Synthaprufe & Render External Blockwork Wall

[jimmy6363]

Hi all, hope you can provide some advice regarding waterproofing and rendering an external blockwork wall I am having some problems with.

A bit of background: the blockwork wall is single skin, plastered internally. Externally, the blocks have an uneven 'splitface' finish - picture attached. I have recently moved in to the house and think the previous owner must have just painted internally as I am starting to see damp patches to the wall.

What I am hoping to do is apply Synthaprufe to the wall externally, then render over the top. I can't Synthaprufe (or batten) internally as the boiler is fixed to one of the walls.

Questions!
- Can I Synthaprufe straight on to the wall as is, or will it require levelling first?
- I am hoping to Synthaprufe it in the next couple of weeks, not ideal I know given the weather but I think the plaster will get ruined if we have a wet winter. Will the Synthaprufe be ok left exposed over winter and then rendered next Spring?

Thanks in advance!

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[ree]

I presume that the slab runs under the walls to become the interior floor? This will make the wall vulnerable to damp penetrating under the wall.

What was the concrete slab previously used for?

Quite how much help rendering the exterior will give i dont know? It would depend on the quality and thickness of the blocks.

Synthaprufing the external surface might give rise to interstitial condensation - you could call the company tech dept for advice?

Is this an extension bathroom, or some kind of converted structure?

 

[jimmy6363]

Hi, thanks for your reply.

The concrete slab does not run underneath the floor, its a separate path that has been cast a little too high in relation to the DPC, but that's not really my main concern as the damp is not coming through the floor (or just low level on the walls...).

There is not cavity/insulation so there cannot be any interstitial condensation - internally, the walls are getting saturated when it rains, simply because they are single skin.

I'm hoping rendering the walls in the spring (with the addition of a waterproofing additive) will prevent the walls getting damp internally.

I have spoken to Synthaprufe who unfortunately have confirmed the product would not be suitable for the walls and cannot carry a render.

I have looked at other alternatives such as Thompson water sealer but from what I have been able to read this also won't carry a render. I have however found a product called 'Rendergrip' from Everbuild.

Does anyone have any experience using this and would it be suitable/could it be left over winter?

Thanks everyone.

 

[shawwwn]

I am a window door and conservatory servicer
I fix leaks etc

Down here in sunny cornwall we do have problems with water coming in through granite especially when you put a conservatory against a granite wall

We use a product called Belzona which is mixed with water and sprayed or brushed on
it seems to do the job of stopping the porosity of the granite and thus the leaks

I have successfully used it many times it is colorless and cant be seen after the job is done.

Im told its expensive but look it up on the net it might be just what u need
Hope that helps