Mold Layup

I finished preparing my mold and layed the glass and epoxy this weekend but think it will be bad. The problem was that I precut the fiberglass cloth an inch wider on all sides and the corners bunched up. Is there a better way to precut and prep the cloth. Should i cut the cloth smaller and use fiberglass tape on the corners?

My mold is actually like a large rectangle, with a 2 degree draft. Any ideas??

 

Not having the most clear picture or what your layup was, I'd ask if you cut the glass at all was you worked it the mold. You can make cuts, or darts, in the corners as needed to get everything to lay all pretty like. Just have a good pair of sheers and clean them off as soon as you're done. Depending on what you are making, some thickened epoxy can help in tricky situations. You can use it sparingly in corners and it has a bit more tack to hold the glass down.

 

Please, take a look at my mold. I heard of maybe fraying the edges of the mat where the corners meet.Also, How long should i wait to remove- used West 106/ slow hardner?

 

Ok after seeing the piece I have a few more thoughts. Please bear in mind It's been awhile since I've glassed anything and there are far more knowledgeable folks here.

My first thought is that your corners may be too sharp for the glass to comfortably wrap around. If possible sand them down or run a router over them to give a larger radius.

In the second photo the glass look dry, that would certainly keep it from staying down. Again rounder corners and a bit of thickened epoxy could help.

Your thought to use tape on the edges may not be a bad idea. This looks like it'll be a cooler or something similar, is that correct.

Finally I'm afraid I'm not sure what you mean by removing the epoxy. If you aren't satisfied with the piece then any time will do I suppose. If you're talking about when the piece will be cured well that depends. I would wait at least overnight. Heat lamps can speed up the cure but don't put them too close to the piece or you could damage it.

Hope that helps.

 

Thanks Jratte. and yes, it's a cooler liner.
I just pulled the part and i was right, a weak gap in the corner where the glass bunched up. Nothing a fillet cant fix. Also, i was amazed of how flimsy the part was. I used two layers of 6oz cloth. Is it possible that i didnt use enough epoxy? I wet it out by brush and then squeegey. Or should i plan on using something heavier, but not quite roving? I plan on making a few of these and would really like it to be durable.

 

It'd be hard to tell from the pics and your description whether or not you had enough resin. You probably want about a 1:1 ratio if memory serves me correctly. You can weigh all the glass you plan to use and mix up that much resin, not necessarily at once. For something like this I would wet out the mold first like you said with a brush, lay the cloth in and smooth it out with a squeegee and cover it with more resin using the squeegee to spread it evenly. Two layers of 6oz may be a little light, not sure. It might have gone for two layers of 12oz, but I've never been accused of under building anything. It may be that it hasn't fully cured yet either. It might still be a good idea to reinforce the edges with tape to provide extra wear resistance and stiffness. Again a lot of this is from memory of working in a composite shop nearly 4 years ago.

 

Agewon, I think that 2 layers of 6oz is on the light side, of course if your gunna stick on some foam & put another 2 layers on the outside it will be stiff enough but have regard for the use of coolers- dropping in bags/blocck of ice & slabs of amber fluid- might be good to put some extra glass on the bottom. Personally I'd lay that in polyester, gelcoat then say2-3 oz of chop strand on the sides, 4on the bottom then 2 maybe 3 mm coremat( cut back from the corners) & 2oz on the outside of that- if your gunna foam(2 part mix) it into another void or box you gotta leave the mold in till the foams fully formed & cured or the sides will push in, 2 degrees of draw angle is pretty tight, 5 is a safer bet but poly needs more in this style(male mold) as it "shrinks" onto & grips the tool- epoxy dont so may be ok but often tooling of this type can be back screwed(with aluminium angle to corners) & dismantled to remove, if you switch to poly use thick sprayed(multi pass) pva over the epoxy fillets you used. Of course if your chasing light weight epoxy & light skins are the go. sometimes if glass wont lay & stick down we'll dust some colloidal silica on & work it with a gloved hand to thicken the resin on the job. All the best from Jeff

 

Thanks guys. i have a few questions.

waikikin- I have a gallon of epoxy so poly is out of the question. I read that wetting chopped mat is not good with epoxy because the glue used to hold the chopped is broken down by styrene which epoxy doesn't have. Will Fiberglass Biaxial Cloth be the same ( FIB-967 BIAXIAL CLOTH 17 OZ, 3/4OZ MAT BACKING) ? Also, i used a few light coats of PVA as a mold release over wax. I saw a few sites that recommend at least 10 light coats to build a heavy film. Which is better? And finally, What would you recommend to use? Please bear in mind that i have around 30 square feet of 6 oz. cloth, and one gallon of West Epoxy. Many thanks.

 

Agewon,, yeah choppy dont go with epoxy too good, you can get it powderbound thats compatible with epoxy but you'll use heaps(2.5 x chop weight per metre 2), it looks like you wanna use current resources to make the box but as you mentioned you want to make a few of these consider the cost of a gallon of west might buy a 5 gallon pail of ortho poly, also if you gelcoat, no need to paint as the finish is included at low cost compared to application of polyurethane. When I use pva, if its for nice I mist coat then shoot a solid coat or two(with interval between shots), if its a quicky job some times I just shoot a quick pass over the modeling clay/putty areas or some times I just sponge wipe it on if I dont want to cloud up my workshop with mist. I'm not familiar with the cloth you mentioned but I've seen some use a similar 600 gram per metre square double bias45/45 with mat stitched to it on epoxy sheathing of timber which looked to go ok but kind of "snotty" looking to work with. unless you want a lightweight box I'd switch to poly cos you want some thickness to acheive stiffness & its heaps cheaper & wets out & sets up quicker in poly, the laminate of 2x 6oz cloth is pretty much whats on the deck of a surfboard which is strong when combined with the bottom laminate but probly wont stand cans etc dropping onto it(just place in gently the're precios cargo). All the best from Jeff

 

OK Fine, I'll switch to poly. However, my source has three types, Laminating , boatyard and finishing. Which should i use, and whats the difference?

 

Agewon, laminating is probably unwaxed & the mos veratile as you can add wax if you want which is probably waxed resin the're calling finishing & boatyard? maybe its an isothalic resin which is more better than orthothalic resin for sub waterline- better ask the doods selling it for confirmation & see if they sell a book on glasswork or some of the resin/glass companys have online guides to their products & process. Regards from Jeff

 

Thanks Jeff, but why don't you just come to New Jersey and help me! Thanks a ton.

 

Agewon, sounds good, just send the fare but then I got a big family & a family business & they like holidays too! Might be cheaper to just have a shot on the learning curve. All the best rom Jeff