# Forum Home Renovation General Odds & Sods  Cement sheet, waterproofing, external tiling and other mysteries of the universe

## frog's wife

So many questions..... 
Can you use ordinary cement sheet externally and tile over it with say slate and grout?   
I have a 60 square metres of cement sheet on the outside of a small cottage which we'd like to face with a stone veneer.   
The stone retailer said I need to replace the cement sheet with waterproof blueboard or get the lot waterproofed.  We originally used the cement sheet because a different retailer of stone products listed ordinary cement sheet as a suitable base for external applications. 
Checked on waterproofing pricing, approx $3000 or Blueboard $870 plus whatever it costs to get it up there.  Was thinking that if I have to do it, I'd just put it up over the existing cement sheet.  
Then I was told that silicone wasnt suitable for the joins.  Polyurethane sealers for joins.  Which?  
What do I have to do?  
Sigh.  
Sonja

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## pharmaboy2

some more info required - you say "outside of cottage" - does that mean cladding - ie vertical surfaces or horizontal. 
how thick is the cement sheet, and whats it attached to and how. 
water proofing is usually only concerned with not letting water through the sheet into whatever is behind - usually this requires the joints only to be waterproofed, and the rest to be primed before tile glue is used

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## frog's wife

ok, 
yes outside of cottage ie external walls.  The current cement sheet is 6ml nailed to a timber frame.  I want to use a thin stone veneer to go over the cement sheet. 
Doing some research on "blueboard" it seems to be listed as only WEATHERproof not WATERproof.  that being the case what is the difference between using it and the cement sheet?  Can I use silicone sealant for joints then prime and "tile" over with stone?  I'll be grouting between the stones.  Is this a weak link? 
I'm so confused?  What's wrong with the cement sheet we've used?  How is blueboard different?  
Sonja

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## myla

hello, 
silicone is no good because nothing sticks to it, you need to use sikaflex or bostix seal n flex which are polyurethane's 
you have probably installed villa board (plain old compressed cement sheet), 
i would look at using a high quality tile glue, something like Ultraflex, no pre-mixed jobs but the expensive bags from the tile shop, 
grout is always porous but a vertical wall doesnt absorb that much water, only bottom is issue 
thankyou 
myla

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## frog's wife

thanks myla, 
so is cement sheet more or less water resistant/proof than blueboard?

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## henlan77

What is currently behind the cement sheet? Just the timber frames? If so, you'll have a really hard time making that waterproof. 
Also don't forget that any cladding you add to the outside will affect the window and door architraves. Sounds like you might need some advice from a builder who can inspect the property.
And research the stone veneer products thoroughly - you can buy everything from cheap and nasty manufactured fake stone panels to hand split real natural granite.
Good luck.

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## frog's wife

Henlan, 
The cement sheet is over timber studs but the research I'm seeing on the net says that cement sheet is no more or no less water resistant than blueboard.  The stone veneer is real stone which actually works out cheaper than the manufactured stuff.   
Sonja

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## autogenous

Ask your stone supplier to specify the adhesive to stick the stone onto the sheeting that you choose. 
How thick is the stone you wish to stick on? What sought of weight are you looking at hanging off your house?

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## frog's wife

the stones are 15-20mm and weight is approx 40kg per m2 
This is the stuff here. http://slatediscounts.com.au/Product...s.asp?PID=1402  
Sonja

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## autogenous

So your looking at 2.4 tonne hanging off the 60m2 studwork 
Do they have data sheet of specifications for this particular product? 
If your concerned about water proofing then Dulux Acrapatch the joins and give the whole sheet area a coat of neate cement hyrdrocrete mix as per directions on the Hydrocrete container. 
Ring James Hardie or CSR and they will tell you minimum @18mm CFC to hang the stone (more weight) 
You will need to screw the sheets at specified centres to hold the weight of the total materials to the stud. 
The CFC acts as a speed brace when screwed off to stop the stud work twisting under 2.4 tonne wieight

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## frog's wife

The stone retailer is recommending blueboard at 7.5mm to hang the product.  His argument for blueboard against cement sheet is a waterproofing issue not a weight issue. 
I'll check with Hardie/CSR/BCG about the vertical weight load of their sheet.  
Sonja

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## Dirty Doogie

I have clad a few exterior walls with stone and slate very similiar to what you are trying to achieve (I think). I did some research about the technical aspects and used Blueboard screwed  to studs set at 400 centres. Then over the blueboard I applied an exterior grade waterproof membrane (Gripset 2 P) over which I glued the slate using exterior grade cement based tile glue and finished with cement based grout. (cement based glues and grouts stick to the gripset like you wouldnt believe) 
To date (5 years later) there have been no problems. I think the waterproofing membrane is the important aspect becuase water can get behind the slate and stones and needs to be kept out of the blueboard sheet becuase all uncompressed fibre cement sheeting will soften if left damp. This could lead to stones / tiles falling off and taking a few layers of blueboard with it.

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## autogenous

Thats excellent information Doogie.   

> Gripset 2 P ?

  http://www.gripset.com/fullarticle.php?a=25 
Thanks heaps and I'm sure FrogWife will be happy to hear what you have to say too.

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## frog's wife

DD, 
where did you get the gripset?  Approx price?  Easy to apply? 
so you did blueboard, gripset, tile adhesive.  Did you have to prime it at any point?  Am being told prime and glue.  That wouldnt be necessary if you'd waterproofed would it?   
Sonja

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## Dirty Doogie

Sonja, you may have to check the yellow pages in Melbourne. Or maybe check website for stockists. http://www.gripset.com/construction/...hp?productid=9 
It is 2 part membrane (1 part liquid 1 part powder and has a strong acrylic latex smell but not dangerous) - a 15 litre  drum is about $120. It can be rolled or brushed or trowelled on.  
I sealed the blueboard with a coat of Gripset sealer (one of those water white PVA type sealers). In the seams between the blueboard I simply used Gripset and a bit of reinforcing bandage.

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