Lack of suction? Create a 'key'

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bigsegs

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As discussed in 'suction control', a complete lack of suction will leave you with no real option other than to 'create' a method of bonding your plaster to the wall. In other words, you need to create a 'key'.
Various methods are employed both internally and externally most of which are essentially mechanical. That means the 'key' will physically hold onto your plaster (think velcro).
I'll kick off with painted surfaces for overskim.
Gloss paint or to some extent silk paint will usually seal the wall to such an extent that you have no suction whatsoever.
Applying finish directly onto this surface will leave the plaster unbonded and will end up sounding hollow when tapped and in extreme cases physically loose and on the floor :eek:
So, there are various products designed to give you a key - 'Thistle bond-it', thistle being the trade name of the manufacturer. 'Wickes plaster bonding agent', same stuff essentially, manufactured by 'knauf' and sold by wickes builders merchants. Betocontakt (is this spelt right?) again same stuff...
These are 'polymer' based liquids containing a fine aggregate or sand. for 'polymer' stick it in wikipedia ;D
Drying times vary per product from 2 hours to 24 hours.
It should be applied by brush or roller evenly over the surface and allowed to dry completely.
It simply bonds itself to your surface, pretty much sealing any residual suction as it dries but gives you back a mechanical key in the from of a gritty texture which plaster will wrap itself around so it stays put.
An excellent tip whilst using products of this nature is not to use 'multi finish' but instead use 'board finish'.
The difference between the two is that multi requires medium levels of suction for ideal workability in use wheras board finish is more suite to areas of low or no suction..
Multi will work but you'll find it difficult to get a decent finish especially using the two coat method.
 

Chris W

Well-Known Member
Schizzlemeister said:
What about just using a scutch hammer and PVA?
nice, but running a devil float over the painted surface is quicker, less messy, safer and wont scare the living crap out of the customer who thought you were a plasterer, not a demolition man, especially if its a stud wall ;D
its a quick and simple method that works, and works well, sometimes however you may find the painted surface is on top of another low suction background, waterproofed render for example, either / or both at the end of the day.
 
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