Determining the dormer render finish

O

OggyP

New Member
Hi all

I'm looking for advice please. Firstly I'm not a plasterer or a renderer and I'm paying a professional to do this for me, however this is a house I'm self building. The drawing the architect supplied for the dormer construction listed as follows,
6x2 stud
Osb
Breathable felt
2x1 treated membrane
Renderboard
Render

We had planned to have the house dashed in 6mm limestone sand cement wet dash and when I spoke to the builders merchant they said that i could have this applied onto the render board ( resistant multirend) but now after ive spent days fitting the boards and spoke to the manufacturers of the board, this way isn't the best practice as they are designed for modern render systems. However They have said to apply acrylic primer to the boards and stainless mesh (riblath?) Then scratch coat and wetdash but no guarantee.

I'm starting to question how well it will last. The boards soak water up like crazy and although are waterproof they dont stop water leaking through them so I want to make sure that whatever render is applied will not crack. We get alot of driving weather hitting the house.
Is there a modern silicone/render that will match the 6mm white sand cement dashing we are wanting to put on the rest of the house? Or shall i put the primer and mesh on and hope that it doesn't crack?
Determining the dormer render finish
Determining the dormer render finish
Determining the dormer render finish
 

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  • Determining the dormer render finish
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i would go for a thincoat acrylic type finish on the dormers.
give the acrylic a bark finish with a roller.
the roller frame covered in a piece of plastic pipe or a mastic tube. this will give you a similar finish to roughcast.
 
Firstly don’t use the multi rend board of yiu don’t know why use google and look in the direction of bba certification, secondly there’s no ventilation on the dormers this needs to be at base level and soffit level so get them boards off and also the timbers that are stopping drainage at base level, install plastic ventilation/drainage beads at base level this also stops any infestation, use a thin coat render system with a silicone finish as minimum
and lastly never take advice from a builders merchants the only thing they are interested in is making a sale they have zero knowledge or experience in our trade, look at manufacturer websites and get them to specify a system and recommend an installer close to you that way if there’s any problems you should have their support.
that’s a grand PayPal will do
you’re welcome
 
themucky1 said:
Firstly don’t use the multi rend board of yiu don’t know why use google and look in the direction of bba certification, secondly there’s no ventilation on the dormers this needs to be at base level and soffit level so get them boards off and also the timbers that are stopping drainage at base level, install plastic ventilation/drainage beads at base level this also stops any infestation, use a thin coat render system with a silicone finish as minimum
and lastly never take advice from a builders merchants the only thing they are interested in is making a sale they have zero knowledge or experience in our trade, look at manufacturer websites and get them to specify a system and recommend an installer close to you that way if there’s any problems you should have their support.
that’s a grand PayPal will do
you’re welcome
Click to expand...
What do you mean by "base level"?
 
Hello buddy

what @themucky1 has said is correct....

now that you have the roof tiles on, the only way to make good is by taking off the boards to do the remedial works - you really MUST do this before you put a render on....

Not withstanding the board issues (go search MGO boards - you have quoted yourself a big issue...) you really MUST drain and ventilate the base of the cladding to the roofline, and ventilate up to the soffit board above

Happy to advise and assist further, if you would like some assistance - I’m back working Monday 4th...

The render finish needs to be a modern thin coat render to boards, the structure of the dorma is timber so will settle and move and the heavy dash finish will crack due to settlement and fail... get a spec from the render system supplier (the board suppliers assist with the boards... the render supplier with the render.... if you get advice from the board supplier and the render fails, will the board supplier warrant the they did not supply...?)

Good Luck

Richard Lord
Knauf
Aquapanel Technical Manager
[email protected]
07918 766577
 
themucky1 said:
Firstly don’t use the multi rend board of yiu don’t know why use google and look in the direction of bba certification, secondly there’s no ventilation on the dormers this needs to be at base level and soffit level so get them boards off and also the timbers that are stopping drainage at base level, install plastic ventilation/drainage beads at base level this also stops any infestation, use a thin coat render system with a silicone finish as minimum
and lastly never take advice from a builders merchants the only thing they are interested in is making a sale they have zero knowledge or experience in our trade, look at manufacturer websites and get them to specify a system and recommend an installer close to you that way if there’s any problems you should have their support.
that’s a grand PayPal will do
you’re welcome
Click to expand...
Don't forget the correct screws:ROFLMAO:
 
Runswithscissors said:
Hello buddy

what @themucky1 has said is correct....

now that you have the roof tiles on, the only way to make good is by taking off the boards to do the remedial works - you really MUST do this before you put a render on....

Not withstanding the board issues (go search MGO boards - you have quoted yourself a big issue...) you really MUST drain and ventilate the base of the cladding to the roofline, and ventilate up to the soffit board above

Happy to advise and assist further, if you would like some assistance - I’m back working Monday 4th...

The render finish needs to be a modern thin coat render to boards, the structure of the dorma is timber so will settle and move and the heavy dash finish will crack due to settlement and fail... get a spec from the render system supplier (the board suppliers assist with the boards... the render supplier with the render.... if you get advice from the board supplier and the render fails, will the board supplier warrant the they did not supply...?)

Good Luck

Richard Lord
Knauf
Aquapanel Technical Manager
[email protected]
07918 766577
Click to expand...
So what I said? Lol
 
Thanks for the replies so far.

As per the original question I would like to know if there is a modern render system that would match a 6mm sand cement dashing. If not, after reading some alarming information on the labc website regarding resistant MGO boards, I'm thinking of ripping the boards off and replacing with a cedral composite type cladding. If I cant match the dormer render to the house render ( that must be 6mm wet dash) then I'll go down the cladding route.
www.labcwarranty.co.uk

Updated Guidance for Magnesium Oxide Boards (MgO)

With effect from 15th April 2020, LABC Warranty no longer accept the use of all types of Magnesium Oxide board (MgO) on any of our structural warranty schemes.
www.labcwarranty.co.uk www.labcwarranty.co.uk


The batterns I put on at the bottom of the dormers were fitted so that the roofer could fit his lead soakers behind the board they cant be removed easily as its roofed in. The top of the boards are vented into the roof space as the soffits are butted upto the render board after the board is fitted.
 
themucky1 said:
Firstly don’t use the multi rend board of yiu don’t know why use google and look in the direction of bba certification, secondly there’s no ventilation on the dormers this needs to be at base level and soffit level so get them boards off and also the timbers that are stopping drainage at base level, install plastic ventilation/drainage beads at base level this also stops any infestation, use a thin coat render system with a silicone finish as minimum
and lastly never take advice from a builders merchants the only thing they are interested in is making a sale they have zero knowledge or experience in our trade, look at manufacturer websites and get them to specify a system and recommend an installer close to you that way if there’s any problems you should have their support.
that’s a grand PayPal will do
you’re welcome
Click to expand...
Sound advice,
It also wants a drainage c section fitting above windows, then any moisture in the wall will be deflected down the cavity, at present it's just going to run down behind Your windows.
 
owls said:
Sound advice,
It also wants a drainage c section fitting above windows, then any moisture in the wall will be deflected down the cavity, at present it's just going to run down behind Your windows.
Click to expand...
Aaahhhhh I forgot to include that one
 
Oggy oggy piggy oi oi oi
Sorry @OggyP I couldn’t help myself it’s been a long lockdown stay safe and prosper
P.s don’t forget that grand
You’re welcome
 
themucky1 said:
Oggy oggy piggy oi oi oi
Sorry @OggyP I couldn’t help myself it’s been a long lockdown stay safe and prosper
P.s don’t forget that grand
You’re welcome
Click to expand...
Genuinely thanks for the advice good sir and the cheques in the post......... I'm just unsure which route to take now that I cant put s and c wet dash on and I dont want render that doesn't match the house.. maybe could be putting cedral cladding on at this moment.
 
owls said:
Sound advice,
It also wants a drainage c section fitting above windows, then any moisture in the wall will be deflected down the cavity, at present it's just going to run down behind Your windows.
Click to expand...
When fitted the windows I siliconed DPM on the reveals and then fit the window(silicone to the DPM) then when I fitted the render board I folded it up so it has created a tray to run any water away.
 
You can use a lightweight system such as parex ehi rough casted, if matching the rest of your house is an issue.
 
OggyP said:
When fitted the windows I siliconed DPM on the reveals and then fit the window(silicone to the DPM) then when I fitted the render board I folded it up so it has created a tray to run any water away.
Click to expand...
It's the timber above the window not the window itself, it's going to hold water if/when any water appears, as your window reveal will be rendered won't it.
 
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