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Maryland
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Discussion Starter · #1 ·
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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Maryland
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Discussion Starter · #3 ·
We have several cans of Great Stuff foam for doors and windows. Would this be considered closed cell? So you would spray the foam in and then re-apply the inside trim/stops? Backer rod and caulk are unnecessary?
 

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Home Performance
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1,542 Posts
We have several cans of Great Stuff foam for doors and windows. Would this be considered closed cell? So you would spray the foam in and then re-apply the inside trim/stops? Backer rod and caulk are unnecessary?
You got it. .... I'd only clarify that a solid, continuous bead of the foam is necessary, as is exterior caulking.
 

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Window Repair Guy
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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?

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.
 

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DAP foam is a good non expanding foam for windows.

I hate to correct people that seem to know what they are talking about, but silicone is not a good choice with anything vinyl. Silicone does not stick to vinyl. Siliconized latex is better than silicone for sealing to the old stops. DAP has products rated at 35-50 yrs., OSI is another good brand.
 

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Window Repair Guy
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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!
 

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Maryland
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413 Posts
Discussion Starter · #8 ·
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.
 

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Home Performance
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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.
 

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Maryland
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413 Posts
Discussion Starter · #10 · (Edited)
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.
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!
 

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Home Performance
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The sill is insulated with foam from the exterior prior to installing the sill angle. The silicone on the backside of the blindstop is really just a wasted step if foam is used, but thats your choice. The rest of your products and usage seem just about right.
 

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Maryland
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413 Posts
Discussion Starter · #12 ·
Really dumb question... when applying the OSI Quad, do you leave the bead alone or do you smooth it out with your finger? I've been finding it difficult to get a nice consistent bead, but I'm sure that comes with practice.
 

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Really dumb question... when applying the OSI Quad, do you leave the bead alone or do you smooth it out with your finger? I've been finding it difficult to get a nice consistent bead, but I'm sure that comes with practice.
The bead has to look good too. If you can’t get it with the gun alone then smooth it out. Have a rag and paint thinner on hand for clean up.
 

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Home Performance
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Quad has some "self-leveling" characteristics, so just try to get it straight. It is one of the easiest caulks to lay a nice bead imo... If you do have to tool it with your finger, make sure you lubricate your finger somehow so it doesnt just stick. Most pros just lick their finger, but there are some pretty nasty chemicals in quad so do that at your own risk.
 

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Maryland
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413 Posts
Discussion Starter · #17 ·
Lots of great ideas, thanks a million! I'm making up some "test corners" out of 1x scraps to try out the different techniques and see what works best for me. Practice will hopefully make perfect.
 

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Home Performance
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Lots of great ideas, thanks a million! I'm making up some "test corners" out of 1x scraps to try out the different techniques and see what works best for me. Practice will hopefully make perfect.
Good idea... Lastly, I'd recommend buying yourself a halfway decent caulk gun, and don't be afraid to pick up some speed as you lay the bead. The key is matching the pressure that you are squeezing with the speed that you move the gun. If you try to be too careful and go to slow, you'll have no chance. That is the #1 mistake that I see.
 
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