After the ravages of the winter, the pointing between my patio slabs has got considerably broken up in places.
How can I best repair this damage with minimal staining of the slabs themselves?
I am thinking of raking out the loose mortar and then refilling with a dryish 4:1 mix of sand and cement, maybe with some plasticiser (e.g. like Unibond).
Would this be a good way of tackling the job or are there better ways to repair the damage?
Yours, Ed
Yes I'd like to know that too: I foolishly chose last summer to repoint some of the crazy paving under where gutters always overflow in heavy rain. After severe frosts and several roof fulls of melting snow, it's all come out again...
S
Use a totally dry mix on dry slabs, brush it all in.
NT
You done this before with success?
What mix you recommend?
Ed
Know the feeling - I've just done the job - and got the bloody scars on the fingers from using a worn out plugging chisel to rake out the joints (I couldn't find my good one at the time).
Use a 1:4 mix of cement and sand, wetting it just enough so that when you squeeze it with your hand, it just holds together in a small ball. You can add colouring to the mix at this stage if needed
Don't use plasticiser or unibond - simply use the above mix and pack well into the open joints, tool it off to the shape you want and then lightly sweep a brush over to clean up an spills.
*IMPORTANT* Choose a dry [1], cloudy [2] day to do this (with no rain forecast for 24 hours) - the reasons are [1] wet slabs will cause the mortar to run and hence stain, [2] hot sun will dry the mortar out too quickly leading to early breakdown of the stuff.The above is about the only way, but a refinement is available if you use a 'pointing gun'. This is simply a bigger version of a mastic gun with a different sized nozzle
Cash
Why not use plasticiser or unibond ?
Ed
I'd better take back what I said, I realised it wasnt a dry mix but a dry wet mix IYSWIM.
NT
Makes things too slippy, thus more likely to stain the patio. If you want more of a wet, pliable (and stronger mix) simply use 1:3 sand and cement and add more water, this will certainly make the mortar stronger, but will also make the staining of the patio a dead certainty.
And remember though, the morter is not there for strength [1], but to help stop rainwater getting to (and possiby washing away) any sand base - or more usually simply to make things more aesthetic.
[1] Such as to hold the slabs in place - if want to stop the slabs moving, bear more weight (for parking a car on perhaps) or impervious to water penetration, simpy lay a concrete base and stick the slabs (touching each other so no jointing is needed) on to that with a normal mortar mix.Cash
I've been did this exact job on a new patio last w/e. I used a 4:1 mix with just a dash of water to make a very dry mix. This was spread along the joints and tamped down with a short batten of suitable thickness. If you don't tamp it down it will soon fail. Then pointed up with a pointing iron and the surplus mortar brushed away. No point bothering with plasticiser as the mix is too dry for that to do anything other than reduce the strength.
I used white cement so that the mortar pretty much takes the colour of the sand, seems to be a lot more able to stain than a grey mix so I'm hoping that'll go with a few rain showers.
mark
Its about right when its like the topping for apple crumble (before its cooked).
Tommy Walsh has a version. Use watering can (no rose) to flood joints, wait for surface to dry, brush in dry mix & tool in.
Had the same patio problem. Year after year clearing out new weed growth and making tedious joint repairs knowing full well I'd be doing the same again the following summer. Fortunately, the slabs are close fitting with average gaps about
5~15mm. Solution was to wait for a hot day and repoint/grout using a few tubes of Silicone Rubber. ('hot glue' also works well) Not had any problems for the past 8 years!. The stuff also withstands an annual patio power wash to remove the green slime that covers everything nowadays . Am currently pondering Siliconing the block paved driveway but don't think I'll have the patience :)
Does that work out more or less cost than epoxy mortar?
NT
Good question. Just done some sums and the rubber works out cheaper!. Ebay ........ Epoxy mortar ~ =A330 for 3000ml ... is =A31 per 100ml Screwfix.....Silicone gunge ~ =A32.20 for 310ml ... is 71p per 100ml I reckon my usage was about 1 tube of gunge per square meter and with benefit of zero waste. Reasons I tried the sealant was it's all weather flexibility, biological inertness and the fact it bonds exquisitely to other Silicon based materials (eg sand as stone or as admixture to commercial flagging). This allowed the flaggings to continue their year on year natural settlements, creepage and differential expansions and variable loadings, without any crevices developing as the rubber just stretches and compresses without bond failure and consequential weed growth. In reality it's only the odd mm or so of movement but this was more than sufficient to break any mortar type rigid infill I'd previously attempted. Offhand, I can't imagine the Epoxies offering the level of resilience that is natural with the rubbers.
Interesting. FWIW Toolstation does 310ml carts for =A31.69, or a 25 pack for =A333.94 =3D =A31.36 each
NT
Halfway down this page there's a polymer modified cement grout
brushed into the joints
B&Q and Wickes do similar products.
Doesn't say that it's polymer modified though. Some of the cement grouts seem to contain nothing but cement, which makes them kind of expensive
Brian
I used this stuff to fill gaps between a block paving mowing strip, easy to use and nothing has shifted. It is a bit pricey but the time it saves applying it is well worth the money.
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