Use of lime in roughcasting.

Members online

markyman

New Member
Its been a while since i did roughcasting and just wanted to ask a question; why is lime used in the mix? Do i NEED to use it or can i do without it?
Cant remember exactly; i used it in my roughcast mix before, but have forgotten why. Is it to do with the age of the building, (my house is 70 years old), breathability on the wall or to help it all bind better? Thanks in advance.
 
A tin of worms type thread here , but i all ways use lime in top coat renders the positives out weigh the negatives imo people talk of permability ,workability and breathability and other words i cant spell but i know how to render lol , and shrinkage causes cracks and lime helps stop that .
 
A tin of worms type thread here , but i all ways use lime in top coat renders the positives out weigh the negatives imo people talk of permability ,workability and breathability and other words i cant spell but i know how to render lol , and shrinkage causes cracks and lime helps stop that .
Ah! now thats what i wanted to hear! (or, read!). I remember two or three years back, i roughcasted an outbuilding wall that had all blown, and as i could only get a standard sized bag of lime, i used it in all the coats, including the scratch coat; certainly didnt do any harm! Thanks; now i'm decided, i'll get a bag. Got another wall 'in the need'! The shrinkage part rings a bell! Thank you for your expertise!:numberone:
 
If you have lime left over and don’t want it to go off, turn it into lime putty, keep the air away in a sealed bucket or paint tub and it will stay good for years
 
I'm waiting for now, the weather is too changeable here just now, but i've been doing some estimating looking into wot i need! I also have the wall to strip before i can do anything! Last time i applied a slurry coat to the wall after looking for any holes and filling them, it helped when i went to do the scratch coat! I'll do that on this job too!
 
Thanks, everyone for your input; i have now considered it and will be using lime in the mix! Out of interest, when i did my outhouse wall about three years ago, i had to do it again because my mix ratios were completely wrong and i hadn't used lime; i dragged everything off the wall and started again. I found that the mix seemed to be much more even (not just at the right mix ratio); i hadn't added more sand for the second coat so the whole thing was naff; AND i'd used soft sand! It dried too fast and cracked up.:muyenojado:
Using sharp sand this time, and with Lime i found it a much smoother mix, the sand has to be sharp because it doesnt allow the mix to dry too quickly! I also learned to add a third extra sand for the second coat, because i know it needs to be a strong scratch coat but weaker subsequent layers. I used SBR in the scratch coat, but used PVA in the top coat. :sisi:
I had been on many different plastering/roughcasting pages online at the time and many of them i left immediately because i was not getting any help there, in fact many people tried to put me off, laughed at my attempts, but i soon proved them wrong! Yes, i ended up doing the job twice but the materials for the job i was doing, weren't that expensive so i just pulled it all back off and did it correctly the second time! I dont have a mixer as i dont do enough to warrant buying one, so i just rely on a well turned and mixed batch. Good mixing shovel and a mixing tray. Works for me!;):)
 
Top