Evening All I've been sitting here quietly building up sufficient knowledge to tackle the installation of some solid wood flooring to our hall and cloakroom. However, I'd like your collective opinions on my situation... The house was originally built in October 1964, so just pre-dates the required installation of a DPM as far as I'm aware, and the front of the hall was extended in 1976. The hallway floor seems to be two slabs of concrete - the original was covered in parquet flooring, which has been removed to leave a lovely black residue. It's not a 100% covering, and is no more than a couple of mm at it's thickest, so guess it was not used as a DPM? The floor also not flat - maxing out at 6mm low in several areas, and is not level - it runs 15mm out across the width of the hall - a span of 145cm. The other slab is approx 12mm higher, now that the parquet has gone, and is also not flat - lows topping out at 4mm and it slopes 15mm up over the 1.1m from the front door to the point at which it joins the original slab. The ceramic tiles in the cloakroom are another 5mm higher still. We were steered towards a local flooring contractor, who initially used some kind of damp meter to conclude the the concrete floor was damp. However, this was straight after lifting a floated laminate floor, and there were suggestions that the combination of underlay and laminate might have made the concrete "sweat", so we agreed that he would come back in a weeks time. A week on, the readings were "normal" - I don't know what they actually were, and I don't think that he recorded them.. The contractor suggested using 12mm ply mechanically fixed to the bitumen covered area, sitting a sheet DPM over the entire area and floating the wood on some kind of adhesive underlay over what would be plywood, concrete and ceramic tiles. Quotes are awaited..... I've got a number of concerns - the method of raising the bitumen covered sub-floor, the moisture levels that were initially present (especially given the age of our home), the effects of a DPM over a plywood base and the fact that the contractor didn't even bother to check the various levels of the sub-floors or the relative "flatness" of them. He didn't ask in which direction I wanted the boards laying, (they will be running along the length of the hall) and I guess that having a 15mm slope over 1.1m and then a "flat" surface might make installation a bit difficult!! Also - all these measurements are mine, not his!! As a bit of an aside, there is a blast of air coming under the wall where the original slab meets the extension!! Although we're not putting any really expensive flooring down, I want the sub-floor to be right. I'm leaning towards removing what bitumen I can (probably using some kind of grit blaster) and then testing the RH of the two slabs before deciding which type of DPM is needed, taking up the tiles in the cloakroom and levelling the whole lot. However, that's a bit of work, inconvenience for the better half and a bit of additional cash. Is there a better way?? Supa
As you have already suggested, the bitumin needs to be removed. Also you are going to be using alot of smoothing compound trying to get the levels correct. Have you thought about digging up the concrete slabs and replacing with new (insulation,dpm,concrete) ? It is not as big a job as some may think. You will end up with a new subfloor with the added bonus of insulation (this makes a massive difference to heat loss and floor temperature) and you will know you will have a working DPM. I should add upp the costs of replacing with new compared to repairing your old floor and you may find it will be cheaper to replace with new.
Thanks Matt I don't think the other half could live with taking up the hall floor!!! How long would that typically take? I was also thinking about levelling off the front slab a fair amount, so that it was broadly in line with the original floor, and the cloakroom floor was also at this level once all of the tiles & adhesive were cleared. Having done some scouring on here, I saw you mention using F-Ball P131 and stopgap 200 as a dpm prep over bitumen residue - could that work? Could I then use F76, more primer and stopgap 300? It's not too big an area - just under 7.5 sq metres in all, and the costs didn't seem soooo bad.... Supa
time to remove and lay new concrete slab? Ummmmm, If i was doing it i would guess at 1 day. But you doing it 2 days max on the size you are doing. (providing you dont uncover any hidden supprises) If installing a solid wood tho you would still need to lay a surface dpm (epoxy) as the moister content of the subfloor needs to be lower than the BS 75% rh that is almost impossible to get in the U.K enviroment. As for screeding over bitumin. It is not a approved method of preparing a subfloor but it can be done. From your first post tho it sounds like you have to much build up so WILL need to be removed. Also i will add that removing the bitumin will be more messy and possible take longer than just digging it up! Im also worried that you have different heights of concrete base and also a join in the subfloor. You could build up to the same layer and then dpm but if either of the slabs was to move it would break the DPM and you will end up with a failed floor. Its rare that i would say dig up the old subfloor and replace with new, but in your case i really think its the best option to guarranty you wont have issues in the future. Trust me its not as bad as it sounds. It will look really bad half way through but i guarranty you that once finished you will be glad you did it. Anyway, have a think about it and if you decide to repair your old floor then come back to me and i will talk you through it.
Just to add, ignore what the manufactorer says there products will cover. What they say there product will do is on a 'ideal' subfloor. I am yet to come accross a 'ideal' subfloor. Basically double what ever you think it will cost for products!
Digging up the floor is a bit scary, but it sounds like it's the way to go.. Using a breaker sounds like manly fun!! Would I need to angle grind around the perimeter of the area to be removed, to save damaging the rest of the floor? Presume that I can lay the insulation & DPM over the existing sub-base without too many problems? Do I need to apply anything on top of the concrete? Sorry for so many questions!! Supa
to start off i need to add that now all manufactores of surface DPM (epoxy etc) no longer recommend using it over a subfloor with no dpm. So if your old floor is damp you HAVE to dig it up. For your questions. Depending on how good you get the finish of the new concrete base will depend on if you need to use smoothing compounds etc. Normally speaking a smoothing compound will be needed. Also you will still need to apply a surface DPM if your installing a solid wood flooring. For other products you dont providing you let it dry to below 75% RH. As for going around with a grinder? The walls should not be built on top of the concrete base so when you dig it up you wont have any issues. Do check tho as there was a few houses that was built off the concrete base. Rare tho. The only place you will need to grind back is in door ways. Dont forget if the other areas do have a dpm you want to be joining into there dpm. You may dig a bit underneath and lap and back fill or pour epoxy etc to join the two.
Thanks again Matt Nearly there, I think! So do I prime the concrete, apply smoothing layer, and then DPM? As for the fixing of the boards - Elastilon looks interesting, and the concept of a semi-floating floor appeals, mainly because you know who will probably want a different wood next time we decorate... What's your experience of adhesive underlays? Thanks again!! Supa
dont prime the concrete if applying a surface dpm. You will need to prime the dpm / epoxy tho before laying a smoothing compound. Elastilon is good stuff but hard to use in hallways. Anyway, hold fire on buying the elastilon as we are running some tests on some new stuff that seems a very good product. I will post back when we get the results. However will be a few weeks as wood takes a while to start moving and we will be pushing the limits of what the underlay says it can do. Also you may want to note that you will need to leave your new concrete at least 1 month before you can think about applying products to it. I would personally opt for a fully bonded wood floor tho. Your Mrs may want to change in a few years time but you can always sand and stain the floor to a different colour in the future. You can also uplift and re-grind the concrete to take a new floorcovering.
don't fit any wood flooring until the new concrete base is dry it can take months. roughly 3 weeks per inch of concrete for drying i think is recommended as a guide time.
Yes take note of this as im not sure if i made myself clear. You have to wait a minimum of 1 month before you can lay a surface dpm. Moister needs to be lower than what the dpm manufactorer states there product can be used upto moister wise (normally below 95%) If letting the subfloor dry naturally then around 1mm per day is adverage drying time. But for a solid wood floor you still need to lay a surface DPM.
Thanks to you both for your advice - without this forum I would have probably had a nice new floor that was just waiting to go wrong!! Will be monitoring your work on the Mapei DPM and the new adhesive underlay. Do you ever mix n match with DPM, smoothing layers & adhesive?
Its not adviced due to the simple fact that manufactorers of products state you should use there dpm with there primer and screed etc. If you start using other peoples products and mix and match you will find yourself in a difficult situation if something was to fail! However it is very rare that a product will fail. It is normally down to user error. Personally i would stick with either Mapie or Fball products. Both are very good. We will see how this new DPM goes and if it is as good as it seems to be so far i will be using all products from a select company soon!
Well the time for the breaking is nigh... I have just unearthed some papers which indicate that the extension area has 50mm of screed on top of a 100mm slab of concrete. Apart from breaking into the existing hall floor, is there any way of finding out if the surface is just screed rather than concrete (I appreciate the difference between the two in terms of content, but not appearance). If they both are screeds, am I able to remove just the seperate screeds and lay one solid bed over a dpm, or do I still really need to take out the concrete slabs below as well?
ye you can remove just the top 'screed' layer and then dpm sheet and new screed/concrete. However you will need to be deeper than 50mm as this will now be a floating screed rather than bonded due to the dpm sheet. Im not sure what the minimum thickness is if it was fibre reinforced. im moving offices at the moment so cant check the regs at the moment.
