Bathroom Skim before Tiling?

[headworx]

Hi peeps,

Just a quick question that may sound silly to some.

I doing the bathroom out, have so far:

Taken back to brick.

Dot and Dabbed Soundboard to most walls (had it spare so used instead of plasterboard)

Where the shower will be I have used Hardibacker 500 so it will be waterproof.

I need to do the pipework next, but my question is can I skim the boards and hardibacker before tiling?

The reason why I want to do this was to seal the boards so they are more moisture resistant, I just dont know if I can skim the Hardibacker - Obviously if this is not suitable then I wont bother skimming any of the walls as there would be a mis match in depth then.

Im using 20x 30 tiles so the plaster should take the weight from what I've.

I thought this would just give the room a bit more resistance to the wet - What do you experts reckon??

Thanks in advance.

 

[Maxsys]

What you do next will depend on what size and type of tiles you propose to use, please post details about the tiles for a full answer.

 

[tpt]

dont bother skimming, it wont help moisture resistance and will bring down the weight of tiles you can use. Acrylic primer can be used to help resistance to moisture but the best thing you can do is tile it soon

 

[Maxsys]

What type of tiles?

 

[Richard C]

Just to reiterate what’s already been said, do not skim the PB; it’s not necessary & is a waste of time/money. It’s also a positive hindrance if your laying large format tiles if they weigh in at more that around 18 kg/sq/m; yours may be marginal depending on thickness, do you know the tile weight? The boards won’t be moisture resistant unless you use moisture resistant boards which you should in a bath/shower room but you should be OK in a dry area as long as you have an extractor fan & good ventilation. Why do you want to skim the Hardiebacker? Definitely not unless you’ve got a ½ tiled wall but unlikely in a shower; just tape the board joints & fill with adhesive as you tile. As already asked what type of tiles will you be having? You need a flexible powder cement adhesive once tiles go above around 25 x 25 & I would not advise tub ready mix. You will have to wait days for it to set & the tiles can move around; on large tiles sometimes the adhesive never sets & they end up on the floor. When using cement powder adhesive over plaster or PB, you must acrylic prime to avoid a reaction between the cement in the adhesive & gypsum.

You must also mechanically fix the boards if you’re going to tile, if you just rely on the D&D, the whole lot could end up on the floor, particularly if you’ve got heavy tiles.

Tiling isn’t rocket science but there are still many things that can catch you out; tile weight, choice of tiling materials & prep, particularly if you intend tiling a suspended timber floor. I would advise you read the Tiling Sticky & Forum Archive posts before doing any more work or buying materials, it could prevent you making disastrous & potentially expensive mistakes. It’s also important to use only quality trade tilling materials of the correct type for your tiles & tile base; cheapo own brand & DIY stuff is mostly crap.

 

[headworx]

Thanks, some very helpful advice as usual - Esp Richard.

Heres a bit more info re: the tiles:


Type: Wall
Colour: White
Material: Ceramic
Length: 200mm
Width: 300mm
Thickness: 10mm
Finish: Gloss
Pack Quantity: Pack of 17
Pack Coverage: 1.0m2
Usage: Kitchen and Bathroom
Tone Variation: Low

Link Here:
http://www.wickes.co.uk/red-plastic-wallplugs/invt/166203/


Basically got them really cheap instore £3.77per box as they were 'end of line'.

So with this in mind, you reckon I should put some screws in the boards too? The room will be tiled from floor to ceiling.

I wont bother skimming now - If I had, I was going to do the hardibacker too as its all flush with the boards and if I did just the plasterboards, there would have been a 3mm depth difference.

Cheers for the advise ont he adhesive - I was going to use good stuff anyhow - I have read and learned a lot from this forum and using decent stuff is one of the biggest things I've learned.
Not Ready mixed tubs in my house


I didnt know about needing the primer so really chuffed you mentioned it!


I will also be tiling the floor not long after - Think I'm going for the Bal flexible adhesive and something like 9-12mm WPB ply screwed every 6inch. Not sure which Tiles i'm using on the floor yet, either 30x30 ceramic, or if I have enough left over, then some porcelain 60x30.

Thanks again all.

 

[headworx]

@tpt

The bathroom is not in use, is that why you mentioned to do it ASAP?

I presume the boards wont take on moisture otherwise?

I just need to get the pipework sorted and then will tile. Prob a couple of weeks?

 

[Maxsys]

So with this in mind, you reckon I should put some screws in the boards too?

Yes you need to fix through the dabs and into the walls as advised, screws and plugs.

I will also be tiling the floor not long after - Think I'm going for the Bal flexible adhesive and something like 9-12mm WPB ply screwed every 6inch. Not sure which Tiles i'm using on the floor yet, either 30x30 ceramic, or if I have enough left over, then some porcelain 60x30.

What material is on the floor now? What size/Pitch and span are your joists, the minimum BS spec is 15mm for plying the floor, you also need to use WBP ply and seal the backs and edges with Acrylic primer ( same stuff you will be using on the wall).

Depending on your answers regarding the floor substrate, and the joist info will depend on what you can and cannot do. I personally would also tile the floor first.

 

[headworx]

Thanks for your reply Maxsys.

Just to clarify something on the way I 'dot and dab' just in case it has a bearing on anything.
I tend to go over the top with things and the amount of dots/dabs is probably 3x times what you supposed to do - It's more like pretty much solid adhesive

As they were on bare brick, there was no making up to do so it goes on pretty evenly.

I will put some fixings in though if it is needed as dont wana get unstuck afterwards.



Currently the floor is just floorboards, I'll have to find the measurements out tomorrow, think they either 400 or 600 centres.

I was thinking about tanking the floor (I believe its like bitumen), or would that acrylic primer be better?

Thanks again.

 

[tpt]

yes - your question seemed to imply that it was in use and you were worried about moisture before you tiled - at least thats how i read it!

just as an out of interest thing - richard/maxsys have you ever had failures down to dot and dabbed plasterboard (if properly dot and dabbed?) any stripping out work i've ever done\been involved with has proved that dot\dab is a lot harder to strip out than anything mechanically fixed. I know it may provide peace of mind but is there anything official that points to this?

 

[Richard C]

10mm thick tiles should weigh in around 22 kg/sqm so you should be OK; been a different story if you’d skimmed; weigh a box anyway just to be sure. Nothing special about them so either a Rapidset or Single Part Flexy if your uncomfortable with a short pot life; use flexy grout. You do need to provide additional mechanical fixings for the boards to support the weight of the tiles. Plugs are pretty useless in this sort of application, use through (frame) fixings on a 200-250mm grid. They should be through the dabs or you run the risk of distorting/cracking the boards but it’s a bit late now; a good way of doing this is to drill a grid of 3mm holes over the boards, dab the adhesive to suite & it will squidge out through the holes so you know where to fix through.

Be careful with suspended floors; the BS & adhesive manufacturer recommendation for over boarding is 15mm but generally 12mm is sufficient, you should not go any thinner that that. A lot also depends on the existing floor construction; check the joist size & span, as well as the pitch. Floorboards are generally OK as long as they are in reasonable condition, flat & you make sure they are well fixed down but fix the over board through into the joists not just into the top of the floor boards; check for pipes cables first. Acrylic seal the underside & edges of the ply before laying (but not the top tile face) & lay boards so the edges are supported down the centre line of a joist; avoid joints in the centre of the room.

Only problem with over boarding with ply is the threshold height; for this reason, I generally prefer to replace the floor with WBP but sometimes tile backer boards are a good option. You will need a flat floor for 600mm tiles so check & rectify any bowing before tiling.

You don’t need to tank the floor unless your building a wet room but NEVER use bitumen based products. Do not prime the tile face unless the adhesive manufacturer recommends you do so & usually they don’t.

 

[Richard C]

just as an out of interest thing - richard/maxsys have you ever had failures down to dot and dabbed plasterboard (if properly dot and dabbed?) any stripping out work i've ever done\been involved with has proved that dot\dab is a lot harder to strip out than anything mechanically fixed. I know it may provide peace of mind but is there anything official that points to this?

Unfortunately yes; I’ve even seen failures on untilled walls because they skimped on adhesive or the mix/prep wasn’t correct. With small/light tiles, kitchen & basin splash backs etc. it won’t be a problem but if you start hanging 10 – 30 kg/sqm onto fully tiled wall/backer boards, you’d be very wise to add some mechanical fixings.