adhesive for foam

[Kevin6q]

Hello All,

I have a project (part of a boat hull) where I need to keep several layers of foam together and hotwire the stack. The pieces need to remain together after the cut. The setup requires the adhesive to be cut with minimal interference of the wire. I have used 3M77 spray but it doesn't work too well since the foam surface is not planar. The foam absorbs too much energy for effective clamping. Polyurethane glue holds the foam together fine but doesn't cut very well.

 

Foam billets are not large enough so they are out. I'm hoping the hotwire experts can help. Thanks, Kevin

[Waiter]

Wooden dowels are used in numerious places to hold pies together during hot wire. The dowels then act as guide pins when the foam pieces are ultimately bonded together (using micro).

 

The bonding "glue" used to bond foam cores together in a LongEZ is a medium thickness slurry made up of glass balloons and epoxy.

 

Waiter

[HardKnox]

Try 'Great Stuff' from Home Depot - it is expanding foam insulation in a can. I understand it is hotwireable. I have not used it yet, however.

[Kevin6q]

Thanks guys,

The dowels won't be feasible. The finished part is rather complex and

only 3/4" thick. It'd be very difficult to place the dowels. I'm

pretty familiar with the construction of the hotwired aircraft. The

Great Stuff might have the same rub as the poly glue. The poly glue

cuts fine but at a different rate than the blue foam. The glue is

slower so the foam melts out, has a larger kerf than the glue, so the

finished part is rather scalloped or has raised ribs which don't sand

out too well. Think of growth rings in soft wood. Keep thinking and

searching the brain cells. I appreciate all of the answers to the

question. Kevin

[brainfart]

Glue the foam with a slurry of epoxy and microballoons or something similar, but don't get any of it on the foam where the cut will be made. The adhesive should hold the foam together but shouldn't interfere with you hotwiring it. Once you are finished with shaping and sanding the foam you can carefully inject epoxy into the joint if necessary and apply micro to the outside.

[rickh]

I think it was John Slade, helping glue up the small blocks for the canopy lip. He tried pour foam, it foamed a bit fast when mixed in a cup. So he used stir sticks. One in Part-A, one in Part-B. Swipe a dollop of each on the block as he laid the foam dominos around the canopy.

 

Not sure how it'll wire cut (toxic fumes too?), but worth a try.

 

Rick

[Kevin6q]

Thanks for all of the suggestions. In the end I took polyurethane glue and diluted the hell out of it with water which also sped up the set time. Mixing the two is akin to getting oil and water to remain together. It works well enough to get the job done. After spreading the diluted glue onto the foam, the stacks of 6 piece blocks were placed into a bag and put under a 28" hg. vac for an hour which applied a lot of even clamp pressure. The diluted glue is more like a bunch of suspended droplets of ploy goo than a continuous film. When cut the disconnected droplets did not form the resistance I spoke of in an earlier post so there were no ridges after cutting.