Waterproofer in scratch or float coat(external)

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cornick8004

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Hi all
Im having a debate with my dick of a mate about what coat to put waterproofer in when rendering externally.

I say depends on weather,i use waterproofer in scratch in summer and in float coat in winter.

what do you think spreads?
 
Doubt you even have to use it in the top coat in the winter if there's none in the scratch it's more to do with holding off the suction it'll still be pourous to a certain extent
 
Depends on what you're going over id use a 4-1 and 5-1 on block with waterproofer in the first coat in winter I'd use feb
 
We have always put waterproofer in both scratch and top. In the scratch in enables greater working time for larger areas. The mix depends on the stength of substrate being rendered.
Typically a light agg block would receive a 4.1.1 scratch ( washed sand/sharp sand/cement) and top with 6.1.1 ( Washed sand/ hydrated lime/ cement) Always bucket guaged.

The cementone integral waterproofer we use has very good plasticising qualities . so no need for bob standard feb.

You may consider no waterprrofer in scratch over dense concrete in colder conditions.

The lime acts as a good binder , making the gear easier to apply and easier to close in and finish.
 
In general, we aways do, its jus a practice we have kept to for years, ans it has worked for us.The system still remains vapour permeable with the additive and mixes we use..
May be on extrenal garden walls of dense concrete construction we would use feb in the scratch, to speed things up when toping.
 
We put about half a much in the scratch as in the top.
around quarter of a pint in the scratch and half pint per mix in top.

You need to kill the suction but not too much.
 
If you speak to the manufacturers cementone, feb etc they all recommend putting it in both coats. There is nothing wrong with doing this is some might argue.

Remember you shouldn't use lime if you are using waterproofer.

I tend to put the full amount recommended in scratch and half it for the top coat.

If 3 coat tyrolean I won't add to top coat just do sand/cement/lime some feb
 
My worry with putting no waterproofer in the top coat is that if it isn't painted, rain/moisture could be drawn into it, freeze, expand and damage the render.
 
It'll still take water in what do you think happens when you skim sand cement if it didn't absorb moisture it'll all come off in sheets
Freed why can't you mix lime and waterproofer
 
spunky said:
It'll still take water in what do you think happens when you skim sand cement if it didn't absorb moisture it'll all come off in sheets
Freed why can't you mix lime and waterproofer
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Because lime has the opposite effect of waterproofer, making the surface more porous. Theres no need for it either as integral waterproofer will plasticise the mix with air entraining agents. Basically it counterproductive, if you read the back of cementone integral waterproofer it says..do not mix with lime.

Another time I wouldn't use waterproofer in top coat is when it gets colder.
 
If you have got the correct amount of waterproofer in the scratch it should be ok to leave it out of the top. If you live in a high weather exposure area i'd definitely be adding it to both coats.
 
DannyMac said:
My worry with putting no waterproofer in the top coat is that if it isn't painted, rain/moisture could be drawn into it, freeze, expand and damage the render.
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Thats the problem with putting it in the top, when it gets in it will freeze and blow the top coat off, Its not completely water proof, your top coat is supposed to absorbe water then it just dries out but will not get past the scratch.
 
Hydrated lime is a by product of slaked lime it doesn't help it breath it lightens the mix like an extra shovel of sand and splits the particles like a good feb mix I've used it with waterproofer and there's no reason not too Ive had too because of thickness Sand cement is brittle including hydrated lime don't get carried away thing hydrated lime is the queen bee and will stop everything cracking and allow it to breathe if you want that you need to look at hydraulic lime
 
flynnyman said:
Thats the problem with putting it in the top, when it gets in it will freeze and blow the top coat off, Its not completely water proof, your top coat is supposed to absorbe water then it just dries out but will not get past the scratch.
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This will happen whether waterproofer is in the mix or not. At least if there is waterproofer in the top coat it won't get as saturated. Lime in the top coat will only draw more water into the top coat increasing the amount it retains increasing the chance of damage to the render, especially in high weather exposure areas. modern paints e.g Weather shield are breathable.

Modern bagged renders have waterproofing additives in them and are not left out of coats.
 
spunky said:
Hydrated lime is a by product of slaked lime it doesn't help it breath it lightens the mix like an extra shovel of sand and splits the particles like a good feb mix I've used it with waterproofer and there's no reason not too Ive had too because of thickness Sand cement is brittle including hydrated lime don't get carried away thing hydrated lime is the queen bee and will stop everything cracking and allow it to breathe if you want that you need to look at hydraulic lime
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I have to m8, its not going to necessarily cause problems using them together there is just no point as a good quality integral waterproofer will do all that lime will do and more, and is a better job.
 
No it won't ask any decent renderer if he wanted to swap feb for lime and he'll go lime every time
 
We did a load of store rooms in a high rise a few years ago when I was first starting out and we used lime sand mortar. Nicest stuff I've used to float with. Not so nice when you're putting the lime in the mixer and the wind blows it in your face
 
You can't beat lime in the mix, especially for floating. But ask any decent renderer who's actually thought about the properties of the materials they are using and the affect they will have on the finished product, will be using waterproofer in the top coat.
 
FreeD said:
This will happen whether waterproofer is in the mix or not. At least if there is waterproofer in the top coat it won't get as saturated. Lime in the top coat will only draw more water into the top coat increasing the amount it retains increasing the chance of damage to the render, especially in high weather exposure areas. modern paints e.g Weather shield are breathable.

Modern bagged renders have waterproofing additives in them and are not left out of coats.
Click to expand...

What will happen?
 
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