edge

http://www.youtube.com/watch?v=HnPY2lHsR1E
video is from a fav boatbuilding site I frequent.

[Steve Frederick]

this is a must see for glass taping an edge

http://www.youtube.com/watch?v=HnPY2lHsR1E
video is from a fav boatbuilding site I frequent.

Good video.
Where this guy had the bump that he chiseled away, would be the center of my painter's tape. Where he chiseled, I would bend my tape up along with that bump, and trim off with a razor knife.

Some day, I'll have to try video podcasting!

[DougH]

I used 4" tape also for this and feel I should have gone with a slightly smaller size to blend in easier. I also think i used too heavy a cloth as it didn't blend in as well as I would have liked. (Of course I could have spent more time sanding etc )

[TomW]

The video was great information. Thanks.

I am going to try a test piece when I get back home. 3 oz cloth. Any special type of epoxy and was it thinned?

Can someone recommend a radius for the seam at the roof/wall?

Once again, Thanks.

[Wimperdink]

The video was great information. Thanks.

I am going to try a test piece when I get back home. 3 oz cloth. Any special type of epoxy and was it thinned?

Can someone recommend a radius for the seam at the roof/wall?

Once again, Thanks.

I won't go less than a 1/4" radius. Also a good idea to wet the area out and let the epoxy dry partially before putting the tape down. This allows epoxy to soak into the grain of the wood so you dont get air bubbles under your tape, and being sticky helps the tape stay in place while your wetting it out. Not a fantastic idea to thin epoxy as it changes its strength properties.

[Steve Frederick]

The video was great information. Thanks.

I am going to try a test piece when I get back home. 3 oz cloth. Any special type of epoxy and was it thinned?

Can someone recommend a radius for the seam at the roof/wall?

Once again, Thanks.

On the four so far with wooden roofs, I used a 1/2" radius bit, but I don't use the whole depth. Cutting to deeply would reveal my framing. Not desirable for my finish preference, Spar Varnish.

Do a test to be sure that you don't expose the framing below the roof, behind the exterior wall. You may not like the look, unless you are painting, then it won't matter.