Okay, let's break down your fire caulking challenge and find a better solution than the cardboard-and-prayer method. You're right, there are definitely more efficient and professional ways to tackle large gaps.

Understanding the Challenge Large Gap

This is the key factor. You can't just squirt caulk into a huge void and expect it to work correctly. You need to properly fill the space.

Fire Rating

Whatever method you use must maintain the fire rating of the wall/floor/barrier you're sealing. Using incorrect materials can be disastrous.

Application Skill

Some methods are easier to master than others.

Cost

Different methods have varying costs.

Your Current Method - The Downsides Rockwool

While a good starting point, rockwool alone won't create an airtight or fire-resistant seal. It needs to be combined with a fire-rated sealant.

Tubes of Caulk

For large gaps, this is slow, messy, and expensive. You'll be going through tubes like crazy.

Cardboard Scraps

Not a fire-rated material and won't contribute to the seal. It is just taking up space and preventing proper application of fire stop material.

Better Solutions for Large Gaps

Here's a breakdown of the materials you mentioned and some other options, along with when to use them:1. Fire-Rated Putty/Mortar (Your "Bucket Stuff") Description

This is likely firestop putty or firestop mortar. It usually comes in a bucket or tub. You scoop it out and mold it to fill the gap.

Pros

Excellent for irregular shapes. Good for large gaps. Generally easy to apply (scoop and pack). Can be formed around cables or pipes.

Cons

Can be more expensive than caulk. Requires a bit of practice to get a smooth, professional finish. May shrink slightly as it cures.

When to Use

This is an excellent choice for your situation. It's specifically designed for larger gaps and is relatively easy to work with.

Application

Clean the surfaces. Pack the putty/mortar firmly into the gap, ensuring no voids. Overfill slightly, then smooth it out with a trowel or putty knife. Let it cure according to the manufacturer's instructions.

Example Products

3M Fire Barrier Mortar, STI SpecSeal Putty, Hilti CP 617 Firestop Putty2.

Fire-Rated Bricks/Pillows (Your "Fire Caulking Bricks") Description

These are pre-formed blocks of fire-resistant material. They're often used for larger openings, especially around cable trays or conduit penetrations.

Pros

Fast installation for regular shapes. Can be removed and reused (some types). Good for maintaining access to the penetration.

Cons

Not suitable for irregular shapes. Can be expensive for small quantities. Need to be sized correctly for the gap.

When to Use

More suitable for larger, regular openings with frequent access requirements.

Application

Select the appropriate size. Pack them tightly into the opening. You might still need some fire-rated caulk to seal around the edges.

Example Products

STI SpecSeal Firestop Pillows, Hilti CP 643-N Firestop Blocks3.

Mineral Wool with Fire-Rated Caulk/Sealant Description

This is similar to what you're already doing, but with a focus on properly using the mineral wool.

Pros

Relatively inexpensive. Good for irregular shapes. Mineral wool provides insulation and a backing material.

Cons

More labor-intensive than putty/mortar or bricks. Requires careful application to avoid voids.

When to Use

A good option when budget is a primary concern, or when dealing with very irregular shapes.

Application



Densify the Mineral Wool

Pack the rockwool (or mineral wool) tightly into the gap. Don't just stuff it in loosely. Compress it to provide a solid backing. You can use a blunt tool to help compress it.

Recess the Wool

Leave a 1/2" to 1" recess from the face of the wall/floor on both sides. This is important!

Apply Fire-Rated Caulk/Sealant

Generously apply fire-rated caulk/sealant to both sides, filling the recess completely. Make sure the sealant bonds to the wall and the mineral wool. Smooth the sealant for a neat finish.

Important

Ensure the fire-rated caulk/sealant is compatible with the mineral wool you're using. Check the product specifications.4.

Firestop Spray Description

This is a sprayable coating that expands when exposed to heat.

Pros

Good for covering large areas and complex geometries. Fast application.

Cons

Requires specialized equipment (sprayer). Can be messy. May require multiple coats.

When to Use

Best for large, complex penetrations, or when fireproofing structural steel. Not ideal for a single, simple gap.

Example Products

3M Fire Barrier Water Tight Spray, Hilti CP 690 Firestop Spray

Recommendations for Your Situation

Given your experience so far, and the large gap you're dealing with, I strongly recommend using Fire-Rated Putty/Mortar. It's relatively easy to apply, forgiving, and designed for this type of situation.

Steps to Take (Using Fire-Rated Putty/Mortar)


Clean the Area

Remove any loose debris, dust, or grease from the surfaces around the gap. This ensures proper adhesion.2.

Read the Instructions

Always read the manufacturer's instructions for the specific product you're using. Curing times, application methods, and temperature limitations vary.3.

Pack the Gap

Scoop out the putty/mortar and pack it firmly into the gap. Use a trowel, putty knife, or even your fingers (wear gloves!) to force the material into all the nooks and crannies. Make sure there are no air pockets.4.

Overfill Slightly

Overfill the gap slightly, so the putty/mortar protrudes a bit beyond the surface.5.

Smooth the Surface

Use a damp trowel or putty knife to smooth the surface of the putty/mortar. This creates a professional finish and helps ensure a good seal.6.

Curing

Allow the putty/mortar to cure according to the manufacturer's instructions. Don't disturb it during the curing process.

Important Considerations



Fire Rating Documentation

Ensure that the putty/mortar you use is tested and approved for the fire rating required by the building code. The product label should clearly state the fire rating.

Manufacturer's Instructions

Again, always follow the manufacturer's instructions. They are the experts on their product.

Training

If possible, get some hands-on training on firestopping techniques. Your employer should provide this.

Inspection

After you've completed the firestopping, have it inspected by a qualified person to ensure it meets code requirements.

Don't Forget



Safety

Wear appropriate personal protective equipment (PPE), including gloves, eye protection, and a dust mask (especially when working with mineral wool).

Proper Ventilation

Work in a well-ventilated area.*

Clean Up: Clean up any spills or excess material immediately.By using the right materials and techniques, you can create a safe and effective firestop that meets code requirements and protects lives and property. Good luck, and don't be afraid to ask for help from more experienced colleagues! Flag for review