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How much waterproofing admix to use?

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In follow up to my other topic about the concrete turning to dust, I'm gonna cover the top with repair cement with waterproofing admixture.

I purchased Sika plastocrete for this, and looking at the instructions, I'm getting confused.

You need to add the solution to the water before you add the water to the cement.

But their instructions are not how much solution to add to the water, but how much solution to add to the cement. Other brands give similar instructions

0.5 kg. (0.43 l) per cement 2 bags (contains 50 kg / bag)

Of course I don't know in advance how much water I will have to add to the cement, to get the repair cement at the correct workable thickness, and neither am I gonna mix 50kg in one go.

So can anyone give me an indication how much Sika plastocrete solution I should add to 10 liters of water?

There are two types of hydrofuge for cement mortars and concretes. The one you are writing about is for adding to the water used when preparing the mix. The other type is applied by brush or spraying to the cured surface to cause it to throw off moisture such as rain. 'Sika' makes both types, but I have only used the former here in Thailand.

https://usa.sika.com/en/construction/repair-protection/coatings-water-repellents/silane-siloxane-coatings/sikagard-705-l.html

Possible additional precaution: afterwards covering the surface with a bituminous paint before re-laying slates?

(Surely not real slates: 50 years ago in the UK they cost a fortune - I had a slate roof).

  • Author
52 minutes ago, ericbj said:

There are two types of hydrofuge for cement mortars and concretes. The one you are writing about is for adding to the water used when preparing the mix. The other type is applied by brush or spraying to the cured surface to cause it to throw off moisture such as rain. 'Sika' makes both types, but I have only used the former here in Thailand.

https://usa.sika.com/en/construction/repair-protection/coatings-water-repellents/silane-siloxane-coatings/sikagard-705-l.html

Possible additional precaution: afterwards covering the surface with a bituminous paint before re-laying slates?

(Surely not real slates: 50 years ago in the UK they cost a fortune - I had a slate roof).

The slate is natural slate stone bought directly from the miner in Sihkio. I bought 30 tonnes of it and used it for multiple purposes.

And although I still have spare, I don't intend to add it again. Also no need for bitumen, because the small roofs have plenty of slope.

The problem is that with the slate the water probably got under it, and didn't get drained.

Leaves the question what is the ratio Sika Plastocrete to water.

33 minutes ago, CallumWK said:

Leaves the question what is the ratio Sika Plastocrete to water.

This is from Sika Cambodia:

"Recommended Dosage 0.5 kg. (0.43 l) per cement 2 bags (contains 50 kg / bag)"

https://khm.sika.com/dms/getdocument.get/0bc5e852-7af1-4b68-b745-305159e47fa2/sika_plastocrete.pdf

This is obviously for the adjuvant type. There are many types of Sika hydrofuge, but maybe only one in Cambodia, since no type number is given. Perhaps the same in Thailand.

It sounds as if you are planning to place a screed over the existing concrete. Might be worth embedding polyester mesh, if available, to reduce risk of cracking. If you overdose, not a problem, but setting time can be very slow.

  • Author
35 minutes ago, ericbj said:

This is from Sika Cambodia:

"Recommended Dosage 0.5 kg. (0.43 l) per cement 2 bags (contains 50 kg / bag)"

https://khm.sika.com/dms/getdocument.get/0bc5e852-7af1-4b68-b745-305159e47fa2/sika_plastocrete.pdf

This is obviously for the adjuvant type. There are many types of Sika hydrofuge, but maybe only one in Cambodia, since no type number is given. Perhaps the same in Thailand.

It sounds as if you are planning to place a screed over the existing concrete. Might be worth embedding polyester mesh, if available, to reduce risk of cracking. If you overdose, not a problem, but setting time can be very slow.

That is the same instruction as I posted in the OP, but doesn't make much sense to me, since you have to mix the solution with the water before you add it to the cement, and I don't know how much water i'm gonna need.

I'm gonna use Crocodile repair mortar, about 5mm over the slate stone, which is supposed not to crack.

Like I said the roof has a high slope, the issues is that the slate was clad on the concrete, and water get under it,then has nowhere to go.

If there is a slab all over, that issue is not possible anymore.

3 hours ago, CallumWK said:

That is the same instruction as I posted in the OP, but doesn't make much sense to me, since you have to mix the solution with the water before you add it to the cement, and I don't know how much water i'm gonna need.

I'm gonna use Crocodile repair mortar, about 5mm over the slate stone, which is supposed not to crack.

Like I said the roof has a high slope, the issues is that the slate was clad on the concrete, and water get under it,then has nowhere to go.

If there is a slab all over, that issue is not possible anymore.

Well, first of all you need to decide how much you are going to mix overall, the ingredients (coarse aggregate or not), and the ratios of the dry matter (which the specs give by weight, but I measure by bucket).

If it is concrete, I normally mix it in my small electric cement-mixer, but if no coarse aggregate, by hand (using a hoe-like tool) in a big plastic mixing trough because the consistency is better that way when making a fairly stiff mix.

If doing a screed I might use three buckets of coarse sand + one bucket of general purpose cement (rather than concreting cement - although in France I would use the latter mixed, say, 2:1 with hydraulic lime [never seen it here]), then choose maybe ¾ of a bucket of water.

If one figures on using roughly a ½-litre of hydrofuge for 2 x 50 kg bags of cement which we guesstimate at about 9 of the relatively small Thai builder's buckets (the French ones are a good bit bigger), call it 10 for simplicity, that makes it about 50 millilitres per mix. You might find a yoghurt pot makes a good measure for one mix.

Precision is not too critical though better to err slightly on the generous side. Consistency is important; and compaction (tamp with trowel). And not too much water: enough that it does not crumble.

Smooth with a soft, wet brush after it has begun setting. And of course keep surface damp until thoroughly cured.

I know nothing about Crocodile repair mortar (contains polypropylene fibres?), so cannot help you there. For a normal screed, if memory serves, the recommendation is 20 mm minimum thickness. I might feel inclined to bed wetted slates on to freshly laid screed before it has time to start setting. But have no idea if that would give satisfactory result.

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