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How to tile onto Villaboard?

bigkid

Hi,

I am nearly finished framing up a ledge in my new shower but just have a quick question regarding a window sill.

I want the ledge to finish flush with the rendered brick window sill as both the sill and the ledge will be tiled.

The frame will be sheeted in 6mm villaboard. So do I finish the frame 6mm lower than the sill to allow for the thickness of the villaboard? Or do I finish it about 15mm lower than the sill to allow for villaboard and render?

I have read that sometimes you can directly tile onto villaboard, though not sure it just seems a bit dodgy.

Cheers,

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JacobZ

Hi @bigkid,

You would finish the framing 6mm below the ledge as there is no need for render in this situation.

Tiling directly onto Villaboard is perfectly acceptable as it is specifically designed as a stable, moisture resistant substrate for wet areas.

In saying this, you will have to apply a waterproofing membrane such as this https://www.bunnings.com.au/crommelin-1l-shower-waterproofing-membrane_p0964589 over the Villaboard to protect the timber frame beneath it. This membrane needs to extend onto the wall behind the framing using https://www.bunnings.com.au/bastion-100mm-x-10m-bond-breaker-waterproofing-joint-band-10m_p0355672 for the junctions. By tying the membrane into the wall, it removes the risk of water dripping down the wall and getting in behind it.

Check out https://www.bunnings.com.au/diy-advice/diy-skills/painting/waterproofing-buyers-guide-what-you-need-to-know and https://www.bunnings.com.au/diy-advice/home-improvement/walls/how-to-waterproof-your-bathroom for some further guidance.

Let me know if you have any further questions.

Jacob

bigkid

Hi @JacobZ thanks for the info.

So even if there are joins in the villaboard sheeting it still does not require rendering? What will stop potential movement between the villaboard and window sill if it is not rendered?

And yes the whole bathroom will be waterproofed by a professional.

JacobZ

Hi @bigkid,

There's no real need for render as everything will be covered by a membrane and tiles anyway. You'd only really render it if that was going to be the exposed surface.

The main thing you'll want to do to prevent issues from movement is ensure that the timber is adequately dry so that it doesn't shrink after installation, and ensure that it is adequately fixed to prevent movement.

Once the timber is fixed in place, you could simply install the Villaboard up to the sill and apply a bead of https://www.bunnings.com.au/bastion-300ml-bond-breaker-joint-sealant_p0363836 between the villaboard and the sill. This will allow for a small amount of expansion and contraction in the materials. You can do this yourself, but I imagine your waterproofer would do it as part of their process anyway.

Your waterproofer will then apply their https://www.bunnings.com.au/bastion-100mm-x-10m-bond-breaker-waterproofing-joint-band-10m_p0355672 over that join which will also allow for small movements between the materials.

If you then wanted to go even further, you could install a small control joint in your tile. This is done by lining up the grout line with the joint and then using silicone instead of grout to finish that line.

In practicality, if there is any movement between the surfaces, which should be minimal assuming the timber is dry and stable, then that movement will be managed by the bond breaker sealant, joint band tape and then the silicone in your grout line.

I hope this makes sense. Please let me know if you have any further questions.

Jacob

bigkid

Hi @JacobZ thanks for the info that makes sense and seems pretty logical and straightforward.

Can you offer any advice on this brick nib wall that will also be waterproofed and tiled, but will have an arched frame built up and over the top of it?

The frame will have a 90x45 LVL jack stud running up and secured to the left and right external brick walls, and will then be sheeted with villaboard. The total thickness of the frame will be 90mm for the stud plus a 9mm sheet of villa board either side, which will result in 108mm total thickness, pretty close to flush with the 110mm thickness of the brick nibs.

I am thinking the brick wall may have to be rendered though as it is not perfectly flat, but that render will then sit proud of the villaboard of the frame.

What do you think is the best way to handle this situation?

JacobZ

Hi @bigkid,

I'd agree that the brick needs to be rendered before tiling, just so everything is nice and flat. Depending on how thick you go with the render, this would likely add somewhere from 10-20mm of thickness to the wall which you'd want to account for.

In that scenario, I'd just pack out the studs so the villaboard lines up with the render. It's pretty common for chippies to pack out studs using strips of masonite nailed and glued to the face of the studs prior to sheeting. You can add a couple of layers to either side of the stud to make up the difference.

You'd then just attach your villaboard as normal before waterproofing and tiling.

Let me know what you think.

Jacob

bigkid

So I have had a plasterer recommend that I finish the villaboard flush with the brick walls as it is, then he will come in and render it. He said the render will only be about 3-4mm thick, anything more would require a second coat and a second site visit.

I had bought 120mm studs, planning on leaving the villaboard about 11mm proud (120 stud plus 6mm villaboard on either side) of the brick walls and then having someone make up the 10-11mm overhang by just rendering up flush with the villaboard. But now I’m not too sure what to do.

Any advice?

EricL

Hello @bigkid

Your plasterer is giving fairly standard advice for a cement render finish. A 3 to 4mm skim coat over flush sheeting is usually the safest and cleanest approach because render performs best as a thin finishing layer rather than being used to “build out” large differences in surface depth. Looking at your photo, the brick nib walls appear reasonably straight and solid, so bringing the Villaboard flush to the brickwork and then applying a thin render coat across the whole surface would likely give the most consistent finish with the least risk of cracking or unevenness later on.

If you leave the Villaboard sitting 10 to 11mm proud of the brickwork and expect the renderer to build the brick side out to match, that becomes a much thicker render application over the masonry sections. While technically possible, once you start getting around 10mm or more thickness in areas, many renderers will want multiple coats or reinforcement mesh to reduce shrinkage cracking and hollow spots. That is why your plasterer mentioned a second coat and second visit. Thick patch-up rendering tends to take longer to cure properly and can sometimes show slight movement lines where different materials meet.

From a practical point of view, your plasterer’s method is probably the more straightforward and lower-risk option. You could either reduce the wall framing depth slightly so the Villaboard finishes roughly flush with the brick, or attach thin, narrow strips of timber to the existing brick wall where needed to help bring the surfaces into alignment before the Villaboard is installed. The aim is to have the Villaboard and brickwork sitting within only a few millimetres of each other before rendering begins.

The important thing is that the final transition between Villaboard and brick is minimal before rendering starts.

One thing I would strongly suggest is ensuring the joint between the Villaboard and brick is reinforced properly before rendering. Where masonry meets sheet material, movement can occur over time. A good renderer will normally use alkali-resistant fibreglass mesh tape embedded into the base coat across those transitions to help prevent future hairline cracking.

Also, because this appears to be a wet area renovation, make sure the Villaboard installation and waterproofing sequence are clear before any render goes on. If this area is becoming a shower or bath recess, waterproofing should generally continue across the rendered surfaces in accordance with Australian wet area requirements.

Overall, based on your photo and what your plasterer has said, I would lean toward bringing the Villaboard flush with the brickwork rather than trying to build out 10–11mm with render. It will likely produce a flatter, more durable result with less labour, less drying time, and less chance of cracking later.

Let me call on our experienced members @Nailbag and @Dave-1 for their recommendations.

If you need further assistance, please let us know.

Eric

bigkid

@EricL thanks for the detailed response, some great info there.

I suppose I could rip down the 120mm studs to say 100mm and then go 6mm villaboard either side for a total of 112mm thickness. Or I could use 90mm studs and 9mm villaboard for 108mm thickness. Either method would get the villaboard close to flush with the brickwork.

I’m thinking the renderer will not render the villaboard, only the brick walls. If that is the case, I was thinking of having some sort of flexible PU sealant or bond breaker between the bottom of the stud and the top of the brick wall. Then once the villaboard is up and brick wall rendered, the waterproofer can use sealant/reinforcing tape across the villaboard-brick interface. Finally I would ask the tiler to put a silicone control joint in that area. Is this a reasonable way to go about dealing with any movement across this area in the future?

I should also note the brick nibs have been tied into the bathroom walls with chemset + rods and the timber stud will likely also be chemset’d into the wall, to try and further limit movement between these two elements.

EricL

Hello @bigkid

You are clearly thinking this through carefully, and I think your approach is heading in the right direction. A lot of the long-term issues in bathrooms tend to occur at transitions between different materials, so it makes sense to be considering movement, waterproofing and finishing details now rather than after everything is tiled.

Bringing the Villaboard close to flush with the brickwork is definitely the ideal direction to go. Personally, I think the 90mm stud with 9mm Villaboard approach is probably the cleaner option if it gets you within only a few millimetres of the brick face, because it avoids unnecessarily modifying structural timber and keeps the system simpler. Either way, the goal is the same: minimise the render build-up required on the masonry.

I recommend being cautious in regard to how exactly the renderer intends to finish the surfaces. I think this is definitely a discussion you should have with both the renderer and the waterproofer together before anything is locked in, as the intended finished system will affect how flush the surfaces need to be and how the waterproofing details are handled.

I would also suggest double checking with the waterproofing agent in regard to the waterproofing sequence. Under Australian standards, the waterproofing manufacturer’s installation requirements matter just as much as the general building principles. Most compliant systems rely on compatible primers, membranes, reinforcing materials and flexible joints all working together as a tested system, so it is important that the waterproofing details are coordinated by the licensed installer.

The Chemset rods tying the brick nibs into the existing walls are a good move for reducing independent movement of the nibs themselves. Likewise, anchoring the timber stud wall well will help overall stability. However, even with all that reinforcement, timber and masonry will still move differently over time due to moisture and temperature changes, which is why allowing for controlled movement at junctions is still important.

Overall, I think your approach is thoughtful and generally consistent with good building practice, but the final detailing should absolutely be confirmed by the renderer, licensed waterproofer and ideally the tiler as well, so the entire wall assembly works as one coordinated system rather than separate trades making assumptions independently.

If you need further assistance, please let us know.

Eric

Dave-1

Good Morning @bigkid

I am afraid I am out of my depth here, knowledge wise :) So will watch the conversation thread as it is interesting. I have not done any rendering as yet tho have several areas that will need to be done eventually.

Dave

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