I have a stone step--the top is loose and I wish to mortar it down. First, is weather a factor? 50s today and tomorrow, 50s are the highs. cold front Sunday. Next, can I just slap some mortar on for a temporary fix or should I build a kind of wooden mold? Is it essential that it be level and how does a novice plan for that? I imagine you'd have to spread the mortar as evenly as the eye can tell--anything else?

  • We'd need a photo, but typically mortar is pretty easy to work with. Slap it on, apply the stone, level with a rubber mallet until it's good. Clean the old mortar off first as well as you an, and be sure to wet the surfaces slightly before applying the mortar. – DA01 Nov 21 '13 at 20:43

You'll need to remove the old mortar - you can't just slap on some new mortar and expect it to hold if the old stuff hasn't been removed. Chisel and brush with a stiff wire brush.

No form should be needed - if you appear to need a form, you need to add more dry mortar mix to your bucket - preferably, don't add too much water in the first place. Consider a brick wall - there's no form on that. The stuff should look a bit too dry when you mix it, but wet up when smacked around with a trowel. If it looks wet when mixed, it's usually too wet.

If you have actual mortar rather than "sand mix" there's a degree of self-levelling from the small stones in the mix - they are trapped between the base and the step, and set a minimum thickness for the joint. Normally you want exterior steps just a hair off level so water drains off them, but not so much as to make them hazardous to step on. A level and a mallet (or a hammer on a block of wood) will get you there. If you run out of adjustment, pull the step up and add more mortar where needed, then smack it back down.

Weather matters - if the mortar freezes before it cures, it will fail. A quick-fix now may need to be redone next spring in order to hold for the long-term - or, you buy a bale of straw and bury the step before the cold front comes through - or make a plastic bubble and run a heater in it.

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    Totally agree with Ecnerwal's comments. And, would add that I always pre-soak the surrounding area and cover the work when done for 3 - 5 days to get the best long-term adhesion. – getterdun Nov 22 '13 at 18:19
  • Prewetting of the old work to prevent the new mortar from being sucked dry is a point I forgot to mention. Mortar (or any cement product) is weakened if it dries (yet, at the same time, it's also weakened if you use too much water in mixing) - the hardening (not drying) process requires water, and once the initial "set" has occurred (24 hours or so), the project will also benefit from having more water applied to the surface as it cures. – Ecnerwal Nov 22 '13 at 19:36

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