Levelling workshop floor - What is "screed" ?

[Maverick81]

Hi.
My workshop floor is currently rugged, cracked concrete as it has been for as long as i can remember and long overdue a renovation. I am wanting a smooth and LEVEL surface as a foundation to reinstall my workshop upon.

I have been looking at "self levelling compounds" as sold in the DIY stores though i have never used this stuff before. Is this what i should be usiing?
While looking for into on the subject on the forum and the net I have come across the people refering to "screed"...."laying screed".
What is Screed? Is screed and self-levelling cement the same thing?

Please advise. Thank you.

I had previously done small areas of basic concreting, but i am not a builder or familar with anything more than basic terminoligy and products.
Thanks again.

 

[kostello]

Just a word of warning about self levelling compounds.

The instructions make it sound like you just pour it on and the floor and it levels itself by magic.......


It doesn't

 

[Phil Pascoe]

:roll: Yes - plus dozens for the above!

 

[pip1954]

hi screed is sharp sand and cement mixed about 4/5 to 1 but don't lay it less than an inch thick as it will crack .
i used floor leveler on my work shop just don't spread it to thin also dampen the floor if to dry ,
any question feel free to pm
pip

 

[Jake]

Just a word of warning about self levelling compounds.

The instructions make it sound like you just pour it on and the floor and it levels itself by magic.......


It doesn't

F Ball Stopgap 300 - it almost does. Spikey roller helps but it really is magic (if you are quick at mixing and pouring).

 

[Maverick81]

So you would first use a sharp sand/cement mix (Screed) to address any significant deviations in the floor (an inch or greater) to bring the surface to rougly level. Then when set, you would then use a self-levelling mix on top of this to truely level the surface.
I have just found some videos on youtube of laying self-levelling and yes, i can see that it doesnt just find its own way....but it seems to need a little encouragement with a trowel. Am i about right?

 

[pip1954]

yes mate about right but let it go of before you go over it a day or two
pip

 

[carlb40]

TBH if the cracked/ broken concrete is an outside slab? It will probably not have a damp proof membrane under it. So anything you build on it will be subject to rising damp.

A few options here.
1 - Use the existing broken concrete as a base. Hire a wacker plate. Wacker it all ver making sure it is solid. Build a form work around it. Put an inch of sand down. Then a membrane. Then at least an inch of insulation. Then at least 2 inches of concrete on top of that.

2 - At each corner and in the middle dig holes/ pour with concrete and then build with a few concrete blocks to form piers. You can then build a timber sub floor on the piers.

3 - If the concrete is still solid enough it won't move? Build a framework of treated timber - min of 4 x 2. Once built, level it up with packers.

Then build off whichever way you choose

 

[Maverick81]

Food for thought, thanks.

I dont think it does have a membrane....is this a big deal?
The workshop is old and has been in its current condition since i was a boy and my grandad owned the property.
Now I have turned my full attention and efforts to rejuvenating it I had thought that resurfacing the floor would be the easiest and most cost effective way of getting a solid level surface. The idea of building a timber frame to lay a wooden floor upon never occured to me actually....though this must be a more expensive option. Bringing me back to my original question.....damp membrane....Is this a big deal?

 

[M P Hales]

Food for thought, thanks.

I dont think it does have a membrane....is this a big deal?
The workshop is old and has been in its current condition since i was a boy and my grandad owned the property.
Now I have turned my full attention and efforts to rejuvenating it I had thought that resurfacing the floor would be the easiest and most cost effective way of getting a solid level surface. The idea of building a timber frame to lay a wooden floor upon never occured to me actually....though this must be a more expensive option. Bringing me back to my original question.....damp membrane....Is this a big deal?

Unfortunately YES

No damp membrane means you will get rising damp.
Think of a wall without a damproof course.
Solid floors have the same problem of water rising through capiliary action (yes my science teacher will be chuffed I remembered something) so the only cure is a membrane of some sort to prevent the problem.

Hope this helps

M

 

[carlb40]

Well if there is no damp membrane, you will always be subject to damp rising through the ground and up the concrete.

Cost wise it will depend on the size of the building?

I know it's b&q
http://www.diy.com/nav/build/timber/saw ... m-12207520

will be cheaper at a proper timber merchant. So not really expensive unless the building is huge?

 

[Maverick81]

Thanks guys. If i can continue.....

The workshop is roughly 6m x 4m.
The brick walls DO have a damproof course. So damp cant rise up the walls (can it? - again, building, not my forte).
So if the concrete floor doen not have a damproof membrane....would the mean damp would effect my wooden units stood upon the concrete floor over time?

Can i not apply some kind of sealer/paint/varnish stuff to the surface of the levelled concrete to act as a barrier?

OR.....if i do now go with the timber frame floor option with treated CLS....would this eliminate the need for a damproof membrane as the "treateed" timber would resist the damp from the concrete ?

 

[DMF]

Hi,

first off bit tricky to tell unless we can see a few pics please how bad is it? First concern should be the structural integrity of the slab. You sound like you've been there a while has the been any movement that you have noticed? Is it solid or has it started to break up? If the slab is shot it doesn't really matter what you try and put over the top of it, if it can be repaired however then there's several rubber type floor leveling compounds that would work regarding leveling and damp proofing.

If there's a DPC on the brickwork then you don't want to bridge that and also i'd expect a DPM in there really, has it had any damp problems?

Dean

 

[Wood Monkey]

I over boarded my concrete workshop floor with moisture resistant tongue and groove flooring boards. I can honestly say it transformed my workshop. The procedure is simple and the results are fantastic.

1. My concrete base was strong and sound and already had a DPM. However, you could first lay a DPM.
2. Cover this with polystyrene insulation. In my case I only used 25mm as I didn't want to sacrifice headroom. I also put a framework of battens down so I could screw the boards down, but I'm not sure this is completely necessary and a 'floating' panel will work just as well. Over the area you are working with the polystyrene will not compress.
3. Lay the 8x2ft boards. If the floor is going to be screwed then you can lay them with dry joints but if it's going to float then glue them. I screwed and glues mine.
4. Stand back and admire....

The result of mine was way beyond my expectation. The floor is warmer to stand on and generally the workshop feels warmer. It is so much easier to clean up than the concrete was. It looks good and feels very solid. Best of all it doesn't ruin a dropped chisel.

You can see some pictures in my workshop build thread (towards the end).

jons-workshop-pictures-t21504.html

Good luck, Jon

 

[Phil Pascoe]

When doing any work like this, it always pays to stop and think - can I alter it afterwards? If, for instance, you put a single glazed window in and later think that a double glazed one would have been better,fine - you take it out and change it. Try putting a damp proof course in after the building is finished.

 

[Lons]

Hi Maverick

You've been offered some good advice and I'd agree with most of it.
You should try to post some pics for more advice and look at the floor very closely before deciding. eg Is the concrete reasonably level or has it sunk in areas. Are the cracks narrow (hairline) or gaps opened and how wide? Is the floor perfectly dry or do you sometimes get signs of moisture, however slight?

My opinion, as a builder would always be to sort the floor out properly or you'll regret it later. Walls, windows, doors and roof are easily accessable, the floor is not, especially once benches etc are installed. Any dampness will wreck your machines and tools and rot the bottoms of cupboard legs.

Self levelling compound is not a solution unless the floor is already dry, sound and reasonably level. Standard product is designed to fill only a few mm and you need to by a re-inforced product for deeper fills and it's expensive anyway as you always need more than you think. It also needs a modicum of skill to float it reasonably level when applying.

Sand / cement screed will work as suggested but insulation is desirable. If it were me, I'd go down the timber floor route which is warmer, cost effective and probably within your skill level to do a decent job.

Cost it out, you might be surprised.

Bob
Edit: just read you posts again and a DPM is definately essential whatever floor you put down or you might as well not bother IMO. Unless you existing floor is bone dry of course.

 

[GazPal]

I'd safely assume there's no DPM beneath the existing concrete and it's very likely the concrete varies between 2" - 4" in thickness or even thicker and regardless of it originally indoor or outdoor. The cracking is very likely due to either overly thin concrete or movement in the sub-base due to moisture driven shifts in sub-soils as they swell and contract seasonally. Sub-layers were often either broken brick (Known as knapping) or course compacted ash. Regardless of re-finishing materials the underlying problem will still exist and the best course to pursue is to identify and resolve the cause before moving ahead.

Self levelling compounds are perfectly fine for evening out comparatively small irregularities in existing surfaces and putting a final finish on screeds without spending too much time on trowel work, but they will crack again and again if movement and cracking issues haven't been resolved.

The same can be said of screeding (Which should preferably be 75mm finished thickness) and neither attempt at repair would be permanent.

Many repair and replacement methods exist, but the one used depends upon the underlying cause of the original problem.

 

[Newbie_Neil]

I over boarded my concrete workshop floor with moisture resistant tongue and groove flooring boards. I can honestly say it transformed my workshop. The procedure is simple and the results are fantastic.

+ 1.

I put down CLS and screwed plywood on top. I also bought some extremely ugly, but cheap, orange floor tiles. Working in there is now sooooo much better than on a concrete floor.

Thanks,
Neil

 

[twothumbs]

Have just read quickly thro this thread. Hope I haven't missed anything. I would tidy up the existing surface with mortar or a thin bed surface screedas used by the flooring trade. Any big carcks filll with silicone or other mastic. Then put two loose layers of thick polythene down and tape the joints rather like a french seam in sewing. Then lay green chipboard t&g, glueing the joints. Lay a layer of polystyrene or a hard slab insulation, the sort of density you can almost stand on. Start at one side with small wood temporary packers and work across the room and on the final sections put small wedges to hold it tight across the room whilst the glue sets. Reasons are , the poly will stop any damp and the two layers will let the floor move/slip (if at all). Chipboard is easier to lay if you are on your own and especailly on the last row. Stagger the joints in the usual way. If you leave spare poly up the wall you can trim it and use tape to seal it against the wall dpc. This should give you a damp proof floor and is not too different from some new floors. Hope I have picked up the salient points made previously. Sometbing like 'flashband' would probably do it. Unless the existing floor is breaking up badly, simply stabilise the surface to allow the floating floor to go on top. You wil not be walking or loading it much after all. OK you may need to put small thresholds in, etc but it would be a job well worthwhile.....all things being equal ! Best wishes.

Spellling corrected.Edit.