Epoxy and matting

bcooke · Post by **bcooke** » Mon Aug 30, 2004 9:43 am

I had planned to start the week by glassing in my chainplate knees using, as the book says, alternately layers of matt and cloth... and epoxy. While purusing a boat repair book over the weekend (kinda sick huh?) I read that matting and epoxy should not be used together - something about the bindings in the matting being incompatible with epoxy. I must have missed that before. So I have two questions:

Should I continue with the epoxy, using only (many layers of) cloth to glass in the knees? Or... should I use polyester resin, and if so, any particular brand? (all I come across in the stores seems pretty generic)

It is kind of hot and muggy today so grinding out the failed repair in the keel sounds like more fun anyway...

-Britton

Post by **Tim** » Mon Aug 30, 2004 11:04 am

bcooke wrote:should I use polyester resin

No, no, no!!! Please!

bcooke wrote:Should I continue with the epoxy, using only (many layers of) cloth to glass in the knees?

Forget the old mat/roving technique. Instead, choose some nice biaxial fabric, most of which come with a thin layer of mat pre-stitched to the underside just for this purpose. You can lay this up to your heart's content with epoxy, and it is easier to deal with and, even better, much stronger than the old way, at least for a given weight.

The mat in a traditional laminate is designed only to help the roving bond better to itself, and to subsequent layers. Mat adds no strength, and is really only a resin sponge. Some mats work with epoxy, others do not. It's just best to avoid it, as there is no reason to use it with the current slew of more highly-engineered materials. The light mat stitched to most fabrics contains no binders, so there are no solubility issues.

Assuming you have decent fillets, you can use something like a 24 oz. biax fabric, which will lay over the contours of the knees without a problem. Or, choose a lighter fabric, like 15 oz., which is a breeze to wet out and roll into place. A few layers of this is ample for the application, but feel free to add more for that "overkill" factor. Three layers of 24 oz. is fine, or go with 4 layers of 15.

Dave, 397 · Post by **Dave, 397** » Mon Aug 30, 2004 12:37 pm

I ...truly hate...to be a dissenting voice. But I gotta.

I have been using plenty of "stitchmat"/"X-mat"/"biax" in my project, in various weights, due to a good deal purchase (and a resultant good deal purchased!), and I hate the stuff. Difficult to wet out, takes time, if it is a warm day or a long layup the chances of having the resin start gelling in the middle of wetting and de-airing a piece are a good bit higher than otherwise. The stuff works, it's sure strong, but I dislike working with it a lot.

Dave

Post by **Tim** » Mon Aug 30, 2004 1:26 pm

The 24 oz. stuff is definitely hard to wet out. I do most of my wetting on a piece of cardboard (for tabbing stuff), and find that pouring the resin directly on the material and letting it soak for a while makes life easier. I also find it is easier to wet it out "upside down"--that is, mat side first.

But there's no denying that it is hard to work with in that respect.

As a result, Britton (and others), perhaps consider using more of the 15 oz. material. This stuff wets out very easily, in my experience. It would be easier to install 4 layers of 15 oz. than 3 layers of 24 oz.

bcooke · Post by **bcooke** » Mon Aug 30, 2004 2:58 pm

No, no, no!!! Please!

Well, that sure got your attention!

I haven't learned to like polyester resin yet so I am glad to hear I can leave it on the store shelf. Are there any times when polyester is appropriate?

As for the biaxial cloth, I thought it was used only in non-structural applications but I am glad to be proven wrong again. I was able to tag some 17 ounce biaxial onto an order that was waiting to ship from Jamestown Distributors (should have it tomorrow). It was all they stocked in biax and I thought it would be a good compromise anyway. And yes, I will use 4 or maybe even 5-6 layers just because I like overkill - especially on something doing its part to hold the mast upright.

Anyone need 9 1/2 yards of 1.5 ounce matting?

Thanks to the quick response I won't have to put the project on hold long.
I would never have guessed the logistical requirements needed to keep a boat project moving smoothly...

-Britton

bcooke · Post by **bcooke** » Mon Aug 30, 2004 3:20 pm

And speaking of logistics...

As I was finishing up that last post I heard a thump at the door. My balsa coring for the cockpit sole finally arrived! I was especially surprised to find the box contained a foam product that I think is Airlite B-5.00 instead of the balsa. Now this foam is twice as expensive as the balsa and I was charged the balsa rate. Any problems with using the foam coring instead?

-B

Post by **Tim** » Mon Aug 30, 2004 5:17 pm

The foam should work out fine, I think. I don't know much about the Airlite, but from a quick look online it seems more than suitable for the intended task. As long as you were charged for a cheaper product, then I'd just use it rather than deal with the hassle of returns and hoping for the right product next time.

Are there any times when polyester is appropriate?

Polyester is used in boatbuilding because it is inexpensive, flexible in its use and catalyzation, and fast-curing. It works relatively well in new construction of a solid laminate where there is no call for adhesive, secondary bonding applications. It is a poor choice for repairs because all repairs are, by nature, secondary bonding applications, and the polyester simply will not bond very strongly with underlying material. Polyester bonds very poorly to wood products, like plywood and balsa core--at least using old-fashioned lamination techniques.

A fast-curing putty made from polyester can have use sometimes, merely as a temporary measure to hold something tightly in place before installing the real reinforcement. Because you can vary the amount of catalyst in a polyester matrix as much as you want, you can create resin that kicks off in mere minutes, which does have a use sometimes. But in my opinion, polyester has no place in a repair shop, other than the limited use described above.

Speaking of which: where are you doing your boatwork? How are the working conditions?

bcooke · Post by **bcooke** » Mon Aug 30, 2004 5:44 pm

Thanks. I will remember that paste trick. I might have tried it when setting the knees in place. As it was, I had to screw in a couple of blocks and secure some braces while the thickened epoxy kicked off.

Green's Point Boatyard in Ipswich MA. A hole in the wall storage yard on the edge of the marsh. The latest WoodenBoat magazine did an article about a boat that just launched out of there - a famous folkboat. I am outdoors which means every project is fitted around the latest weather report. The view from the deck is nice though. I was outbid at the last minute for some covered storage but I am still trying to get myself in. Then again taking my trailersailor to the Keys when it gets too cold is an interesting option too...

-B.

Post by **Tim** » Mon Aug 30, 2004 5:51 pm

Don't overlook the utility of a hot glue gun either, in place of and in addition to the putty thing. I use the hot glue for all sorts of temporary tacking im place. It's terrific for all that. Just don't get the glue on you--yeeeow! They're not kidding when they say "hot" glue gun!

Dave, 397 · Post by **Dave, 397** » Mon Aug 30, 2004 6:17 pm

There is nothing quite so cheerily thriling as coating a piece of foam rubber about 3" x 3" or so with hot melt glue (AKA some kind of molten plastic) and then fumbling it. Reflex is to try and clasp at it, which can do an excellent job of coating the fingertips and thumb (cuticles included) on the offendingly reactionary hand with molten plastic. Tim's not kidding...this stuff can BURN you!

Best,
Scratchy Sawzall