# Forum Home Renovation Waterproofing  Getting the subfloor right

## PTrenovator

We're planning our bathroom reno.  I've lined up a plumber and tiler/waterproofer and a friend who's done several renos.   I am doing as much labour as I can, but I want to make sure with proper planning we end up with what we want and a leak/hassle free end result. 
What we have is a suspended concrete slab (sloping) on a brick base wall around the perimeter of bathroom. Years of water damage and  the bottom of the studs and the bottom plate that make up the shower wall are almost non existent. The joist and end of the bearer below the shower wall have rotted to the point they provide no support at all.  The house has obviously been restumped a few years back as they're prefabbed concrete stumps and house is circa 1930-40s.  End of bearers that support adjoining rooms finish/sit on the brick base wall of the bathroom.     
Plan.. rip out suspended slab and brick base wall and replace bathroom subfloor with stumps, bearers,  joists and FC sheeting. 
We want/would like the bathroom floor tiles flush with the timber floors in hallway. Ideally we would like a small step down <50mm into the shower or at least have it flush with the rest of the bathroom tiles.     
Firstly can the entrance to the bathroom be flush or do you have to have the aluminium angle slightly above the timber floor in hall? 
I am allowing .. 18mm FC sheeting, 40mm screed at entrance to bathroom, 10mm for tiles and adhesive.  (18mm+40mm+10mm=58mm).  Top of joists need to be 58mm below the existing timber floor. Am I missing anything? 
Have I allowed enough screed to achieve required fall. Bathroom is only 2.8x2.4m. and if we do decide to step down into shower I'd need to notch out the joists. Maybe Im better to lower joist further and pack them up for rest of bathroom... really unsure on allowance and want to get this right.. 
Cheers

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## Oldsaltoz

Adding a floor waste as well as a shower waste will reduce amount of screed needed as the distance to a drainage point is reduced. 
Work out you levels first to calculate the fall, floor outside the shower can one in 100 and shower can be set at one in 80. to minimise screed. Base the depth from the shower base. 
Setting the full floor down takes no extra material or labour and will improve the whole renovation. 
You will still need a watertop in the doorway, but it will be a flush fit to the bathroom tiles. 
Good luck.   :Smilie:

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## barney118

Sounds like you are proposing a major job for no reason. Timbers rotting etc is a function of no waterproofing and easily fixed. the concrete is there for structural purposes just like the timber option you have mentioned, the only issue is drilling for pipe holes etc. I hired a bloke from the yellow pages to cut new holes in my floor with his diamond drill core hole cutter for $100 a few years back now. all you need to do is screen a base over the top then waterproof over the floor and walls, obviously the weak points such as the joins wall/floor is where potential water gets in and your last room wouldnt have had any waterproofing at a guess so replacing the subfloor with something else is not going to solve this problem.
Waterproofing is like a paint on PVC and this is the product that protects the subfloor. IMHO I would work with the concrete over a timber subfloor in a bathroom, concrete is porous a little water will take decades to become a problem whereas a timber floor you could end up in a mess after 1 decade if waterproofing not done right.
A bucket of waterproof costs ~$150 and add at least 3-4 coats and you will still have half a bucket left, of course not the whole story on waterproofing but our expert oldsaltoz will point you in the right direction when the time has come.

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## PTrenovator

I think it's best to replace the concrete slab as its sloping and cracked.  But am still a little unsure of a few things 
Can the water stop at the doorway be flush with floor level outside of bathroom.  
Is 40mm screed at highest point too much....or better question might be what is the minimum at the waste.  I can work out the thickest based on a fall of either 80:1 or 100:1  
what about having a small step down into a walk in shower?   The length of the shower (1200mm) runs same direction as joists. so if i wanted a 20mm step down into shower i would place joists running under shower 20mm below other floor joists in bathroom and only have to pack up or screed the small area outside the shower entrance.    1200mm long shower needs a fall of 15mm at back wall with a grate drain so i would also notch 15mm out of the joist at that end before placing on bearer it will pretty much have its 80:1 fall in place.  ....does any of that make sense?

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## Oldsaltoz

> I think it's best to replace the concrete slab as its sloping and cracked.  But am still a little unsure of a few things 
> Can the water stop at the doorway be flush with floor level outside of bathroom.   As the name imlies, it's there to stop water getting out of the room from under tiles, so if you have tiles outside the room no problem. If you have carpet still no problem ( some people keep a small rug at the door to prevent damp foot prints and avoid the small step as well).  If you have floor boards, the oly practical method is to lower the floor and the agle can be installed flush with the boards outside. 
> Is 40mm screed at highest point too much....or better question might be what is the minimum at the waste.  The floor waste can sit almost on the puddle flange with just tiny bit of packing, most are aroind 20 to 25 mm installed to grate level, However bod standard screed will crack if less than 25 mm thick, there are lots of products available that will work fine right down to 3 mm. 
> The trick is simple, use standard screed till it gets 30 mm then use one of the alternaive leveling compounds to finish the area left. 
>   I can work out the thickest based on a fall of either 80:1 or 100:1  
> what about having a small step down into a walk in shower?   The length of the shower (1200mm) runs same direction as joists. so if i wanted a 20mm step down into shower i would place joists running under shower 20mm below other floor joists in bathroom and only have to pack up or screed the small area outside the shower entrance.    1200mm long shower needs a fall of 15mm at back wall with a grate drain so i would also notch 15mm out of the joist at that end before placing on bearer it will pretty much have its 80:1 fall in place.  ....does any of that make sense?

  If you are lowering the whole floor you should be able to install shower angle (water stops) around 40 mm and still have enough fall for the shower base, the end result will 40 mm screed less the thickness of tile and glue combined outside the shower and the levelled to the same formula, so no step up or down. 
Good luck.   :Smilie:

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## Oldsaltoz

> I think it's best to replace the concrete slab as its sloping and cracked.  But am still a little unsure of a few things 
> Can the water stop at the doorway be flush with floor level outside of bathroom.   As the name implies, it's there to stop water getting out of the room from under tiles, so if you have tiles outside the room no problem. If you have carpet still no problem ( some people keep a small rug at the door to prevent damp foot prints and avoid the small step as well).  If you have floor boards, the oly practical method is to lower the floor and the angle can be installed flush with the boards outside. 
> Is 40mm screed at highest point too much....or better question might be what is the minimum at the waste.  The floor waste can sit almost on the puddle flange with just tiny bit of packing, most are around 20 to 25 mm installed to grate level, However bod standard screed will crack if less than 25 mm thick, there are lots of products available that will work fine right down to 3 mm. 
> The trick is simple, use standard screed till it gets 30 mm then use one of the alternative levelling compounds to finish the area left. 
>   I can work out the thickest based on a fall of either 80:1 or 100:1  
> what about having a small step down into a walk in shower?   The length of the shower (1200mm) runs same direction as joists. so if i wanted a 20mm step down into shower i would place joists running under shower 20mm below other floor joists in bathroom and only have to pack up or screed the small area outside the shower entrance.    1200mm long shower needs a fall of 15mm at back wall with a grate drain so i would also notch 15mm out of the joist at that end before placing on bearer it will pretty much have its 80:1 fall in place.  ....does any of that make sense?

  If you are lowering the whole floor you should be able to install shower angle (water stops) around 40 mm and still have enough fall for the shower base, the end result will 40 mm screed less the thickness of tile and glue combined outside the shower and the levelled to the same formula, so no step up or down.  Good luck.   :Smilie:

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