TOPIC: Ok, now I am really confused!

I went to our local fiberglass store today to pick up the epoxy, cloth, mat and other assorted bits I will require to do the new transom and floor in the Red Fish. Everything I have read thus far - including Jamil's instructions - say to lay down a schedule of mat, cloth, mat, cloth, mat. The guy at the store insists that you are
not use chopped matting with epoxy. He says you use mat with polyester resin and that I should only use cloth with epoxy. Now I am confused. HELP (please).
Andrew

You use a layer of cloth or mat between the skin and the plywood. Then another layer between that plywood and the next plywood if you are using more than one.

I don't think it matters if you use cloth or mat, it's just used to help bond the dissimilar materials together. Epoxy is definitely the right stuff.

If it's a curved transom, you can use 1/4 inch ply layers.

The binder in chopped strand mat dissolves in polyester and vinylester resin systems, since they contain styrene which dissolves the binder.
Epoxy does not contain styrene, that's why you don't use csm with epoxy.
The guy at the counter is correct.
Will it work? Might, you could try a test patch, but csm is not necessary with epoxy.
Go download the System Three Epoxy Book at their site and I believe it addresses this very subject.

Thanks for the replies guys. I did a bit more reading and found the answer that coincides with the way I was thinking of going. I will use the CSM with the epoxy even though it may not necessarily be the right product for the epoxy resin. I think the CSM's superior barrier properties outway any negatives.

www.westsystem.com/ss/chopped-strand-mat-epoxy/

So here is the schedule I am thinking of using:

1. Outer skin
2. mat
3. new transom
4. mat
5. cloth
6. mat
7. cloth
8. mat

Any thoughts?

Andrew

What thickness is the cloth? Ie, is it 1708 biaxial or 6 oz woven, etc.?

How thick is the wood for the new transom? What type of wood are you using?

Andrew,

That is NOT how you build a transom using Epoxy!!! You do NOT use CSM with epoxy for exactly the reasons stated by "billr". It is a waste of money and can actually weaken the bond of the epoxy. When gluing two layers of wood together with epoxy you do not NEED to use anything other than the epoxy. The PROPER method for installing a transom is to use THICKENED epoxy using Cabosil and chopped glass fibers mixed to the consistency of Creamy Peanut butter and trowel it onto the outer skin of the hull AND onto the New Wood Transom. Then Clamp it together. I use some special made clamps to accomplish the clamping. I like to drill some 1/2" relief holes in the transom to allow air to escape during clamping ensuring no air pockets form between the wood and the hull. The resin will fill these holes. The resin will squeeze out around all the sides and edges and a Large plastic spoon dipped in Mineral Spirits can be used to cove the resin to the sides and bottom of the hull.

Thanks for that Mr Flamingo. I am totally clear on that aspect now.

The finished thickness of the original transom was 1.75"
I am using marine grade plywood 3/4" X 2. The outer hull is about 1/8" thick, so this leaves me with about 1/8" to make up for the inner skin.

Now I am still a bit unsure of what weight of cloth to use, and was planning to talk it over with the fiberglass store guy.

Boy, this sure has been a learning curve for me. And I have not even ripped out the deck yet. LOL. I want to get this right, as I plan on restoring this old girl back to near showroom condition. ...hence all of my annoying newbe questions.

So you all generally use cloth only when installing transoms with epoxy?
What about all the hype behind using mat as the outermost layer to protect against water intrusion?

Cheers,
Andrew

Absolutely use Mat to finish the inner layer and tab the transom to the sides, and bottom of the hull. Two layers of 17oz is what I'd recommend with the first having a 4 " overlap and the last a 8 to 10" overlap. You do NOT have to use epoxy, you know! The boat is made from Polyester Resin and it is totally acceptable to use this to repair it. Lot's cheaper!!!

The purpose of cloth is to be used on top of mat to allow you to work the air bubbles out without tearing the mat. It's not absolutly nessecary to use cloth, but it makes for a nice finish. There is no structural strength to cloth by itself. If you were to apply layer upon layer, like in helmet construction, then yes it's tough as nails. In boat lamination, it's to work the air out, or used for cosmetic reason over the mat. Some cloth, like deck cloth, is used on top of a wood deck hull but only to seal it, not for any strength. On some of the lighter race hulls we did at Rogers and a few others, as soon as the air is squeegeed out the cloth was removed for less weight.

In boat construction 3 oz mat is used to install the transom wood to the transom. 3oz on the wood and then 3oz on the transom, wet both out, roll out bubbles and clamp. No cloth is needed when bonding the wood in place. Only after the resin's kicked and the clamps have been removed can will you use the mat/cloth combo. I've never in my life seen 17 oz mat. Must be something new but in boat construction the sides of a typical 18-19 foot jet hull total about 8-9oz of thickness. Less on the boats messed with by owners on this site. The boats built in the 50's and early 60's are sometime tissue thin, 3 oz sides.

Never use cabosil to install wood in a transom, it becomes brittle and has no strength like mat does. It's fine for filling small voids like the bonding surface on the transom which must be absolutely flat, or repair work but not for major bonding.

When using several layers of mat, like filing a crack, or changing the shape of the bottom, fray the edges of the mat. Tear off about 1/2 with your thumb and finger so the ends look like wild hairs, not the factory straight edge. When you do this the edges disappear once you start laminating the layers in place. A hard edge will leave a ridge.


I can't stand using epoxy resin.

Just so we're all on the same page...
cloth


mat

MyFlamingo wrote:

Absolutely use Mat to finish the inner layer and tab the transom to the sides, and bottom of the hull. Two layers of 17oz is what I'd recommend with the first having a 4 " overlap and the last a 8 to 10" overlap. You do NOT have to use epoxy, you know! The boat is made from Polyester Resin and it is totally acceptable to use this to repair it. Lot's cheaper!!!

MY BAD!!! I meant use 17 oz CLOTH!!!! NOT Mat!!!!

MyFlamingo wrote:

MY BAD!!! I meant use 17 oz CLOTH!!!! NOT Mat!!!!

Oh, I just thought I was out of the loop. My kids say I am all the time.

After almost driving myself mad with research and differing opinions on the matter, I have purchased the Polyester product (for less than a third of the price of Epoxy I might add). I plan on filling the bolt holes and cutting the transom this weekend.
Wish me luck...

Good luck Andrew, I'm right beside you on the learning curve (and madness) on this! We'll get there with a lot of help from our friends.

I have attached some drawings on how I recommend building Transoms, Stringers and decks using Polyester Resin. The major drawback in using polyester resin is the STINK. It is NOT NASAL Friendly and if you are working inside then proper ventilation IS required. I use MDO plywood or Regular Ext Grade Plywood for my Transoms, Stringers and Decks.I use 1.5oz Chopped Strand Mat and 1708 Biaxial Cloth. I use Cabosil and 1/4" milled fibers to make my thickened resin and mix it to the consistency of Creamy Peanut Butter. I also use PL Construction Adhesive to Bed my Stringers. I use 1/4" spacers to hold the stringers off the hull while the PL cures for 48 to 72 hours and then remove the spacers. I then use thickened resin to cove the stringers to the hull. I use a full face respirator to protect me from the fumes and dust. I wear a full cover Tyvek suit when grinding. I use a Porter Cable 4 1/2" grinder with a BackupPad and 34grit Sanding discs for quick removal of material. Sawzall, Circular Saw, Hammer, chisels, etc....

Hope this helps.


Transom

(Click the pic to enlarge)





Stringers and Deck