skaha

I am trying to layup a mold for a 1/6 scale beaver, I started with a layer of 2oz followed by a layer of 6oz, I then went to chopped strand matt and ended up with a gooey sticky mess, what am I doing wrong, is there a trick to using the matt? It is also taking a whole lot of epoxy to wet the matt out. What weight matt do you guys use to build up your molds?
Any help would be greatly appreciated.

rcalfred

Some will argue the point, but chopped mat is designed for use with polyester resin. In its raw form it is stiff as a board but the binder relaxes when poly is applied. Others say that epoxy can be used if you wad up the mat before using it. What does the manufacturer say about using it with mat. There was a thread that stated that one manufacturer said not to use it with mat. Regards.

chelapa

I use it fine on ALLL of my molds and it works great. the trick is, goey mess? well u might be mixing your epoxy wrong.


but what i do is, use a very light fiber first with epoxy. and then pull apart the matt from itself in pieces and lay it up layer by layer. i normally do about 3-4 layers. its about 1/2" thick

skaha

Thanks for the replies, I emailed West Systems with the question about using matt, they did not bother to reply, I think I will just use up my epoxy and go back to polyester.

Ed Smith

I would suggest you do not do that. Long after the plug has been removed Polyester molds will still be reacting. They shrink and twist. None of my epoxy molds have done that.

I use mat with epoxy with no problem. As was previously stated screw up the mat before using it makes it soft and pliable. Or separate the layers and apply. Mat will soak up a lot of resin be it epoxy or polyester. The size of your mold will quite easily use a 1/2 to 3/4 gallon of either resin.

Ed S

dclancey

I have had great luck with building up my molds with silica sand and epoxy. It is cheap and easy to use. I mix about a cup of resin and harder, then add enough sand to make it about as thick as mayo. It trowels well around all complex shapes as well. Build up the mold about 1/2 inch thick with this mixture. I have been using this process for many years without any problems of mold shrinking or twisting.

TOMMYSTA

My Feedback: (15)

Tell me more about the silica sand/epoxy method......
Do you prepare the plug any differently than normal? When I say normal I eman waxing with numerous coats and using a release agent on top of that....I'd like to try the sand/epoxy method for a cowl....
How rigid are the molds and how many pulls can you expect after the epoxy/sand has cured..
I'm sure I'll have more questions to come!!!
Thanks
Tom

dclancey

Prepare your plug like normal, wax, PVA etc. then pour the tooling epoxy over the plug about 1/8" thick. This is followed by the thickened sand and epoxy mixture to build up the mold. Hope this helps.

Doug

Ed Smith

Does "Silica Sand" have a more common name? If I was to go to my local builders supply would they know what I was asking for?

Thanks.

Ed S

davidfee

Ed,
I went to my local DIY store and bought "sandbox sand." It has been washed and graded for relatively uniform particle size. As you can imaging, the washing is pretty important. If you wash it yourself, you shoulf bake it in an oven to completely dry it afterwards.

-David

Ed Smith

Thank you David,

I think I will give this a try on my next mold. I will still lay on a couple of layers of cloth over the gelcoat then build up the thickness with the sand method.

Ed S

davidfee

Ed,
Sorry about the typos in my last post. I must have been amped on coffee (or maybe I was too low).

-David

skaha

Doug, I must be missing something here. I went out and bought a 100lb sack of Dolomite sand 35 grain, and mixed epoxy with it to the point of hardly being able to stir it, but it would not stay on the vertical surfaces of my mold. How do you get it to stay put?
Terry

chelapa

u have to make an enclosure

Toomanyplanes

A word of caution here. You need to be sure of the type of epoxy you are using and the cure rate it is designed for. The epoxy sand method will work in layers of compatible thickness with the ambient temperature and type of epoxy you are using. Epoxy DOES shrink but at much less of a percentage than polyester. ALL resins are exothermic and will give off heat when curing. The hotter they cure (faster) the more shrinkage will occur. This can be due to the chemical reaction, the application of an outside heat source, or both. Experimentation is the key before you commit to a full out layup.