Green chipboard vs WBP

[gregch]

We're renovating our two bathrooms that currently have a suspended timber floor with old chipboard 19mm T&G boards that are in a bit of a state, ie it'll need removing and replacing to get a sound base to tile onto.

I'd planned to go with 18mm WBP ply, but the builder we've been talking to about doing the work is proposing to use green chipboard instead - is that better or worse than WBP ply?

Also - for the walls - the existing plasterboard is almost certainly going to fall to bits when the tiles are chipped off, so I'd like to replace it - we'll use the waterproof tile backer board around the shower (WEDI?) but is it OK to use regular plasterboard for the other walls? or should we use the backer board on all the walls? or WBP?

Finally, as a bit of an aside, any ideas how much we should be paying for the work. They are small-ish bathrooms (about 4 sq metres each) but a bit of a job since the loo and soil are moving to the other side of the room in each case, the new WCs will be wall hung with a boxed in cistern and frame, the bath and shower mixers are concealed, etc. and as mentioned the floors (and prob wallboard) need replacing. Oh, and a 1m section of the (stud) wall is being moved and a doorway moved.

We've been quoted roughly £7,000 in total (excl VAT) for the installation (incl. plumbing work, floors, walls, boxing in, moving the doorway, tiling) - excluding the sanitaryware, taps, bath, shower, and the tiles. Does that sound about right?

 

[tictic]

wbp ply for the floors,prime the underside and edges with SBR....

wedi for wet area and the rest off walls(money permitting)..or mr plasterboard...

as for price(london area)...get at least 3 quotes....

 

[big-all]

no no no chipboard its the work off the devil ---------
--------well not really but the life span off chipboard is far less than ply it can stand less abuse as it only just does the job with little margin for things going wrong ply will stand more abuse and best off all wont crumble and squeak with use

builders like chipboard cos its cheaper and quicker and easier to lay especially in confined spaces

 

[gregch]

Thanks for the advice, must admit I wasn't keen on replacing the knackered chipboard with more chipboard, even if it is "green". Last time I did this, I used 9mm WBP screwed onto solid wood floorboards and the tiling stayed perfect for the 11 yrs I was living there.

Would it be OK to replace the chip entirely with say 18mm WBP, ie is that thick enough to be rigid on its own across 406mm centres? It'll then have at least 6mm backer board to go on that, with electric underfloor heating and 11mm porcelain tiles - so quite a thickness, hence I don't want to go any thicker with the ply if I don't have to!!

 

[tpt]

dont touch the green chipboard - tiling adhesive wont stick to it (and shouldnt as if it did the tiles will crack). the green bit is actually a treatment that makes them very hard to stick anything to.

I'd consider upping the ply thickness and not using a backerboard. dont be drawn in by using an insulating backerboard for your UFH, if your onto wood you really wont need it.

 

[HERTS P&D]

Marine ply/Wedi

Andy

 

[Richard C]

Chip board is crap; it’s cheap & nasty. Now almost universally used in new construction; not too critical if your laying carpet or laminate but as a tile base it’s just about the worse you could possibly imagine; whatever you do don’t let your builder use it. WBP ply 18mm-25mm, actual thickness will depend on your floor joist size/pitch/span. Screw fix into the joist every 150mm acrylic prime the underside & edges before laying; support any cross joist edges with noggins. With the correct thickness ply, you won’t need to overboard before tiling. You don’t need to go to the expense of marine ply, WBP uses the same waterproof veneer adhesives in construction, just doesn’t have the decorative face veneers which you don’t need.

For the walls, 12mm waterproof tile backer board in all wet areas but you can use MR plasterboard in dry areas or backer board if you prefer it; do not use WBP for walls. Don’t plaster tile surfaces it’s not necessary & will reduce tile weight which can be a problem if you’re planning large format tiles. If you need to plaster ½ tiled areas do this first wasting just below the tile line but you need to prime MR board before skimming.

Be very careful with your choice of builder & tiler!

 

[gregch]

Thanks everyone for all your help on this, I had a feeling green chipboard would be a bad idea. The problem we have where we are is that despite the recession there seems to be no shortage of work - so customers are competing for builders rather than the other way around. The end result is that the builders tend to try and tell you what they want to do - which isn't always the same as the best way to do it.

Hence, I'm trying to find out a bit more so I can be certain what I want, and be clear on it from the start. Even if I want someone more experienced/skilled than I am to actually do the work I'm happier if I know what needs to be done, and how, if I was to do it myself.

Richard, that's a very detailed and helpful reply, thanks. As regards the weight of the tiles, that might be an issue. We're planning on using porcelain tiles that are 60x30 and 11mm thick, would plasterboard struggle to cope with that?

 

[Richard C]

I'm trying to find out a bit more so I can be certain what I want, and be clear on it from the start. Even if I want someone more experienced/skilled than I am to actually do the work I'm happier if I know what needs to be done, and how, if I was to do it myself.

Tiling isn’t rocket science but there are many things to catch you out, particularly if you intend tiling a suspended timber floor. I would advise you read the Tiling Sticky & Forum Archive posts before employing anyone, doing any work or buying materials; it could prevent you making disastrous & potentially expensive mistakes. It’s 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.

As regards the weight of the tiles, that might be an issue. We're planning on using porcelain tiles that are 60x30 and 11mm thick, would plasterboard struggle to cope with that?

11mm porcelain tiles are going to be heavy & could be near or over the limit; I would advise you find out the exact weight. Unplastered plasterboard will take 32 kg/sqm (plaster of any kind is only 20 kg/sqm) but that includes around 4 kg/sqm for the adhesive & grout. It’s likely there is a safety margin (possibly around 10%) but I’ve no idea if there is. If your tiles come in at anything above 28kg/dqm, officially you’re over weight for PB, if in doubt go with a suitable tile backer board. Flexible powder cement (solid thick bed) only with tiles that size/weight & gypsum plaster/plasterboard must be acrylic primed to avoid reaction between the cement in the addy & gypsum. Glazed porcelain are OK but polished porcs are porous & usually require sealing; some come pre-sealed but check with your supplier.

 

[gregch]

Thanks Richard really useful info again. The tiler chap we're planning to use seems to know his stuff and wants to use his own addy and so on (although he did say he'd use what we source if we prefer). I guess we trust his experience on the best stuff to use for the situation, but very useful to have your comments so I can run those issues past him.

The tiles are from Porcelanosa, I believe their (butech?) stuff is supposed to be OK, so maybe that's another option. Flexible powder cement I guess is the way to go in any case (the floor tiles are 60x60 and the same thickness).

Sounds like we might have to use the backer board on the walls (rahter than plasterboard) throughout to take the weight of the tiles and wouldn't need to seal?

Also, good catch with the polished porcelain - we're planning to use essentially the same tile on the floor and the walls (Porcelanosa "City Cube") but the matt version on the floors and the polished version on the walls. I hadn't thought about needed to seal the polished ones so I'll check with them!!

 

[Richard C]

Ask him what materials he proposes & post it on here for comments.

On the subject of backer board; Wedi is fully waterproof & an excellent product. I generally use Aquapanel, it will not disintegrate when wet but is specified as water resistant as it will still absorb water. Knauf specify Aquapanel as suitable for showers in domestic situations & unless you’re constructing a wet room, is perfectly serviceable & cheaper.

If it will support your tile weight, Moisture Resistant PB only needs tanking in wet areas; tanking dry areas is OTT unless your constructing a wet room.

 

[gregch]

I've asked Porcelanosa to confirm re sealing requirement and the weight, but it sounds like Aquapanel might be the way to go on all the walls (only small rooms so hopefully not too expensive) to be on the safe side.

I guess we need to skim any sections of wall that won't be tiled with Aquapanel's skim.

Really glad I posted on here, I've now got a much better understanding, I think. I'll also run all this past the tiler before work starts.

Back on the floors, I'm a bit concerned about 25mm ply as it adds 6mm to the floor height, not a huge amount but once we've added underfloor heating mat, adhesive and 10mm tile that's quite a bit of added height even assuming we don't use a backing board. Do you think we might get away with 19mm at 400 centres, or will that not be rigid enough?? Maybe best to be on the safe side, and I guess as we work our way through the house a lot of the remaining chip will be replaced and so all the levels will rise accordingly...

 

[Richard C]

Aquapanel might be the way to go on all the walls (only small rooms so hopefully not too expensive) to be on the safe side.

I guess we need to skim any sections of wall that won't be tiled with Aquapanel's skim.

I use Aquapanel framed with steel plasterboard stop trim to construct service access panels & I skim these with standard Multi Finish after some additional prepping rather using than Knauf’s expensive “special” plaster; I’ve never had any problems but I have never tried skimming larger wall areas. If you need to skim where ½ tiling, I would use MR plasterboard in these areas but if your tile weight comes back under 32kg/sqm total, MR PB will be perfectly adequate in all dry areas, tile or plaster but it must be primed before plastering.

Back on the floors, I'm a bit concerned about 25mm ply as it adds 6mm to the floor height, not a huge amount but once we've added underfloor heating mat, adhesive and 10mm tile that's quite a bit of added height even assuming we don't use a backing board. Do you think we might get away with 19mm at 400 centres, or will that not be rigid enough?? Maybe best to be on the safe side, and I guess as we work our way through the house a lot of the remaining chip will be replaced and so all the levels will rise accordingly...

You may not need to go to 25mm ply; in light load/use areas such as bath/shower rooms, 18mm WBP is often sufficient but it depends on your floor joists. 400mm centres are pretty much standard but what is the joist size & supported span length? 18mm WBP or T&G timber floorboards will be perfectly adequate where laying carpet, laminate or vinyl.

I would question the wisdom of electric UFH as a secondary heat source. It sounds luxurious & is very “in vogue” but a major drawback is the response time; it will take 20-40 mins. to warm up, even longer if you don’t use insulation board under the mat; I believe your also restricted to 100W sq/m over timber floors but not certain. So do you wait half an hour after turning it on? - Most will have showered/bathed & be long gone by the time it’s up to temperature. Do you leave it on all the time running on the thermostat? – Expensive. Do you set it to go on/off the same times every day? – OK if you’re bathing habits are regular every day of the week I suppose.

I have an electric UFH system in a large conservatory which works well (if not somewhat expensive) but it is the primary heat source & we rarely use the cons from November through March. I know others who have installed them as secondary heat sources in bathrooms & kitchens & never use them because they just don’t provide enough flexibility; I also think putting one in a kitchen is madness; unless all you do is make tea & eat microwave ready meals, they tend to be hot enough places anyway.

You should also lay an SLC over the heater mat before tiling to ensure a flat tile base, protect the mat (during tiling) & if you want to have any chance of repairing it in the future if it breaks!

 

[gregch]

Hey Richard thanks again.

Sounds like we'll use MR Gyproc for the part-tiled/non-wet areas and Aquapanel in the shower room. Your advice has been really helpful.

For the floors, I'm just a bit concerned that 19mm might not be rigid enough for the tiling (same 10mm porcelain as the walls)? The joists are 40x90 at 400mm centres and obviously there'll be noggins under joins.

As to the UFH, we put that in the bathroom in our previous place and it was the best £150 we spent. It stays on all the time, at a very low level (running costs when used that way are actually really low in my experience over the 10 years we had it) and takes the chill off the tiles and helps keep the bathroom dry, rather than being a secondary heat source as such.

Ours was a Devimat system, and we'll use that again - not sure if other brands are the same but we were pleased with the Devi and they seem less expensive than most other brands.

In other rooms, I'd only use UFH if the floor is tiled, to take the chill off the tiles. Not sure heating of any kind should be necessary in a kitchen otherwise so I do agree on that front!

Final question: what's an SLC?

 

[Richard C]

I'm just a bit concerned that 19mm might not be rigid enough for the tiling (same 10mm porcelain as the walls)? The joists are 40x90 at 400mm centres and obviously there'll be noggins under joins.

40 x 90 joists, is that mm? 90mm deep doesn’t sound right or are they supported directly from a concrete slab? I would usually expect to see joists 50mm thick either 150mm or 200mm deep depending on the span; you still haven’t said what the joist span is?

Final question: what's an SLC?

Self Leveling Compound. Most of the heater element manufacturers recommend it. Many bed the mat directly into cement based tile adhesive but you will never be able to get at it again to repair if there is a problem; it’s also not unknown for the mat to be damaged by ham fisted use of a tiling trowel!