[windowrepairguy]

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.

 

[windowrepairguy]

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!