Hi, I have a question to the experts on this forum. I have an out-building which has been built of concrete blocks externally and celcon/ breeze blocks internaly. What I would like to know is, it best to render the internal blocks as the external blocks are only pointed or should the internal walls be plastered with browning. If rendering is the best option than should a scratch coat be applied before the top coat, and then be finished with multi finish. Also how do i avoid cracking in the plaster work in such a large area. I did consider the dot and dab method of plaster boarding but want the best method. Advice greatly appreciated and many thanks in advance.
out-building plastering question
- Thread starter zk
- Start date
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rendering it will allow you to add some waterproofing to the mix where as browning (which would be the correct plaster type for the block you have) wouldn't allow for any additional waterproofing to be added so it depends on the state of the building really.
Browning would give the added benefit of some thermal insulation as it it gypsum based however.
Either way, both should be put on in 2 coats, scratch then float coat for best results and then skimmed with finish.
as long as the correct materials are applied correctly in correct mixes etc etc there should be no cracking.
Browning would give the added benefit of some thermal insulation as it it gypsum based however.
Either way, both should be put on in 2 coats, scratch then float coat for best results and then skimmed with finish.
as long as the correct materials are applied correctly in correct mixes etc etc there should be no cracking.
What’s it being used for? How is it built? Is there a damp proof course in the walls & a damp membrane in the floor?
The use of plaster or plaster products is not a good idea in outbuildings; if they are generally unheated or the walls subject to even the slightest damp, plaster or plaster board will eventually crumble & fall off the wall.
A painted render finish may be more suitable depending on your answers to the above. Cracking is down to incorrect preparation/application.
The use of plaster or plaster products is not a good idea in outbuildings; if they are generally unheated or the walls subject to even the slightest damp, plaster or plaster board will eventually crumble & fall off the wall.
A painted render finish may be more suitable depending on your answers to the above. Cracking is down to incorrect preparation/application.
Thank you for advice and replies Trowelmonkey1 and Richard C. TM1 for a scratch coat 4:1 mix ok with waterproofer and a 5:1 for top coat, and is it best to pva the breeze blocks before the scratch coat and also before the final multi finish coat. Also would each render coat of 6-8mm be ok.
Richard C the out-building is pretty much like a bungalow, its built with building regs approval. It has an outer skin in concrete blocks, 100mm cavity insulation and inner skin breeze blocks, concrete floor and a tiled pitch roof. It will have heating inside it.
Richard C the out-building is pretty much like a bungalow, its built with building regs approval. It has an outer skin in concrete blocks, 100mm cavity insulation and inner skin breeze blocks, concrete floor and a tiled pitch roof. It will have heating inside it.
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have to hold my hands up zk and say i'm not an expert on rendering but 4:1 for scratch and 5:1 on float is correct, with waterproofer in the scratch, you may want to consider an all in one waterproofer and plasticiser?
make sure you don't leave it any longer than 48hours before skimming otherwise the suction will be way too high and the finish will just crack, skim the next day if you can.
make sure you don't leave it any longer than 48hours before skimming otherwise the suction will be way too high and the finish will just crack, skim the next day if you can.
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