Bonding Cement To Cement

Peter C

Peter C

Well-known member
1000+ Posts
Fellow Frogger
Joined
Aug 10, 2004
Messages
5,797
Location
SWOTR
To correct the back porch which is slightly sloping towards the house, I'm planning on laying a roughly 20mm layer of cement on the top of the existing cement porch.

The existing cement porch will be dust free and almost completely free of paving paint after a thorough washing using a commercial pressure cleaner.

Internet advice seems to vary. What I plan on using is a 1 to 3 mix using Boncrete.

I'd greatly appreciate any advice.
 
Ive done a little bit of concrete over concrete and the advice from a few sources was to start with a thin slurry.
I used a modified or fortified product for a bathroom, but it was not cheap, and possibly unnecessary.
 
That is a very, very thin topping. Cure it well. 20mm is more like the thickness for a trowelled on epoxy finish.

You must scabble the existing surface first to get a key, and it would be best to use a much stronger concrete adhesive compound than that proposed . Look up Sika's epoxy, for example. Bondcrete would be a solution for a thicker topping than your proposal. Make sure there is no loose material on the base.

Steel trowelled thin granolithic (very strong concrete with fine metal aggregate was once common on external stairs - the surface aggregate glinting a bit is a giveaway. It needed a suitably rough unfinished base, and no large dimensions, to avoid cracking (it has a high cement content). It takes practice.
 
Last edited:
I've found out that cement doesn't bond to cement. Cost is a major issue, which precludes simply replacing the portion of the slab, in question. The whole porch slab is about 2.4 x 8.6 metres, and the problem portion is about 1.5 m wide.
 
It can be done, but needs some skill. I hope you don't want to feather it down to nothing.
 
Hadn't thought of feathering it down being an issue, till you mentioned it. Hmm.

If it's too difficult, I wonder if chasing a drainage channel towards the outer edge of the slab could be an option?
 
Check out Fosroc Renderoc HB products. They have many choices for different applications
 
Those concrete repair and steel baseplate grout products are pretty pricey over large areas like this.
 
Could you just tile the back half of the porch ? I'm guessing the transition up onto the tiles is then a trip hazard :unsure:
 
I'd say you almost need a floor screed mix at that thickness - can be bought in bags/tubs (I made the mistake of getting a 'self-levelling' screed when doing a shower base some years ago, cheated - mixed it with too little water & it went to falls OK & the topping tiles never cracked / dislodged so I think I got away with it). I'd paint the existing concrete with diluted water/pva glue (think that's what 'bondcete' is?) & let soak in before applying screed.
 
I'm glad I started this thread. I can now see that what I thought was a relatively straight forward job, isn't.

Of the 2.4 m x 8.6 m porch slab, it is only the middle part that is the problem, which is about 1m x 1.3 m. The house was built around 1960 and is at a stage where it isn't worth spending a lot of money on. Any works need to be frugal!

I had thought of tiles or slate, etc, but I agree, it would become a tripping hazard. I'm just on the right side of 70 years of age and live on my own with very few visitors so I really need to keep the place safe.

I remember a mate of mine using a screed that came in a powdered form in a bag. I wonder if this would be the go? If I'm understanding it correctly, this stuff can be applied to a surface so that there is a fall away from, in my case, the house? This area of the porch will not bear anything heavy.

After whatever course I end up taking, I will paint the whole porch with paving paint to seal it.

Apart from killing the mildew and pressure washing it down, I've sealed up some fairly wide cracks with polyurethane caulking compound.
 
Ultimately, it may be cheaper and simpler to chase a drainage channel. There was a crack of about 15mm which I have sealed up with polyurethane caulking compound. I could open it back up, put in some 20mm conduit, with a suitable drainage entry point, and seal it back over.
 
Parchem Patchroc GP as a repair mortar which can be applied down to 15mm. Prime with Nitobond EP , look them up online as parchem have pretty easy to follow specifications. This won’t be suitable for a “feather” finish however you’d need to use another product on top like their Renderoc FC
 
I placed a 25mm topping over 10 year old cement based. I used bondCrete mixed at 4 water to one bondcrete. It is in my carport and still there today 25 years later
 
One reason why I thought of Bondcrete was that I used it many years ago to re cement a 150 mm x 200mm triangle that had broken off the corner of the front porch.

One thing I'm learning is that there is a lot to know.
 
You must log in or register to reply here.
Top