1/2" on top of 1/2 or 5/8 seems to be the ticket.  I Used 1/2"  Screw homasote to plywood and make sure anything on top is not screwed in further than your homasote (no noise/vibration transfer across the 2 media).  Some glue, but if you want to cut in to place a structure, it is easier than chipping out glued pieces from the plywood board.

As for cutting.  The sawing method above works, but I used a dermal saw-Max with a vacuum in the other hand.  No muss, no fuss.

If you do a thorough search on this subject you could write a college dissertation and come out with more questions than you posted here.  It is a somewhat common subject. I think you will be glad you are suing the homasote.


TCA 18-73717

Cut it by hand using an Airway #6 knife.  4 or 5 passes.  Clean no dust.  Cut curves easy.  Replace blades frequently.


This knife uses the #25 straight blade, order them with the knife.  Sometimes at HD.

This is like a box cutter but much thinner and way more sharper.   It has a shaving quality edge on it.   It will not bind up in a deep cut.  Caution:  you can cut a finger to the bone before you feel it enter the skin.  Ask me how I know.


No dust, just a clean cut.   I use a lot of blades.  I love neat crisp edges.


This is one of my TT locations.

Knife and blades available at floor covering supply houses.


Eternity is a long time to have been wrong.


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Tom, Thank you for showing us the Airway #6 knife.  I have been using a straight box cutter/utility knife.  The angle on the handle looks much easier to use!

I hadn’t mentioned I started using a knife instead of a saw, but I agree with Tom, 5 or 6 passes does it.  Make sure to keep fingers out of the way.  No, I do not know from experience.

For Airway hand cutting:

Using A CARPENTER PENCIL OR BALL POINT PEN, draw a fine line with a firm hand to make a slight depression.  Then drag the knife, with a new blade, lightly over the groove which further pronounces it.  Pass a second time and add a little pressure.  Now you have a workable slit. 

Proceed with increasingly firm passes.  If you go out of the slit then reverse direction so as to avoid repeating the error.  After a couple of slices you will have it down pat.

Eternity is a long time to have been wrong.

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