How to fit things to a Bungaroosh wall

Question

The walls in my house are made of Bungaroosh which means that attaching anything to them is most likely to hit some issues. Recently I've been trying to fit a floating shelf to the wall, but no matter what I do it ends up coming away.

The steps I've taken so far are:

1. Drill hole
2. Place vacuum nozzle up against hole to get all the fallen bits out
3. Fill hole with filler and put wall plug in
4. Wait for this to dry and then attach item with screws

This approach seems to work normally, but this shelf has turned out to be fairly heavy so it's pulling itself off the wall. I also tried some Gripfill but not sure if this is appropriate for this job - it also didn't work.

Can anyone suggest any alternate approaches I could try?

Answer 1

Accessing any substrate as jamietre suggests is probably the best bet if possible. Otherwise Tester101's epoxy will be best. The sort of shelf you want places fasteners in withdrawl, which is a difficult load to resist in marginal materials such as bungaroosh. If you attempt an epoxied anchor, you should attempt to undercut the hole with a small hard chisel to further help resist withdrawl forces. This way, you are not entirely dependent on the epoxy bond strength. Unfortunately, you still need to depend on the shear strength of bungaroosh anyway, which is marginal at best.

The deeper the hole, and the greater the undercut without damaging the surrounding wall material will yield the strongest anchorage.