Sealing Replacement Windows

Pittsville said:

I'm installing a number of vinyl replacement windows and looking for the best practice as far as sealing them. All windows are being installed from the inside.

I'll be laying a bead of acrylic on the outside stops and two beads on the sill when installing the windows. I'll then caulk the stops from the outside. This approach is in line with the mfg recommendations.

Where I could use some advice is on the inside. I was planning on pressing foam backer rod into the side and top gaps and then caulking over top. Its been suggested by a friend of mine that I spray a minimally expanding foam in first, followed by the backer rod and caulk... Which of the approaches will yield the best results? Is there another preferred approach?

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I would consider using 100% Silicone Caulk rather than acrylic caulk. Depending on the substrate you are bonding to, acrylic may not last very long. If you're bonding to brick, use a urethane caulk as the adhesion properties of urethane is perfect for brick. If you’re bonding to vinyl or aluminum siding or even wood, I’d use silicone. It’s more expensive for a reason. As far as the foam insulation, yes it’s a good product but be careful. Even foam products that call themselves low expansion will deflect vinyl window jambs. Go slowly and don’t over fill the cavities. You can always re-apply more if needed but it’s a [email protected] to clean off of walls and vinyl. If you use the foam, you will not need backer rod or caulk for the interior. It’s a great water seal as well. The foam is insanely messy and will stick to your fingers for weeks so USE LATEX GLOVES when working with the foam.

That is just not true. Silicone adheres to vinyl perfectly fine. You may want to tell all the vinyl window manufacturers that currently use silicone to install their insulated glass units into the vinyl sash frames that they are all doing it wrong.

OSI does have a wonderful product and is always a good choice, but is often times difficult for the average homeowner to find locally. It can be pricey as well. Dap has a couple good products, but caulk is not one of them. Other than OSI, GE and DOW are the best choices for caulk when it comes to big box stores.

I understand your concern with silicone and vinyl because you probably heard that from someone and now you may think that's the law, but I've been in this industry for many decades, manufacturing, installing, and glazing and I can say with confidence that silicone DOES indeed adhere to vinyl. It also stands up to the elements better than composite caulks. But to be frank, it's to each his own because there is ZERO consistancy in the window installation and munufacturing world. Most of us use what we know and what we trust.

I certainly don't want to get into a lengthly discussion about which caulk to use because eveyone has their opinion. I'm sure you know what you're doing and so do I. Oddly enough, we both think we're correct. Got to love the USA.

Have a nice day!

I've been using DAP Alex Fast Dry to seal all of the exterior seams (ie: where the blind stops meet the jambs and sill) This product is an acrylic latex caulk plus silicone and is paintable in 40 minutes. Claims to be good for 35 years. Seems to be a decent product.

The manufacturer of these windows suggests applying silicone to the inside of the exterior stops and then pressing the window into it. I assume they're referring to 100% silicone, so I purchased some of GE's product for this task. I'm a little confused about where to use silicone vs. caulk or if they're interchangable. (Assuming the silicone is paintable)

My window is only hitting about 1/8" of the top blind stop, so I'm going to install the head expander to get a larger bonding surface. Any opinions on what to install between the window and expander? Fiberglass insulation? Rigid foam?

The manufacturer recommends leaving two small "breaks" in the silicone bead between the sill adapter and the sill. These breaks are supposed to act as weep holes. I've looked at other manufacturer instructions and most have you completely seal the adapter to the sill and then drill two small holes in the adapter. Which is correct? Are they both correct?

Thanks to everyone for the advice! I will be filling the gaps along the sides with foam only. Foam + backer rod + caulk seemed like major overkill.

HomeSealed said:

Why foam the sides but not the top??? Do not use the head expander, and do not bother trying to caulk that inside edge of the blindstop. Foam all four sides, then caulk the blindstop to the window from the exterior. Practice using the foam a little bit, and you really should make no mess at all. Just make sure that you have the window square, shimmed, and secure prior to foaming, as there won't be much adjustment left after the foam cures... The Alex product that you are using is junk and will probably last a couple years. Home Depot carries OSI Quad which is probably the most commonly used caulk by pros, and for good reason. You might consider hiring someone to come out and cap the exterior for you with aluminum. It would finish off the job nicely.

Click to expand...

Ok, I've decided that the head expander is a PITA, so I agree there. I was going to use it because the window was only making contact with about 1/8" worth of the top blindstop. I've decided instead to cut new stops that are deeper to allow for more like 1/2" worth of contact with the window. The manufacturer suggests applying silicone to the inside edge of the blindstops and then pressing the window into them. Why do you suggest that I NOT follow this instruction?

You mention foaming all four sides. I can easily apply foam to the sides and top, but how the heck would I foam the bottom? :huh: As far as products go, I've taken your advice and started using the OSI Quad for sealing up the outside. Here's what I'm currently using:

OSI Quad Sealant (White) - All exterior sealing including: Seam between blindstop and jamb, seam between blindstop and window and seam between vinyl sill adapter and wood sill.

GE 100% Silicone (Clear) - Sealing between the inside edge of the blindstops and the window. Would another product make more sense here? Is the caulking on the exterior of the blindstops sufficient to make this step unnecessary?

DAP Alex Fast Dry (White) - All interior sealing including: Seam between window and interior stops and the seam between window and stool. I've been caulking the seam at the stool after the window is already installed. Should I lay a bead of something (silicone or caulk) on the edge of the stool before installing the window? Similar to the silicone on the inside edge of the blindstops... Is there another caulk that I should be using inside instead of this one?

DAPtex Door & Window - Insulating around the edges of the windows.

DOW Safetouch R-19 - Insulating the old sash weight bays.

Would you recommend any changes to these products or how they're being used? I'm looking for longevity here, so I'm open to any and all suggestions.

Also, some instructions that I've seen have you lay a bead (or two) of silicone horizontally across the center of the sill prior to installing the window. I tried this and the window doesn't actually make contact with this bead. Is this simply to act as a dam for any water that might make it's way up the sill? Thanks again for all of the great advice!