Should I remove these wall coverings back to brick?

[kingandy2nd]

Hi all,

These are pictures of our bathroom which I've removed all the tiles from. There's a lot of grout left on the walls.

This wall is plasterboard which has been skimmed and then tiled. I intend to cover this wall with new green plasterboard. Can I board over the wall as is, or should I remove all the old plaster/plasterboard?

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This wall is an external wall which is grey plaster onto brickwork, which was then tiled. Could throw on a coat of bonding and then skim, or should I hack it all off?

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Thanks in advance
Andy

 

[Karis]

What is the plasterboard fixed to, dot/dab over brick/block work or timber stud?

Is the external wall cavity construction or solid brick?

Don’t use plasterboard in wet areas, even the green MR stuff unless you going to tank it; a waterproof tile backer board is a much better choice.

Don’t plaster areas you intend to tile, it’s a waste of time & will restrict tile weight which can be a problem if you’re planning to use large format tiles. You will also have to wait anything between 14 - 28 days for it to dry out before you can tile.

Don’t tile over Bonding (or any base plaster), it’s not a suitable tile base.

Don’t just rely on dot & dab if you’re going to hang tiles, the whole lot could end up on the floor; you need to provide additional support with mechanical fixings.

MR (green) plasterboard must be primed if you intend to plaster over it.

If you intend tiling, you may do better to post the Tiling Forum regarding the materials you should use & preparation required. There are many things that can easily catch you out leading to disastrous & potentially expensive mistakes.

 

[kingandy2nd]

Hi Karis,

Thanks for your detailed rely.

The wall in the first picture is plasterboard on timber stud. The wall in the second picture is a cavity wall.

No plasterboard in the wet areas, I’m using hardiboard 500 for the shower cubical.

The wall in the first picture will be skimmed with the exception of a couple of course of tiles above where the bath will be and the rest will just be painted.

The wall in the second picture will be bonded, and then skimmed. The lower half of the wall will be tiled (for where the sink and toilet are) and the top have painted.

I’m thinking it’s going to be easier to remove the old plasterboard on the first wall in order to get a good surface onto which I will screw the new green plasterboard.

On the second wall, you’ve said that bonding isn’t a suitable tiling base. I’m unsure if you mean that tiles directly onto bonding coat isn’t suitable (but this won’t be the case as I’ll be skimming the wall) or just if generally it won’t be any good irrespective of the skim.

The purpose of the bonding coat was just to take the unevenness out of the wall that’s been left by the old grout. If bonding isn’t suitable, what alternative(s) do I have?

Also what primer should be used on green plasterboard? I usually pva before skimming, but should I use something else?

Thanks again

 

[Karis]

The wall in the first picture is plasterboard on timber stud. I’m thinking it’s going to be easier to remove the old plasterboard on the first wall in order to get a good surface onto which I will screw the new green plasterboard.

Best to, far easier to rip the lot down & start again than trying to level it out with over boarding.

No plasterboard in the wet areas, I’m using hardiboard 500 for the shower cubical.

Personally I use Aquapanel but HardieBacker 500 is a good choice.

The wall in the first picture will be skimmed with the exception of a couple of course of tiles above where the bath will be and the rest will just be painted.

A bath should still considered as a wet area, to avoid risk of failure I advise you use HardieBacker around that as well.

The wall in the second picture will be bonded, and then skimmed. The lower half of the wall will be tiled (for where the sink and toilet are) and the top have painted.

What type, size & weight are your tiles (see below for weight limit)?

On the second wall, you’ve said that bonding isn’t a suitable tiling base. I’m unsure if you mean that tiles directly onto bonding coat isn’t suitable (but this won’t be the case as I’ll be skimming the wall) or just if generally it won’t be any good irrespective of the skim. The purpose of the bonding coat was just to take the unevenness out of the wall that’s been left by the old grout. If bonding isn’t suitable, what alternative(s) do I have?

You should never tile directly over a base plaster (except Thisstle Tough Coat). You can tile over finish plaster (Multi) but all plaster finishes will restrict tile weight to 20 kg/sqm including up to 4 kg/sqm for adhesive & grout. Plaster was not a problem when tiles were relatively small but is increasingly a problem where large format tiles over 8mm thick are being used as they will usually exceed this weight, the plaster bond may fail, bringing the tiles with it.

Also what primer should be used on green plasterboard? I usually pva before skimming, but should I use something else?

Whilst PVA is OK for priming/suction control on general plastering (although not usually necessary on wall board), MR boards contain water repellant additives & you need a bonding primer such as Thistle Bond it; http://www.british-gypsum.com/produ...le_plaster_bonding_agents/thistlebond-it.aspx
I believe some use PVA mixed with cement but I’ve never tried it as I can’t afford the risk of it failing.

Never, ever use standard PVA as a tile primer, it remains water soluble & can cause adhesion problems but if used in a wet area can fail & your tiles will end up on the floor. If you need to prime, use a good quality SBR/acrylic tile primer.

Don’t use tub ready mix adhesive on tiles larger than around 250mm & never use it on floors. Only use quality trade tiling materials of the correct type for your tiles & tile base, avoid cheap own brand & DIY (shed) products, they are mostly inferior.

 

[kingandy2nd]

The tiles I'm using are 400mm x 150mm ceramic wall tiles. Not too sure of thickness or weight but they're bog-standard tiles.

I would use hardiboard around the bath, but I wasn't sure how to marry up the edge of the hardiboard with that of the plasterboard where the tiling stops and the plaster skim would start. Or can hardiboard be skimmed?

Thanks for the pointer on the thistle bond-it too.

 

[Karis]

The tiles I'm using are 400mm x 150mm ceramic wall tiles. Not too sure of thickness or weight but they're bog-standard tiles.

It’s important you find out either the sq/m weight or weigh a single tile, post the weight back & I’ll work it out for you. If the tiles are under 8mm thick you should be OK but 8mm+ maybe not, depends if the tile is flat or recessed.

I would use hardiboard around the bath, but I wasn't sure how to marry up the edge of the hardiboard with that of the plasterboard where the tiling stops and the plaster skim would start.

Apart from being slightly cheaper, another reason I use Aquapanel is it’s 12.5mm thick & the same thickness as plasterboard. Hardi 500 is only 12mm but you can pack it out over studding or allow for it with thicker adhesive if using dot & dab. If you’re tiling over both the backer & plasterboard, just reinforce tape the joint & tile over; avoid tile grout lines coinciding with board joints as far as possible. When plaster up to tiles, I extend the backer board slightly outside the tiles, reinforce tape & plaster over, wasting the skim around 60mm or so behind the tile line.

Or can hardiboard be skimmed?

Knauf (Aquapanel) say you must use their special & expensive plaster but I skim removable service access panels & the bit where they meet (as above) with ordinary Multi. I prime the board the day before with 3 coats of neat PVA & let it dry overnight, just before I skim I give the PVA a light mist spray to re-activate the surface & then skim over as normal. I use an old 1 litre kitchen cleaner spray bottle which I also use when troweling up rather than flicking dirty water all over the plaster with a brush

Not skimmed Hardi but as it’s cement based similar to Aquapanel, I assume the above would work on that as well.

 

[kingandy2nd]

Thanks again Karis for all the helpful info.

On checking the box of the tiles today it say that the box weights 17kg (and has 1.02 sq m of tiles in it) - so looks like I might be just over the limit.

However, the wall with the window (that's to be skimmed) will have a vanity unit and also the end of the bath up against it I don't think there will be any part of the wall that will have a whole meter square of tiles upon it.

I got the hardiboard 500 as it was on offer at one of the sheds for £11.25 each - which was a decent price I thought, although I've not seen the aquapanal for sale for comparison. I'll look to board out around the bath with the hardiboard too - better safe than sorry!

Cheers
Andy

 

[Karis]

On checking the box of the tiles today it say that the box weights 17kg (and has 1.02 sq m of tiles in it) - so looks like I might be just over the limit.

Maximum weight of adhesive & grout is around 4kg/sqm so using the thickest adhesive bed would only put you just over. I would think there is a safety factor of 10% or more in the maximum loading but I don’t really know. Without seeing it, I obviously can’t give you any guarantees but I would think that as long as the plaster is in good condition with no blown areas, you should be OK.

However, the wall with the window (that's to be skimmed) will have a vanity unit and also the end of the bath up against it I don't think there will be any part of the wall that will have a whole meter square of tiles upon it.

I’m afraid it doesn’t work like that; although it’s specified as 20 kg/sqm, it’s an equally distributed load so the unit loading on the plaster bond is actually the same for any given area. But, as above, if the plaster is well bonded & not blown (sounds hollow when tapped) I reckon you should be OK.

As I said previously, use quality trade products only & a cement powder adhesive for those tiles. Use a flexibly adhesive over the Hardi boards but you could use straight powder adhesive on the block/brick walls but it’s often more economical to use a flexy for the whole job, depending on individual adhesive quantities you need. When using powder adhesive, you must acrylic prime plaster to avoid a reaction between the cement in the adhesive & gypsum in the plaster. Let the plaster dry out thoroughly before tiling - 14 days for a skim, 28 days for a base coat & skim.