Rendering over painted brick.

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SLIPPY

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I have been asked to k-rend a painted brick wall. Whats the best way to prepare this for the best key?
 
I'd be interested to see what the guys say here - I'd use Weber Rend aid, but I'll probably get laughed of the forum and told to use Bostik with a bit of grit thrown in lol
 
sand blast the paint off!! then slurry with SBR/OPC MIX you can paint this on and as it go's tacky render into it this will stick like s**t to a blanket!! ;D
 
Very simple hpx straight over with mesh with a few plastic fixings then top coat a few days later this way never fails
 
i would get it sand blasted off ---

the problem with anything over a painted surface is that the paint is still the only thing holding it on the wall

yes it may be well stuck and you may get away with sbr or hpx ect and render over --- but long term ?


if unable to sandblast fix galv/ss mesh to brickwork with fixings


sure there are other ways but that's the way i would look at it...



martin



www.emjenkins.co.uk
 
Other than what has been said about the paint coming of what is wrong with the first answer of using rendaid instead of SBR or HPX
 
lucius said:
Other than what has been said about the paint coming of what is wrong with the first answer of using rendaid instead of SBR or HPX
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Krend make hpx so thats why you would use it ! mixing differant brands is pointless :-\
 
spongebob said:
lucius said:
Other than what has been said about the paint coming of what is wrong with the first answer of using rendaid instead of SBR or HPX
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Krend make hpx so thats why you would use it ! mixing differant brands is pointless :-\
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True in some respects that products from the same manufacturer work better together but - all these products contain the same ingredients and are there to do the same job plus krend make half of the render companies gear anyway so most is the same with a different label but as far as using rendaid with krend colour over the top makes no difference if it was weber colour over the top plus rendaid is a prep coat (like an sbr slurry) hpx is a very high polymer basecoat and they would still want mesh pinned back with it.

Remember if you go for rendaid leave for three full days to cure and where poss always get the paint off
 
think parex do a product that they guarantee over painted substrates if you need reps number for more info i will dig it out for you
 
kevmc said:
think parex do a product that they guarantee over painted substrates if you need reps number for more info i will dig it out for you
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would it be microgobetis that you are thinking of
 
Try our P100 we always use it on smooth surfaces it sticks to any surface, has a bonding ability of 1.2n per mm2 which is massive. From what I have heard rendaid shouldn't be used on a painted surface.
 
Agree with martinmj and a couple off others on this,.....There is no product or company that will offer a guarantee if going over paint (or should i say if your trying to bond a product to paint) the bond is only as good as the paint bond to the substrate, the only way to guarantee against de-lamination is to create a mechanical fix, Okay you may get an adhesive coat to fix to the paint or a slurry of some sort but this needs to be backed up with a mechanical fix, so it's hack off , score through the old render to the substrate (diamond blade cuts at reg intervals, with and an adh coat and mesh with additional mech fixings, or Eml would be my preferred method, if not removing render ), fix rib-lath Eml or similar , or cuts and adhesive coat with mesh and mechanical fixings at regular intervals.
If you find a product that does guarantee for this without any other type off assist then please let me know :eek:
 
Ive done a few similar jobs in Spain and as Warriour says it is always better to get the paint of but often the client dont want to pay for it so we do as Warriour suggested and score with an angle grinder then prime with the Spanish equivalant of WBA, Betoncontact not sure if its exactly the same stuff as it is often used outside but ive not heard of WBA being used externaly but i dont see why not perhaps someone knows.
 
Would you recomend scoring the mortar joints with a disc cutter. then coating walls with a similar product to wba? With the sbr are you sying to paint onto walls, then splaterdash after, or mixing sbr in with splaterdash?

Cheers
 
Thanks for all the feedback, I was thinking of using exterior unibond mixed in with a s&c slurry and paint it on, I have used this method before on smooth steel lintels that have been treated with fireproof paint and then rendered as normal and as far as im aware its still on years later. Opinions please
 
SLIPPY said:
Thanks for all the feedback, I was thinking of using exterior unibond mixed in with a s&c slurry and paint it on, I have used this method before on smooth steel lintels that have been treated with fireproof paint and then rendered as normal and as far as im aware its still on years later. Opinions please
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Would that give you enough mechanical key thought ??? its a lot of weight hanging on a few grains of sand which is stuck to PAINT
 
Wouldn't do mate you need to think that this render is 15mm think and hanging on for dear life on a thin layer of paint you need a mech fix.
 
Would a needle gun be the way to go on this 1 and scud the brickwork as normal? Or go the grinder route?
 
Couldnt find anything that says you can use WBA externaly but it does say it can be used to support render.
The stuff i use in Spain is called Implafix and is made by Grupo Puma it looks exactly like WBA but you can mix it with water, apply it with roller of brush and when dry render over for some reason if it has been on the wall for more than three days its no good and you cant render over it.
 
I suppose they are just covering theire arse realy as if the EML fails if not fixed properly they are safe, i would imagine it would be cheaper to needle gun paint of rather than EML.
 
The problem with applying anything over paint is you don't know how it will react when rendered so the only way is to sand blast it off then apply a pre rend like rendaid / HPX . If its on a real tight budget, you could rack the joints and pre rend and embed mesh into the pre rend then use a mechanical fixing every 12" to hold the mesh and then krend over the lot.
 
the blaster that i was gonna use offered a chemical strip as well but they dont charge as much as you might think
 
Needle guns leave a perfect finish for rendering onto (with minimal prep) , i use them regularly on painted cellar walls when i'm tanking ,
 
SLIPPY said:
Thanks for all the feedback, I was thinking of using exterior unibond mixed in with a s&c slurry and paint it on, I have used this method before on smooth steel lintels that have been treated with fireproof paint and then rendered as normal and as far as im aware its still on years later. Opinions please
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If you aint gonna remove the paint i would still say rendaid or similar with mesh pinned into the substrate using fischer fixings or similar - or eml fixed first then a polymer based scratch coat.
 
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