Using fiberglass tape with mat for stitch and glue

[Stoutcat]

Hi,

The issue has come up of what tape to use in stitch and glue construction for the outer chines and inner seams for a 15' power boat... (If you're not familiar with stitch and glue, just think of gluing down stringers.) Everything I've ever read (or used) is regular 6 or 10 oz. cloth and epoxy. Now one of the guys is wondering about using 12 oz. X 4" double bias (+/- 45) w/mat tape and epoxy.

I've never used fg cloth/mat... Will that work with epoxy? How will it look? I'm guessing the cloth side should be visible...

Any thoughts would be helpful...

Thanks,

Alan

 

[fiftiesoutboards]

Re: Using fiberglass tape with mat for stitch and glue

The mat/tape choice would be overkill, and lead to very bulky looking seams. A good bit of the strength in stitch and glue joints comes from the fillet that you do before taping. Prime the joint w/epoxy, fillet the joint with a thickened epoxy mixture and a radiused applicator, and after the fillet has started to cure, apply the tape and a couple coats of just epoxy. There is a new biaxal tape out there which is supposed to give extra strength because each strand crosses the joint at an angle, rather than one paralelling the joint and one crossing, as in standard tape. It comes in two weights, 6 and 9 ounce. I suppose you could use the 9 for the inside joints, and the 6 for the outside, so it will be easier to fair. I'd be secure with the 6 for both. Here's a link for the tape: http://boatbuildercentral.com/products.php?cat=1

 

[Mark42]

Re: Using fiberglass tape with mat for stitch and glue

.... Prime the joint w/epoxy, fillet the joint with a thickened epoxy mixture and a radiused applicator, and after the fillet has started to cure, apply the tape and a couple coats of just epoxy. ......

Have to be careful here. Epoxy gets anime blush, a wax coat that forms on the surface as it cures. If you mistake the sticky wax for unhardened epoxy you will be applying the next layer on top of goo and it will just not stick.

Most epoxy gives you 8 to 24 hours after initial cure to apply a second coat and still get a chemical bond. So if you are new at this, I suggest letting the epoxy set hard (usually 20-60 minutes depending on hardener) then wash it clean with dish detergent and water to be sure its clean. Then apply the next coat.

Better safe than sorry.

 

[BillP]

Re: Using fiberglass tape with mat for stitch and glue

Most of the strength is in the epoxy glue. Cloth helps a little but you probably wouldn't know the difference if NO cloth was used. Anyway, regular mat is made for polyester resin and has a binder that epoxy can't dissolve. What that means is that type cloth is impossible to fully saturate. There is a mat made specifically for epoxy so be sure to use it if going with mat. Mats random fibers will give it stiffness at the cost of double resin and more weight. Cloth will give it higher tensile strength and be more flexible but with half the resin use. I'd personally not worry much about it and use standard cloth between 6-10 oz.

Do yourself a favor and make a test sample of each. Then do a distructive test to see how tough it is. You will be surprised and likely find the cloth peels or breaks long before the glue joint fails.