Friday, September 21, 2012

Cutting Fiberglass Batts

Here is the best tool I have found for cutting fiberglass insulation batts:

Victorinox 12-Inch Wavy Edge BreadKnife, Rosewood Handle
by Forschner, Victorinox, Swiss Army Brands.

Use it for cutting Rockwool batts, too. They cut best with a long knife. Taping knives sold as usable with insulation batts and always inferior, are useless with Rockwool.

I found mine among quality knives at  a locksmith shop, and have used it for six years with complete satisfaction, never dulling. It is twice as hefty as my previous choice, a standard bread knife. I like to cut against decking plywood when I can, not leaving a score with the dull knife tip. I measure length or width by tape measure, always to over-fill a space. End cuts are always by eye upon measure. A length cut is often guided by some slot or by an edge over-hang. Cut full-depth without compression, or angle across the batt; an initial accurate lineup is easy to maintain.

Anyone may readily buy one from Kerekes, Item 40146, at price $56 just now. 

This knife will not cut cotton batts, which are best put down whole. Even a sharp hand saw struggles with batt tie threads, making a mess. The irregular cotton batts, not compressible, demand periodic fill-in with easily-cut fiberglass batts.

Basement wall insulation, to be tucked over half-buried heating ducts, is sliced with large scissors, following a drywall square.


Anonymous said...

I've always read that basement wall insulation should be semi permeable to water vapor, allowing the wall assembly to dry to the interior,... but I don't recall ever reading why.

insulated plasterboards
Plaster board laminates

Phil Norman said...

Hello carrytim,

I believe you are correct to want semi permeable basement wall insulation. Your links to Styroliner products guide a better choice than the material I lay over heat ducts. I will stop calling it Basement Wall Insulation. The material in my photo is a substitute of the Johns Manville product with the name I used.