Questions Regarding MDF vs MR-MDF

[Baz]

Hi All,

I am having some decorative wall panels made out of MDF - just simple rectangles around 750mm x 400mm. Ideally I wished for a depth of either 12mm or 15mm. I have been advised to use 18mm instead as this will lessen the chances of the MDF "bowing" when using standard MDF.

18mm is a bit thicker than I would like but if it mitigates against any potential bowing issues, then I guess I will have to live with that. I would still like to ask however:

1) If using standard MDF, how great is the likelihood of 12mm/15mm MDF bowing?
2) Is MR-MDF much better dealing against bowing than the standard stuff? If so, then if I get 12mm/15mm MR-MDF instead of 18mm Standard MDF, can I assume that it will not bow at all at the sizes that will be painted?

The Panels will will affixed to walls so only one side & outer edges will be visible & part of the reasons I wish to use 12mm/15mm is that it would be lighter & hence less weight to bear but also that it would look better aesthetically.

A painter told me that he would prime all sides of the panels & edges but then only paint the front facing side & edges with two top coats - will just one coat of primer on the back face & then one coat primer + 2 top coats on the front face be OK without fear of bowing? The primer will probably be the Zinsser Bulls Eye 123 as I understand that is one of the best & Zinsser say only one coat is required? The two top coats will be Acrylic Eggshell.

If what the painter proposes is not a good idea (just applying a single coat of primer at the back), then can I just apply a couple of extra coats of any old paint that I might have lying around my shed & use that to sort of balance out the more costlier stuff at the front & edges? I ask that as I wish to avoid buying extra new paint & applying it the back of many panels when it will never ever been seen once affixed to the wall!!

Many Thanks!!

 

[deema]

There are a few things to consider, if it's to be fitted within a modern house with a proper moisture barrier what is proposed should IMO be Ok. If it's an old house where the walls can be subject to damp or high moisture content then you need to look at stopping the damp / isolating the cladding before applying. Irrespective of the paint coatings a damp wall will cause problems and many older building suffer from a lack of a cavity / bridging between the inner and outer walls causing high moisture / damp areas that go mainly unnoticed as they dry out due to the temperature of the house. Again IMO it's not the thickness that's an issue, it's the sweating that it creates by covering the walls with an impermiable covering.

 

[Baz]

There are a few things to consider, if it's to be fitted within a modern house with a proper moisture barrier what is proposed should IMO be Ok. If it's an old house where the walls can be subject to damp or high moisture content then you need to look at stopping the damp / isolating the cladding before applying. Irrespective of the paint coatings a damp wall will cause problems and many older building suffer from a lack of a cavity / bridging between the inner and outer walls causing high moisture / damp areas that go mainly unnoticed as they dry out due to the temperature of the house. Again IMO it's not the thickness that's an issue, it's the sweating that it creates by covering the walls with an impermiable covering.

Hi,

Many thanks for replying - much appreciated! It is a 1920's-1930's built house & the internal walls are the old Plaster & Lather type which then have a top coat of plaster skimmed over & then wall-papered. The walls are hollow. It is pretty dry as far as I know - been living there for a great number of years with no damp issues whatsoever. Also it is an upstairs internal wall that divides two bedrooms & not connected to any exterior walls if that helps.

Thanks Again!

 

[deema]

A good cheap test if possible is to buy a plastic sheet for protecting floors (a few pounds from B&Q and use masking take to attach it to the wall and seal the edges yo the wall. Leave it a few days preferably when it's raining and see if condensation forms upon it. If it does you need to resolve it as there is bridging / porous wall. It replicates cladding the wall and shows you what will happen.

 

[petermillard]

I'd always recommend MR MDF over regular MDF simply because it's a much better quality board for little extra money. Assuming your walls are dry enough (easy and cheap to find out, simple moisture meter for a tenner on eBay) then a 12mm MR MDF board at the size you state, primed all round and painted on the exposed faces shouldn't bow at all, IMHO.

I make a lot of stuff from MR MDF and it is mostly primed with an off-the-shelf water-based acrylic primer/undercoat, one coat on the face, two coats on the cut edges, followed by two coats of water-based acrylic eggshell, usually applied with a foam roller, sometimes sprayed. Zinnsser BIN is a fine product, but total overkill as a general primer, again IMHO.

Out of interest, how were you planning to fix the panels to your walls? Mechanical fixings (screws, plugs) or a grab adhesive??

HTH Pete

 

[Baz]

I'd always recommend MR MDF over regular MDF simply because it's a much better quality board for little extra money. Assuming your walls are dry enough (easy and cheap to find out, simple moisture meter for a tenner on eBay) then a 12mm MR MDF board at the size you state, primed all round and painted on the exposed faces shouldn't bow at all, IMHO.

I make a lot of stuff from MR MDF and it is mostly primed with an off-the-shelf water-based acrylic primer/undercoat, one coat on the face, two coats on the cut edges, followed by two coats of water-based acrylic eggshell, usually applied with a foam roller, sometimes sprayed. Zinnsser BIN is a fine product, but total overkill as a general primer, again IMHO.

Out of interest, how were you planning to fix the panels to your walls? Mechanical fixings (screws, plugs) or a grab adhesive??

HTH Pete

Hi,

Thank you also! I will get one of those moisture meters from ebay as you say just to check for moisture then! It is great that you feel 12mm will not bow then - I was getting really worried about having to use the thicker & heavier 18mm stuff. Just to be sure, even though one will apply only one coat of the primer at the back with the front having a coat of primer & two coats of paint, it still will not bow then? What would you personally go with - 12mm or 15mm or in the end will it make no difference?

As you say that the MR-MDF is not that much more expensive, I will just get that then - I assume it will give a better finish/end result?

You mentioned you use water based Acrylic eggshell - I am planning to use the same & do not know much about paint finishes - I basically want something that is not reflective but has a mild sheen, tough lasting & easy to wipe clean & was told eggshell would be a great option - is it a smooth type finish or a bit rough? There are so many options like Semi Matt, Satin, Mid Sheen, Soft Sheen etc so it gets a little daunting for a novice to be able to imagine the differences. Is Eggshell the best of out these options do you feel?

Is the Johnstone's Acrylic Eggshell a good paint then & not too glossy?

As for the primer, I have read so many positive things about the Zinsser stuff that I thought I should play it safe but if you know of something else that is cheaper & just as good, please kindly let me know! Half the panels will be painted in a Brilliant White so I can use a standard White Primer as most are but the other half will be painted a very dark grey-anthracite colour & I have been told that on these, it is far better to use a darker colour Primer & I am having a hard time finding them. I have found a Zinsser 123 version of both colours & from another brand called Rustins. The Rustins stuff however recommends two coats & takes a few hours to dry at least for each coat but I understand the Zinsser stuff is much quicker? They are both similarly priced.

As for the fixing of the panels on the wall, someone else who did this & from whom I got the idea from said they used "No More Nails" & it worked out perfect for them so I was going to use something similar like the green Gripfill etc? Any you can recommend that will be strong enough?

If the grab adhesive is not a good idea, the how else would you suggest I fix them onto the wall so that no screws etc are visible otherwise it will really ruin the look! I have attached a small pic to show the sort of thing I am looking to achieve - it is the work of the fella I got the idea from & he used 18mm thick MDF:

Thank You!

 

[porker]

I've recently done some more traditional panelling using a thin ply backing board and MRMDF. Agree with the previous comments MRMDF is well worth the little extra as it gives a better finish. I used a grab adhesive to fix (Gripfill) some of the panels and it is fine. Just two points I would made about it though. You will need to support the panels while it dries otherwise they will slip. I used a brad nailer to hold in place and the tiny marks from the head are easily filled. The other point is that the adhesives are only as good as the backing so if sticking onto a painted finish you will need to key it by roughening.

 

[HOJ]

I am of the view to use mechanical fixings, not keen on gluing to plastered walls, I have used these extensivley for mounting various parts, http://www.button-fix.com/
I made a router jig to recess the fixing plates in flush on the panels, needs about 8mm depth, then simpy fix the button to the wall, using the available marking pins to set out, and hang the panels on, easy to take of if needs be.

 

[RobinBHM]

+1 for mrmdf.

Dont buy budget plain mdf from a builders merchant unless you want fluffy edges.

12 or 15mm mdf would be as good as 18mm in 750mm squares. Painting 1 face only could cause tension in the board -it may be worth painting 1 as a test first in case you find both sides need painting for stability.

I suppose you could stick the panels on with double sided tape but with a bead of silicone or gripfill too. Tape for instant adhesion, silicon / gripfill for long term. Georgian bar tape from reddiseals or similar. If the walls are poor condition or papered mechanical fasteners are an alternative but precise drilling into masonry is not easy.

 

[petermillard]

What would you personally go with - 12mm or 15mm or in the end will it make no difference?

12mm, but not much to choose between them - more a question of how much relief you want the panels to have against the wall, I think.

Is Eggshell the best of out these options do you feel?

Yes.

Is the Johnstone's Acrylic Eggshell a good paint then & not too glossy?

Haven't used Johnsons specifically, but no reason why it shouldn't be; why not buy a small pot and try it?

As for the primer, I have read so many positive things about the Zinsser stuff that I thought I should play it safe but if you know of something else that is cheaper & just as good, please kindly let me know!

Zinder is very good but it's a more of a speciality primer/stain block really. I haven't found any difference between Leyland, Johnson or Wickes basic acrylic primer/undercoat, all decent and all about the same price.

Half the panels will be painted in a Brilliant White so I can use a standard White Primer as most are but the other half will be painted a very dark grey-anthracite colour & I have been told that on these, it is far better to use a darker colour Primer & I am having a hard time finding them. I have found a Zinsser 123 version of both colours & from another brand called Rustins. The Rustins stuff however recommends two coats & takes a few hours to dry at least for each coat but I understand the Zinsser stuff is much quicker? They are both similarly priced.

Yes, a darker undercoat / primer is best for a dark colour. I have another brand of water-based grey primer, can't think what it is offhand but I'll check when I'm in the workshop later. I've been using a lot of Farrow & Ball exterior eggshell recently and it's a very nice paint, if pricey; they do a range of primer/undercoat in various shades too.

As for the fixing of the panels on the wall, someone else who did this & from whom I got the idea from said they used "No More Nails" & it worked out perfect for them so I was going to use something similar like the green Gripfill etc? Any you can recommend that will be strong enough?

I prefer PinkGrip, personally, but there probably isn't much to choose between them. Similar to the trick mentioned above, I've used a hot-melt glue gun to provide quick adhesion, while the grab adhesive cures to give a long-term bond; perfectly valid points made, too, re. gluing onto a papered wall...

I have attached a small pic to show the sort of thing I am looking to achieve - it is the work of the fella I got the idea from & he used 18mm thick MDF

I think I'd be more concerned with the flatness of the wall over the area than I would be with the MDF bowing!

HTH, Pete

 

[Baz]

Hi All,

Many thanks for the great advice!

@Pete - Thanks for confirming Eggshell would be the best option - really gets rid of all the second guessing & doubts about all the various finishes for me! If you do manage to find out the name of the Grey Primer you use, please let me know & thanks for giving me answers to each of my points - I just hope the walls are flat after all this!

That F&B Paint is a little costly! I have read that their Eggshell finish veers towards the matt side - is this true? Do you know if they can mic up RAL7016 for me or do they only offer their stock colours?

@Porker - I have attached a pic of my current wallpaper that has matt paint on it - should I be OK just to apply Gripfill (if I use something like that) to the back of the boards & apply directly or should I rough the wallpaper up by scorching it & if so, how much?

As for keeping the panels in place while waiting for the Gripfill to dry - I was planning to use a number of 5mm dowels (as that is the gap I want between panels) - will they work OK? I do not have that gun you mentioned & would be a little scared to nail into a freshly painted surface just in case things go wrong.

@ RobinBHM - I will do as you say get a test panel done just in case. If I have some spare paint lying around, would it be a good idea just to apply a couple of coats at the back (to even/balance out the two top coats the front side will have)? If so, I guess it will not matter if the finish is not super smooth & that nice as they will be affixed to the walls anyway or am I wrong in assuming that?

I will definitely look into getting some of that tape you mentioned - I have enclosed some images of the number of panels (mainly 750mm x 370mm) - how much tape will I need & what size/width

@HOJ - Thanks for letting me know about those fixings - they look really great but if used as standard, I fear they might make the boards might protrude out a little too much. With the recesses cut into the boards would be far more preferable but I do not have the tools to do that (nor the experience) & I do not think the painter would either but just in case, per board, how many of these fixings would be needed? - I have 24 of them at W750mm x H370mm.

My worry is that my walls are the original plaster & lathe type & the plaster between the wooden lathe runs is now quite dry, brittle & powdery if broken/disturbed so I do I take it then the best way to deal with this is to possibly use Rawl Plugs to mount the back plate securely? The product video demo shows it being screwed into a solid wooden board but if I did that on my walls, there would be no grip at all!

Any idea of what it might cost for me to get someone to router those recesses for me for the 24 boards?

-----

At worst, at least I now know for sure thanks to all here that something like Gripfill will work well so I have that to fall back on! May I ask, how many tubes might be needed & how much should be applied to the back of the panel - does it just have to cover the whole area or just lines of it at regular intervals? I will get the MR-MDF for sure - thank you all for guiding me towards it - just need to find place that stocks it & can cut it for me accurately!

Baz!

 

[petermillard]

Hi All,

Many thanks for the great advice!

@Pete - Thanks for confirming Eggshell would be the best option - really gets rid of all the second guessing & doubts about all the various finishes for me! If you do manage to find out the name of the Grey Primer you use, please let me know & thanks for giving me answers to each of my points - I just hope the walls are flat after all this!

The other grey primer I'd used was the Rustins, and there's also a Dulux one I'd forgotten about.

That F&B Paint is a little costly! I have read that their Eggshell finish veers towards the matt side - is this true? Do you know if they can mic up RAL7016 for me or do they only offer their stock colours?

No, the older oil-based F&B eggshell was quite a Matt finish, but the currently available water-based eggshells are a nice mid-sheen - though as I mentioned further up, the small investment in a pot of paint to try it out could save you an expensive mistake, especially where personal preferences come into play. And they do stock colours only - though they do a *lot* of stock colours, and there are several very dark greys that may be suitable.

Good luck - let us know how it works out.

Pete

 

[HOJ]

original plaster & lathe type & the plaster between the wooden lathe runs is now quite dry, brittle & powdery if broken/disturbed

I fear what ever method you choose to fix with will be problematic with walls in this condition, may be worth considering a back board fixed to the existing wall, then fit the tiles to that.

With the Button fix you could use a Forstner bit to drill a recess for the the back plate, hole does not need to match the shape, you would need 2 per tile.

 

[porker]

original plaster & lathe type & the plaster between the wooden lathe runs is now quite dry, brittle & powdery if broken/disturbed

I fear what ever method you choose to fix with will be problematic with walls in this condition, may be worth considering a back board fixed to the existing wall, then fit the tiles to that.

With the Button fix you could use a Forstner bit to drill a recess for the the back plate, hole does not need to match the shape, you would need 2 per tile.

I agree, if you use a backboard you will be able to position accurately before fixing the whole thing to the wall and I think from the design it has to be spot on to get the full effect. To test adhesion I stuck a short block of wood on the wall where I knew I was going to cover. Once dry, if it pulls off too easily you need to rethink, if it is firm enough you should be OK.

 

[Baz]

Hi All,

Thanks for the info on the backboard - what is it exactly & where can I get it? Is it like a sheet of normal wood & how much of it would I need - just enough to cover the areas the screws/Button fixes would go
or would the whole area (say W1.5m x H2.4m) need to be covered?

How thick is it or what is the thinnest that I could use?

How is this bars applied onto the wall - by screws & rawl plugs or other? Is it reasonable in cost may I ask?

I searched everywhere for place that would cut MDF for me & it was a real challenge in my area - I eventually found place that did the MR-MDF & would cut the many pieces I needed but they only had the 18mm one so I bought that.

If you could be kind enough to provide me with some links to this backboard product that might be the correct one, I would be very grateful in case I get the wrong type!

Many Kind Thanks!

 

[Baz]

Hi All,

Was looking at the Button Fix website & it stated that they can, in some cases be mounted/attached in different ways to different materials such as plaster board & the type of fixings one can use - as i am not too technical & understanding of some terms, I wonder if you might clarify for me.

1) They state in some cases the button fix can be glued/bonded instead of screwed in - is that an option for my situation & will something like Gripfill do?

2) For Plasterboard, they state that one can use some "RAWL M5" Fixings - is this an option?

3) Not sure if I understand this correctly, but they seem to state that one can even just fix the buttons on directly on the wall (without the plastic guide?) & affix them with some "RAWL 4ALL" fixings? So, one just screws the buttons to the wall & the puts the plastic guide to the back of the panel (instead of the wall) & affixes it that way?

There seem to be two types of RAWL M5 Plugs - which would be better?

4) To make the "Stepped Recess" they recommend using their tool but I do not have it, nor the skills to use one but I do have access to the Forstner drill bits too make them but again, skill level might be a problem - is it something novice can do without too much to go wrong?

Forgive my ignorance & silly questions if any but I ask as I am seriously considering this option as recommended!

Many Kind Thanks!

 

[deema]

I think if I were doing the job, I would cut into the plaster and attach a 50mm wide by 25mm baton (planed square edge or PSE) across the top of the wall and one at the bottom and in the middle running horizontally. You will then be able to secure them fully to the actual wall and not have any issues with the plaster. It will also enable you to add a sheet of damp proof membrane between the wall and the MDF. The batons can be packed to enable you to flatten out the wall and over come any irregularities. I would be amazed if they were sufficiently flat for mounting the boards easily. With the battens mounted (I would use a few screws and also an adhesive to mount theme to the walls) you can then be confident you will have a nice flat surface onto which you can mount the boards. Run a bead of glue along each baton and then as suggested earlier a couple of small nails or brads to secure whilst it dries.

Removing the plaster will be a dirty job, and I would do it by hand rather than use an angle grinder. Mark out the outline of the batting, and the use a hammer and brick bolster to tap a line in the centre of where the baton will go. Then go back and tap along the edge of the line for the baton. The centre line creates somewhere for the plaster to move to when you tap on the baton line. If you don't the plaster will break anywhere. Be gentle, take your time and you should easily be able to remove the plaster between the two lines. As a first timer I would always recommend scoring the lines of the baton as deeply as possible with a Stanley knife before attacking with the brick bolster.