How to install a window sill

This article is about how to install a window sill, in order to add style and character to your house. Generally speaking, there are may types of window sills: sills made of wood, typical for American houses, granite sills for homes with a classical design or PVC sills, which have gained market share, due to their low price and long-term durability. Nevertheless, in this project we will show our method of installing a PVC window sill. This is not a heavy duty project, so you should be able to do it by yourself, provided you pay attention to safety regulations and follow our guidelines. Nevertheless, before installing the window sill, you should consider several key aspects.

If you are replacing an old sill, you have to make sure the surface is free of dust and residues, otherwise the adhesive won’t bond the materials properly. When buying the window sill, you have to choose the type that best suits your needs and tastes. In other words, the material of the sill must fit with the rest of the room and add value to your home. A PVC sill has a modern look,  is cheap, easy to maintain, durable and comes in any dimension you might want. On the other hand, the granite sill is much more expensive and comes in several standard dimensions. It is possible to order a customized window sill, but it will cost a little fortune.

You should secure the PVC window sill, according to the base surface. Consequently, if you have to install a wooden sill on a wooden surface, you can fix it with nails. On the other hand, a PVC window sill has to be glued with adhesive or mortar. After you attach the PVC sill into place, you have to place several heavy items on to, as to enhance the bond with the base surface.


Made from this plan



In order to install a PVC window sill, you need the following:




  • Use a smart setup for precision cutting of the sill board
  • Make sure you seal the window using acrylic sealant




Preparing the surface before installing the window sill

PVC window sill

As we have already said, in this article we will show you how to install an interior PVC window sill. Although, we are accustomed to installing wood sills, in this article we fit a PVC window sill. In the image you can see a white PVC window sill, but you should remember that you can choose from a large variety of colors.

Smart Tip: Measure the base of the window sill, as to buy the right sill for your needs. Some stores cut the boards at the needed length, as others sell them at several standard lengths.


Base surface before installing window sill

Next, you have to prepare the base surface before proceeding to the actual installation of the window sill. Consequently, use a spirit level to check if of the base is level. If you face several issues with the surface, you have to make it straight using mortar or self leveling compound.

Smart Tip: Clean thoroughly the surface, as to remove the dust and other residues. In addition, the surface should be completely dry and without grease.


Applying adhesive to the surface before installing the window sill

After you have leveled the base surface, it is time to apply the adhesive as to be able to fix the PVC window sill. Therefore, you have to lay the adhesive in straight lines, every 2”/5 cm or so, as to lock firmly the sill into position.

Smart Tip: Try to apply the adhesive as uniformly as possible, otherwise the window sill might detach from the base surface.


Applying adhesive on the whole surface

In this image, you can see the way we have applied adhesive on the concrete surface. You should remember that the adhesive beads have to be spaced from each other when installing the sill and they shouldn’t overlay. This is a key aspect, as the adhesive needs air in order to dry out.

Smart Tip: If you want to protect the coat of paint on the wall, install paper tape on the edges of the base surface.



Installing the  PVC window sill

Using tape measurement and L-square to mark the cut

Next, we have to cut the PVC sill to the proper dimension, as to fit inside the window frame. If you managed to buy the PVC sill at the needed length, then you should skip this step.

First we have to measure the base surface, using a tape measurement. Next, we use a L-square as to draw a straight mark on the PVC sill, at the appropriate length.

Cutting the window sill

Afterwards, we used a special setup, in order to obtain a professional cut. Therefore, we used two C-clamps to lock a straight board,over the PVC sill. You should notice that, the blade of the jigsaw is exactly over the drawn line, at both ends.

Smart Tip: After you make sure the setup is firmly locked into position, you can make the cut, using a fine tooth  blade . The second board will guide you, as to perform a precision cut.


Installing the window sill

Then, you have to attach the PVC window sill over the adhesive. First, make sure the sill is properly aligned with all the four corners. Next, use a level to check if the PVC window sill is perfectly horizontal.

Smart Tip: Push hard on the PVC window sill, as to make sure it will  get glued properly to the base surface. Remember that you have to apply the pressure uniformly, over the whole area for at least 5 minutes. You can place several water bottles on top of it, just make sure you don’t scratch the sill.


Pvc window sill

If the window frame is narrow, then you can choose to cut the PVC sill as in the image. Therefore, you have to notch the ends of the PVC sill so the section between the jambs fits against the window.

First, you have to cut the sill (the width of the window + 5” on each side). Next, center the PVC sill on the window and mark the ends of the window frame on it. Last but not least, use an L-square to mark the depth of the notches on the sill and cut them with a jigsaw.

Caulking around window sill

The last step of installing the window sill is to caulk the gap between the window and the PVC sill. Caulking is essential, as it gives a neat look to your windows and insulates properly the room, as to save energy during winter. Use a waterproof sealant, and make sure you  apply it on a continuous bead, without leaving any space between the line of caulk.

Smart Tip: Use paper tape to mask the window sill, as to avoid getting it dirty with silicone.



Thank you for reading our article on how to install a PVC window sill and we recommend you to check out the rest of our indoor projects. Please share our projects with your friends, by using the social media widgets.

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