Rendering Repair Work

lucernarian

Hey there,

I've been looking around on the net but there really seems to be little info available on how to do a bit of rendering. I can't figure out why this is.

I've got a garden wall which has cracks and holes in the render, and another wall which may need some channeling done to accommodate PVC trunking for a light. Both of these cases involve render on cinder block walls.

So what mixture exactly is used for render, and is there anything I should be careful about when applying it?


Any help appreciated!:)

AckwelFoley

Plaster is best mixed at 6:2:1

sand:cement:lime

Fill the hole / channel and let it set for a short while, it depends but then the cement is getting stiff that its not like butter, give it a rub of a pvc float, sprinkle with water lightly as to not mark the plaster too much, this will blend in the channel / hole if its a float finish.

If its napped, you need a sponge float to napp it after you have evened out the hole / channel that there are little or no deep marks in it

AckwelFoley

:pac:

kristyle wrote: »

you are tight..i agree with you..

No, my missus is tight.


I am right. :pac:

jack of all

Make sure you use a washed plastering (sharp sand) grade sand; if you use a regular building sand ("soft" and containing more fines) you'll get a poor finish which won't be as durable. Also it's a good idea to use PVA primer to repair old areas/ backgrounds to improve bond.

AckwelFoley

jack of all wrote: »

Also it's a good idea to use PVA primer to repair old areas/ backgrounds to improve bond.

I sometimes refrain from advising the use of PVA, because if people use it needs to be used right otherwise its more of a hinderance than a help


If you were to prime an area with pva and let it dry, the finish is glossy, and is worse to adhere any adhesive to than the surface probably already was...

Put plaster too soon after priming and the adhesion is disolved.. it needs to be tacky... than plaster...

jack of all

Fair points Snyper.

lucernarian

Thank you all very much! Gentlemen here as ever on this forum.:cool:

It does sound fairly similar to ordinary cement mortar I have to say. I'll get some sharp plastering sand and that should be that! It's only a small area on top of concrete blocks so I doubt I'll have to worry about scratch coats etc.


While I'm at it, I may be fixing up the wall with replacing/getting precast capping stones on the block wall. Two questions, can I re-use the rendering mixture for laying those stones, and for the joints between the stones should I use mortar or a good heavy duty silicone like tech7?

There's another wall with capping stones and the joints between each other are all but gone or cracked to hell. Mortar was used for those. I did completely re-lay the mortar in one joint but even that has a hairline crack running with the joint, through the middle of it.

AckwelFoley

To_be_confirmed wrote: »

Two questions, can I re-use the rendering mixture for laying those stones, and for the joints between the stones
.

Yea, the same sand will be fine, just the ratios of mix is different.

4:1 or 5:1

Sand:Cement

Dont use lime, just water with some plastaciser, if its only a small job you can use some washing up liquid instead, BUT A VERY SMAL AMOUNT, Literally a few drops in a bucket of water. Adding too much of plas or particularly washing up liquid makes the mortar too biscuity when dried due to the excess air in the mix from making it fluffy, but if you dont add it, its very unworkable, perhaps not for a small job like this, but you try lay 6000 blocks without some form of admix and you''know what i mean

To_be_confirmed wrote: »

or a good heavy duty silicone like tech7?

.

No.. not for that job

lucernarian

Any way from stopping the joints from developing cracks?

Thanks for the answer above!