Hi all, i have just made my 1st tool using woven glass. The tool has come out with lots of voids in it and its almost too poor to fill and sand. I bought easy composites epoxy tooling gelcoat. After applying the gelcoat i used an LY epoxy resin and woven glass. I really arent sure why its come out as bad as it has. I sanded my part down with wet and dry to start with then applied several layers of meguiars wax whilst also rubbing off. I then applied a coat of easy composites pva release. Then i applied the tooling gel coat with a brush........ i just let the gel coat get to a tack before applying my epoxy resin and woven glass. Should i have applied the gel coat and let it go hard before doing anything else or should i have also applied some chop strand mat after i applied the tooling gel coat and then let the whole thing go hard? Thanks in advance

Did you apply the first layer of glass on its own or immediately put all the reinforcing layers on top?  If the latter, then I would suggest this is the problem.  I have had several molds go like this if I try and do things too quickly.

some pictures would help indeed

Matthieu Libeert
Founder MAT2 Composites X Sports
website: www.mat2composites.com

Hello Wacker,

Using woven glass is a perfectly fine and acceptable way to make molds.
Unfortunately wet layup isn't as easy as it sounds, there are many things that can go wrong. Your description is insufficient to pinpoint the specific problems, a few pictures might indeed help. I can only assume what went wrong, probably the mistakes that most beginners make.

I find that woven glass can sometimes be very prone to trapping air, when wetted, and chopped strand can be very stiff to get around tight radiuses and smaller details, so for almost all small parts wit a lot of "contour" i use the EC "Epoxy putty"   its just so easy to work with..

For medium sized moulds with a lot of detail I also use the putty, but just as a first layer, maybe down to 5 mm thickness.. that way you can even out the sharper details. When the putty has hardened, I add reinforcement using woven  glass, or CF cut -offs ... the putty cures to a very rough surface, that you can just wet-lay more reinforcement onto.

Chopped strand works really well with larger parts, and once the contact layer closest to the tooling gelcoat is void free, the follow up layers are not that critical, a few voids in the top layers of chopped strand  are not critical, but I work hard with the rollers e.t.c. to get rid of them.


 

"Sapere Aude"... Dare to KNOW!

The written word is the only truly efficient vehicle for transmitting a complex concept from mind to mind...

103% of all people do not understand statistics...

Do not adjust our mind, theres a fault in reality :-)

You don't mention what weight woven cloth you used, if it was a heavy weight one then this is probably the issue. Woven cloths are much harder to wet out and conform to profiles/contours without practice/experience. With CSM the fibres are short and in random directions so when wetted thoroughly will conform much better. Just remember as you are using epoxy resin it will have to be powder not emulsion bound CSM.
The epoxy putty is basically chopped glass in epoxy resin anyway so yo can make your own. Shred some glass and mix it with the resin to form a paste.

Carbon Copies Ltd

Wozza's right ... heavier woven cloth is harder to work with.

If I'm not using the putty, i normally cut up the Chopped strand into long narrow strips, or rip it apart in little patches, that makes it much easier to work with.

The powder bound Chopped strand takes a while to soften up / dissolve to leave the mat workable, a lot longer in my experience than emulsion bound in Polyester.

Has anyone seen this as well ?


Oh... plain forgot ... I always use 2 coats of Epoxy tooling gelcoat .. let the first cure to "soft tack" ..   That way you can avoid "thin spots" in the Gelcoat.

"Sapere Aude"... Dare to KNOW!

The written word is the only truly efficient vehicle for transmitting a complex concept from mind to mind...

103% of all people do not understand statistics...

Do not adjust our mind, theres a fault in reality :-)

After the tooling gelcoat, as already said ideally applied in 2 layers, fill all the sharp corners and edges with flox because the glass will never go into them properly. Let the gelcoat layers harden enough so that the glass won't sink in and will later show up on the mold surface, but don't wait too long either. Before applying a first glass layer of lightweight cloth paint everything with thickened epoxy so you will get a chemical bond. First layer should be lightweight glass, the following layers successively heavier. Ideally the layup schedule should be symmetrical and quasiisotropic (0/90 and +/-45°). If done right this will result in dimensionally stable molds without telegraphing of the fibers (the weave pattern showing up on the surface).