Fix plank to lathe plaster wall

[unionworkeruk]

I have a 2.5 metre x .5 m x 19 mm plank of oak I want to fix to an old lathe and plaster wall. It is a total of 11.5 kg in weight. I can drill in 4cm until I hit something solid. I would think Molly Bolts but I prefer not to have the white screw fitting showing on the surface as I guess I would have to use at least 10 bolts.

I would prefer a brass screw or even a hexagonal head I could tighted with a spanner if that is possible with any alternatives. It is a great lump of wood.

I would also be grateful for advice from professionals on which fitting to use. Are Molly Bolts the best, considering the wall and the weight ? The wall could be up to 100 years old and I would think tend to crumble easily.

 

[JohnD]

is this plank a shelf?

the laths are pretty certain to be nailed to vertical studs. You can screw through the plaster into the studs. You may be able to locate them by tapping or looking across the face of the wall while holding a torch.

If not, drill an 8mm hole through the plaster at the height you want to screw your brackets. Insert my Special Tool through the hole, pushing it sideways until it hits the first stud. Withdraw it and use the Special Tool on your side of the wall to indicate the distance from the hole, and make a pencil mark. Then insert the Special Tool into the hole, pushing it to the other side. Mark the wall with your pencil to indicate the position of the stud in the same way. Drill as many more holes as you need to mark the position of all the studs acros the length of the plank.

I sell the Special Tool at £50 plus p&p.

 

[JohnD]

The Special Tool will arrive folded, to fit into a large envelope for ease of posting, and in a shape that you can conveniently hang on your workshop wall. You need to unfold it, straighten it, and bend it into a gentle curve. I offer discounts for bulk purchases.

 

[unionworkeruk]

Its not a shelf I just want to screw it to the wall to match a wood and steel staircase I made (not the steel bit) so I would think the same method would work. Not sure the screws into wood after the 4cm of plaster and a gap would old the 11k though

 

[Deleted member 174758]

Umbrella fixings (Molly fixings) are designed for smooth plasterboard, not lath and plaster, which is very uneven at the back because if the "snots", so they tend not to give a reliable fix. They can also damage the snots causing minor cavitation of the plaster as well as the "claws" at the front of the fixings not biting firmly into the softer and more durable lime plaster. As John says, fix to the existing studs. A couple of 5.0mm steel wood screws are capable of supporting a man's weight. That's a bit more than 12kg. If you'd ever ripped out lime plaster lath you'd appreciate just how heavy that is, too.

 

[JohnD]

the studs will be at something like 600mm centres, so you can screw into quite a few of them to spread the load. If you countersink the screw holes a little the heads will be below the surface and not obtrusive. You can use brass-plated ones, but not solid brass as they are weaker than steel. If you wanted an invisible fixing you could screw a French Cleat to the wall, and another to the back of the board.

Do you want to order the Special Tool studfinder?

 

[Deleted member 174758]

Could be 16in (406mm) centres, John. As to strength, if you can hang a 100kg door on 12 no. 4.0 x 38mm screws, in sure that 6 no. 5.0 x 75mm brass or (better,) stainless steel screws will carry the weight. Stainless or brass are preferable to steel when fixing oak

BTW "French cleat" = split batten in English joiner speak. Any decent timber merchant can supply (in other words not a DIY shed)

 

[JohnD]

yes

It's been a while since I had one.

ta

 

[Deleted member 174758]

BTW I use an old rare earth magnet to find studs. It will hang on screws in PB or the tacks which are used in.profusion to attach the laths to the studs. Mine came out of a discarded computer disc drive

 

[unionworkeruk]

Umbrella fixings (Molly fixings) are designed for smooth plasterboard, not lath and plaster, which is very uneven at the back because if the "snots", so they tend not to give a reliable fix. They can also damage the snots causing minor cavitation of the plaster as well as the "claws" at the front of the fixings not biting firmly into the softer and more durable lime plaster. As John says, fix to the existing studs. A couple of 5.0mm steel wood screws are capable of supporting a man's weight. That's a bit more than 12kg. If you'd ever ripped out lime plaster lath you'd appreciate just how heavy that is, too.

I think I might be hitting brick after 4cm. Checked with long bradle and it does not sink in. I did have another internal wall wall where, after I took the old plaster off or more likely fell off I found a wall of single brick on edge set between a wooden frame work of large squares for the bricks.

I have drilled a couple of times now and always found a solid surface after 5 cm. I need to check more but what length screws would I need for a firm fix through the 2cm wood, 5cm old plaster and the wood or brick in the wall. 150mm ? More or less ? Should I use self tapping screws if brick and 150mm steel screws if wood ? I was hoping about 10 screws ,5 top and 5 bottom should hold but the fewer the better , but thats just cosmetic. I would rather be safe

 

[bobasd]

its not clear to me what kind of lath & plaster wall you have - is it a stud partition?
or is it a brick wall faced with lath & plaster ( this method was sometimes used in older properties)?

for studs just send a long, thin bit through the surface and when you hit a stud open up a little and measure your centres from that point -
proving at each measured centre that you do indeed have a joist.

 

[unionworkeruk]

is it a stud partition?
or is it a brick wall faced with lath & plaster ( this method was sometimes used in older properties)?

It is about 100 years old I thought it lathe and plaster but now think it may be brick faced with lathe and plaster which I found in another room I will be able to check more in the morning but the screws will need to be a hell of a length, 150 mm whether brick or wood becuaae of depth of lathe and plaster and wood before I reach the brick or wooden stud

 

[Deleted member 174758]

Regardless of where the masonry wall behind is, if it is laths and plaster there will be studs supporting the laths (due to the massive number of tacks required to fix the laths in place onto any surface and the fact that you can't nail into solid masonry, lath needs to be fixed onto studs) - and it is the studs you need to find and fix through into NOT the masonry wall behind it. Good grief, if we had to fix to the masonry behind this type of infill every time it would be impossible to ever get any work done in listed buildings (and it's difficult enough as it is)! A minimum of THREE 5.0mm (or #10) x 100mm (or 4in) screws into brick stud will easily cope with the relatively small weight you are trying to hold up.

 

[unionworkeruk]

"it is the studs you need to find and fix through into NOT the masonry wall behind it." So about three/four 5mm x 100mm steel screws into the wooden studs will hold it OK . Great

As you say that saves me a lot of work. I have just drilled thro 50 hole thro steel stringers to fix wooden planks as treads and was not looking forward to drilling the brickwork.

Thanks