Wood Filler or Caulk?

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Hi, I have installed a number of new MDF architrave sets and need to fill some gaps at the corners (see photo). For these gaps, would 2 part wood filler or caulk be best? I also have some internal corners on skirting boards that could do with filling also. Would the same apply here? If Caulk, which is the best brand to go for? Cheers.
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Caulk and 1-part fillers invariably shrink, so 2-pack wood filler is always going to be a better option, providing you have a machine sander (it is nearly impossible to hand sand the stuff - very, very slow going). Good brands include Everbuild and Metolux, although you can actually get by with a 2-pack car body filler, which is much the same sort of stuff
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But I am left wondering why the gap at the mitre? Ideally you should have pushed the joint up tight and glued it together with a 2-part mitre adhesive (e.g Mitre Mate, Mitre Bond, etc), let that set (30 seconds or less), then nailed/pinned the architrave legs to the door casing (assuming you followed the traditional approach of fixing the head first). The judicious use of a sharp block plane can correct minor problems with the fit of a mitre joint
 
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Thanks. Do those two part fillers have any resistance to cracking? This is upstairs so wooden floors and stud walls. There is no noticeable movement but i can imagine over the years things will flex and shift etc.

As for the gaps, put simply i am a first time DIY'er so i am still learning the tricks and best ways of doing things. I have managed to get the gap round the door casing even all the way round and when filled and painted hopefully it will look half decent!!
 
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If you glued your architraves they shouldn't move. If they do move, then you have much bigger problems. Outside corner mitres on skirtings should also have been glued, if not then need to be cross pinned, so they can't move. Despite your concerns mitres rarely move if glued and properly fixed
 
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I seldom disagree with @JobAndKnock but with your existing mitre gap, I would use a "lightweight" filler such as Red Devil OneTime or Toupret RedLite rather than a two pack filler given that the gap is pretty small. He is a carpenter par excellence, I am a pretty good decorator.

I would however agree that the mitres should have been glued. You might benefit from pushing some PVA glue in to the gap (wiping away the excess). When dry, fill with the light weight filler (and not a tub of 1 part old school filler- or powdered filler that you add water to).

The light weight fillers do not shrink. Please be aware that the "regular" tubs of 1 part filler will shrink, as will the fillers that you mix with water (as @JobAndKnock said). A disadvantage of the lightweight fillers is that that they are very soft but they are ideal for tiny gaps (and pin holes). I normally sand them using 180 grit silicone carbide paper (the grey paper).

2 pack fillers do not shrink, but they are not flexible. If, for example, you were to fill a counter sunk 5mm screw hole in MDF skirting board, After a year or two, the filler will be pushed out by about 0.25(?) mm as the MDF expands and contracts. Regular (rubbish) 1 part fillers will possibly (almost) fall out after 10 years. The light weight filler will be the most forgiving but given the hole size it is the most difficult to sand flat without leaving a very, very, slight divot. If you had timber architraves, given the gap size, I would have used 2 pack filler, on the flat surfaces.

One major plus for the light weight filler is that you will be able to sand it (by hand) without cutting through the pre-primed finish on the MDF. It might sound silly but once you hit the brown of MDF, it takes quite a few coats to obliterate the colour change.

Where the architrave meets the plaster and door liner, I would use a decent caulk. My go to brand is Everbuild 125. I would however prime the door liner first with water based primer. If you don't you may find that the caulk will soak in a little bit to quickly and when you run a wet finger over it, the thinner (outer) edge may be slightly ragged (ie not smooth)

Personally, I hate painting pre-primed MDF architraves. The manufacturer routers them and then sprays waterbased paint on them without any consideration of the "grain" raising. If faced with your architrave I would expect to spend an hour trying to flatten the finish on the rounds/curves. If it were timber, 10 minutes. Sorry, not a criticism of you, I understand why people use MDF mouldings but if you want them painted to a high standard, it requires a lot more work than well machined timber.
 
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Good brands include Everbuild and Metolux, although you can actually get by with a 2-pack car body filler, which is much the same sort of stuff

I think I once used the Metolux (made by the same company that make the Timbabuild epoxy resins- Chemfix). It was rebranded as Leyland SDM- they, Leyland Specialist Decorator's Merchants are big here in west London- now owned by the Dublin based Grafton Group who also own Selco BM. I didn't like the stuff. It had a slightly tacky feel even after it had cured. To be fair once you start sanding it it isn't a problem. My go to 2 pack polyester filler is Easy 1 by Upol. I can purchase 3.5L for just over £20 via Ebay, etc. I find it a far more stable/reliable product. Most importantly, I can gauge when it is ready to sand. With the metolux stuff, because it still feels sticky, I wait longer (than I probably need to).

I have never seen the Everbuild stuff, probably because I have never looked for it, or because none of my west London suppliers sell it.
 
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Thanks for the advice on fillers. I'll bear that in mind, although I would point out that in general I make my mitres and splices as tight as I can so as to avoid the need of filler completely (often by the use of a block plane to fettle the joint), but that when I do fill stuff I lay it on with a very flexible stopping knife (with nice rounded corners) with which I get the filler into the joint with very little build above the surface. That way I minimise the amount of sanding required and I minimise the amount of sand-through that occurs. I had wondered about how good the Toupret filler with fibres in it was (and for that matter what it is now called)

As to Metolux, yes, it can feel a bit "sticky" once it has cured, but it does sand out reasonably well. One difference between you and me is that when I am going round doing this sort of work it's generally a bulk task with a large office, or a full apartment to deal with, so how long it takes for a 2-pack to set isn't much of an issue, providing it isn't more than an hour (and it rarely is, even in an unheated building in winter)

I would however agree that the mitres should have been glued. You might benefit from pushing some PVA glue in to the gap (wiping away the excess).
It might sound silly but once you hit the brown of MDF, it takes quite a few coats to obliterate the colour change.
I'm not so sure I'd bother with the PVA. Probably better to remove the legs, mitre glue them and then renail. Trying to squeeze a wee bit of PVA isn't going to prevent the mitre opening (a problem with softwoods but not with MDF), and in any case PVA really doesn't hold a mitre joint together all that well unless you can cramp it together for a while (which is what "mitre spring cramps" were created for)

I have never seen the Everbuild stuff, probably because I have never looked for it, or because none of my west London suppliers sell it.
Different wholesalers? Joinery firms rarely buy stuff from decorators outlets - and as a sub I often have to work with what I'm given! Metolux is a favourite (and sometimes specified by the architect) for sash window repairs. See comments above about curing times
 
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Personally I wouldn't use caulk for anything, it's a horrible material. Any place you might use caulk, filler or no-nails works better.
You use No Nails, a construction adhesive, in place of caulk? I had a lad do that on a job once - the decorators really kicked up a right old stink because they said it was a PIA to paint over (with water-based gloss - they had to resort to something like Zinnsser BIN to start with which was a waste of their time). In any case, it's a lot more expensive than deco caulk and doesn't smooth out as well. How do you use filler at the top of a skirting if there is a 2mm gap to the wall?
 
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You use No Nails, a construction adhesive, in place of caulk? I had a lad do that on a job once - the decorators really kicked up a right old stink because they said it was a PIA to paint over (with water-based gloss - they had to resort to something like Zinnsser BIN to start with which was a waste of their time). In any case, it's a lot more expensive than deco caulk and doesn't smooth out as well. How do you use filler at the top of a skirting if there is a 2mm gap to the wall?
True it does make a difference which kind of no nails you're using, some dry 'glossy', other matte (can be painted over). Since I have probably already used the no nails to stick the woodwork to the wall, the cost of smearing a bit in the gap is nothing.

Why would 2mm be a problem? Filler comes in caulking tubes, squeeze on and smooth with a finger, same as actual caulk.
 
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Why would 2mm be a problem? Filler comes in caulking tubes, squeeze on and smooth with a finger, same as actual caulk.
In thin layers it can crack if there is any movement (as you might see with softwood skirtings). Also, because of the density of most construction adhesives, it can be a problem to get a thin bead into a gap without ending up smearing it on the wood - the water-based adhesives like GripFil yellow do clean-up a lot better with a damp cloth, which is why they are handy on pre-finished skirtings (e.g. [pre-lacquered oak, vinyl-wraped MDF, etc).
 
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Personally I wouldn't use caulk for anything, it's a horrible material. Any place you might use caulk, filler or no-nails works better.
Next time glue all your mitres.

The last time that I had to paint over "no nails" (the waterbased Gripfil) the emulsion kept cracking. I had to hit it with shellac paint first.

On other occasions I have seen hairline cracks in the "no nails" before any paint was applied. When faced with that, I end up caulking over it.
 
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Thanks for the advice on fillers. I'll bear that in mind, although I would point out that in general I make my mitres and splices as tight as I can so as to avoid the need of filler completely (often by the use of a block plane to fettle the joint), but that when I do fill stuff I lay it on with a very flexible stopping knife (with nice rounded corners) with which I get the filler into the joint with very little build above the surface. That way I minimise the amount of sanding required and I minimise the amount of sand-through that occurs. I had wondered about how good the Toupret filler with fibres in it was (and for that matter what it is now called)

I would imagine that your mitres would be fine with paint fill and no filler.

There are two types of Toupret filler with fibres. I don't recall recommending either in this thread though. On my current job, the old Victorian horse hair plaster walls had been reskimmed at some point, there were loads of hairline cracks. I used a grout removing blade on my fein to open up the cracks, brushed in PVA and the gunned in some Toupret Fibacryl (it is the caulk with fibres in it). I then used Toupret TX110 ("rapid drying) filler over the top. Before discovering the Fibacryl I did once try the Toupret powered based filler with fibres in, it cracked after a few months (again a Victorian house).

BTW, I would only use Fibacryl as a product to filled over, not as a final filler. Like regular caulk, it shrinks.

I'm not so sure I'd bother with the PVA. Probably better to remove the legs, mitre glue them and then renail. Trying to squeeze a wee bit of PVA isn't going to prevent the mitre opening (a problem with softwoods but not with MDF), and in any case PVA really doesn't hold a mitre joint together all that well unless you can cramp it together for a while (which is what "mitre spring cramps" were created for)

Fair call.

Different wholesalers? Joinery firms rarely buy stuff from decorators outlets - and as a sub I often have to work with what I'm given! Metolux is a favourite (and sometimes specified by the architect) for sash window repairs. See comments above about curing times

I only buy my 2 pack fillers from decorators' merchants when desperate. Car spray (bodyworks stores) shops are typically 30 to 50% cheaper because of volumes of sales. I actually found the Metolux slightly more difficult to sand. From memory, It clogged my abrasives which is why I didn't buy it again. It is the stickiness of the initial sand that clogs the paper. I don't have that problem with Upol Easy 1 (2 part filler).

BTW, Chemfix also sell a 2K filler in a tube that doesn't require nozzles.


It too feels sticky until you start sanding it. I have only used it once, it too clogged my abrasives (more than my go to 2K fillers). I have only used it once though. Price wise is is extremely expensive per litre or kg. I like the Timbabuild epoxy resins but given that my local supplier now charges £40 per tube, I am hoping to try the Oxera stuff which seems to £25 (ex vat)

 
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I would imagine that your mitres would be fine with paint fill and no filler.
That's what I aim for - if only because the decos gripe so much if we don't deliver! (only kidding). The worst thing in the world is to walk round a job and see all the mitres grinning at you (i.e. they are open) because you know that there's a 50/50 chance that the decos won't fix it and it will reflect on your firm

Car spray (bodyworks stores) shops are typically 30 to 50% cheaper because of volumes of sales. I actually found the Metolux slightly more difficult to sand. From memory, It clogged my abrasives which is why I didn't buy it again. It is the stickiness of the initial sand that clogs the paper.
Are you using conventional abrasives (and if so are you using a stearated abrasive?) or a mesh abrasive like Abranet? I found it needs a stearated abrasive, but yes, it can clog
 
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Are you using conventional abrasives (and if so are you using a stearated abrasive?) or a mesh abrasive like Abranet? I found it needs a stearated abrasive, but yes, it can clog

I normally used the Festool Granat when trying to sand the Metolux.


I honestly don't know if it is stearated coated or not. I thought that coated versions were limited to silicone carbide papers. That said, I can see that the shedding of the stearated coating will provide the dust required to de-stickify the Metolux.
 

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