I've just blocked up my garage door and plan to render tomorrow. It's only a small panel, 2.2 x 2.1m with a 1.0 x 1.2m window and I'm going to use a sand / cement mix with plasticiser.
I haven't rendered before and would welcome any advice or tips
Thanks
What are you rendering on to?
7N blockwork
Look in Yellow Pages or similar and find someone who knows how to do it.
That size is fairly easy to do, using a length of 6"x1" to level it with the surrounding render. The difficult bit is matching the surface texture.
Oh dear. Which part of d-i-y did you struggle with?
The bit about d-i-y ing what you can, and knowing when to leave things to someone else?
>
I'd PVA it first.
You can buy packs of fibre to mix in with the mortar which helps prevent cracking.
All Bran?
My eyes!
Too late now if he has built it to finish flush but a slight step in would have made life easier all around.
Use a 4 to 1 mix and apply a scratch coat. Next day the final.
Your biggest problem is rain falling on it before it is dry. You shouldn't have too much trouble with cracking, that is a summer thing.
4 metres isn't worth getting a mixer for.What you do need is a flexible trowel. A cheap one will be hard to use.
Too late now if he has built it to finish flush but a slight step in would have made life easier all around.
Use a 4 to 1 mix and apply a scratch coat. Next day the final.
Your biggest problem is rain falling on it before it is dry. You shouldn't have too much trouble with cracking, that is a summer thing.
4 metres isn't worth getting a mixer for.What you do need is a flexible trowel. A cheap one will be hard to use.
The wall panel is recessed, so I'm rendering up against brickwork at 90 degrees at both ends and up to a bellcast at the bottom. Eaves soffit board at the top. Cornwall's overcast at the moment with the sun trying to break out. If this goes okay today, then I'm planning to render all my new internal walls, which are part of my garage conversion / small extension.
Not sure what the surface of those is.
Liberally slap on well diluted PVA (1:5) and let it soak in. If it completely vanishes in seconds, wait for it to dry, and repeat (second coat can be less diluted). In response to the suggestion to wet with a hose - you don't want the blockwork soaking wet as it will have no suction and the render won't stick. Also, some concrete blocks (thermal blocks perticularly) expand and contract slightly when wetted, and this can cause the bond with the render to break if the blocks shrink after the render sets.
Apply scratch (under-) coat render before PVA dries (at least, start before it dries). Apply max 10mm thick. Rule the surface off flat with a piece of straight edged timber, using a sawing motion to cut away peaks. Fill in any troughs the straight edge didn't contact and repeat. The whole surface should be left rough, but flat. If it's too smooth, scratch over it with a comb made from some nails poking out of a piece of wood or hammered through an old float (called a devil float). The purpose of the scratch coat is to leave a flat surface for the finish coat, but with a rough finish so the finish coat can key onto it.
Finish coat needs to be applied between 24 and 48 hours later, when scratch coat is part set but still wet. Lightly brush off any surface lumps (_lightly_ being important - at this point you can brush off all the render if you keep going). Finish coat is normally much thinner - thick enough to ensure that it completely covers the rough peaks by a few mm, but doesn't need to be any thicker as the scratch coat should have left a flat surface, and if you make the finish coat thick, you risk undoing that flat surface. Depending on the finish you want, you can polish the surface, but you may have to wait for it to set a bit first. The mistake people often make with both plaster and render is to try poilishing it too much too soon, and end up making it worse. At least with render, it sets slower, so you have more leaway. The polishing is done with the straight metal edge of the rendering trowel, dampened. Do not use a long straight edge (derby) or your wooden straight edge, and never apply the face of the trowel to the render, only the edge.
Protect from frost and rain for as long as possible. Render takes about 6 weeks to reach full strength. Avoid rubbing the surface before then, as you'll mark it.
I would use a 1:4* cement:sand mix. Scratch coat must be sharp sand. Finish coat should be too, but you might get away with building sand for an easier finish but possibly shorter life. You should include plasticiser for ease of use, and can include waterproofer. (Strickly, the waterproofer should only be in one of the coats, and it depends if your doing in winter of summer which one that is, but I can't remember which way round, and it probably doesn't matter on a garage.)
*I've had a couple of builders mention to me that cement has got harder over the years, and you can go with weaker mixes nowadays.
I've watched plasterers go over the skim coat with a decorators' sponge to get the texture. Never worked for me but timing is of the essence I think.
Andrew
Thank you for taking the time to explain things. I've used building sand, which here in Cornwall is derived from granite and comes more gritty anyway. I've applied the scratch coat and am now waiting for the set to float it off flat, as a trial for the finishing coat tomorrow.
In the meantime, I'm slurry tanking the single block skin garage walls
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.