mdf+concrete ?

[ShinOBIWAN]

Originally posted by cyclotronguy
You add % of PVA to supplant the water, not replace. Very common in construction to bond new concrete to old or to make for waterproof concrete.

Yep, pinkmouse suggested the same thing. I've yet to try it but I can imagine it works.

[johninCR]

PVA + concrete sounds like an old wives' tale, but maybe it works to some extent. There's a special epoxy based resin for bonding new concrete to old. It's about the consistency of latex paint when mixed. I used that for creating the final bends of concrete in a Fostex 108Esigma horn. I felt this was a good option to bond the concrete to the plywood (along with screw heads imbedded in the concrete for security) and prevent the water in the uncured concrete from soaking into the plywood resulting in problematic expansion right off the bat. I still maintain that even 1/4" of concrete is simply too brittle to be of any benefit except maybe as a constrained layer.

[deaf monkey]

I've been experimenting with the acrylic gap sealant you get from builder's supply shops. Very cheap. Comes in big tubes. You mix this with builder's sand and a bit of water and you have a very flexible, dense, water-based medium which will stick to anything. You can trowel it on, give it texture etc - may be worth a try.

[noah katz]

jackinnj ,

So howeffective iwas it in keeping the panels from vibrating?

"I still maintain that even 1/4" of concrete is simply too brittle to be of any benefit except maybe as a constrained layer."

If you mean constrained layer damping, it sure won't work for that.

The constrained layer needs to be viscoelastic, i.e., gummy,sticky, lossy, etc.

[johninCR]

Originally posted by noah katz
jackinnj ,

So howeffective iwas it in keeping the panels from vibrating?

"I still maintain that even 1/4" of concrete is simply too brittle to be of any benefit except maybe as a constrained layer."

If you mean constrained layer damping, it sure won't work for that.

The constrained layer needs to be viscoelastic, i.e., gummy,sticky, lossy, etc.

Sorry, "Sandwiched layer" is more appropriate.