Mortar guns

[Onoff]

Pretty sure my mortar gun instructions say not to get sharp sand anywhere near it. 

 

 

[JohnMo]

I just bought a grout bag from b&q for a few £, like a heavy duty decorating bag you would use for cakes.  Only used quickly, seem pretty good.

[Radian]

6 minutes ago, Onoff said:

Pretty sure my mortar gun instructions say not to get sharp sand anywhere near it. 

 

 

The sand I had wasn't supposed to be sharp but it wasn't particularly well graded. However, the makers of the gun with the wide nozzle actually do claim it can be used with sharp. It was a right faf sifting it before I discovered it wasn't necessary.

[Onoff]

I'd be well happy if I can get this mix through a mortar gun:

 

 

- 3 soft
- 1 sharp (figured it'd add strength and maybe some interest with the fines in it)
- 1 opc
- 1 lime (for plasticity/self healing)

[Radian]

16 minutes ago, Onoff said:

I'd be well happy if I can get this mix through a mortar gun:

 

 

- 3 soft
- 1 sharp (figured it'd add strength and maybe some interest with the fines in it)
- 1 opc
- 1 lime (for plasticity/self healing)

 

I'm sure that would go through the pointmaster. If you look at the dimensions of the nozzle (say 10mm x 50mm) then there's no reason it wouldn't flow - BUT if compressed into that space it could interlock. That's the whole thrust of my diatribe here... keep the pressure as low as possible yet keep the volume moving and it all works out. The deeper the pocket you can fill, the easier this is to acheive.

[Brickie]

Interesting observations. I’ve used them on re-pointing in the past (though not the Pointmaster) with all the problems you’ve described & ended up preferring Grout bags-much quicker to sort any blockage issues. I think they’d be harder physically to use on a patio-you’d need to be on your knees. 
If I get a substantial amount of re-pointing to do in future,I’m going to invest in one of the drill attached machines. Again,probably not suitable for a patio though. 
I’ve seen the ground workers on site using a rubble sack with a corner cut off for pointing cobbles & the like. 

[Onoff]

I have a feeling that if not properly mixed the water in the mix either runs out the nozzle or maybe sits atop the mix if the gun is pointing down. Either way you end up pushing too stiff a mix and it's impossible! 

 

When they work they great. 

 

 

[Gone West]

We used a Roughneck mortar gun for pointing our patio slabs. A bit of trial and error but once we got the mix right, it was straightforward.

[Roundtuit]

22 hours ago, Radian said:

Anyway, I wanted to relate all this because it could save someone a lot of time, money and effort.

Great post, and full marks for effort! 

As an alternative to mortar I took a punt on a jointing compound for ours (Joint-it) as I didn't trust myself to do a decent job and keep the sandstone clean.  Not cheap, but quick and pain-free;  25 sq m done in a couple of hours.

[Radian]

Coming up for one year on and I have some more to add to this topic.

When I started pointing by hand, before I got the gun, I hadn't used any SBR addmix in the mortar. Now it's very evident which bits were done without SBR:

 

 

The perpendicular joints on the first row of slabs by the hedge remain saturated for much of the time while all the other pointing with SBR in it dries at the same time as the concrete slabs. I can't imagine a better demonstration of the value of using a drop of SBR in the mix. I expect these joints to blow with frost first. Thankfully its pretty much just this initial row that missed out.

[Radian]

Just sharing the experience I've had with some of these things to point over 100m2 of paving (512 off 450x450 saxons). I want to share this because I was sceptical of these tools having read many, many bad reviews on the likes of Sfix, Amaz etc.. So sceptical that I started out doing it with a trowel, tuck pointer and pointing iron like I've always done. But I got fed up with that because this job was way bigger than anything I've tackled before.

 

OK, so I give in and try a gun. I figured one that operated like a sealant gun should have the advantage of some extra pressure to squeeze the mortar so I bought a Cox Solpointing Ultrapoint Gun:

I Watched all the video's and followed all the tips such as the mix & additive to use but  I just couldn't get decent results. It frequently jammed which was the general criticism I was seeing of all mortar guns. I even sifted the sand to remove any tiny stones as it always seemed to get hung-up on these. Then no amount of pressure on the trigger would 'push through' so the whole thing had to be emptied and cleaned. The enormous pressure often resulted in squeezing all the water out of the mortar and back up the tube! So I gave up and went back to the trowel in disgust.

 

For about a week. During that time I had plenty of time to think about it, while troweling away, and realised that the relatively small nozzle wasn't helping so I had a look again and found some with a wide rectangular slot:

 

Image removed at request of copyright owner. If you want to see it you might find it on the companies web site it is the one with paving slabs. 

 

I figure that if I could get it to work it would be worth it so I bought one of these too. This time it went better but I was still getting regular clogging. As before, no amount of pressure would shift it. But I could actually do ah few slabs before having to dismantle it - so I persisted. The usage tips for these made it clear that the mix should be thorough and that was better than just making it sloppy. So I began making the smallest batch of mortar I could in my cement mixer (a 14L bucket of sand 4:1). Leaving this running for a good 30 minutes, with plenty of plasticiser and the mix was super-smooth. Before I'd been doing it in a bucket with a paddle on a cordless drill.

 

This smoother mix helped and I could get maybe 10 slabs done before clogging, so by now I'm thinking it out like crazy because I can see this being a great time saver. What I began to realise is that the clogging was always happening when the joint was shallower than the depth of the slab due to the bedding mortar having splurged up when laying. In this case the mortar was 'grounding out' too soon as it was extruded resulting in it not being able to flow sideways - bunching up directly below the nozzle. In this situation applying more pressure would just compress it until it clogged altogether again.

 

SO the 'trick' was to always apply very little force and to move on quickly if it were to show any resistance because the joint was probably too shallow. I got used to pressing down on the plunger with just my fingers, not the palm of my hand, to limit the pressure. Of course raking all the joints before filling them is obviously a good idea but some would inevitably be missed.

 

Now I could use the gun continuously (only stopping to clean it by plunging in a bucket of water at each fill) and made such a lot of progress that I was mixing batches of 28 Litres (with slightly sharp sand) and having the time to gun it all in (this is with SBR in the mix which makes it go off pretty quick). Still took a couple of weeks but I think it would have bee more than double that without the gun. Of course by the time I'd nearly finished I was even quicker at it! TBH  I was quite sad when there was no more left to do ?

 

Anyway, I wanted to relate all this because it could save someone a lot of time, money and effort.