# best caulking for concrete window sill gaps?



## Arkitexas (Mar 10, 2011)

The best, in my opinion, is Sonneborn's NP-1. It's usually only available through commercial building suppliers so it may be harder to find. In our local commercial work it is a standard. It comes in a moderate range of colors and costs about $5 a tube. It is very long lasting but is also super sticky, so don't get it on anything you don't want it on. Tip: you can smooth it out a little if you first dip your finger in very soapy water - but it is best to get it applied correctly straight out of the nozzle. The instructions say "no primer required", but we always clean and prime the joint first, then add a foam backer rod to control the caulk depth (D= 1/2 the W). 

Rick


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## kwikfishron (Mar 11, 2010)

NP-1 is available at the Orange Store. Vulkem and Quad are also good Polyurethane caulks and are more readily available.

Be sure to have a rag and some mineral spirits close by for clean up when using any of these.


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## wantboost (Nov 1, 2011)

can i use tape to make straight lines


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## dwoloz (Aug 3, 2010)

Sikaflex sounds a lot like what Arkitexas is describing. Has worked well for me


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## Arkitexas (Mar 10, 2011)

Sonneborn NP-1 is a polyurethane caulk and doesn't play well with taped edges like paint does. While wet, polyurethane acts like luke-warm nacho cheese. Once dry, it sticks to tape (or anything else) with a vengeance. It works best if carefully and skillfully installed straight from the tube without subsequent rework. Every time I mess with it after it's in place usually makes matters worse. If you still want to use tape, I recommend that it be pulled shortly after caulking while the sealant is still soft. Don't let much, if any, get onto the tape or it may "string cheese" itself onto the clean surface.

When applying, I make sure I have a lot of illumination on all the surfaces, I go very slow and evenly apply the sealant. I try to make one-shot runs without a letup. 

May the force be with you,
Rick


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