# Cutting Roxul



## rightit (Mar 5, 2011)

I'm installing Roxul and have found a need to cut some R-23 (5.5") batts down the length to insulated the offset cavities in a staggered wall. To clarify, I'll be cutting so that I end up with a 3.5" batt and a 2" batt, retaining the original 15'x47". The wall is 20' long.

An 8" bread knife works great so far, but I'd like a 16" blade for this operation to make the cut as neat as possible and avoid 'the crumbles'.

The only problem is that they're not to be found locally, and it will be next week before I can get one delivered (unless I want to pay $70 for next day air for a $6 bread knife).

Any suggestions for another tool? I think even a fine cut saw would be prone to ripping and increase the dust output.

Thanks for any ideas.


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## ttech (Sep 18, 2008)

How about a blade from a bow saw. Use only the blade and wrap and end with duct tape to make a handle. The big box stores seem to call them pruning saws.


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## rightit (Mar 5, 2011)

ttech said:


> How about a blade from a bow saw. Use only the blade and wrap and end with duct tape to make a handle. The big box stores seem to call them pruning saws.


Hi ttech. Thanks for the input, but it's too 'toothy' and will create more dust and possibly damage the insulation. This stuff will crumble under the wrong conditions.

I guess the closest I could get would be a hacksaw blade, but in 16", I'm looking at 10 to 16 TPI. Again, too toothy (just tried it with a sawzall blade.

I guess I'll just have to order the 16" bread knife and move onto something else while I wait for it to arrive. Thanks again.


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## Fix'n it (Mar 12, 2012)

i have heard these work very well.
http://www.google.com/search?hl=en&....,cf.osb&fp=ddf43e08a6251ac4&biw=1024&bih=681


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## rightit (Mar 5, 2011)

Fix'n it said:


> i have heard these work very well.


Hi Fix'n it. Thanks for the link. The 8" bread knives I'm using actually work quite well. I was looking for a 16" bread knife to slice the batt into two (i.e., as in separating 2 pages). The upshot is that I ordered the 16" knives this morning and should have them next week. Sometimes patience is the only choice.

The 16" will allow me to slice the batt through from one side rather than slicing twice with an 8". It will also allow me to use the 2 studs on each side of the cavity as a guide for the blade. It should do a much nicer job.

For those in the future who might need a 16" bread knife to cut Roxul:

http://www.plumbersurplus.com/Prod/Oxo-International-89451-16-Bread-Knife-3-Pack/249458/Cat/1488


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## M3 Pete (May 10, 2011)

You realize that is 16" overall length. Not a 16" blade.


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## rightit (Mar 5, 2011)

OK. Back with the "results". As M3 Pete mentions, the knife in the link is 16" overall. Not long enough. I noticed it when I posted the link and was able to cancel the order before shipping. I've actually finished the insulation and discovered that the cleanest cutting method for this circumstance is a grinder sharpened machette. I tried a few different tools, including: 

1. a PVC saw with a high TPI count (the longest I could find...a 15 1/2" cutting edge, but just not long enough)

2. A 26" carpenter's fine cut finish saw (would cut, but damaged insulation)

3. And the winner...the 22" machete. I had to sharpen it with a grinder to make it sharp enough to make a smooth cut, but it worked really well. The 22" length was definitely a necessity. To quicken the process, I put together a cutting box. Below are some images.

I doubt many will find a need to split Roxul in this way, but if so, this method worked well.


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## Pittsville (Jan 8, 2011)

Clever! Thanks for the tip!


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## Fix'n it (Mar 12, 2012)

why did you feel the need for extra insulation ?


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## rightit (Mar 5, 2011)

Fix'n it said:


> why did you feel the need for extra insulation ?


R-value, sound dampening. The top (2") layer was a snap, as I just pressed it in between the new staggered studs. The back 3.5" (original stud cavities) was the bear. Lots of notching and time involved. The R-value of the 5.5" Roxul is R-23. Between that and the staggered studs, the wall assembly R-value should be pretty high.


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## Fix'n it (Mar 12, 2012)

yeah, sounds good. i am doing it to lower my gas bill in the winter.


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