Is plaster from around 1900 going to need replacing?

[Gary111]

Hi, I have a 2nd floor bathroom with an external wall in a 1900/1910 house which I am preparing for tiling, with basic tiles, not the large heavy ones.

Under the bath the old plaster is loose and I have removed it back to brick, (I guess it doesn't matter there?)

I used a wallpaper steamer to strip off a small area of paint to tile on, but this caused a large area of modern skim coat to fall off so I am left with The top part of the wall still skimmed.
The rest I need to re skim, or remove?


There are still some hollow sounding areas on the original underlying plaster.

I am wondering what's the best to do please?

possibly cut out the hollow sounding areas and use bonding coat, then skim it all?

or if there are some areas that sound hollow is it just a matter of time before other areas start to do the same?

if that's the case should I hack the lot off and fit new plasterboard?

thanks

 

[JohnD]

Plaster needs to be removed if it loose, not if it is old.

Rather than plasterboard, you would do better, in a bathroom, to use a cement based backerboard which will withstand damp. If you hack off the old plaster you can use an insulated board, which will reduce condensation and heat loss. In such an old house you most likely have cold, solid walls.

Insulate under the bath as well, and draughtproof the gaps.

 

[Gary111]

Thanks John, I like the idea of insulating it, as it's a cavity wall without insulation at the moment.

To avoid fire risks I have seen some rockwool board with ablative coating, would I be able to fit the cement board to that?

How would I best do that?

Adhesive?

Or drill and screw?

Thanks

 

[JohnD]

Don't know. Is the ablative treatment damp-proof?

Foamglas is also fire and damp proof, but not readily available in UK.

I think, ask on the Tiling section.

 

[mrrusty]

If its an external wall in an edwardian house with a ventilated 2" cavity then it will really benefit from internal insulation. You could use 72mm insulated plasterboard (60+12) or put some 50mm battens up and insulate between with tile backer over the top. The old plaster is probably 25mm thick, so you don't lose that much space, and the difference is enormous. Drill and plug through the insulated PB if using that. 5mm screws and red plugs with 5.5mm drill will go straight in and the heads are big enough to secure the insulated PB in addition to the adhesive. You can use either foam or dab adhesive with insulated PB - just make sure the wall isn't too dusty.

The key thing IMHO is the cavity must be ventilated. If any condensation occurs behind the insulation (in the now colder wall) you need that ventilation to dry out the internal brick should it get damp from condensation.

We have done exactly this - cement board over battens/insulation on the wet external wall with the shower, insulated PB on the non-wet external wall.