# How to insulate gap behind quarter round?



## Rav (Dec 7, 2011)

House built in 1930. Exterior is stone, interior walls are plaster. In certain places there is a good deal of cold air coming in from behind the quarter-round. There is no insulation in the walls which we are quite aware of, but we have chosen not to tackle that at this point. Anyway, I removed a small section of quarter-round next to our front door (see attached pics). There is an about 1/2" gap there where air is coming in. There are two long strips of some sort of fabric with some fuzzy stuff on them going the length of the gap. The fuzzy stuff is disintegrating and coming off. If that was meant to be insulation, it isn't doing anything. Should I remove those strips, and what would be the appropriate material to use to plug that gap? I have Great Stuff foam and I have caulk. I have a feeling that Great Stuff wouldn't be flexible enough to handle normal expansion and contraction, so I'm thinking some backer rod and some kind of flexible latex caulk, but don't know which would be best. Suggestions? Thanks.


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## Dave Sal (Dec 20, 2012)

I would try some backer rod. I'm sure you know it comes in various sizes. You could probably get it large enough where it would fill the gap completely without the need for messy caulk.


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## Rav (Dec 7, 2011)

Dave Sal said:


> I would try some backer rod. I'm sure you know it comes in various sizes. You could probably get it large enough where it would fill the gap completely without the need for messy caulk.


Interesting idea and definitely easier and less messy. But while I'm sure it would stop at least some of the air flow, isn't backer rod air permeable, meaning that at least some air would continue to flow through? Or asked another way, if backer rod can be used to fill gaps completely, why ever caulk over it? Just trying to understand. Thanks.


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## Dave Sal (Dec 20, 2012)

I'd guess that the backer rod alone would reduce the air flow at least 80%. You could also add a strip of plastic sheeting along the gap and place the back rod on top, thereby creating the air barrier. It won't be perfect but it will probably do the job.


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## Bud9051 (Nov 11, 2015)

Backer rod is intended to act as a stop for the caulking. It fits firmly into the gap and allows the caulking to fill and seal the front. But it should stop must of the air leakage if it fits tight and fills the gap. 

My personal choice would be a silicone caulking. Recently did some renovations where I had to remove some 30 year old silicone and it held tight and had remained very flexible. 

Another option would be a layer of tape, but not duck tape (that's another discussion). They often tape the seams of the exterior sheathing and not sure what they use. I had used duct mastic, messy but it brushes on and seals and remaining gaps. Commercial installations then cover the mastic with a fiberglass mesh.

One last comment. When you clean up that area use wet rags and throw them away, just in case that old fiber material contains asbestos. A vac would just blow the fine fibers back into the house.

Bud


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## Rav (Dec 7, 2011)

Bud9051 said:


> Backer rod is intended to act as a stop for the caulking. It fits firmly into the gap and allows the caulking to fill and seal the front. But it should stop must of the air leakage if it fits tight and fills the gap.
> 
> My personal choice would be a silicone caulking. Recently did some renovations where I had to remove some 30 year old silicone and it held tight and had remained very flexible.
> 
> ...


As suggested I may try just tight-fitting backer rod (without caulk) in this one place first, and see how that performs. If it does well enough, I'll leave it at that, since there are other areas I need to do too.

Re possible asbestos, thanks very much for the warning. Unfortunately in order to get good pictures I already did vacuum that area, but it's only about two feet long. I will refrain from cleaning out and vacuuming other areas, and I will just leave those fabric strips where they are. Thanks again.


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