HELP! Glass-clothing operation.

Tips, hints, ideas wanted please - I will shortly be glassing (cloth & epoxy) the hull of the Ches 17LT.   It will be upside-down at this stage.   The stem (bow) rakes steeply and the cloth is unlikely to want to sit nicely as I apply the epoxy.   I want a nice bump-free finish here - any tips, please.   I expect to put a narrow bias-cut strip of cloth on the stem first, overlapping each side by 2 - 3", then apply the full cloth after this has cured.     Do I cut the full cloth to match the stem shape before epoxying?   Do I let it hang and trim at the just-cured stage?   What's best?

And - on a similar subject - is there a way to prevent loose glass-cloth threads from detatching themselves from cut edges when brushing epoxy on?

Thanks in advance


Lol from Oz

10 replies:

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RE: HELP! Glass-clothing operation.

You can make the glass fit nicely by pulling and stretching on the cloth.I don't know how to describe it any better than that but once you have the cloth draped over your hull, just give it a try and you will see what I mean. I have seen it demonstrated but can't remember exactly where, maybe on the CLC DVD.

Let us know how you get on.


RE: HELP! Glass-clothing operation.

I didn't have any trouble out of the glass cloth at the bow, it will bend around there nicely, like Robert says.  There is some finagling to be done at the stern.

I am wondering why you are adding the extra bias strip first?  You're introducing an irregularity onto a (hopefully) regular surface, then putting a big piece of glass cloth over it.  It will be much harder to get the big piece of glass to form to the bow that way.  I'd do the big glass first, then you can reinforce all you want.

RE: HELP! Glass-clothing operation.

For the loose threads - First, plan to cut the glass a couple of inches wider than you actually need. Next, apply some kind of adhesive tape (I like the blue painters tape available in the US) centered on the cut line. Finally, cut down the center of the tape. The threads are immobilized.

Once the layup is done, let it cure to the point where it's soft, rubbery and ever so slightly tacky. Use a razor blade to trim the glass to the original cut line and peel away the section with the tape. Push the edges of the layup down, if necessary, to stick them to the boat.




RE: HELP! Glass-clothing operation.

Fiberglass cloth is so slippery and loosely woven that it will conform to just about any surface.  I use a carpenters dusting brush to spread it smoothly.  I strongly agree with Ken that you should put the reinforcing strips on last.  Work from the widest to the narrowest to avoid air pockets and ridges in the cloth.

RE: HELP! Glass-clothing operation.

As previously mentioned, the cloth will smooth out fine. You can just pat and smooth it down, as if you were patting a small mammal. Work from the center out towards the ends.

Bias cut strips on the stems are a good idea but put them on after you have glassed the entire hull. 

I just roll out the length of glass over the upturned hull and cut it to length. Then go around the outside trimming so that about 1-1/2 to 2 inches hang down below the sheer. Using very sharp shears will leave little to no fraying. I got some inexpensive shop shears at the local Megahardwaremart with slightly serrated edges that cut very cleanly.

On the hull glass, since the edges hang down below the sheer, it isn't necessary to fiddle with the epoxy as far down as the cut edge, some will driibble down, no big deal. And that edge can be easily cut off the next day with a box cutter or other sharp knife so fraying really isn't an issue there. I've generally had very little trouble with threads and fraying, even when the edge needed to be wetted out, simply because my shears were sharp enough to cut a very clean edge to begin with.

On the Chesapeake, I had to cut off, sand and add a small piece of bias cut cloth to roll over the stern as that is one place where initial hull glass can't really conform well.


Ogata (eric)

RE: HELP! Glass-clothing operation.

There are some pictures here of the hull glassing for a CH17LT as it was done in class at CLC. You can see the result of smoothing the glass down, wetting it out, and what happens at the stern. I got into a little trouble because there were a lot of shared cups of epoxy being handed around and I eventually got one that was a little over-ripe. Had to cut off a section of the bow glass and lay down another piece. Keep your epoxy cool and fresh and get it out of the cup and onto the glass as quickly as you can is the lesson I learned from that:)


Ogata (eric)

RE: HELP! Glass-clothing operation.

Drape the glass cloth over your hull. If the hull isn't smooth, the cloth will catch on rough areas/burrs and distort the weave.  So be sure you can run your bare hands over the entire area you are going to glass, without snagging them on anything (be reasonable, don't rip your hands, it's a test of smoothness after you've sanded), then drape the cloth.

Carefully adjust the glass so you have 7 to 10 cm hanging over one edge of the hull at its widest point.  A large, clean brush really helps here.  And take your time.  Be neat.  If you jerk on the glass you will probably distort the weave (this means more work for you later).  Then use the brush (hands are used by many, but for your first couple of glass jobs, a brush is far better) to smooth out the glass, starting at the middle and working out radially, even over the sides.  It will take a bit more patience and TLC at the bow but the glass will slowly conform to the shape.  THE STERN WILL NOT!

The excess glass hanging off the sides and bow can be trimmed so 7-10 cm is left loose.  If, when you apply the epoxy, you don't let it drip off the edges and then try to save it, you won't have to deal with too many threads.  You want to spread the epoxy around so you only have a cm or so of the overhanging glass wet.  That insures you have covered the hull and makes the glass overhang easier to trim with a sharp blade when the epoxy has turned green (i.e., stiff but not rock hard).

At the stern you'll have to overlap the glass and later add a small patch.  Not a big deal, but can be messy.  Leave it for last, make sure you've left plenty  of time, and don't use epoxy that is ready to gell in the cup.  Relax.  Then take a SHARP blade and slice the glass along the keel where it is not conforming to the sharp bend of the stern.  Once that cut is started you can finish with sharp scissors (when my scissors are sharp I use them here so I don't distort the cloth and make a lot of loose threads), but cut along the extension of the keel line while trying not to lift too much of the glass you've smoothed out already.  I usually leave the last 5-8 cm along the sides free of epoxy until after this cut.  Trim the glass so each flap will overlap the other side by 5-cm.  Then bend back one flap toward the bow and wrap the other flap around the stern and epoxy it to the hull.  Some of the glass at the curve of the keel to the stern is not going to stay down on the hull; it will stick up like a picket fence.  Carefully trim off the offending threads.  Now wrap the last flap around the stern, over the first flap, and epoxy.  You'll have the picket fence effect again at the curve.  Don't worry about

Carefull go back over the hull using a smooth squeegie and remove excess epoxy (glossy and puddling are bad) and making sure all of the glass is wet (white is bad) and you have no pinholes.  An hour or so later go over the hull (and floor) again looking for drips and runs.

When the epoxy is green (6 hours or so at 30C), trim the overhang around the hull and the picket fence or threads at the stern.  Smooth the glass at the stern, fairing it some to the hull but not cutting into the hull.  Then apply the bias-cut glass patch.  (Bias cut means the threads are at 45-degrees to the edges of the patch.)  The patch will conform easily to the curve, you just need to be carefull applying the epoxy, don't drag the patch around too much.

Be aware of potential for out gassing by the plywood.  This can occur if the temperature increases before the epoxy seals the air in the wood.  You'll want to work when the temperature is max or cooling.  And don't put the hull in the sun to speed the cure; that will really heat the wood and let the air escape out under the fiberglass.

Apologize for the length of this.  Good luck.

RE: HELP! Glass-clothing operation.

Thank you very much for all the helpful replies.   I have printed some off and will carefully re-read, learn, and inwardly digest  before hitting this critical step.   Yes - I take the advice and will (if at all) add the reinforcing strip at the stem AFTER the main cloth is done - it's purely for reinforcement there as I don't plan to do the full epoxy-pour.

Another ? though - my fillets are taking longer than normal to become rock-hard, despite the near 30 deg (C) temperature.   The thickener is a form of silica, I believe, judging from its 'sandy' texture (my dealer here doesn't sell/ doesn't want to sell wood flour).   Has the silica in some way slowed down the curing process?

Many thanks for all help.

Lol from Oz

RE: HELP! Glass-clothing operation.

I've never noticed any slowing caused by silica.  Must be something else I think, if you're sure it's really slower than should be.  Not mixing well enough, and measuring errors are by far the two most common reasons I've seen cited by the experts here, in CLC doc, and elsewhere.

Musing on "WHY?" is fun for me but not for most folks, so skip the following if you're the pragmatical type.  And I hope it don't turn into a hijack of your post ;-)

Silica is completely inert, so it has no effect on the chemistry, (right Laz?) other than diluting the active ingredients by a miniscule amount--every once in a while an epoxy molecule will bump into a silica crystal, when if the silica hadn't been there, it would have found an amine molecule to add to its harem.  But no measurable effect, I think. 

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