Refitting cast iron fireplace

If the wall is plasterboard, use heavy-duty hollow-wall fixings or, better, screw a timber batten into the studs and fix the fireplace to that.

If the wall is brick or block, drill new holes and use larger masonry plugs or expansion bolts.

If the old holes are loose, don’t rely on filler alone for the weight of a cast iron fireplace.

try expanding the holes with a larger drill bit to accommodate a thicker, more robust plug or even a different type of fastener. If that fails, consider using a chemical anchor system for a stronger hold. If you're still having trouble, you may need to reinforce the wall, potentially with a piece of plywood or other backing, before reattaching the fireplace.

The most suitable solution would be to use chemical anchor resin or frame fixings for a secure hold. Here’s what you can do:

1. Remove Loose Polyfill – Polyfilla is not strong enough for structural fixings, so clear it out as much as possible.
2. Re-drill the Holes – Use a masonry drill bit to drill slightly larger and deeper holes in the brick or masonry behind the plaster.
3. Use Chemical Anchor Resin
4. Heavy-Duty Wall Plugs & Screws
5. Fix the Fireplace Securely

You need to make the whole a bit bigger add a two part resin into the wholes and you will get a secure fit

holes in the wall must be filled with a more durable material than polyfil . You can use for instance polyester resin .

Maybe use a strong silicone grip filler like gap filler or use two-pack wall filler

Drill bigger holes and use bigger raw plugs.

It sounds like the wall where you're trying to refit the cast iron fireplace may have weak or crumbly masonry, making it difficult for the new rawl plugs to grip securely. Since the fireplace is heavy, it’s essential to create a strong and stable fixing.

Solutions to Fix the Issue:

1. Reinforce the Fixing Points:

Remove Loose Material: Clear out any loose or crumbly filler or plaster from the holes.

Use a Chemical Anchor or Resin Bonding System:

Fill the holes with a two-part epoxy resin or a chemical anchor (e.g., Fischer or Rawlplug chemical anchors).

Insert the rawl plugs while the resin is still wet.

Once it cures, the plugs will be firmly bonded to the wall.

2. Try Larger Plugs or Wall Anchors:

If the wall is brick or block, you can drill deeper holes and use larger, heavy-duty wall plugs or metal anchors.

For plasterboard walls, use spring toggles or cavity anchors designed to spread the load.

3. Consider Frame Fixings or Sleeve Anchors:

If the wall is solid masonry, frame fixings or sleeve anchors can provide a more robust hold compared to standard rawl plugs.

4. Reinforce Behind the Wall (if accessible):

If it’s possible to access the back of the wall (e.g., via another room), you could add timber battens or a plywood backing board to provide additional strength behind the fixing points.

Final Tips:

Test the Fixings: Before reattaching the fireplace, test the strength of the fixings by applying some force to ensure they won’t give way under the fireplace’s weight.

Seal the Edges: Once refitted, use a fireproof sealant around the edges to ensure no gaps and improve stability.

If you’re still struggling, it may be worth consulting a builder or fireplace specialist to secure the fixture safely.

With a fireplace that is very heavy it will need a very strong drill to get a good hole for a heavy duty raw plug. I would make sure the plug can also take either a heavy duty screw out bolt to secure it well.

Get some Rawlplug R-KEM II that will fix it

Refitting a heavy cast iron fireplace can be tricky, especially when the original wall plugs are no longer viable and the wall material is not holding the new fixings. Since you’ve already tried polyfil and new raw plugs without success, it’s likely that the material behind the plaster (whether it’s brick, stone, or something else) is either damaged or too soft to support the weight of the fireplace.

Here are some options and advice for securing the fireplace properly:

1. Use Heavy-Duty Wall Plugs (Raw Plugs):
• Heavy-duty wall plugs or masonry plugs designed for more substantial weight should work better than standard raw plugs, especially if the wall is brick or stone. Make sure the plugs are appropriate for the material you are drilling into.
• Toggle bolts are also a good option for plaster walls. These expand behind the plaster, offering better grip than a regular plug.

The issue is likely the wall not providing a solid grip. Here’s what I’d suggest:

1. Drill into solid masonry: Check you’ve gone deep enough into the brickwork for longer, heavy-duty plugs.
2. Use resin anchors: A chemical anchor (resin) can secure threaded rods firmly in place—ideal for heavy items like fireplaces.
3. Patch with strong mortar: If the filled area is weak, remove the Polyfilla and use a proper repair mortar for strength.
If the wall is still struggling to hold, discreet metal brackets can help distribute the weight safely.