Fibre Glassing

What weight woven cloth would be best to use to make a Marblehead hull and deck moulds? How many layers. I would use polyester resin.

I have 225gr cut fibre, 200gm, 102gm, 85 gm and 25gm woven cloth on hand.

There will be one mould cast from an existing hull, and one from a plug.

The above is all to practice with, first the mould, then a few hulls. When I am confident then CF cloth and good epoxy will be used.

How many layers and what weight cloth combinations would you suggest for hull and decks?

I intend to make modular deck moulds (3). Centre would be mast and controls module, then bow and stern sections to match in. The idea is that I can mix and match deck profiles to suit individual hulls without having a to make a complete deck mould for each boat. It make experimenting easier too.

Hi Devc,
personally I will esclude the 25g and 102g. No problem with polyester resin except that will smell for long due to the styrene. I will prefers the Epoxy resin.
I will start with the 85g on top the first thick coat of Gelcoat. (gelcoat for moulding without paraffin). The gelcoat will be presenting a good smoth finish.
Attention ! if uncorrect gelcoat is used the model will stick for ever.
For the 3 following layers I will use the 200 or 225g Glass Mat, Woven Glass is a luxe . Resin weight as for the Glass.
There is no avantage to use CF for future moulding . Expensive for nothing more.
Multiplex wood beams shall be used to reiforce and stabilise the form .
Of course the model shall be surface treated with good Mold Release Wax. (4 or 5 layers). Modular deck moulds ? why not, but carefull , the overall weight will go up. Window cutouts will be necessary to reduce weight.
Go to this site : and download the Studio 2 History ( at the bottom of the page >> "la storia di un Classe M " - a photo records during construction. Finally I did not used the deck mould.
Here below 3 images of my last (2004) mould preparation. Notice the Edges that will serve to trim the hull with a simple cutter.
Good work

Hi Nevc, I would skip the polyester and go to epoxy to start with, wax the plug first and then sray on a good coat of PVA, after this dry spra a good coat of epoxy primer (automotive), then lay up 2 layers of 6oz CF and 4 layers of 8oz CF, and wood for reenforcement. This is just for the mold, for the hull I would use 3 layers of 6oz CF.

John -

just curious - 18 oz. total cloth weight - plus resin weight for a model boat? Seldom do I go over 8 oz. (2 layers of 4 oz. cloth) and some even then consider it overbuilt. I have since scaled back to one layer of 4 oz. and one layer of 1/2 oz. for general hull layup - with reinforcement layers only where needed.

My opinion is the fabric keeps the water out for most areas of a hull - just use multiple layers where stress it possible - keel, trunk, rudder log area and perhaps near chain plate attachment locations. At 18 oz. I think you are getting close to big boat scantlings. Just an observation/opinion. Your observations or comments appreciated.

Dick, I just checked the cabin cover I just did for my Santa Barara, I used 3 layers of what I thought was 8oz CF it is .050" thick, Gary is using 2 layers of 6oz CF on his hulls .025" thick, I think that is a little light, Are you mopping up the extra epoxy with bath room tissue?

Claudio, thats nice work you do. I have 2 moulds here of similar contruction.

John, I am using the polyester at present, partially due to cost for experimenting, but mostly due to thats whats available here where I live. Also I have not as yet found a CF supplier, so the FG cloth named is the range at hand. I can get good epoxy about 2 hours drive away.

Dick, the layers and weight of cloth used is most interesting. It seems there is a variety of options and it is good to hear them.

What reinforcing do you all use for areas of stress such as mast tubes, keel boxes and points of rigging attachment?

I plan to use 4mm inside diameter CF pipe for rudder tube, and 4mm cf or stainless rod for the rudder post. Any comments?

Thank you all for your input so far

Mould should be roughly 3 times thicker than the part min.

I would typically use 2 layers of 6 oz (200g) woven cloth and epoxy on most of my model boat work.


To all, sorry for any mix up I may have caused, I guess my fingers aren’t hooked to my brain. I’m using FG not CF.

Just for interest, this is the supplier of the good epoxy products I can get, there is good info here to download.

Can anyone give me a supplier for CF cloth suitable for hulls?

The specs I have are 2.5 times the weight of the cloth used for the hull if polyester resin is udes - or equal weight of the cloth used if the quality epoxy is used. What is the opinion on this?

Nev have you downloaded the History of a Class M ?
Many of the questions are answered there.

Hi John -

I have used what I call a “dry-epoxy” technique - using only enough epoxy per layer to wet it out, and cure hard. I do not worry about filling the cloth weave on every layer - and I use a credit card to scrape off any excess resin. This results in a final layup that only requires a final layer of finishing. I have noticed from time to time, that many builders spend countless hours trying to get a glass smooth finish, only to then add another layer of cloth. When done, I “paint” the inside of the hull with thinned (I know, I know) epoxy which will find and seal any pin-holes. This is for a glass only hull. Outside, a coating of epoxy thickened with Microfillers (or talcum powder) in a peanut butter consistency allows me to get a good final surface. I also use a piece of common window glass to scrape the epoxy smooth before going after it with various grades of sandpaper.

On the inside of the hull - I have used uni-directional carbon to run from gunwale to gunwale and across the area where the keel fastens. This allows transfer of stress to the entire hull, and is usually in the same area as my side shroud attachment points. I epoxy a small piece 1/2 inch square of very thin plywood right where the rudder steering tube is located to (again) spread stress over a larger area.

In my big boat days (and hanging around with builders) I picked up on the theory you build it lighter and lighter - until it breaks - then build the next one just a “touch” more robust. If you build a hull at 48 lbs. and then at 46 lbs. and then at 42 lbs. - what is optimum weight? Turns out it could be 36 lbs. A builder from the UK having a similar discussion asked me if I planned to stand on my boats - based on my layup schedule. Since then I have become more watchful of how much I use. I’m talking total weight here - not just thickness (or thinness) of the hull skin. Also, like an egg - when you introduce a curved surface or camber to the hull panels, additional strength is also gained. Finally - in most cases, we aren’t crashing off 40 foot waves in the ocean - so all taken into context and considerations, we all probably overbuild our boats.

I do want to be clear I am suggesting the hulls - NOT the molds. There, strength and rigidity all play an important part to assure quality hull shapes, and multiple uses for many hulls. Thickness, and wood bracing do play an important part in holding a hull in position until it has cured.


Yes I have, but I can only read english so am trying to interpret. Its a good history and the pictures are very easy to follow.

Hi Dick, I think the epoxy primer is the way to go, when the hull comes out of the mold it is ready for paint, (no pin holes) or just leve it in primer, I use white primer and it looks good. I don’t do anything more to the inside, just adds more weight. I use West System slow set epoxy. Used to use polyester but after I started using eoxey I’ll never go back.

That seems to be a tried method that has had good results. Since pretty much all of my hulls are one-offs for design reasons, I haven’t had a need for fooling with molds, polishing and all the other efforts needed.

I do recall someone, posting here (perhaps) that once the mold was waxed, he used simply Krylon paint as a “gel-coat” - with a followup of his cloth layers. When removed, the paint color film was adhered directly to the glass layup. Even though the paint was dry, the epoxy and glass caused it to stick to the hull, but the PVA and mold release alowed paint to leave thehull with the glass. I don’t recall who posted - and if I even got this right - it just sounded like a great idea for minimal thickness of color on hulls.

Evryone that I’ve introduced to Epoxy has thanked me - mainly because they find so much else to use it for around the house - and on other projects. Pass on the good word !