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Rendering and airtightness


ToughButterCup

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Well, here's the first go at rendering Durisol for airtightness. I used a 4 :1: 1 (or more) mix and applied it with the only brush that was lying around on the site stillage - an old house broom;

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There's a degree of sloppiness in the mix that's just right

 

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It's a very therapeutic process. 

Until I noticed I was rendering our car at the same time as the wall. She's going to kill me. 

(If you are reading this Deb, sorry love. I've got some flowers from the petrol station for ya!)
 

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3 hours ago, recoveringacademic said:

Until I noticed I was rendering our car at the same time as the wall. She's going to kill me. 

(If you are reading this Deb, sorry love. I've got some flowers from the petrol station for ya!)
 

 

Well if it's airtight render on the car = rustproofing it!!! Bonus!

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The one above is mine, cost about £65 

you need the little blue thing on the air connection it is a second regulator and makes adjusting the pressure at the gun so much easier. 

Will run off a standard diy compressor. 

Watch the grit size in your sand I would use a very fine sharp sand or as some would call it plastering sand or Leighton buzzard. 

Plenty of cement as it will make it a bit slicker 

i use a figure of eight pattern. 

 

Dont scoop the muck muck out of the barrow like the Neanderthals in the vids, make a scoop or you will end up in the biggest mess ever

i would lend you it but it needs a new set of seals in it. 

Plenty on e bay, but I would avoid the smaller round hopper as you can't get a lot in it. 

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4 hours ago, Russell griffiths said:

The one above is mine, cost about £65 

you need the little blue thing on the air connection it is a second regulator and makes adjusting the pressure at the gun so much easier. 

Will run off a standard diy compressor. 

[...]

 

Yo! Sushi!

Ahhhhm   ahnn it maun! Mmmmm Hmmmm! 

SPONS has the price at £4.00 / sq m cost (inc materials).    I have 240 m sq to cover . 'S a no brainer.  

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3 hours ago, Russell griffiths said:

[...]

If I was doing a rough parge coat just for sealing purposes I would slap it all on with a broom head. 

[...]

 

Wot with  my delicate forearms? I'm simply exhausted by a morning's rendering, exhausted. And all that mixing and mess going everywhere : even over the car. She'll never forgive me.

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  • 3 weeks later...
On 13/09/2017 at 11:22, MikeSharp01 said:

It seems to me that the only challenge to the sand and cement scenario is the likelihood of cracking if there is any movement[...]

 

A wise old bloke came a' visiting last week. Looked at this and said

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Tha'll need lime in that , fella. 'S Gonna crack, else.

 

So when both  @MikeSharp01 and a wise local both say the same thing, I think I ought to take some notice. (All it needs now is for @JSHarris to pile in and I'll have to )

 

I am using plastering sand in a mix of 4:1, and adding a bit of plasticiser. If I were to add some lime how much should I add? 

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Hydraulic lime is added to cement render to help prevent cracking, but not normally to a parge coat like this, AFAIK.  Our sand and cement rendered wall has has hydraulic lime added for just this reason, but that's much thicker, and was applied in two layers, a rough base layer on the blockwork then the finish layer.

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Hein ?

God this learning curve is steep. Thanks so much for the nudge.....

I thought hydrated lime is a plasticiser, and so would do the job of compensating for minor movement.

 

This page has a comparison table for both types of lime against OPC (Ordinary Portland Cement). I treat it with a good deal of caution because of the Internet-as-Shared-Ignorance  factor.

 

It's of interest because all types of lime are breathable. And, in this case, the end-in-mind is air-tightness. According to the table, the choice appears to be sand and cement and a high risk of cracks, against putting some non-hydraulic lime (hydrated lime) in the mix. 

 

The decision matters because I have 240 square meters to cover. But luckily I have a test bed in the Piggery.  I am also quite happy  listening to conflicting but apparently authoritative advice. The key issue is the mental wrestling done on the way to taking a decision. 

 

 

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Hydrated lime takes for ever and a day to cure, as it cures by carbonation from CO2 in the air.  Both end up the same eventually.

 

If you really think that you need more flexibility in your parge coat (and I'm far from convinced that you do, given that the base blocks are cementitious, anyway, plus the fibres will tend to resist cracking), then using a lime based mix  will increase flexibility, but will tend to delay the cure a bit.  Something like a mix of 1 part  NHL 3.5 (Natural Hydraulic Lime), 2 parts fine sand, will work much the same as your previous cement mix, and give a reasonable cure time, but frankly I'm not convinced it's worth the additional cost and hassle.

 

Be aware that you need protective gear with this - the lime can cause skin burns.

 

 

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Our renderer is adding a large scoop of hydrated lime to a standard 4:1 mix. He says it just provides a little more flex whilst also improving workability and retards the drying a little which helps with sponging.

That's about as far as my knowledge goes!

 

If would only stop raining we might get it finished :(

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