# Expanding foam to make a mold



## naiku (May 28, 2008)

Is it worth while to try and make a mold using expanding foam? I want to build a fiber glass subwoofer box, but the area I need the box to go into is somewhat of a pain to get inside with any kind of tools. The top half is fine, and easily accessible, but the bottom half is kind of like reaching down into a hole. 

Since I don't want to end up making a huge mess of the back of my car, would it be sensible to use expanding foam to create a mold. I would put plastic sheeting inside the area that I want the box to go, then fill it with expanding foam. Once the foam has set, pull it out, make any adjustments I need to the shape (really just smooth off the front edge where the sub would go) and from there cover the outside of the foam with blue painters tape / foil, put down a layer or 2 of fiberglass, allow that to try enough to hold its shape, remove the foam mold, and then add additional layers to the inside of the box.

I feel like that would be far easier than trying to reach down and into the sides of a 7" wide hole and laying mat and resin in there. Is this a stupid idea? 

Thanks.


----------



## 60ndown (Feb 8, 2007)

most expanding foam ive used wont go hard in big lumps, it stays wet and soft in the middle, if you do it, let small parts of the foam get hard at a time.


----------



## naiku (May 28, 2008)

60ndown said:


> most expanding foam ive used wont go hard in big lumps, it stays wet and soft in the middle, if you do it, let small parts of the foam get hard at a time.


Thanks, how big a lump are you talking? The box I will be building is going to be about 0.5cf. Would you say to do pieces around 6" square at a time? I imagine I could use cardboard pieces to divide up the parts, and then tape them together in order to have a single piece that I can use as a mold. 

Any idea how much foam you can get from one can?


----------



## PorkCereal (Nov 24, 2009)

They do sell sheets of insulation foam at lowes. that might be easier to shave and fit then carboard. And still strong enough to maybe use it as a fiberglass base?


----------



## nineball (Jan 17, 2008)

go to any craft store and buy some floral foam. it's cheap and shapes super easy.


----------



## sqshoestring (Jun 19, 2007)

The latex foam does that it stays sticky in the center. The old stuff does not in my experience, but it can be hard to get it to fill without big bubbles/voids in it. Right I would go with the craft foam. Styrofoam can also be a good one for that.


----------



## naiku (May 28, 2008)

nineball said:


> go to any craft store and buy some floral foam. it's cheap and shapes super easy.


Is that stuff not in blocks though? Although if they have a block that is big enough it could work, as I could slowly start sanding/shaping it until it fits where I need it to go, and then use that as the mold for the fiberglass. I don't think that I can find a block big enough though, I would need something that starts around 18" x 13" x 8" to work with. 

I imagine a big advantage with that foam as well is that it is already pretty solid as well as being easy to shape.

Now I am wondering if finding some chicken wire is probably easier/cheaper.


----------



## nineball (Jan 17, 2008)

yes it is sold in blocks. all you have to do is glue a few of them together and then do a rough shaping on it, stick it in your area and then trim as needed. they do make larger blocks as well but they get to be more expensive than the 3 or 4 piece packs.

edit

just found this. for under $7 (4 piece minimum order) you will have more than enough to do your project.

http://www.createforless.com/FloraC...245.aspx?utm_source=googlebase&utm_medium=cse


----------



## naiku (May 28, 2008)

nineball said:


> yes it is sold in blocks. all you have to do is glue a few of them together and then do a rough shaping on it, stick it in your area and then trim as needed. they do make larger blocks as well but they get to be more expensive than the 3 or 4 piece packs.
> 
> edit
> 
> ...


Great, thanks, figured gluing a few of them together would also work.


----------



## jimbno1 (Apr 14, 2008)

I was considering using this to make a mold in the kicks them FG over the top. Not sure if it would do the trick but it could save some taping and allow to work outside the vehicle. 

Amaco Wireform Mesh - BLICK art materials


----------



## naiku (May 28, 2008)

That stuff looks pretty good, and would probably add a good bit of strength to the box as well.


----------



## nineball (Jan 17, 2008)

that won't really add anything to the glass. build up your layers and you will not have problems with flexing or strength.


----------



## naiku (May 28, 2008)

You are probably right, I think I am just getting impatient to get this done. I wish I could afford to head out today, pick up all the supplies I need (not only for the box, but also a mono amp and wires) and spend the weekend installing everything.

Every time I look in my closet and see various things sitting there it bugs me.


----------

