Need to waterproof block retaining wall before rendering?

[lk1]

Hi all, just wondering if anyone has experience with rendering a cement block retaining wall?

It seems we may have jumped the gun a bit by backfilling behind the retaining wall without first waterproofing the blocks? We wanted to space the job out a bit & put off rendering for a while, but have just had a quote for rendering & were told that if we don't waterproof the side holding the soil, that the blocks would suck up the moisture causing the render on the front to possibly crack & fall off. Does this sound right?

We have weep holes, agi pipe & gravel in for drainage - I guess I'm just hoping there's another option besides digging it all out again to access for waterproofing?

 

[The Fence]

Sorry to say it but this is true, you need to waterproof the back of the wall plus have all the drainage options in place as well.....

maybe get away with bagging the wall instead of rendering....in other words bagging involves minimal amounts of cement needing to "stick' to the wall....just fill the perps basically.....depends upon what you want to look like....this would still need dryer conditions behind the wall rather than constantly wet...

hope this helps....

 

[lk1]

Thanks....I think

It's for the front fence, so I think we'd better do it properly. Any suggestions for best product to use for waterproofing?

 

[The Fence]

I use (I'm a landscape construction Contractor) HiChem Proctecta Seal which is a tar based paint you brush on.....messy sticky stuff but it does the job right......

Bunnings will have it......

 

[gerd.]

Waterproofing on the negative side is possible.
Waterproofing the render with the appropriate product will waterproof your wall.

Gerd

 

[Zeddy]

Waterproofing on the negative side is possible.
Waterproofing the render with the appropriate product will waterproof your wall.

Gerd

This is true, but it's not the preferred solution. Tanking the positive side would be considered better.

 

[The Fence]

This is true, but it's not the preferred solution. Tanking the positive side would be considered better.

Agreed, and we are not trying to sell something.....

 

[lk1]

Thanks guys.

Gerd, you've given me hope - but I really don't want to have worse problems down the track.

 

[Zeddy]

Thanks guys.

Gerd, you've given me hope - but I really don't want to have worse problems down the track.

If I were in your shoes and intending to hold it long term, I would tank the positive side. This is the most effective method possible and would greatly reduce the probability of future problems.

If I was intending to sell the property, then I might consider tanking the negative side to provide a cost and time efficient solution. This would give it a decent lifespan if done properly.

The problem with tanking the negative side is that problems can still occur depending on the magnitude of the water pressure.

The simplest analogy I can think of is to imagine a piece of plastic being your tanking. On the earth side of the retaining wall, soil and water pressure pushing on it will just push it against the wall.

On the other hand, if I put it on the open side of the wall, there are a number of things that can go wrong. If the bond is ineffective, the tanking may be pushed off the wall by the water pressure, forming bubbles or unsightly blisters. If the tanking layer allows some evaporation of water to occur, any ground salts present may lead to bits and pieces of the wall falling off.

I hope this helps clear things up a bit.

 

[The Fence]

Kudos Zeddy...! very good advice IMHO.

 

[lk1]

Well Zeddy, when you put it that way

OK, we'll definitely dig it out & do it properly. Thanks so much for all the help guys.

 

[The Fence]

Good Karma if you decide to sell....

 

[spikingviking]

negative vs possitive

its always better to waterproof the possitive side of a wet wall.
anything put on the negative side has good potential to "blow off" or loose adhesion. this is standard new construction waterproofing practice.

there are products made to waterproof negative side walls when there is no other option, but they are all topical (except crystaline products which are still applied topicaly) and rely on the adhesion to the substrate.

there is another issue as well with not waterproofing the possitive side of porous below grade substrates. any water that passes through your block wall will bring minerals and other items that will work its way to the surface and leave unsightly deposits on the face of the wall which could very well contribute to failure of anything applied to the surface.

i think the consensus is to dig it up and do it 1 time correctly, and i would have to agree in the long run this will save you money and heartache.

 

[lk1]

bumping for Kisha