Can I use out-of-date cement if it's just for repointing?

Kernel_Sanders

I have most of a 25 kg bag of Portland cement left over from a project a couple of years ago. I need to repoint an old wall with a lime mortar, so what problems could there be in using it? Is it just a case of using a stronger mix?

FreeBear

NO. Do not use cement to repoint a lime mortar wall. Get yourself a tub of lime putty and mix three measures of sand to one part lime. Rake out the joints, give the wall a good soak, and then pack the lime mortar in.

Cement will have absorbed a degree of moisture of the last couple of years and is highly unlikely to be good for anything. Lime putty will keep for ever (almost) as long as it has a bit of water on the surface.

Kernel_Sanders

FreeBear wrote: »

NO. Do not use cement to repoint a lime mortar wall. Get yourself a tub of lime putty

I'm not sure it is a lime mortar wall (it's an external wall of a 110-y-o terraced house); I just meant I intended using a lime mortar. I have an equally old large bag of builders' lime, so can I not just soak some of this in water to produce a putty?

FreeBear

You could try soaking type S (builder's lime) in water - One usually has to wait around three months for it to turn in to a sticky mass. But personally, I wouldn't bother messing around with it if it has been sitting around.

Although portland cement has been around since the 18th century, it wasn't until around 1860 that its use became common - Even then, lime mortar was the predominant material for brick construction well in to the 20th century. Chances are, your walls use lime mortar.

southcoastrgi

Personally I wouldn't use it, a 25kg bag of cement is less than £6

diamond_dave

What's the problem with using old cement. If I've got a part bag I keep it dry and in a closed bag.As long as it's not gone hard, just up the ratio of sand/cement and it will be fine. I've never had a problem with old cement.

Kernel_Sanders

FreeBear wrote: »

mix three measures of sand to one part lime.

I've done this but the mixture doesn't seem to stick as well as cement mortar does. Do you need to have it slightly wetter? I will be painting over this mortar, so how long will it take to dry sufficiently?

Furts

Kernel_Sanders wrote: »

I've done this but the mixture doesn't seem to stick as well as cement mortar does. Do you need to have it slightly wetter? I will be painting over this mortar, so how long will it take to dry sufficiently?

You are using ancient cement then commenting about the mix being unsatisfactory. No competent builder would do this, so why do you expect to be successful at it?

Some bags can keep for years but these will be the plastic bags, and they must not have any little holes in them. I have used these, but only for items like slab laying. No way would I use old cement on pointing.

Kernel_Sanders

Furts wrote: »

You are using ancient cement then commenting about the mix being unsatisfactory. No competent builder would do this, so why do you expect to be successful at it?

What part of my previous post says or even implies this? I even quoted the mix Freebear recommended but if this wasn't clear enough, how can 'the mixture doesn't seem to stick as well as cement mortar does' mean anything other than cement wasn't used?

FreeBear

Kernel_Sanders wrote: »

I've done this but the mixture [3 parts sand one part lime putty] doesn't seem to stick as well as cement mortar does. Do you need to have it slightly wetter? I will be painting over this mortar, so how long will it take to dry sufficiently?

What I've been doing is spray the wall with a hosepipe several times and get it quite wet. The lime mortar is quite stiff (about the same consistency as margarine) - I use silver sand (not soft builder's sand) & lime putty and do not add any extra water. Sticks a treat to just about everything.

Don't go adding water to the mix unless absolutely necessary - Too much water, and the mortar will crack as it dries. If it isn't sticking, then you probably need to wet the walls down more.

Did I say lime putty gets better the older it is - Lime mortars & plasters can be kept for months/years in a tub with a bit of water on the surface. As they age, the mix seems to get stickier and will stiffen up. Scooping a dollop out of the tub and mashing it on a board (often called "knocking up") quickly makes it workable again.

The three to one ratio is not hard and fast. Depending on the sand, a two to one mix might be more appropriate and for a finish plaster one to one.