Insulation is a fundamental element in constructions. Unless our walls and ceilings are solid concrete, we have to fill in the space created by the plywood. This is the only way that the wall is resistant, does not allow the entry of insects, and keeps the best temperature. For costs and features, fiberglass is the most popular insulator, but working with it is difficult. If you want to know how to cut fiberglass insulation without accidents, you have reached the right place.

Fiberglass is usually found in spongy fiberglass or glass wool presentations. This is placed in panels inside the walls, avoiding bending as much as possible, or else the thermal resistance of the material is compromised.

In order not to bend it, it is necessary to cut it. However, cutting fiberglass is a risky task if we don’t know how to do it. If you have ever touched fiberglass directly with your hands, you will know that this is one of the worst mistakes you can make, since it will seriously irritate the skin.

As if this were not enough, cutting it is not easy either, because it is a flexible material with thick layers, and comes in long fiberglass insulation rolls. Working with fiberglass is a challenge, but we can make the process suitable for everyone.

Fiberglass hazards

We already indicated it before, but it is good that we remember it before beginning. Fiberglass is a compound made up of tiny glass particles. These will cause skin irritation if we touch it directly.

The particles can also fly through the air, causing an atrocious itching. In the worst case, we could inhale the fiberglass and develop strong allergies and respiratory tract irritations.

If we do not have the appropriate protection measures, it is best not to try to cut fiberglass.

How to cut fiberglass insulation – The right method

Before you begin, you must be sure you have all the necessary tools for cutting insulation. The most important thing (after protection) is the insulation knife. You must have multiple additional blades to replace them each time they are splintered.

To ensure a perfect cut, you need to have a carpentry frame. This will help compress the fiber when cutting, making it easier to slide the knife.

Protection is essential.

We don’t need to wear a full suit to protect ourselves from fiberglass, but it is advisable to wear a long-sleeved shirt and pants to the heels.

The feet can be protected using long socks and tight shoes, preferably sport shoes that you no longer use. A cap is also a good complement to your set.

As for the face, you must have safety glasses with side protection, as well as a mask or dust mask so as not to inhale the fiberglass particles while we cut it.

Find a smooth surface to cut on

If we do not want imperfections when cutting the insulation sheets, we need to rest it on a flat surface.

It is not advisable to do it on ceramics or the like since you will leave cracks with the knife. Concrete is not an option either since it damages the edge of the blade. It is best to use a sheet of plywood or a plastic blanket designed especially for crafts.

The trick of 2×4 plywood

To accelerate the process of cutting fiberglass, we can use a 2 x 4 plywood as a guide. We will simply place the plywood over the fiberglass, and try to cut the fiber with an additional 12 inches.

These measures will be enough to have a constant guide to the fiberglass sheets that we will cut, and it will leave us enough space to be able to rest on it and use it as a press.

Mark the cut lines

Before cutting, it is best to mark each of the cuts we will make. For this, you will have to unwind the fiberglass completely, and with a pencil, draw straight lines on the foil that holds the insulation firm.

Press hard

The plywood sheet must be strongly pressed on the fiberglass to keep it as compressed as possible while cutting it. It is practically impossible to get a precise cut when it is in its spongy form.

There are two ways to do this pressure. The first is with brute force, placing our body weight on the plywood sheet if we are making the cuts on the floor, or using our free hand to exert pressure on the wood in case of working on a table. The second is placing heavy objects on the wood.

How to cut fiberglass insulation with a knife

Place the plywood sheet that we are using to compress the fiberglass on the mark we previously made with a pencil (as if it were a ruler). The blade knife must be exposed at least 2 or 4 inches to cut the fiberglass.

With a firm pulse, place the blade close to the edge of the board and start cutting the fiberglass. Keep the blade as close as possible to a 45-degree angle. If the blade is sharp, a single cut should be enough to separate the sheet.

If our fiberglass includes a decorative coating, make sure it is facing the floor to avoid damaging it.

Before installing the cut sheets, remove excess and imperfections by hand (using gloves).

Adjusting it to strange measures

Although the fiberglass rolls come with the standard measures to adapt to the spaces between beams, we will not get rid of having to cut sheets in special sizes to fill certain places.

An example are the spaces left above a door, above and below a window, or the final corners of a wall.

In these cases, measure the height and width of these spaces and cut a piece of fiberglass insulation that has an additional inch in both directions. This ensures that it fits without being excessively tight.

Last-minute settings

We can perform certain touch-ups once we install the fiberglass on our wall or floor. Just consider that you can scratch the wooden frame if you are not careful.

The positive side is that the beams will work as a rule to accurately cut off excess insulation. In this case, to compress the fiber you must tighten it and fold it in the corner that joins the wall with the floor of your building. Now, just cut along the corner.

However, we remind you that there is no problem if the fiberglass is a little tight, so it is recommended that if the excess is not large, just leave it.

Perform a clean installation

Now that you know how to cut fiberglass insulation, you need to know how to clean it. Dust and particles generated by construction work should be collected using a vacuum cleaner.

The problem is that this is not enough to clean the fiberglass that is floating in the air. For this, it will be necessary to spray water with a sprayer. In this way, the particles will become heavy and fall to the ground.

The clothes you used to install the fiberglass should be washed separately from the rest. Also, after washing, you must clean the washer cylinder to remove glass particles. You will also have to clean the walls of the tub or shower after you bathe.

We have finished protecting our building

Now you are ready to enjoy all the benefits of fiberglass insulation. While its installation can be intimidating, it is still the best material for walls and floors.

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