Workshop floor question

[rkchapman]

I've just about finished fixing up the beams and walls of my old shed (see https://www.ukworkshop.co.uk/forums/view ... hp?t=15727) and want to start thinking about a floor. I was thinking I would patch the worst of the cracks in the slab first, then put down a DPM, 25mm polystyrene sheet, and moisture resistant T&G chipboard. But I was unsure about a few things:

1. I have a can of liquid DPM (hyprufe) that I could use first wherever the slab is cracked - is this a good idea?

2. Can the polystyrene support the floor by itself or should I also put some (treated) timber strips to take the weight of the chipboard with the polystyrene filling the gaps between them? Might be easier to compensate for any un-evenness in the floor if I add the timber strips...

3. Should the DPM go above or below the polystyrene (and timber strips if needed?

4. I was thinking of allowing the DPM to carry on up the walls for a bit to act as a vapour barrier (with some insulation added behind it at some point. Is this a good idea?

Thanks

 

[Woody Alan]

From past experience polystyrene is not good at supporting point loading, eg if you have constant traffic through a doorway the polystyrene will eventually collapse, so if you want to use it this way I would certainly advise battening. If used in housebuilding it's best put under the concrete where the load is spread.
Liquid Dpm will more than likely attack the polystyrene unless designed for the job, check first.
Alan

 

[OLD]

1 yes if its pitch based. 2 yes but heavy point loads will not be good so battens in the load areas at least. 3 below for either case. 4 it will work but there are cheaper vapour barriers.

 

[9fingers]

I don't disagree with Old but vapour barriers should be on the warm side of the insulation.
However you dont want battening on the wet side of the DPM.
So ideally DPM on the floor first, then battens with isulation between, then a light vapour barrier (polythene dust sheet?) then the floor decking on top. Same on the walls.

Bob

 

[Dave S]

I have concrete, 50mm polystyrene, DPM, floating T&G chipboard painted with garage floor paint.
Whilst not taking issue with what Woody Allen says, I would question whether the amount of traffic you get in a shed will be enough to cause a problem - I've certainly had no problem myself. However I have no heavy machinery - if you do then that might be a consideration.

Dave

 

[Woody Alan]

Dave S said not wanting to cause offence

Whilst not taking issue with what Woody Allen says, I would question whether the amount of traffic you get in a shed will be enough to cause a problem - I've certainly had no problem myself. However I have no heavy machinery - if you do then that might be a consideration.

Dave I understand entirely, these things are subjective and relative to experience (hopefully) and not hearsay. To explain further my father built a house some twenty years ago the floors were filled with roughfill and a suspended cast concrete sub floor laid. Then polystyrene 2" was put down under chipboard. this was fine for some 10 years or so then we noticed the vinyl floor was "rucked" to some extent in the doorway thresholds between kitchen and dining area. When checked you could feel the "spring in this area. It was not so readily noticed between carpeted areas, because carpet can stretch in two planes. My feeling is I would always put the polystyrene under concrete given the choice. As an aside I used 10mm fibre board under MR chipboard in my workshop over Poly DPC for the last ten years has been OK and I do have heavy machinery.
Hope that helps Cheers Alan

 

[rkchapman]

Thanks everyone for your help.

I don't disagree with Old but vapour barriers should be on the warm side of the insulation.

Doesn't the warm side of the insulation vary by season?

Sounds like the best plan is:

1. Hyprufe over any cracks

2. DPM (should I use 1000 or 1200 gauge?)

3. Battens with polystyrene between - how do I fasten down the battens without puncturing the DPM?

4. (optionallly) another layer of polythene to act as vapour barrier

5. MR chipboard (just floating or should I screw it to battens? and if I do won't it compromise the vapour barrier?)

I probably will carry the DPM up the walls a bit - it may not be the cheapest vapour barrier but I think that I'll have some left over from a standard roll.

Sorry for all the questions but it would be a shame to spend the time and money and get it wrong!

 

[9fingers]

Hi Richard,

I think you have it about right there with the floor build up.
Yes fixings will break the vapour barrier but you are not aiming to be waterproof just moisture resistant.

I take your point about the 'warm' side of the insulation being variable.

In the case of the floor the ground will nearly always be the coldest. In the case of walls, when the outside of the wall is warmest there will be little risk of condensation but for the low cost of light gauge polythene sheet, possibly best on both sides.

The Rolls-Royce of walls would be as follows:-

external cladding
breathable membrane
insulation
vapour barrier
inside cladding

Bob

 

[SVB]

I have 50mm polystyrene with a floating 3/4" ply floor. I have a Vicmarc 300 lathe (300kg) on the floor, turn out of balance pieces and have had no problems.

Therefore, intermediate floor joists I think from my experience are not required. (Search for my posts - build photos somewhere in the archives!)

 

[Benchwayze]

As I have to use a concrete floored garage for a workshop, I plan on using a 'mat' to stand on, in front of the bench whilst working. (or sometimes to sit at the bench!)

It will comprise of 5' x 2'6" of Marine ply. Underneath that a layer of carpet underlay, sponge rubber to the ply.

I think it will be a good shock absorber for joints (The anatomical variety!)when planing or otherwise moving about. Plus it will be safe if I drop precious edged tools. It should also keep the cold from creeping upwards in the winter.

I'll let you know how it goes. If it works, I might go 'posh' and make a parquet version!

John

 

[White House Workshop]

I have a 2'x6' piece of chipboard in front of my workbench. Very easy on the feet, even without a rubber mat - and the chisels stick into it when they drop :roll:

 

[Con Owen]

Hi Richard
I believe there may be two types of polystyrene. When I did the floor of my conservatory about 15 years ago the City engineers where I live recommended that I use 50mm high density polystyrene, this is very difficulty to compress. At that time it was £7.50 an 8 x 4 sheet from Jewsons IIRC.
Regards
Con