Cut a 300mm hole in lath and plaster ceiling?

[john999uk]

I have to fit a condensation control fan (PIV) into the hall ceiling. The hole needs to be about 300mm and the ceiling is lath and plaster!

Any tips for cutting the ceiling without damaging the surrounding lath and plaster?
Cheers

 

[Riley]

Slowly slowly catchy monkey. I have had success in the past with a really good sharp blade on a fein saw just don't push too hard and let the blade do the work. Some of these lath Jobs unfortunately Are just destined to fall down so it may just need a little bit of patching

 

[ShaunCorbs]

Why does it need to be 12" what fan is it?

 

[joni os]

Impossible to make neat round hole. Expect joists at 400c/c giving clear space of 350mm. This determines location of fan. Cut square hole flush with side of joists 400 long, minimum. Cut 18mm plywood to fit between joists 350X400. Screw battens to sides of joists and with 300mm hole precut in ply, screw ply to battens. Battens fixed to allow thickness of ply plus plasterboard to finish 3mm above existing ceiling. Scrim edges and plaster/ make good.
If you can get others to do the making good leave it to others. It is tempting to omit scrim and plaster flush to existing but without scrim vibration of fan will cause cracking.
Cut hole in plasterboard after plastering and making good.

 

[gmartine]

Assuming you have full access for running pipe you could, stabilise the rear of the area you want to cut by squirting a "thin" layer of builders foam and pressing on a bit of hardboard basically turning the area into a bit of foam board, once cured it should be straightforward to cut cleanly as well as leaving good support for the fan.

Done it on smaller holes successfully but it's a large hole with weighty fan so you may need more belt n braces as recommended above.

 

[john999uk]

Cheers all. The fan doesn't actually sit on the loft side of the ceiling it is hung from above on a rafter. So its just an outlet in ceiling then a flexi pipe to the actual fan unit.

As I suspected it's going to be a very delicate job. I like the idea of foam and ply on the loft side.

I was going to use a very fine toothed pad saw or a Dremel Spiral Cutting Bit?

Cheers for the suggestions.

 

[joni os]

Consider a 400X400 square of MDF, round edges and screw to ceiling, It will protrude below ceiling but, when painted, look part of the fan.

 

[john999uk]

All done . The multitool was great. Actually once I started it was easy as the ceiling had been overboarded so the laths and their plaster were all contained. So no need to worry.
Cheers for all the advice it was very helpful.

 

[jonnyswamp]

Cheers all. The fan doesn't actually sit on the loft side of the ceiling it is hung from above on a rafter. So its just an outlet in ceiling then a flexi pipe to the actual fan unit.

As I suspected it's going to be a very delicate job. I like the idea of foam and ply on the loft side.

I was going to use a very fine toothed pad saw or a Dremel Spiral Cutting Bit?

Cheers for the suggestions.

That's one strange looking elephant
Hope you reinforce your roof rafters if that's hanging from it :smilewinkgrin:

 

[john999uk]

It's smaller than it looks and only weighs 3.5kg.