Mortar beds on walls and floors?

[Rob Z]

How many of you are called on to do mortar work? It's few and far between here in most markets in the US. There are selected markets where mud is still king, however. I learned from a guy who had been floating mud since the 60's, and I think he learned it from a guy who had started back in the 1930's.

A lot of old houses have mortar over wooden lath, but after about the late 30's metal lath was used.

Here is a picture that shows both a finished float (on the left) and a wall with the scratch coat (rear wall) and the wall that is prepped for mud with paper and galvanized metal lath (on the right).

Here, floor mud is usually 4 or 5 to 1 (coarse sand and cement). Wall mud is usually 4 or 5 to 1 to 1 (sand/cement/masonry lime). Some areas of the country use something called "fireclay" instead of the lime, which I have never seen.

We really love to do this work because it is old-fashioned and is done the same way it as been done for centuries, all by hand.

 

[White Room]

Your talking about 13m3 (cubic metre) 30mm is the minimum thickness to lay, I'd use ready mix screed with fibres added

 

[Rob Z]

Hi X,

Here is how I do it here, and all of this is imperial measurements, so you can adjust the technique accordingly for metric.

I multiply the area in sq ft by the average depth of the mud bed (in feet-have to keep all the units the same). This gives me cubic feet of mud needed.

If I am buying bagged mud, then I know that one 60 pound bag gives me 1/2 cubic foot, so I can just do the division and buy accordingly.

For a larger area where we need to mix our own and avoid buying bagged mud because it would be too expensive, I get the volume of the mud bed (as described above) and then buy that much sand.

We do a 4 to 1 mix for mud on floors, so I divide the amount of sand needed by 4 to determine how much portland to buy (measured in cubic feet).

Portland here is sold in 94 lb bags, which is equal to one cubic foot.

One 5 gallon drywall mud bucket or paint bucket is ~ 1/2 cubic foot, so we use those to measure out the dry sand and cement into batches for mixing.


You can use the same method to work out your volume of mud needed, using metric and the sizes of the bags or portland that you can buy.


Whoops, I didn't see that Whitebeam already answered you!

 

[White Room]

It all depends on the surface you are screeding onto, a scabbled concrete floor will take 30mm but anything smoother will need more prep and thicker screed

 

[Rob Z]

Hi Whitebeam,

What sizes are the bags of portland in the UK?

 

[White Room]

25kg Rob for any bagged gear, sand and cement anyway

 

[Rob Z]

As I get older, the 94 lb bags here seem to be getting too heavy.

I'm liking the sound of a 25 kg bag.:smilewinkgrin:

 

[White Room]

Believe me Rob I'm glad the weights went down

 

[Rob Z]

My handy calculator tells me that 25 kg = 55 pounds. I like it!

Maybe this metric system thing isn't so bad after all!