Fiberglass weight

[TK1]

Hi,

I am about to start stitching and gluing the seams of my ply kayak (yes, yes, pics coming soon, probably this weekend ).

Instructions call for 6oz or 9oz fiberglass tape. Now, I have some sheets of 15oz (425gram) fiberglass mat, probably enough to cut strips for all the seams. Being a cheapskate, having it on hand means I'm inclined to use this.

So, my question is...

Will the 15oz fiberglass be too heavy/thick/hard to use/etc compared to 9oz, or just a bit of overkill?

Does the weight refer to the weight of a certain area of the mat? New to this so not sure.

I'm not aiming to make this kayak ultralight, it's really a practice build and will be a solid, knockabout fishing/paddling kayak compared to the racing boats I'll make. So a bit of extra weight is OK as long as it's not going to add another 5kgs or anything.

I'll be buying lighter cloth for the hull sheathing, this is just so I can be cheap and impatient and get on with the construction...

Interested in people's thoughts...

Thanks,
Darren

[bitingmidge]

Darren,

If you are going to sheath the hull, why are you taping it first?

Heavier weights (per square foot/yard/metre BTW) won't be disastrous, but will add weight and use more resin to fill, and take more to fair when you want to get a nice looking transition.

If you aren't used to working with glass, you have the potential to get into an awful mess if you cut your own strips, as the warp (or is it weft?) threads will pull out along the edges as you are working and you'll end up covered in bits of fibreglass . You'll also have to contend with the joins. What you save in fibreglass cost, you'll spend in fairing compound and sandpaper!

Glass Tape is woven with a continuous edge so that won't happen, but you'll want to shave it down with a spoke shave and/or cabinet scraper to get a nice transition. There's a bit of a diagram on the PDRacer thread a few pages in from memory. I'll try to remember to find a link to it later.

Cheers,

P

[TK1]

Hi BM,

The taping is done on the inside of the hull, to provide joint strength (and cover the stitches if they're left in). Apart from the taped joins, the rest of the inside of the hull is just coated with epoxy.

This is what the instructions say, so this is what I do...

The instructions suggest either tape or cutting your own strips, the advantage of cut strips being they don't have the bulge at the sides and possibly lay against curves better as the sides aren't as stiff.

If I can get lighter-weight tape at the chandlery I'm going to tomorrow to get some more resin, I'll pick some up. May try both to see how they go.

That's what this boat's all about...learn and experiment!

Thanks,
Darren

[bitingmidge]

I remember the "advantages" well! I tried to take some well meaning advice once, and cut off the edges of the glass tape too. The problem I had was that the cut isn't exactly straight, and neither is the weave. This leaves a lot of little strands along the edge and parallel to it, all of varying lengths. When comes time to brush/squeegee them, they just want to pull out all over the place.

You may be a bit better at cutting and handling the strips than me, but I got into a shocking mess the first time it did it. Then you get blokes like Storer who've done it a bit, and they can tape a whole boat without getting a drop of goo on them! (pics on the PDR build thread too) The bulk at the edge of the tape can be planed off with a spokeshave, preferably when the epoxy is green, say within the first 24 hours.

I wouldn't try to talk you out of taping the inside. Do as the plans say, particularly until you've got some runs on the board.

I wasn't thinking of glass on the inside because I've found it a bit hard to clean up (Lack of skill ) so on the Eureka, I've used bog fillets and glassed the outside. I'm just a bit neater with bog than I am with glass. You might file that one away for next time!

Cheers,

P

[malb]

Darren, I haven't worked this stuff for many years, so take my comments with a grain of salt, as they may be worth less than that.

My understanding is that tape is woven on the bias, i.e the strands are at 45deg to the edges. This makes the fabric much more pliable for laying up into edges and corners.

Normal cloth is woven like normal fabric, with strands parallel to the edges, and strands at right angles to the edges. This is a general purpose fabric, but narrow tapes cut from cloth can be difficult to work with, particularly in fairly tight spaces. In desperation, tapes can be bias cut (45 deg) from cloth but are harder to work with than tape because the cut ends fray during layup.

Mat(t) is a fabric with layered strands arranged in a random fashion, (length and orientation) normally used to provide bulk to distribute loads. Trying to tape with strips cut from matt would be very dificult and rather pointless as the random strand pattern would not add much strength, and the layered buildup makes it difficult to work in tight angles.

[bitingmidge]

I've just had Boatmik looking over my shoulder and we've had a bit of a chat about the double bias tape.

"Normal" tape is woven parallel, so don't buy it thinking you are getting double bias.

If you can get double bias, (it's not that common and only available from specialist suppliers) it's great stuff, because you have double the strands crossing the joint, so you can effectively use half the weight again.

Mik has had a bit more luck than I with cutting tape, using a straight edge and a sharp knife. He suggests the secret is if you get into a mess, just leave it and fix it later. Wish I'd known that twenty years ago!

Cheers,

P

[TK1]

Ok, OK, I'm convinced....I'll see if I can chase down some double bias tape. If not, I'll at least buy some tape and save myself the grief of cutting the mat. I've had a look at it and yes, the weave is all over the place so I can see it coming apart when cut.

Will let you know how I go.

(Being the curious type though...maybe I will cut up some sheet and try it on a test piece....)

Thanks for the advice.

Darren

[bloggs1968]

Darren,

for your boat all you need is some 6 oz or 200 gsm (grams per square meter) plain weave tape ( or 9 oz if you want). it has a selved edges to stop the strands from pulling out and is very easy to use. Most of the double bias tapes I have used are cut from full 1270mm wide rolls and the edges can tend to fray a bit when wetting out. I reckon that the double bias is stronger as midge has said. Most chandleries will rip you off on glass so look up the yellow pages and find a fibreglass supplier for cheaper gear.

if you do want to cut your own tapes, I have found the best thing for cutting glass is a rotary craft cutter. These little beauties easily cut 1150gsm triaxial. The only online pic I could find in a hurry is http://www.catherinesplace.com.au/in...rget=d143.html
and look at the "OLFA Ergonomic Cutter". I normally buy supercraft ones and they are around 10 bucks from memory with a spare blade.

With regards to using chopped strand mat for taping, by all means try it but it will probably give you the s##ts in the first few minutes and will be heavier. As a guideline, it will take the number of grams per square meter of cloth in resin to wet it out. For example, one square meter of 400gsm double bias will take around 400 grams of mixed epoxy resin to wet out.

When do we get to see some pics mate!

regards,

AD

[Boatmik]

Howdy Bloggsy,

The glass bill will be so tiny in the cost of the whole thing that it is probably worthwhile to get it from where it is the most convenient.

Generally I've found chandlery prices for glass tape bought per metre to be a bit more expensive, but a roll is not too bad.

But many glass suppliers are only happy selling a whole roll when it comes to tape even though there may be some who do.

Yep - just ask for 6oz glass tape of the width you want.

Best wishes

Michael Storer

[Eli]

Not that you would really, but has anyone ever tried fibreglas drywall mesh tape for something like this? Certainly wouldn't be as messy, might be cheaper, benefits are ?

[Fugley]

Eli
You may find some info on this link
http://www.simplicityboats.com/jointtest.html
mostly using constrution glue etc ... worth a look

cheers
Jim P

[Boatmik]

Going cheap is a valid choice - but remember that it cuts longevity and increases maintenance.

The greatest advocates are the Americans who can still get OK ply for $10/sheet and lumber for tiny prices too.

So they can make a boat kinda sorta disposable. But even when it costs you as little as a few hundred ... maybe it is worth making last longer with better materials.

For example ... how much of the threads in a gyprock fibreglass tape would cross the join?. From memory it is not many - so you would need to look carefully to see how much of the strength you retain.

If I am thinking of the right stuff it would be a tenth or 20th of the strength because there are so few fibres.

Look at the purpose too. To hold plasterboard together. Plasterboard is not strong or stiff - so a few strands of glass will hold it all together enough. It never gets any real loads.

Whereas you can try and break a glass tape join of any ply up to 6mm and you will be more likely to fracture yourself!

BEST WISHES
MIK

[Eli]

I was thinking more layers, but you're right, it would never be as many fibers as true glass tape even if you put ten layers of it on.

mea culpa.

[bloggs1968]

Howdy Bloggsy,

The glass bill will be so tiny in the cost of the whole thing that it is probably worthwhile to get it from where it is the most convenient.

Generally I've found chandlery prices for glass tape bought per metre to be a bit more expensive, but a roll is not too bad.

But many glass suppliers are only happy selling a whole roll when it comes to tape even though there may be some who do.

Yep - just ask for 6oz glass tape of the width you want.

Best wishes

Michael Storer

Mik,

I suggested a non-chandlery supplier as Darren sounds like he is building a few boats and he would get better value in buying a larger quantity from a specific glass supplier and, if need be, would have access to a better rangeThat's from my experience anyway. We have a dedicated place here (actually called the fiberglass shop believe it or not!) and they will sell by the metre or by the roll and are heaps cheaper than the chandleries.

Agreed if it is only a small amount, then go to the most convenient place as the cost difference is minimal.

regards,

AD