Sink Worktop - Hardibacker or ply?

[pt44]

Hi

Making a sink worktop to be tiled in Porcelain 600x300's. I need something structural for the weight of the sink - waterproof ply would do 12mm or 18mm. However, would people recommend that I then use something like 6mm Hardibacker on top of that? Or is it fine to lay direct onto the ply - as its not going to be getting that wet - like a shower for example.

Paul

 

[grumpygrouter]

You would be fine to lay on ply IMO. Ply is used on floors so why not a worktop. My only reservation would be potential for water to get through to the ply. Even marine ply if it is not sufficiently protected would be damaged. Maybe put a tanking membrane down first and then tile on top of that?

 

[White Room]

I would go the hardie backer route IMO

 

[sweaty sock]

i would look at wedi board for this countertop and you will have no probs with tiling direct and easy cutting and prep -:8::8:

 

[grumpygrouter]

i would look at wedi board for this countertop and you will have no probs with tiling direct and easy cutting and prep -:8::8:

I have never used Wedi, is it sufficiently strong to have a cut out for a sink and give enough support?

 

[pt44]

i would look at wedi board for this countertop and you will have no probs with tiling direct and easy cutting and prep -:8::8:

Hi Sweaty - I use wedi board extensively, and I love it, but I don't trust the thin stuff for a worktop - i.e. 12.5mm

I could of course go thicker, but then it becomes a really thick top - which I am trying to avoid - the 50mm wedi is great to use. On the other cabinets I've made to cover up toilets and sinks etc. I like to use something a bit more substantial. In the project I'm doing now, the sink is one of those vanity type - that hangs over the front edge. So all that is holding it in place is the plumbing and some silicone. I like the feel of having a solid board as the structure for the top - that is well screwed to the frame. So the 6mm hardibacker is merely acting as a waterproof layer, for the ply - belt and braces and all that. For the front of the cabinet, I will just use the 6mm hardi on its own, with no backing. This is so that I'm not bringing the existing cabinet too far into the room - as I would have to alter the toilet position etc. too much. I'm replacing a basic 12mm painted mdf, with 6mm of hari + 10mm tile and adhesive. Hopefully, keeping the plumbing as is (tho I may need to tweak it).

 

[pt44]

I have never used Wedi, is it sufficiently strong to have a cut out for a sink and give enough support?

Wedi is fantastic stuff. But does have its drawbacks when making sink tops - imo. For example, because its not strong on compression, I wouldn't like to be the one tightening up a tap under it. It will just compress - its just foam with a skin of cement on either side - no body to it.

Wouldn't be so bad for a sit on sink bowl - where there is nothing needing to be tightened to it. With the tap coming out of the wall or something.

Also applies to building under sink cabinets. As it has no body, you can't screw a door hinge into it. Would be great if you could. Don't get me wrong - its well strong enough for a lot of jobs - and a unit built out of simply 50mm panels will be well strong and quick to make. But then you couldn't easily put a door on that cabinet. You'd end up making a wooden frame inside - to hang the door - thereby defeating the need for the thick wedi. So you'd be back to 12mm for structure - but that can be too thick for something like a cabinet - hence - back to good old Hardi (though I hate cutting hardi).

Wedi is perfect for making wet rooms, their preformed trays and drain fittings are superb and the waterproof tape etc. works well (tho is expensive). The boards are just like putting up plasterboard - dead easy.

Paul

 

[Alberta Stone]

If you are making a working countertop then go with3/4" exterior grade sheathing plywood and prime and tile.
If there is a sink in it, do the cut out and then use one of the liquid waterproofing products (like mapei HPG) and apply that around the sink hole area (including the sides of the cut out) and up against the wall, where water is likely to get to.

Wedi is nice, but is foam and is not structural like wood.
CBU are also not structural and they absorb water like a sponge.
Both of these are not practical.
Stick to ply.

 

[pt44]

Not heard of Mapei HPG - will do some research. Normally on ply I have always just coated the edges in PVA - not perfect, but a good sealant. I presume the HPG stuff does a better job? When you say prime the Ply - would that be PVA'ing it? Or does a dedicated primer (I've used the ardex blue stuff before) do something more?

 

[grumpygrouter]

The Mapei is a proprietry brush on waterproof coating.

 

[Alberta Stone]

Here is the link for the HPG:

broken link removed


Here is the link for the primer:

broken link removed

Here is Mapei's web site:

mapei.ca

By PVA you mean polyvinyl acetate:huh2:
If so, then, it does not make a good primer.
It will work in a pinch, but you should use the professional bonding agents.
There are other companies which make just as good a product that may be more convenient and cheaper such as can be found at masonry supply shops.
The dedicated primer penetrates better and is far stickier and is designed chemically to adhere to concrete products.
PVA is designed for wood primarily, but they say it is universal and you can use it on anything. So they say.

 

[pt44]

PVA - as in the glue is a wonderful substance. And it does bond to anything, almost. I, along with most builders use it extensively, to seal walls before plastering, to seal concrete, before adding more concrete (patching etc.). It can even be added to mortar or concrete, to give it extra sticking ability. Fantastic stuff.

And it glues wood too :hurray:

However, although it does seal wood and add a waterproof layer, how well it does it has always been something that I've questioned in my mind. I'll check out some of the products you've mentioned.

Paul

 

[Alberta Stone]

PVA does absorb moisture after it dries and turns milky from clear and so will allow concrete layers to shear as a result.
The cheaper pva's turn brittle, the more expensive ones stay rubbery.
It does work, but from my experiments with concrete work, the dedicated stuff works better when exposed to extremes in temp and moisture.
I agree that its good stuff, for its purpose.
I did use it for years, for tons of different things, but came to the conclusion that the other specified gear is better, so I have put that opinion to the test.