Hardwall thickness and application

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jack88

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Hi guys, few querries i've got with hardwall which i don't seem to get any clear answers on, so thought i'd see what peoples thoughts were on here

Firstly - To what thickness can we go with backing plasters, hardwall, bonding, browning and what implications does this have??

Secondly i have had probs in the past with floating and setting in the same day where the devil key shows thru the finish with the air's escaping in to the finish coats...this does go after a while but only after i've waited with it and gone over it a few more times....so will this go on its own without the need to keep trowling it up or i'm wondering what peoples thoughts are on floating up on one day and setting on another, or even floating and setting without the devil key, as i've been told by a few this is ok??

finally when is it best to set the float?? what signs are we looking for to know its the right time...up unitl now i've been waiting for it to firm up so the devil scrapes its key as opposed to dragging and collecting plaster on the float and leaving an otherwise thick devil key

finally, when going back to a house brick substrate where there could be a risk of efflorescence drawing thru (which i have had happen a few times) whats the best solution in elliminating this risk...should we be sealing with pva or using a salt retarder or somekind??
 

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spark2010

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backing plasters can go upto 20-25mm, built up in coats (scratching in between), anything over 25mm will have to be supported with EML lathe, same with the other backing plasters as well, making sure there is no moisture in the wall as it will loose its strength.

Float and set in the same day is normal, althought depending on the size of the job, a lot of people float all then skim following day.. depending in temperature, thickness in coats etc. The devil float screws should only be slightly protruding thru the float as the skim is only thin anyway. This is a problem some people have as they devil float and break the bond between coats by exposing the coat behind the one they are devil floating. tosing the gear around the hawk a few times before application extracts any air. But when you say air escaping through the skim then it sounds you skimmed it too early. Technically hardwall sets in an hour or 2 but again depending on conditions. But you can normally skim onto hardwall quicker than skimming onto bonding as hardwall is a high suction plaster and its for high suction backgrounds hence why it sets quicker, and please forget about PVA before hardwall. Bonding dries from the back and hardwall dries from the front in, so you got to be careful when skimming it as its normally damper at the back. You can see the hardwall change colour as its drying

The last point - efflorecence, again NO PVA.. wire brush all over.. this is a tricky one as if there is moisture in the wall and u render it then it will trap the water in the wall and encourage capillary action (rise of water). u have to make sure all the moisture is gone and wall injected if necessary. Hardwall can be used on the brick but render the int/ext

You can use renderspel salt retarder mixed at 40-1 with the render or apparently vinegar and water mixed together and brush into the wall!
 
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