Priming Plywood for Tiling with Masonry Paint

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I am rebuilding a shower/bath & the walls around the shower area are 12mm hardwood faced WBP ply. These need preparing for tiling. As the plywood is boxing in pipework & is vented at the base, does it need sealing on the back?

I have a large quantity of masonry paint & wondered if it would be a suitable sealant/primer instead of purchasing Unibond? I did read that if the back of the ply is sealed, the substrate surface should not. Could anyone offer advice on this?

 

[jctilingservices]

I am rebuilding a shower/bath & the walls around the shower area are 12mm hardwood faced WBP ply. These need preparing for tiling. As the plywood is boxing in pipework & is vented at the base, does it need sealing on the back?

I have a large quantity of masonry paint & wondered if it would be a suitable sealant/primer instead of purchasing Unibond? I did read that if the back of the ply is sealed, the substrate surface should not. Could anyone offer advice on this?

this will depend on what adhesive you are using ( tubbed or powdered) also the size / weight of your tiles will dictate what adhesive can be used.
NOT ALL adhesive manufacturers advise the use of a priming agent

Masonary paint NO NO, by unibond do you mean PVA, if so NO NO.
if you need to prime/ seal, use an acrylic based one such as SBR or APD

 

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I am using Bal White Star (tubbed) adhesive. Tiles are 200mm square Johnsons wall tile.

 

[Richard C]

I am rebuilding a shower/bath & the walls around the shower area are 12mm hardwood faced WBP ply.

Why on earth are you using ply? It’s not really suitable as a tile base on walls & not at all in a wet area unless you tank it. Water proof tile backer board in wet areas, MR plasterboard outside wet areas; tile straight onto these.

These need preparing for tiling. As the plywood is boxing in pipework & is vented at the base, does it need sealing on the back?

The back should be sealed to prevent moisture getting in & warping the ply; this is one of the main reasons it’s not a suitable wall tile base.

I have a large quantity of masonry paint & wondered if it would be a suitable sealant/primer

No

instead of purchasing Unibond?

Don’t use Unibond (PVA) either.

I did read that if the back of the ply is sealed, the substrate surface should not.
Could anyone offer advice on this?

Use tile backer boards, read the tiling sticky & Tiling forum archive posts; you are about to make some fundamental mistakes which could ultimately affect your project & how long it lasts.

 

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I'm using ply as I have to box in service pipes. I had the sheets cut to size at the builder's merchants as we have limited work space.

The boxing that I am replacing was plywood & I was merely imitating the traditional techniques. I am aware that there are many new products on the market but does that make the use of exterior grade ply such a no, no? Surely, if properly prepared, with adhesive of the quality mentioned (Bal White Star) & properly grouted (Bal Microcolour Wall Grout Brilliant White) the result would be as good as a tile backer board?

Could I not install the ply (sealed back) & then use a BAL WP1 kit to prime & seal? The ply wall is part of a shower-bath 'corner', the other wall is currently oil-painted plaster.

 

[Richard C]

I'm using ply as I have to box in service pipes.

Plasterboard or tile backer boards are far more effective & easier to fix.

I had the sheets cut to size at the builder's merchants as we have limited work space.

Backer boards (which is what you should be using in a wet area) can cut to size with a Stanley knife or ordinary rip saw; like a knife through butter.

The boxing that I am replacing was plywood & I was merely imitating the traditional techniques.

Traditional maybe but no longer appropriate. Times move on & modern alternatives are far superior, even "no more ply" would have been better & I wouldn't use that either.

I am aware that there are many new products on the market but does that make the use of exterior grade ply such a no, no?

WBP ply is made from timber using a waterproof veneer adhesive so it won't fall apart when it gets wet. But it's still timber & timber is not dimensionally stable when subjected to even ambient seasonal moisture changes, if it’s not totally sealed then moisture can get in casing it to warp & curl & there go your tiles. I only ever use WBP on floors & then sealed on the back & edges, as per standard practice.

Surely, if properly prepared, with adhesive of the quality mentioned (Bal White Star) & properly grouted (Bal Microcolour Wall Grout Brilliant White) the result would be as good as a tile backer board?

Not unless it’s tanked; unless you use an expensive epoxy adhesive/grout (OTT for what your doing), even the very best waterproof adhesive & grout is only waterproof in the sense it won’t disintegrate if it gets wet, it will still absorb moisture; hence the need for a waterproof tile base, especially in wet areas. Tile backer boards will always remain dimensionally stable when wet so will not cause tile failure.

Could I not install the ply (sealed back) & then use a BAL WP1 kit to prime & seal?

Yes that will work for the front tile base but if you haven’t sealed the back & edges then (ambient) moisture can still get into the ply and cause warping. I generally find the tiles over ply boxing usually come off clean with very little effort & that's usually just around soil pipes; wet areas are just as likely to be a black gooey mess underneath.

The ply wall is part of a shower-bath 'corner', the other wall is currently oil-painted plaster.

Are you tiling over the oil based paint? If so you will need preparation & possibly a different adhesive.

 

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If I were to use the backer boards as recommended, do they have any structural strength? Being able to cut them 'like a knife through butter' suggests this is not the case.

I do have to box in service pipes & a Trevi Boost shower mixer.

 

[Richard C]

Plasterboard has a thick lining paper covering & cement based tile backer boards similarly have a woven fibre covering front & back. Score through one side of this with a sharp Stanley knife, support one side of the board & knock the other sharply with the palm of your hand & it will snap cleanly along the line; cut through the other side to separate the two. For cutting odd shapes or non cement backer boards, use an old rip saw.

Backer boards (& even plasterboard) can be very rigid but it has no structural strength in the sense you can just screw one bit to another or, say, rely on it to support a shower mixer valve. For boxing pipes, it’s usual to build & fix a timber frame from, say, 40 x 20mm sawn timber around the pipes & fix the boards to that. For mixers/valves, you should either fix through firmly into the wall behind the board or, in the case of studwork, provide additional internal studwork.

 

[Paul348]

Sorry to butt in Richard (not having a dig at what you say as i know you are much more experienced in this sort of thing ) but would like to raise a few questions if i may.

I note you are not in favour of the use of plywood to tile onto as “is not dimensionally stable when subjected to even ambient seasonal moisture changes" instead you advise the use of backer boards, however as the OP has said they cannot be fixed to each other without the use of a timber support.

Now if you use a saw timber 40x20 for a frame is this not more likely to twist and not be dimensionally stable as say a man made sheet of WPB ply that is known to be more stable in these conditions. ?

What’s you take on that ?

 

[Richard C]

Interestingly & by a complete fluke due to using an old browser version (I’m still configuring my new PC ), I found this;
//www.diynot.com/forums/viewtopic.php?p=1152940#1152940
I had completely forgotten about it (understandably with my brain as it was a while ago ) but it gives more info & may be of interest.

 

[Richard C]

Sorry to butt in Richard (not having a dig at what you say as i know you are much more experienced in this sort of thing )

It’s an open forum & your quiet at liberty to “butt in” whenever you want but with a comment like that, my immediate impression is your "blowing smoke up my asre".

but would like to raise a few questions if i may.

You’re at liberty to post what you want whenever you want as long as the mods are happy but advice is generally “on topic” rather than “hijack” with questions you may have to satisfy your own inquisitiveness or having a “poke”

I note you are not in favour of the use of plywood to tile onto as “is not dimensionally stable when subjected to even ambient seasonal moisture changes" instead you advise the use of backer boards

No I’m not in favor of using ply for a wall tile base as you well know & as I advised on your post a while back for the reasons stated! Were you not happy with my advice

A single thickness of WBP is, however, my preference on replacement floors, very well fixed & sealed back & edges; this I generally prefer above a (whatever) floor base + tile backer boards.

however as the OP has said they cannot be fixed to each other without the use of a timber support.

Did the OP say that? I thought I said that! But see my subsequent post as this has come up before which I had forgotten about.

Now if you use a saw timber 40x20 for a frame is this not more likely to twist

A 40 x 20mm timber frame on it’s own fixed to the wall will be quiet flimsy (build one & you will see) but whatever you fix to it will stiffen it up very considerable; it's only there to provide support for the boards. If it’s a ply face, the whole lot can still "float around" under the influence of moisture; a well fixed, dimensionally stable facing board, however, will hold it all together & it won’t move very far & if there is any movement it will certainly be within a (decent) manufacturers/BS flexible addy & grout product tolerance. It’s not normal to box in pipes in a wet area (if that’s what is happening) which is why I was rather more concerned over the stability of ply.

and not be dimensionally stable as say a man made sheet of WPB ply that is known to be more stable in these conditions. ?

That is totally incorrect; there is no way on gods earth that a timber product which can/will absorb moisture & expand/contract (unless totally sealed) will be more dimensionally stable than a board made from inert material which is unaffected by moisture, whatever that may be. Many different materials are use for backer boards some of which are actually absorbent (classed as water resistant) but the difference is, they still remain dimensionally stable even when saturated, anything made from timber will not. But I think weve been through this before!

What’s you take on that ?

My take on it is that if you want to debate & argue the merits of ply as a tile backer base for walls, you should post in your own right instead of confusing the OP’s thread.

 

[Paul348]

Jesus Richard you are MR grumpy aren’t you! And don’t take to well to being questioned

My point is you don’t advocate the use on ply wood for boxing as in your words is “not dimensionally stable when subjected to even ambient seasonal moisture changes” but making a frame out of says spruce pine is ok ? I understand the tile baker boards are the best to use but they have to be attached to wood at the end of the day.

Regarding my project, i have shared Emails with Bal and they have no issues with tilling over WPB and when asked it i need to use backer boards they said ply is better to work with as you can “fix it together better”

There is an article here on plywood http://en.wikipedia.org/wiki/Plywood note “Plywood is used instead of plain wood because of its resistance to cracking, shrinkage, and twisting/warping, and its general high degree of strength”

 

[Richard C]

Jesus Richard you are MR grumpy aren’t you! And don’t take to well to being questioned

I don’t mind answering any questions the OP wants/needs to ask on his thread but I don’t see why I/he should be distracted by 3rd party questioning rather than someone offering contributory/better advice.

My point is you don’t advocate the use on ply wood for boxing as in your words is “not dimensionally stable when subjected to even ambient seasonal moisture changes” but making a frame out of says spruce pine is ok ? I understand the tile baker boards are the best to use but they have to be attached to wood at the end of the day.

I thought I explained that one already but I will have another go. The boxing frame itself is rather flimsy, usually 3 vertical lengths of timber with some horizontal noggins around every 600mm, it’s not intended to be structural & doesn’t need to be; have you ever made one? The whole thing only becomes “stiff” when you fix the outer boards to it & any shrinkage/twisting in the timber frame will not have enough force to distort the boards that are fixed to it unless you’ve built it to 4th bridge specification which is completely unnecessary.

Regarding my project, i have shared Emails with Bal and they have no issues with tilling over WPB and when asked it i need to use backer boards they said ply is better to work with as you can “fix it together better”

I never said you can’t tile over ply but why bother if it posses risks without additional prep; backer boards don’t need any prep! I also know for a fact that BAL would not advise you use ply in a wet area unless the tile face is tanked & they always advise the back face & edges are sealed with acrylic/SBR primer, which I’ve already stated; it’s in their warranty conditions!

There is an article here on plywood http://en.wikipedia.org/wiki/Plywood note “Plywood is used instead of plain wood because of its resistance to cracking, shrinkage, and twisting/warping, and its general high degree of strength”

I’m fully aware of the properties of ply & timber, nothing there I didn’t know already (still got my grandmothers eggs to suck) as I’ve used some very exotic faced ply & structural blockboard in the past on specialist installations (not bathrooms or tiling). But, as I said before, it’s still wood & wood WILL expand & contract with varying moisture content, hence it’s not dimensionally stable unless fully sealed but why go to all that trouble; backer boards are made from materials that are unaffected by moisture, although some may absorb it, they won’t expand, contract or warp, that’s the whole point.

If the OP was just being used for boxing in pipes in a corner of a bathroom then no real problem (although I would use MR plasterboard) but the guy appears to be using this in a shower enclosure &, from what I can make out, fitting a shower valve to it as well & that leaves the back (untilled) ply face open to moisture/water unless sealed.

I don’t mind justifying my advice to anyone &, equally, anyone else is free to offer theirs but give your own advice don’t “nit pick” at mine without contributing anything other than “debating” on someone else’s thread. You obviously have a questioning mind & perhaps you feel that after a couple of “Es” from BAL, you’ve gained enough “experience” to become “an expert” & offer up your own advice; feel free to do so but why question the advice of others! & if you really want to get into a debate about it, post your own thread rather than “Trolling” which only detracts from specific advice being given to the OP.

Post what you like now, I will not enter into any further debate here; I suspect the OP’s rather ****ed off with it & already done a runner; oh, loose the rollies or I really will become Mr Grumpy.

 

[Paul348]

Richard, you have your way and others have their way maybe you need to allow room for other peoples “opinions” rather than shooting them down as i have seen you have a habit of doing in your replies.

And just for you

 

[jctilingservices]

Richard, you have your way and others have their way maybe you need to allow room for other peoples “opinions” rather than shooting them down as i have seen you have a habit of doing in your replies.

And just for you

Paul,
Not having a go mate, but, how can you come on this forum, leave a post for Richard asking for his help, then hijack another thread and contradict Richard, it beggars belief that you would ask him for advice then have a go at him.