Some Basic rendering questions

[men8ifr]

I want to cement render part of my garage.

I have some basic questions:

Do I need to use hydralime as per the rendering spreadsheet stikied on this forum? - what is it, what does it do?

Is 20mm a good thickness to work to - I was thinking 10mm would make it flush and fit in with other parts of the garage better.

Can all of that go on in one coat?

How do I get a slightly rough/matt finish, or will it have that anyway?

Do i just use a couple drops of washing up liquid as plasticiser per bucket as per mortar mix?

Thanks in advance

 

[jeds]

I want to cement render part of my garage.

I have some basic questions:

Do I need to use hydralime as per the rendering spreadsheet stikied on this forum? - what is it, what does it do?

Not necessary on a garage.

Is 20mm a good thickness to work to - I was thinking 10mm would make it flush and fit in with other parts of the garage better.

10mm will be fine.

Can all of that go on in one coat?

10mm yes, 20mm tricky.

How do I get a slightly rough/matt finish, or will it have that anyway?

Once floated (with a wooden float) to reasonably flat, finish with a damp, flat sponge. Don't try to float or sponge too early. The render needs to be quite firm.

Do i just use a couple drops of washing up liquid as plasticiser per bucket as per mortar mix?

No. Use a proper plasticiser. Fairy will have a negative affect on final strength and may trash the job alltogether.

Thanks in advance

 

[ajrobb]

Do I need to use hydralime as per the rendering spreadsheet stikied on this forum? - what is it, what does it do?

A lime render will allow the wall to dry out. An ordinary Portland cement (OPC) render can trap any condensation or other damp in the wall and weaken it. Assuming your 'garage' is not plastered on the inside and is used as a shed/garage with a poorly sealed door, there should not be a condensation problem. An OPC render will make it difficult to convert the garage later.

 

[men8ifr]

thanks!

 

[men8ifr]

By the way this is for the external side of the wall - is that still oK?

 

[Alastairreid]

By the way this is for the external side of the wall - is that still oK?

Yes it is.

 

[maaaaaaaaat]

if you want a matt finish you should check out mattmolloy,on the web or the gallery section.

 

[men8ifr]

As it's for an external wall should i use hydralime? (sorry to previous respondants I did't mantion it was external).

If so where do you get the stuff - bnq don't sell it.

 

[Alastairreid]

You should get it at your local b/m

Non hydraulic lime hardens by a slow process of carbonation, reacting with atmospheric carbon dioxide over a period of weeks. Hydraulic limes and cements set rapidly by reacting with water in a matter of hours. A non hydraulic lime can be made to set much more rapidly by the addition of an hydraulic or 'pozzolanic' additive. This practice is known as 'gauging'. The additives include finely crushed brick powder, PFA, HTI, pozzolana, trass or cement (white or OPC). These all contain finely divided and therefore highly reactive silica and/or alumina, which are the constituents necessary to obtain a rapid chemical set by reaction with water. Of these, cement is by far the most widely used in this country, and the cheapest. Typical proportions, commonly in use, are 1:1:6 (cement: non hydraulic lime: aggregate) and 1:2:9.

There are, as one would expect, both advantages and disadvantages in gauging non hydraulic mortars with cement to make them hydraulic.