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The small town where I live gets below freezing in winter and above 100º F in summer. I need to know which mortar joint width and ratio is best for laying a brick patio myself. As far as I know, mortar joints will break into pieces because of thermal expansion and contraction. Using just fine sand as a joint filler does not seem workable because my neighbor's patio which used this method has weeds growing at the joints.

Which ratio would expand/contract less? A 1 part cement and 3 parts fine sand; or a 1 part cement and 6 parts fine sand ratio? (In the local construction store they only sell cement and fine sand bags; so I will have no opportunity to buy additives or lime to increase flexibility.)

I plan to lay the patio bricks directly on my sandy-earth rather than on a sand base.

Each brick is 2.5 inches in height and width.

So what are the recommended mortar joint width and ratio so the patio will last for decades and not break into pieces within a few years?

Or are there other approaches I should consider?

This is what I intend to build: Brick Patio

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Putting the brick on a sand base or directly on the ground is what will crack your joints. You want pavers to hold up, lay a 4" base of concrete with reinforcement down first, then lay your brick on a full mortar bed. Then fill the joints with mortar. To lay on sand or earth, forego the mortar joints, and lay it tight joint, as iLikeDirt answered, and pull and spray the occasional weed. A mortared joint will not stay in place, freeze/thaw will see to that....

Here is a pic of my cousins sidewalk, done with a cement base as mentioned above. It has been in place for over 10 years. Long enough for the expansion joints to erode and allow weeds to grow through them. The placement of expansion joints are critical for the longevity of any concrete slab.

enter image description here

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alas in a freeze/thaw environment, your joints will still crack even with the concrete. If you're going to take the time to lay down concrete, you should go with a concrete patio to begin with...perhaps stamped to look like pavers. –  DA01 May 18 at 23:31
    
It took a while to back up my expectations of what a slab would do. I could imagine that weeds would grow in some occasions in the joints, only if there is room for the weeds to take root. This is why I specified a FULL mud bed. Any voids, for water to pool, therefore ice, then cracking then dirt infiltration, then weeds.... This is in Maryland where the temps match the conditions of the question. –  Jack May 27 at 5:14
    
You may be right, if it's done right this might work. That said, I've never seen a fully mortared brick path nor steps in Minnesota survive more than a few years. Remember mortar isn't waterproof, so it will always absorb some amount of moisture and that won't last more than a couple of springs of constant freeze/thaw. The big benefit of a sand (on top of a properly compacted base, of course), is that once they are 'locked' in with a compactor, they are incredibly solid--HOWEVER if they ever do migrate, it's trivial to fix. Pry them up, re-level, put them back. –  DA01 May 27 at 5:24
    
Yup, I agree with your sand base scenario, and absolutely, masonry/concrete is a BIG sponge, there can be no voids for water to collect, that will be it's downfall. Consistency is a must. The OP's area sounded a lot like mine though with the freezing to 100 degree weather. In Minnesota, yes the winter are certainly more extreme, then the science of masonry becomes more important, the type of brick used the type of masonry cement used (type S,N, or I) –  Jack May 27 at 10:27
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Weeds grow anywhere...whether you mortar or use sand.

If you live in a freeze/thaw area, you definitely don't want to use mortar, as it will eventually crack, and cracked mortar is a lot harder to maintain and remove weeds from than sand is.

Also note that you don't want to use just 'fine sand' but polymeric sand. Polymeric sand needs to be wetted after application and it will 'lock itself' into the joints.

Regardless, every other year or so you will need to likely brush a bit more sand in and pull a few weeds. But that's still a lot less work than maintaining mortar joints.

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Polymeric sand is not sold at my location. I know, I know, I live in a very small town... –  Enzo Trew May 20 at 18:49
    
I don't know where you live, but any big-box should have it. That might be a hike depending on where you live, of course. –  DA01 May 20 at 19:29
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You could put down a layer of thick (e.g. 12 mil) polyethylene sheeting and then cover that with sand and bricks. That would defeat the weeds but allow you to use ordinary sand as joint filler.

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After a few years dirt and weed seeds will accumulate and guess what...they will germinate and grow into weeds right in the sand joints. –  Michael Karas May 18 at 14:51
    
@MichaelKaras Exactly what happened to neighbor. –  Enzo Trew May 18 at 14:56
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