Hi, I have just built some raised garden walls using blocks. I now want to render/plaster these. Can anyone give me advise on what the best mix would be. I certainly don't need anything as smooth as an inside skim and am quite keen on that slightly rougher sandy finish. Do I use a simple building sand and cement mix, skim it on and then use a wooden float? Can't imagine this being too workable.. Also, being an outside wall, should I put a waterproof additive into the render? Lastly, is a sealant applied to the blocks before applying the render advisable? Any advice would be great. Thanks Kyle
Kyle, you'll need to do at least a two-coat render (scratch-coat and top coat) on those raised beds. A single coat would simply fall off in next to no time. The problem here, is that the render will be 'attacked from behind' by damp from within the beds - unless you're provided adequate drainage for the trapped water in the beds. It will also be 'attacked' on its front face if the render is in contact with the soil/lawn - so it might be best to have a 100mm gravel trench at the foot of the wall (or a drip bead)...... By all means use a waterproof additive for the scratch-coat - and diluted PVA on the blocks. I'd use a quite strong mix of 4:1 sharp sand and Portland cement for this application - but I wouldn't expect it to last forever..... Raised beds are better done with brick or stonework without a rendered finish. Lucia.
Thanks for your response. The gravel edging is not a problem and the inside of the beds will be lined with plastic, so hopefully not too much water will get into the blockwork. I will most probably seal everything before I apply any renders. Out of interest, I bumped into someone yesterday who said that a single coat render made up of 1 part cement, 4 part plaster saned and 1 part lime with some waterproof additive added would be fine. Does anyone disagree with this?
It seems that it's just me and you on this one, Kyle.... Naturally, I disagree with a one-coat external render as stated previously. If you are DIYing, then you can afford the time to do it properly with a scratch-coat and second finishing coat. But you never know: A 'proper' builder might chance by here and give his blessing to a one-coat external render......... Lucia.
shocking, 1 coat of any plastering shouldnt even enter peoples minds!!! im a plasterer and theres nothing worse then when people advise that 1 coat is ok, scratchcoat, topcoat. no other option!! and i would agree with lucia that a 4:1 mix would be ideal
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