Waterproof additive for rendering

Hi, I wonder if anyone can help?
A single skin garage wall is wet internally (1.5m
high wet/damp across wall)due to someone laying a
patio behind it well above the dampcourse. This guy
can't get his neighbour to sort the problem, so has
decided to have the wall rendered. Please can anyone
recommend a reliable/working waterproofing additive
for rendering and who stocks it? Many thanks.



No. But I can imagine a problem if you are going that way.

If the patio is above the dpc and causing problems, it must be close to, or touching the wall.

You would need to render right down to the dpc.

How you gonna do that ? Rendering down to the patio level is just going to make the problem worse.


What you really need to do, is get down between the wall and the patio with tanking/bitumen, right up to and 6" above the patio level. Then, if you wish, render down to the bitumen level(although rendering would not be necessary after your initial treatment).



Mr. HandyAndy - really

 

I was reluctant to ask the question, "I hope you don't mean, render the inside of the wall" because I didn't want you to sound foolish.

Rendering the inside is not an answer. It will fail miserably.

If it is your wall, you can force your neighbour to either rectify his cock-up, or allow you to rectify it.

This sort of thing is written in the regs somewhere.


Mr. HandyAndy - really

 

One word...


Vandex.

Go forth and vandex....

 

Seriously though, vandex is your answer here.

It can hold back a river.

You basically render a layer, score - then wait to dry.

Then apply vandex with a brush.

Splatter coat that.

Wait.

Then apply a top render layer.

I'd advise adding the flexible additive to the vandex since if it ever cracks then water will **** through the smallest pinhole.

You'd be amazed at how much damage a pinhole leak can cause.

 

Hi,

SIKA 1 is another additive. Available at Travis Perkins. We did a couple of basement conversions once (which believe it or not is below dpc and ground level) and used this in the rendermix then skimmed on top.

If I remember rightly - apply a scud coat 1:1, allow to cure, apply a scratch coat (gently scratch enough for a key but not too deep) leave to cure then float as normal. All the coats contain the sika1 additive but check the tub for ratios.

The only problem I can see is that we did all 4 walls with rounded corners to give a continuous 'seal' all round, whereas if you just do the offending wall the water will just go to the extremities and come where the render stops.

 

Just found this - covers vandex aswell


http://www.safeguardeurope.com/products/sika1.php?OVRAW=sika&OVKEY=sika&OVMTC=standard

 

So all 4 walls and the floor have to be done.

But remember the water will still have to go somewhere!!

 

With reference to the water going somewhere - it should just soak away elsewhere, the fact that the OP's area below ground is tanked by vandex means it is protected - whoever else is next door or next in line will cop it instead...

 

If you are worried about the water "going somewhere else" you could inject a vertical DPC at the edge of the Vandex treatment.

 

Have the water pumped up and outfill onto next doors patio.

Good for the goose, etc


Look. Go out and collect a load of water damaged goods for nothing(say worth a couple of grand if it were new). Lay them up against your wall inside.

Claim it on your insurance, and let the insurance company recover the cost from the pratt next door.

Use the winnings to get a jolly good job done, and paint smilies on the outside.




Mr. HandyAndy - really

 

there are proper tanking systems for below dpc that come with guarantees but are very expensive. where does the water go? you would need to lift the screeded floor and place a pump in the middle.then apply a membrane on the floor running up the wall at least a metre.the water goes behind the membrane and away through the pump to the nearest drain. all four walls are renderd normally and the floor screeded. fix the membrane with large plastic washers and plugs covered in silicone. use sika in the mix as an extra barrier. it works, we cured a soaking wet basement .

 

My experience with sika 1 isn't good. According to the instructions it has to mixed in a special machine which looks like a vertically inverted cement mixer. I used it in a mix in a normal cement mixer and I have small patches of damp at the mortar joints through a cavity wall using 7n blocks.

 

you could ask the neighbour to lift the row of slabs nearest to the wall and lay a row of "aqua channell"drainage. the fall in the patio probably runs to your wall.