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I'm laying a small retaining wall for a garden and I'm having a lot if trouble getting a proper mortar joint.

If it is on the soft side it is squished out of the joint with the weight of the block.

If it is drier it crumbles and doesn't seem to have a good adhesion.

I'm using course sand (concrete sand) mixed with fine sand. I tried to sieve to get something like a medium sand (I think you call that boulder's sand) but it didn't seem to make a difference.

  • Mortar mix has a very specific ingredient ratio, with water content being critical. Did you follow a recipe? – isherwood Mar 9 '16 at 15:16
  • I used 1 part cement 4 parts sand, an additive that increases plasticity (replaces lime) and water until it reached what I thought was the right consistency. – Luiz Borges Mar 9 '16 at 15:17
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Brick laying is an art form. It takes a lot of time to get the technique down. Professional masons make the process look much easier than it really is.

One thing that can help is to buy a pre-mixed mortar instead of trying to make your own. It should have a better consistency than what you are using. There are also many different kinds of mortars. A type M or type S mortar would be well suited for putting in a retaining wall.

Type M mortar is the strongest on the market. It is used most when the wall you are building is below grade, and has the best compression strength and is much less likely to squeeze out than other mortars when you are using heavy block. The downside of this kind of mortar is that it is actually too strong for most kinds of concrete block. If there is any movement in the wall, the block is more likely to crack instead of having it crack in the joints. This kind of mortar should never be used for standard brick.

Type S mortar is similar to type M, but it is not quite as strong. This is probably going to be the best type of mortar to use in your application. It is still very strong, but it is a little easy to work with. When using this kind of mortar, you want to make sure that you don't stack too many courses of block in a short time period since having too much weight on the block would squeeze out the mortar.

If you are going to lay brick over the top of your wall, then type N mortar is the way too go. It is still fairly strong, but not so strong as to destroy the brick if the structure is removed. There is a much better chance of being able to reuse the brick later on with this type of mortar compared to type M and type S.

There are also other types of mortar, but those types are generally not well suited for outdoor use, especially if it is load bearing.

You may have a hard time finding all of these different mortars locally. Type N mortar is usually marked as general purpose, and it is the most common.

  • Actually I can't find any ready mix mortar in Brazil. Here with exception of thinset and mortar for glass block, every other mortar is mixed per preference of the worker using cement and sand... – Luiz Borges Mar 9 '16 at 15:22
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    It looks like you will need to mix your own mortar. Here is a site I have found that shows how to mix your own mortar. rosieonthehouse.com/faqs/… – Jason Hutchinson Mar 9 '16 at 15:45
  • From the site it looks like my recipe is correct. The only thing that I can change is the type of sand (now I'm using mostly course sand instead of builders sand), or keep trying to get the mortar to a point that is stiff enough to work while still doesn't crumble – Luiz Borges Mar 9 '16 at 16:05
  • It appears that most of the recipes are using lime. That might make a difference too. – Jason Hutchinson Mar 9 '16 at 16:22
  • I'm using an additive to replace lime. – Luiz Borges Mar 9 '16 at 16:26

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