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Exterior blow of cellulose in stucco-covered walls?

Gordon Kelley | Posted in General Questions on

We run a weatherization crew and have a project coming up where we have been allotted the funds to do interior installation of dense pack cellulose (including lead safe and interior clean up) of a stucco-clad house (probably 75 years old).

Are there any feasible ways to accomplish this from the exterior? I am willing to consider specialized tools, if necessary. Typically we would do the job from the interior, but on this one, there are too many interior obstacles to do a good, complete job. Any suggestions?


  1. TJ Elder | | #1

    Gordon, cellulose retrofit from the exterior is not uncommon, but you're probably wondering about leaving holes in the stucco. Patching the blow holes would probably never be invisible. Maybe you could turn it into a kind of design feature, by covering a neat horizontal row of holes with a piece of trim, after patching the stucco.

  2. Gordon Kelley | | #2

    Thanks for the design idea. more in question is how todrill the holes, core bore bits?, what about the metal lath/mesh?

  3. James Morgan | | #3

    I'd be very, very careful about using a trim detail to cover exterior stucco patches. For one thing you would have just punched a regular series of holes into the home's WRB (presumably there's a layer of lapped felt behind the metal lath). The trim would create a water table just above these patches, which will be most vulnerable part of the whole wall assembly for water intrusion. Unless you are prepared to let a continuous flashing into the stucco above the trim or otherwise provide for reliable water shedding to the outside be ready for further problems down the road. And just running a caulk gun down the seam is NOT going to be sufficient or reliable.

  4. GBA Editor
    Martin Holladay | | #4

    I'd do the job from the interior -- or be prepared to install a new exterior WRB and new stucco over the entire house.


    Instead of trim to cover outside patched holes, paint an accent stripe. I doubt the patched holes would be an issue with the WRB and or moisture. Dense packing the cellulose and finding every nook is the difficult part.

    Stucco paints wonderfully.

  6. draginfly58 | | #6

    Mr. Kelly, I think that I would probably do a sample spot some where that won't make much difference before I would decide on the best way to do it. If you use one of those carbide grit hole saws they cut through the metal lath without a snag. Then use a regular bi- metal hole saw that is smaller than the hole thru the stucco to bore thru the wood siding and or sheathing.Save the wood plugs if you can or make some out of new wood. You can put some of that expand urethane glue around the plug and stick it in after the cavity is filled enough. then you can stick in a piece of metal lath the size of your first big hole thru the stucco and then patch that bugger up. If you brush a little bit of that masonry bonding stuff around the edge of the old stucco hole everything will stick just fine with no leaks or problems. I would surely do this one from the out side.

  7. draginfly58 | | #7

    You gotta patch and paint inside or out and with all the new lead law stuff doin it on the outside is safer and a whole lot less mess.


    I fully agree with staying away from the lead issue. That alone would cost the homeowner if done to EPA and OSHA procedures some serious pocket green.

    Great posts Mr. Anonymous

  9. Gordon Kelley | | #9

    lot's of input, i appreciate the ideas. i don't think there is a WRB under the lath (poked around a couple existing holes and didn't find any) and lead safe practices are a non-issue (we do them every day), so issue becomes whether client and the agency we do the work for will allow painted wood plugs (while not attractive, cost effecient) and whether we can sufficiently seal the stone stucco to prevent water intrusion.. Unfortunately, the funding we use very seldom allows the ideal remedy to a project like this one.

  10. Gordon Kelley | | #10

    game plan is now in place. we are going to cut out strips of the stucco and metal lath with diamond circular saw (did test today, cut wonderfully) drill through the sheathing and insulate, plug the holes and then fill in the "trenches" with1X cedar (sealed and caulked). intend to cut the strips out in area between window, allowing us to blow both up and down. it also allows us a uniform detail all around the house. will report back when project is complete to let you know if all goes as planned. thanks again for all the input.

  11. James Morgan | | #11

    Sounds like an excellent resolution. Suggest you bevel the top of the cedar with about 5° slope to the exterior just to be on the safe side.

  12. Gordon Kelley | | #12

    Job is complete and here's how it went...we cut 8" wide bands around the house - on the main level at height about 36" AFF (above finished floor) and where necessary on 2nd floor about 24" AFF and beneath windows. This was a balloon framed house so we dense packed wall using a tube to reach height of 9' above holes. Once blown (and with this method we were able to do entire house except in area of walk out bay window - not enough uninsulated wall space to justify the cost/effort and end appearance), we installed 1X cedar boards with about a 5 degree bevel on top into trench caulking where the trim board met the wall sheathing and top dressing it with caulk also. Due to weather conditions (snow/rain/cold temp) used about 45 tubes of high quality LEXAL caulk (at about $5.50/tube!). To cut trenches we used worm-drive saw w/dust muzzle attached to shop vac to catch dust. Saw blades were segmented edge diamond blade (2 ea). Total time and material was about 32 man hours and $800 in materials more than normal for a wood sided house. We were allotted $1000 for the wall prep, so it was not a money maker for us, but we now know that it can feasibly be done, and what we need to add for similar jobs. When considering that we would have only gotten about 75-80% done from the interior, and the mess it would have made, we believe this is certainly a viable option to consider, and with some real forethought, it can end up looking fine.

  13. James Morgan | | #13

    Good job - thanks for the report back. Maybe you'd be willing to share some photographs?

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