Cracked Plaster Around multi-fuel stove

[synott.nicola]

Hi, I am a diy amateur enthusiast. I have recently completed my first tiling job (kitchen splashback) and it turned out really well!! My next project is to tile (ceramic tiles) the back of a multifuel stove (situated in a corner of the kitchen) to protect the walls from marks etc (plastered and painted). There were what I thought were some hairline cracks in the plaster but when I went to check for loose paint and clean down the walls it turned out to be more than hairline cracks and the plaster is just falling off the wall. Photos attached. Anyway my questions are: What would you advise? 1) Remove the plaster in the area to be tiled completely and tile onto the plasterboard? If so use what adhesive? I have evo-stik rapid curing quick set ceramic tile adhesive, would this be ok? 2) replaster using a sand, lime, cement mix? If so what proportions? Would 4 weeks be required for this to dry fully before tiling? 3) Install some fireproof board behind the stove and tile onto that? If so what board and how would I attach this to the wall? Thanks a million in advance!! 4) Any other advise greatly appreciated. Nicola

 

[Ajax123]

Tis cracking looks indicative of the plaster being over heated and dehydrating. It s shot basically so you shold be able to scrape it off reasonably easily so that you can tile directly to the plasterboard underneath. You might need to gently sand it once you ave taken the plaster off in order to get rid of any dust. Vacuum and the wipe with a damp cloth followed by priming with a heat resistant primer. Acrylic should be fine. Then tile with a flexible tile adhesive

 

[synott.nicola]

Thanks Ajax123. I will be tiling an area to match the dimensions of the limestone plinth under the stove. Should I chip away the plaster for this entire area (not all heat damaged) and if so will it look funny if the tiles are set below the level of the rest of the plaster/wall i.e. less than half the depth of the tile would sit proud above plaster not chipped away? Thanks, Nicola

 

[White Room]

Gyproc plasterboard including Gyproc Fireline is not suitible for use in temperatures above 49 centigrade.

 

[Ajax123]

Gyproc plasterboard including Gyproc Fireline is not suitible for use in temperatures above 49 centigrade.

Sunds about right... We normally say maximum temperatures of 55degrees c for gypsum. The issue is basically that the gypsum molecule contains two molecules of water I.e CaSO4.2H2O. This is a very stable molecule but not as stale as the anhydrous form of calcium sulphate also known as anhydrite. The gypsum molecule is slightly larger than the anhydrite molecule (due to the water molecules being there) so if you heat it beyond the point at which it can hold on to the water it reverts back to anhydrite slowly and gradually. If you sustain high temperatures typically over 60degrees for a long period it will go through solid state dehydration, and will shrink and crack. I'm quite surprised that the plasterboard itself is not considered suitable though as it is generally not a highly compacted form of gypsum so is very very flexible so will stand a bit of shrinkage.

 

[Perry]

I tile quiet a lot behind wood burning stoves have a look at these real brick tiles

BrickIt

You can always cut out the plaster board and replace it with cement board Beam what about fire proof plasterboard ?

 

[White Room]

Sunds about right... We normally say maximum temperatures of 55degrees c for gypsum. The issue is basically that the gypsum molecule contains two molecules of water I.e CaSO4.2H2O. This is a very stable molecule but not as stale as the anhydrous form of calcium sulphate also known as anhydrite. The gypsum molecule is slightly larger than the anhydrite molecule (due to the water molecules being there) so if you heat it beyond the point at which it can hold on to the water it reverts back to anhydrite slowly and gradually. If you sustain high temperatures typically over 60degrees for a long period it will go through solid state dehydration, and will shrink and crack. I'm quite surprised that the plasterboard itself is not considered suitable though as it is generally not a highly compacted form of gypsum so is very very flexible so will stand a bit of shrinkage.

Thats from British Gypsum themselves but it may be a figure that ensures that theres no chance of any failure.

 

[synott.nicola]

Do any of you guys give any credence to the idea of replastering the heat damaged area with a lime render? Cutting out the plasterboard sounds like a big and very dusty job. ??

 

[Perry]

It is quet easy just work out where your tiles will finish cut 30 inside that line with a padsaw or sharp knife replace with board and you won't see the join

 

[synott.nicola]

It is quet easy just work out where your tiles will finish cut 30 inside that line with a padsaw or sharp knife replace with board and you won't see the join

That sounds do-able. Any suggestions on chipping off the plaster so I don't overun the area I want to tile? Also do I just use an extra thick layer of mortar to set the tiles in so they are level with the rest of the plaster/wall i.e. not set beneath the level of the plaster on the rest of the wall or will I need to plaster over the fireproof board? Thanks

 

[Perry]

Just cut though the paster with a stanly knife the plaster will only be a couple of mm thick so it won't make any difference with the thickness of the adhesive

 

[White Room]

Is your finish plaster on a gypsum undercoat....

 

[Perry]

Is your finish plaster on a gypsum undercoat....

Sorry Nicola I thought it was already plasterboard if it's plaster it changes things a little more difulcult to solve if you are not a compertent DIYer

 

[synott.nicola]

Anyone have any opinion on whether plastering the damaged area and then tiling over that is a good idea?

 

[White Room]

I would mark out where you will tiling and cut out the plaster 25mm in from the mark and use a rapid setting render, pre bagged type to speed up the work.