External render querie

[paulandlaura]

Dear plastering wizkids.
I have a 3 bedorom extension which is block / cavity block construction, with an exterior render finish. My Architect specified Thermalite shield. My local builders merchant only stocked Tarmac Toplite, but assured me that they where the same product. I have since learned the Tarmac toplite blocks are very prone to blowing render.
Have I made a cocked up??

Thanks Paul

 

[Mick Leek]

paulandlaura

I have just built my own extension and used the exact same blocks as you. The bit that puzzles me is that it sounds as if you have used these for the external skin as well ??

If that is true, i think you have dropped a clanger. " But i am probably wrong" I used the tarmac toplite (which are thermal insulating blocks) for the inner skin, and concrete blocks for the outer.

Formed a 4" cavity and installed 2" of Xtratherm... Yes i know far too much but saves on the gas bill.

I rendered the outer wall with a 4.1 scratch then a 5.1 top coat.. looks the business and the BCO guy said i had done a good job for a DIY project.

I hope i am wrong thinking you cant have these for external skin

Good luck

Mick.

 

[paulandlaura]

Mick
I have got these for the external skin (bungalow).
The only place concrete blocks where required was bellow ground and bearing the beam and block floor.
My architect specified Thermailite shields for the outside, which are also a 3.5kn low density block. I know that this is correct because I already have one extension built from these.
I do not think I have dropped a clanger with using a 3.5kn block, I had heard that Tarmac Toplite are "unofficially" not great with render unless you mesh.
Although I did have problems with blown render, using the thermalite shields the other side.
I am pleased you did good with b-control and hope you had fun and are proud of your hard work.

 

[legs-akimbo]

There is a product on the market that you mix up with a scud coat for applying to thermalite type blocks...I used it once a few years ago when rendering internally to a new build and you needed to wear a mask as the fumes made you as high as a kite...sorry though I dont recall what it was called. If you can get hold of it and when you use it with the scud coat to (a dampened wall) you can then apply a scratch coat with waterproofer ((Yes J.B. this is one time I would advocate a W.P) This will help with the finishing coat and suction ...I would advise looking toward a dash finish as this would be less troble to attain the perfect finish than when overconing the problems for a plain floated finish on high suction backgrounds.
All in all good preperation will overcome any problems.

Another product I have been told about but not been able to get myself and is used as a waterproofer in the scratch coat when dashing is "Medusa" J Bonding have you come across or used this I have been told it is the Bees Knees?

 

[legs-akimbo]

If you tried enquireing at Quinn light blocks ( Irish equivalent of thermalite) based in Ulster somewher I think they should be able to help you with the technicals

 

[paulandlaura]

legs, forgive my ignorance but there seems a bit of luck and a load of differing factors in your trade, especially so with my product. Is it simply worth a few hundred quid/euro's, to simply mesh the damn lot up and be done with it

 

[legs-akimbo]

I.M.O. that is a drastic and non necessary course of action.
90% preperation means 10% persperation.

 

[paulandlaura]

Not doing this work myself. but forearmed ect ect..
Cheers

 

[Mick Leek]

Legs,

What is a SCUD coat ? Is that a type of key to ensure scratch adheres?

Thanks,

Mick

 

[legs-akimbo]

Yep....Its generally a p**s wet slurry of 1:1 sand cement dashed onto the wall to act as a key...if you can get the scud ( or spattter coat) to cover the best part of the surface area with waterproofer or the product mentioned it will help enormously with the high suction.

 

[Mick Leek]

Thanks Legs,

I went to my friends today and installed 3 new door casings in the room i am plastering tomorrow.. Anyone had dealings with Accrington brick ? Bloody hard stuff.. burnt out 3 drill bits trying to drill the stuff.

Going back to the SCUD coat, is it really necessary internally has i dont want to cause a big mess flicking a sloppy sand cement mix around.

Also would you advise rendering with sand and cement rather than bonding ? it is a very old house and has lat ceillings ( is that the term)
also has wooden lintels, the brick work internally is the roughest i have ever seen. You wouldnt beleive how un level the walls are.

Cheers

Mick

 

[jbonding]

applying it with a roller will do the same job, would you not consider dabbing and skimming?

 

[Mick Leek]

Hi JB

Well after today YES i would... had the worst day ever. Just couldnt get it level, had hollows all over the place. Mangaed to kind of sort it in the end but it isnt to my usual standard. How hard is it do dryline ?

Got to be easier than plastering a 100 year old house with bloody huge holes everywhere.

mick

 

[legs-akimbo]

I thought we were talking external rendering here???

 

[jbonding]

I thought we were talking external rendering here???

ill be honest legs once i posted i then thought it was refering to external rendering but looked again and the post changed with mick so i left it but i can see what your talking about.