3M 71 - Composite Spray Adhesive

Looking for experience with this stuff: composite strength degradation vs application density, actual tack time window vs temperature, bond strength vs application density, gotchas ...

Replacing deck balsa core from underneath. Using 71 to hang flow media on outer skin, then possibly 1/4" balsa to the flow media.

Then new inner skin, peel ply, bag and infusion ...



Super Anarchist
Upside down infusion. What could go wrong until you get the bag under vacuum?

Sorry I don't have any experience with 71 or this technique. But let us know if you fail or succeed because it is an interesting idea.

My first thought was how about a few dots of hot melt glue in strategic spots to hold the balsa in place upside down.

Reading the product description it sounds like just the right stuff for this - if its bond is strong enough. Lots of people use 77 and this might be an evolution of it optimized for composite stacks.

That's my question. If there's no adhesive the composite has all the strength one expects. If there's a continuous layer of adhesive, it's the strength of the adhesive that rules. Reality is somewhere in between. Unless the resin somehow combines/absorbs/dissolves the adhesive. Which would allow the layup to sag ???

My current plan is to apply the 71 with a roller, lightly to one side of the flow media to stick it to the overhead inside of the outer skin. I can't talk myself into attempting to hang the balsa with 711 too. I will apply beads of Six10 parallel to the resin flow on the flow media side of the balsa and stick it up, using tape if necessary, then closing the bag and applying vacuum until the Six10 cures, calculating size of bead vs spacing between beads to achieve ~1/3 fill when compressed to the thickness of the flow media it will extrude thru.

Next, lay up the new inner skin, peel ply, and more flow media. rebag and infuse, keeping a partial vacuum on the resin supply to keep the bag from yielding to gravity when full of resin.