I keep having problems with the joints in my patio flags, after each winter the joints often break up and it is a major job to keep the patio in good condition. I usually use a mix or Portland cement and Sharp sand in 4:1 ratio but it is clearly not doing the job correctly, Ideally I want strong mortar joints that are hard and preferably able to withstand jet spraying when the patio is cleaned. Should I be using an additive such as a platicizer to strengthen the mortar mix? If so any particular brand?

  • The problem is not the mortar - the problem is an unstable base - if what's under the patio moves, any mortar will crack. – Ecnerwal Apr 9 '15 at 14:00
  • I've never heard of cementing patio stone gaps in a freeze zone. Joints are always filled with lose sand or even gravel. Is there any reason to believe you can do this? – feetwet May 3 '15 at 3:47

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