procedure for rendering dense bricks

[tiger]

Hi there, I am new to the forum and would like some advise on the best prodedure for rendering a an external wall whick has mostly dense bricks.I have keyed up the bricks with a grinder to form criss cross all over as I was told they might be too smooth a surface. when getting estimates for the work I am getting various opinions on how it should be rendered with regard to the mix ratio of cement/ sand/ and lime, the type of sand, some say plastering sand others sharp sand and should waterproofer be used and should the walls be primed beforehand with a unibond or similar.
appreciate any advise :RpS_cursing:

 

[theblones]

weber rend aid or equivelent is a cement based primer

 

[bubbles65]

Welcome to the forum mate...............you'll find loads of info if you do a search - then you WILL be confused. As you have already discovered ther are different opinions from different people. Question for you - where abouts in the country are you?

 

[lucius]

Potteries i guess, youve done nothing putting a mechanical key in but as has been said rend aid to be sure and normal two coat render with what ever plastering sand is local.

 

[lucius]

I meant youve done nothing wrong putting a mechanical key in

 

[tiger]

Welcome to the forum mate...............you'll find loads of info if you do a search - then you WILL be confused. As you have already discovered ther are different opinions from different people. Question for you - where abouts in the country are you?

Thanks for the advise , I live in the telford area shropshire.:RpS_cool:

 

[plasterjfe]

deppends what render product you want to use. you could go with an sbr slurry coat and sand/cement render

 

[lucius]

Thanks for the advise , I live in the telford area shropshire.:RpS_cool:

Is that near the Potteries:RpS_scared:

 

[plasterjfe]

no lucius it aint but it wont take long down the m6

 

[lucius]

:RpS_thumbup:

 

[hollybank]

Is that near the Potteries:RpS_scared:

Why do you ask????Do you like us clay heads????

 

[lucius]

Just remember going to Stoke several times for footy many years ago and all the houses were dense red bricks.

 

[spark2010]

Hi there, I am new to the forum and would like some advise on the best prodedure for rendering a an external wall whick has mostly dense bricks.I have keyed up the bricks with a grinder to form criss cross all over as I was told they might be too smooth a surface. when getting estimates for the work I am getting various opinions on how it should be rendered with regard to the mix ratio of cement/ sand/ and lime, the type of sand, some say plastering sand others sharp sand and should waterproofer be used and should the walls be primed beforehand with a unibond or similar.
appreciate any advise :RpS_cursing:

Dense blocks have liitle or no suction, keying the wall is good as the raking the mortar joints on blocks is no good as unlike bricks the joints are not frequent enough on blocks. You could use a splatterdash coat of 1 SBR/ 2 cement and brush or harl it on (harling trowel) and leave it a day and thats your key . or you could use RENS-AID. Wouldn't advise PVA on any external render as when the PVA is applied and you apply the render the PVA re-emulifies and its not waterproof unlike SBR. Using a fine sharp is ideal and what they mean by plastering sand is a medium wash (leighton buzzard). You could always put a shovel full of coarse sharp into your scratch for strength. You cant use building sand as it has too much clay and its permeable and makes way for cracking. Sharp sand should have no more than 5% clay for the spreadability. So many people use different methods in rendering, On the scratch coat 4-1 you could put feb mix and waterproofer and leave to dry 4-6 days. Then applying a thinner top coat 5-1 with no admixtures and you can use lime if you want.

You said the wall has mostly dense blocks which means there in another substrate there, You might need to put some EML when changing substrates (backgrounds). Other thing as well, as your working outside you might want to use stainless steel beads as sand and cement is an abrasive it will - galv beads will rust eventually. But as its only a wall its up to you

hope this helps a little

 

[spark2010]

sorry just realised you said bricks, i thought it read blocks...lol

- rake the joints / key the bricks, or splatterdash coat

cheers

 

[lucius]

Dense blocks have liitle or no suction, keying the wall is good as the raking the mortar joints on blocks is no good as unlike bricks the joints are not frequent enough on blocks. You could use a splatterdash coat of 1 SBR/ 2 cement and brush or harl it on (harling trowel) and leave it a day and thats your key . or you could use RENS-AID. Wouldn't advise PVA on any external render as when the PVA is applied and you apply the render the PVA re-emulifies and its not waterproof unlike SBR. Using a fine sharp is ideal and what they mean by plastering sand is a medium wash (leighton buzzard). You could always put a shovel full of coarse sharp into your scratch for strength. You cant use building sand as it has too much clay and its permeable and makes way for cracking. Sharp sand should have no more than 5% clay for the spreadability. So many people use different methods in rendering, On the scratch coat 4-1 you could put feb mix and waterproofer and leave to dry 4-6 days. Then applying a thinner top coat 5-1 with no admixtures and you can use lime if you want.

You said the wall has mostly dense blocks which means there in another substrate there, You might need to put some EML when changing substrates (backgrounds). Other thing as well, as your working outside you might want to use stainless steel beads as sand and cement is an abrasive it will - galv beads will rust eventually. But as its only a wall its up to you

hope this helps a little

See now you know, spot on answer mate, good forum this.