6mm is the advised thickness. However, nothing wrong with 4mm if the subfloor allows. If the wooden subfloor is perfect you are only applying a plywood to cover up the floorboard joints and also to give a more stable base. Personally i will sand floorboards flat and use 4mm where i can. If the subfloor is a little rough then jump to 6mm. BUT with 6mm you have to be careful as it wont cope with cupped boards etc. Really you should be going to 9mm. As 'ozzy' suggested, you would be better using 4mm plywood if skimmimg over the top as the plywood will follow the contour of the subfloor better than 6mm (less voids) Its all down to what the subfloor needs. You the professional need to make the call on what subfloor prep you will do, its you that has to offer the guaranty.
I don't use 4mm for floor prep, there's not really much for the staple or screw to hold on to is there?
depend on quality of plywood. With what is on the market at the moment then you are correct. Same goes for 6mm also. Dont be fooled that because the plywood is thicker that the pins holding wont end up trying to hold on to the same amount of material. Plywood should have equal thickness cores and should be made up of a suitable species of wood. (equal thickness hardwood cores are rocking horse poop at the moment) The plywood we are being supplied at moment tends to be of 3 core with a soft center species with what is nothing more than a 1mm veneer if your lucky. The pins are shooting all the way through and grabbing the last 1mm of hardwood. Like i say this is the same for both 4 and 6 mm. What should happen is the pin should only fire 1 mm in so you are left with another 3mm minimum of holding strength. Sadly with what is on the market at the moment the pins fire almost all the way through. Even with 6mm as the core is soft and thicker, the veneer so to speak is the same thickness as on 4mm so the holding power is around equal. To be fair it shouldn't be classed as plywood. We should call it softwood veneer.
I've been toying with the idea of running a chamfer on the edges of 9mm ply to almost replicate that of plasterboard, the theory being that feathering will bind better into the layers of the plywood and reduce any build up that then needs rubbed back. It should also reduce the amount of feather being used/wasted. I realise I am adding time/expense by running all these edges but have the kit at my disposal anyway. Any thoughts?
matt, this maybe a stupid question but why would you use 4mm and not 6mm if the thinner material is going to follow the undulations of the subfloor more. surely you then have more work to do/more feather finish to use when you try to level the floor.
I had a job about 34sq. a couple of weeks ago and laid 12mm ply to fill the gap under the skirtings after laminate had been lifted. I have to say the finished job had that little extra .....really flat looking and felt so solid underfoot.The problem is 12mm ply is just so much harder to handle and much messier to cut. I reckon it took at least 50% longer to fit as 6mm would have.
And the cost of it sandy, I used it a few weeks ago too, think it was about £19 a sheet. Not seen invoice yet.
Got told by another fitter/trainer that when he had his own firm that they as a rule when plying would if the floor was flat no cupped boards use 4mm ply then latex with 700 over the top, then jump up through the ply thicknesses depending on needs of the floor, but always skimmed completely over the top with 700 as sometimes with feather you can make out where the boards are over time with a load of natural light on it. With latexing they always put a DPM down first unless in a new build as your covering yourself incase anything ever happened or on that new extension in mrs jones kitchen where the new floor meets the original floor there is the potential for the builder to not add a dpm inbetween which could cause a failure which your liable. Ive followed suit on all my own jobs as a bag of renovation is half the cost of 700/feather as well, just sticks a little extra time on the job but does look better.
