Do I need to lay a damp-proof membrane?

[richard7761]

I am building a pillar of bricks 350mm x 450mm that will go up to the ceiling, that will sit on top of concrete that is about 900mm in depth. For 750mm of that 900mm, from the top, the concrete is bounded on three sides by sub-surface brickwork. One side though, is not against brickwork, it's against soil after about 150mm.

This brickwork pillar will eventually hold the weight of an "I" beam 2450mm long, holding up bedroom ceiling. Pillar perfectly strong enough.

Now, I'm about to build that pillar of bricks, (not a pillar of bricks on it's own, it's within the rest of the house structure) but should it sit on a damp-proof membrane? I can see that brickwork adjacent, (also load-bearing) does sit on a damp-proof membrane.

My house does have a concrete floor by the way (150mm thick).

If I can get by without using a damp-proof membrane, I would not use one.

I'm basically bricking up the fireplace right up to the ceiling. And later the "I" beam is going to sit on the brickwork.

Thanks.

 

[richard7761]

It sort of seems counter-intuative to place brickwork that is load-bearing on a waterproof membrane. One thinks the brickwork won't be stable. But this is done all the time.

So, I guess, just to be sure, I ought to build my "pillar" of brickwork on top of a damp-proof membrane.

P.S. I see I can use a liquid as well, and paint the membrane over the concrete.

The issue is that laying a damp proof membrane will not affect the load-bearing capacity of brickwork.

Unlesss anyone knows different.

 

[^woody^]

It sort of seems counter-intuative to place brickwork that is load-bearing on a waterproof membrane.

Do you mean just like all walls are built?

 

[richard7761]

It sort of seems counter-intuative to place brickwork that is load-bearing on a waterproof membrane.

Do you mean just like all walls are built?

Ha.

I really don't know much about building. I have to post things just to double- check. I sort of know that my house is built with a damp-proof course under the load-bearing walls, but I'm scared of making a mistake.

It does seem weird placing the column of brickwork on a plastic damp-proof course. It must be weight that gives a lot of structures their stability.

 

[Perry525]

Damp only rises 4 feet from the supply of water, ie;usually the ground.

 

[^woody^]

The idea is that the DPC is bedded on a smooth layer of mortar and this prevents any punctures.

There is relatively very little point loading on the DPC as the weight is spread over a large area. But either way, they don't squash.

Whatever you do, do not leave it out - and don't paint one on either

 

[tony1851]

The previous poster is correct. As your pier is 2 bricks x 1 1/2 bricks, and not carrying a particularly wide-spanning beam, the actual compressive stress at dpc level will be very small. Ask yourself; if the dpc somehow 'failed' stucturally, where would the pier go?

 

[RonnyRaygun]

I think the OP is concerned that the DPC creates a weak point in the masonry due to the lack of bond between the mortar and DPC.

If this is the concern, the idea is that brickwork is loaded axially so that the masonry is always in compression, so no tensile cracking can occur.

If you are worried about the masonry sliding on its bearing, there is an added risk due to the lower coefficient of friction.

If the pier is at the end of a wall, you've got nothing to worry about. If it stands alone it might be more of an issue, depending on the load the pier is carrying - the less load, the more chance of it shifting if someone knocks it a bit hard.
I don't know what kind of forces would be involved, but if this is your concern omit the plastic DPC and build in a couple of courses of blue engineering bricks.