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Rendering with gun


Me0wp00
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Hi, Im tinkering around with re-rendering some

walls as part of a renovation project. Im using a 1 part chaux blanc to

4 part sharp sand mix for the render to give me a traditional finish

and to let the wall breath still.

However, having been all traditional with the material, I'd like

to apply it to the wall with a render applicator gun as I tend to get

lots on the floor and take all day flicking it with a trowel

I have purchased a render gun which goes on the compressor, and its

arrived with no instructions whatsoever. I tried the same mix that I

would apply with the flick method (consistency of warm butter) but the

gun wont spray it, even at 90psi. Also the gun came with two nozzles,

and the only real difference is the depth of the cone where the render

comes through, should I be using the "sticky out one" or the "flat

faced" one?

Can anyone suggest where Im going wrong? baseline setup of the gun pressure and mix consistency?

Just to be clear its a top hopper fed compressor gun for raw bulk render application, not a tyrolene gun.
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If it wont spray your mix is too thick. When our neighbours house was done the mix looked like thick custard.

I gave up on the 'trowel method' and simply threw it at the wall with a pair of Marigolds' on. Clean plastic sheet on the floor means you can pick up what drops and so less waste.

Good fun.............
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I thought the guns were for pointing rather than rendering and the mix required a plastifing chemical in it.

I also thought that sprayed render needed a huge piece of kit with a very large compressor. Have you checked out the hire shop pages to see how your equipment compares ?

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Me0wp00,

I take it your not naming the machine as it maybe against forum rules but I  don't think it is as you are neither selling it or slating it , yet at least [:)]

It would be helpful if you could either name it or post a link.

A lot of render guns are in fact re-pointing guns for brick work that use building sand and cannot cope with course grained sand. Not saying any more until I know which one it is. [blink]

 

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Meawpoo

I have done several hundred square metres of rendering and crepi-ing with the same gun as you, I have also experimented massively so I think that I can answer your questions.

First thing if your gun like mine passes air continously you will need to fit and use an on-off tap (use a plumbing sphere à vanne) to avoid it emptying down the compressor when you are not spraying.

The crepinette guns are really made for spraying crepi (the textured paint) which has to be thinned with water using a malaxeur to the required consistency, this can be judged by filling the hopper (without the air connected), with the largest nozzle fitted and the trigger opened the mix should dribble through the nozzle by gravity. The fan of the spray pattern is quite narrow so sometimes an even thinner mix helps but not so thin that it runs.

For a decorative enduit finish it will spray chaux based the enduit de renovation quite well but again it must be made up much thinner I find that the cement mixer is buch better than a malaxeur for this, it actually flows very well through the gun but the very thin coats and the weight of the loaded gun make it very time consuming and laborious, you have to do many coats to get up to the needed 15-20mm thickness.

I usually put it on as thick as possible until it sags and then rub in the sags with a trowel when semi dried, sometimes this makes it more fluid and makes matters worse, for finition gratte you need to scratch off the surface with a taloche à pointes. I limit myself to bays of 5m2 max using the gun.

I have never persuaded it to spray my own made up render using 0-5 sable rivier, the addition of chaux may help but the particles are just to large and irregular that they will not flow, I did once manage to throw up a very thin and runny gobetis coat but I had to run the sand through a tamis first.

So to recap for sharp sand render forget it, for premixed chaux based enduit de renovation you can get very good results with care but it is very heavy work and has to be broken up into small maneagable areas, for crepi it works really well.

PS I start spraying at about 90 psi but the discharge is greater than even my 3hp proper horses compressor can keep up with so it is down to around  70 psi by the end of the hopper which is just sufficient but dictates a differing spray technique. You are advised to use the most powerfull compressor with the largest reservoir that you can find.

I hope that this helps and not disencourages you, I have had some really good results but they involve a lot of time and hard work.

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Still waiting.........

Could have applied it by hand by now [:D] throw it with a scoop not a trowel, if it hits the floor pick it up and use it again no worries.

For spray application could add Calcium Stearate at the ratio of 40grams to 25kg mix, also recommended by St Astier to reduce the water content, improve the flow properties and reduce the small cracks on drying.

Still usually a problem with particle size as you say J.R. It takes a big machine and compressor to do it effectively IMO


 

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thanks for all the replies, I posted on behalf of my DH and tbh am going to have a blonde moment (i'm brunette) as I don't understand render/crepi at all.  DH is busy putting beams back in but i'm sure he'll reply to your posts later.

thanks very much

Pippa

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DH here, my wife cross posted my original from somewhere else...

JR, thats a great response, thanks for taking time to respond in such detail.

The gun is indeed the cheap 70e budget one with the plastic hopper and the anodised alloy body, significantly mis-sold it seems, hence the lack of information. Id guess the 350e-ish ones with the steel hoppers on top that keep coming up when I google render guns are maybe more suited, and its not beyond the bounds of possibility that Ill get one of them if needs be.

Gun does indeed not have a air valve, but I have it on a pcl connector so it just snaps onto the end of the self sealing line, so when I want to stop the airflow through it (to shut it up!), I just snap the connector off. Ive been mixing the render in the mixer as I don't posses a drill mixer or the like.

Compressor power really isnt a issue, its a 40+ cfm 3phase fiac industrial unit with a 500L air tank. Its piped to the start of the airhose roll with 25mm i/d hardline and that itself is 14mm id bore rather than the small bore stuff you normally see, so airline velocity isnt really a limit either. If it is, I have a portable 50L tank I can use as a accumulator right near the gun head as the compressor house can be some distance from the workplace at times I have a 100m hose reel, as you can imagine the compressor is not exactly portable unless you have a forklift and a long 3 phase extension!

So, really the gun's for finishing  but it can be muddled along with if you apply a bit of common sense, I suspected as much and it did work quite well ages back when we did some crepi with it. I'm tempted to try my portable sandblasting pot, since thats designed to spray sand at stuff (albeit with quite high velocity, maybe if I leave the ceramic nozzle off the reduction might make the goo stick instead of bouncing off) so it may just be able to handle the chaux based render too with some adjustment of mixer settings.

Ill have a tinker and see...

I could have done it by hand, well the tiny test wall we're tinkering with now, but ultimately I have to render a 10mx14m two storey house and outbuildings. I don't fancy trowling that on by hand, but the budget won't run to 5k for a proper cement pump...

Thanks for all the replies.

If anyones tried the blasting pot experiment, I'd be interested in your results, save me some time if its a faliure :)

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I chickened out on my large building and repointed by the old "bagging method" followed by spraying on crepi, the bricks used had been reclaimed after the WW1 bombardment and possibly WW2 as well for some of them, there was not a square face showing so traditional repointing would have looked naff as do most of the buildings around here that are done by soi disant "artisan renovateur de facades" who slap on typex white chaux cement with a cake icing bag.

The main front elevation I spivved up with faux joints followed by painting with cheap pliolite mixed with brick dust, it looks a treat although I didnt replicate the white painted pointing which must have been done by one of the first asian residents of these parts [:)]

I very nearly bought a compressor and pump on E-bay UK and would have made a very nice profit reselling it in France after the job but not having a second pair of hands I would have been up and down my scaffold like a yo-yo, perhaps you might consider this route?

Re the blasting pot, before discovering my beloved crepinette I used to use a schutz gun in the UK for spraying textured masonry paint but it had a very narrow fan, funnily enough I still use it here for bords d'humidite.

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