We have a set of concrete steps that are only about 15 years old but some of the steps are already beginning to crumble. Is there anything I can do to repair them?
Thanks for any help / suggestions.
Depending on how crumbly they are, if firm but broken away then yes to repairing them by shuttering and adding fresh concrete. If they are really soft and crumbly then cutting back until you find good material is best.
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Thanks Corona. Will I get a good adherence between the new concrete and the old? Should I do something special?
A bit of sika adherence SBR will be good in the mix and painted on the old concrete before the new stuff. I used to āgreen upā old concrete with dilute hydrochloric acid in the old days but SBR does well.
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Thanks for posting the photo Sue, as it makes it easier to see the nature of the problem.
My suggestion is as follows;
- Thoroughly pressure wash the whole thing to remove all that dirt, lichen, mould, weeds, and all the loose material.
- Buy some 5cm thick concrete blocks and install them vertically against the front edge of the broken steps so that the top of the blocks are level with the existing surface for the top step, and 7 cm above the existing top surface of the step for all the others. Use a waterproofing admix when making up the mortar. Waterproof PVA will do just fine.
- Once the mortar for the blocks has dried for at least 24, and preferably 48hrs, then fill with fresh concrete using either the product @Corona has recommended, or more waterproof PVA. The PVA does need to be the waterproof type and not the general use stuff which is for indoors only. I get mine from Screwfix in the UK.
Lay half the depth of concrete, then a layer of chicken wire for reinforcing, and then the remainder of the concrete on top. - Keep the work area loosely covered with planks and plastic sheeting to keep the rain off and stop animals from walking on it. Leave plenty of air gaps at the sides so that the air can circulate freely to aid drying.
- Leave it covered for at least 14 days, and preferably 28 to give the new concrete time to ācureā to full strength. Do not be tempted to walk on it just because it looks dry.
- Do not do the work at all unless you are sure that the temperature will remain above 5degC for at least 14 days afterwards. Remember that the new concrete is effectively sitting on damp / wet ground and so can only dry from the top at this time of year.
Probably better to wait until Spring so that there is drier ground and weather.
Assuming that the steps were all straight and level when first installed, the end result will make the āriseā of the top step 7cm less than that which exists now, and the bottom step will be 7cm higher than at present. If you wish to keep the rise of each step all the same (which is much better from a safety point of view), then lay some 5cm thick paving slabs on a mortar base in front of both the top and bottom steps which will even everything up.
Itās a fair bit of work, but you will have a nice neat, and safe set of steps at the end of it all, together with a nice level and safe approach at both the top and the bottom.
A nice finishing touch is to tile the risers of the steps, which will cover the concrete block surface and make a bit of a feature of it. Perhaps you may have a selection of tiles left over from a previous job in the back of the shed / barn.
Alternatively you can use āCrepiā which covers a multitude of sins and is in fact waterproof while still allowing things to ābreatheā.
After that, it just needs spraying with anti-mouse once a year following a good pressure wash to keep the mould and fungus away.
Also, itās a good idea to install some sort of stout handrail at the same time if there isnāt one already in situ. I donāt know how you get on these days, but I find that stumbling seems to become easier as my years progress. 
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Bleach the steps in preference to doing more damage with a pressure washer.
Dont use PVA use SBR, its actually designed for the job. The chemical reaction of curing cement products does not need 14 days.
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I would make sure that the steps are not perfectly flat - make them lean forward by a tiny amount so that rainwater does not sit on them.
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Remember that concrete āsetsā rather than dries. Itās a chemical process
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Thanks all of you for your very helpful suggestions and for how to have done it properly in the first place. Sadly it wasnāt and weāre not that thrilled with them and will at some point get them completely changed. So @Robert_Hodge your careful post telling me how to do it properly and the suggestions for slope (@Mat_Davies ), handrail etc are very useful for the future. For the moment, I just want to patch/repair what is there to make it look neater.
If you just want to patch it upto makeit look better, I would just use a strong coarse sand and cement mix (an aggregate/concrete mix will probably be too coarse). Clean all the loose stuff off, put some bonding on, make some simple shuttering for the faces to extend 1 or 2 cm above the existing height, trowel it on, smooth it off (you can get a profile tool for the edge so its not sharp )and when just set lightly wire brush the surface to give a non slip finish. Repeat for the rest of the steps
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Well if you just want to make it look neater, as opposed to being able to safely walk up and down the steps, then you could just clean up what is there at the moment and plaster it all with Crepi which will temporarily fill the cracks and cover the worst of the sharp broken edges. On the flat surfaces you can apply it with a trowel to fill the holes.
However, it will be temporary, and how long it lasts will depend on how much frost you get in your area.
What the Crepi will not do is withstand folks walking up and down the steps.
Well Iām not a chemist, but I surmise that the length of time required depends on both temperature and thickness. When I had a 25cm thick suspended concrete floor installed over a 7.5 metre span, the supervising structural engineer from Point P insisted that all the supporting Accro Props stayed in place for 28 days while the concrete cured to full strength.
Perhaps he was mistaken, or perhaps French concrete is different, but the contracted builders were not at all happy at his insistence on the 28 days.
Additionally, Iāve found that if you donāt want someone to walk on something for a week, then tell them to keep off it for a fortnight, and you stand a better chance of achieving the objective. Itās sort of a matter of managing intrinsic human nature.
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Big difference, huge.
The formal strength of concrete is measured after 28 days but will be predominantly cured long before this. Initially concrete hardens āgoes greenā but at this time it has not gained full strength.
Thickness of concrete does not effect curing as it is a chemical reaction.
For the purpose of these steps - if mix has the correct moisture content, it could be walked on after 48 hours.
A suspended floor is a very different case which will have been designed for the fully cured strength of the concrete and if supports are removed too early it will fail.
Portland cement will even set if submerged (as does Roman cement) so it has to be something other than ādrying outā.
Look up ātobermorite gelā and learn 
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Isnāt that something to do with small creatures that live in burrows on Wimbledon common?
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Bizarrely, yes. Keep researchingā¦
Interesting, Iāve known about it, but not its name.
why not see how they look after a good clean???
will they be in much use over the winter???
if notā¦ Iād clean 'em and leave remedial work until it can be done āproperly/completelyā
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