The Framers Forum

If like me, you cut your inner mount slightly smaller than the outer mount - use some PVA as well - more permanent.

Below is a quote from this link on TFG


"The issue is that the top mat layer, in direct contact with glazing, is the one most reactive to temperature changes, so it expands & contracts more and faster than mat layers below it. The difference of expansion & contraction imposes a sliding force on the surfaces.

ATG alone may flow under that kind of force. So, if ATG is used on four sides of a mat, only the strongest of those bonds may hold. A mat may expand in an unpredictable direction (up, down, or sideways) and then, in contraction, re-stick in a different position. Thus, the margins on top, bottom, and sides may shift over time.

Hard-setting glue will not flow and holds securely, preventing that movement.

Many of us notice unequal accent mat margins in framing and assume the assembly was just sloppy. But I KNOW the mats on the photos in my bedroom had equal margins originally. Now, instead of 1/4" all around, the margins are more like 5/16" on one side and 3/16" on the other. I've never actually witnessed mat creep as it happens, but this is my theory"

Roboframer wrote:If like me, you cut your inner mount slightly smaller than the outer mount

Having always used PVA between mount layers, this fascinating slippage issue does nor concern me. However, the above comment has me intrigued.

When cutting a double mount to size, I have always paired up the two sheets and cut them together as one. So top and bottom layer have identical outer dimensions.

Until Robo's comment, the thought of making the bottom layer smaller has never crossed my mind. Try as I might, I can't think of a reason for going to this extra effort.

And without a bit of packing, doesn't this differential in size give the back a tendency to bow out?

Yes John,
The quote by Roboframer has me intrigued as well.
We see it time and again on reworks. The inner mount being smaller than the outer.

Surely if both mounts were cut to the same size, then effectively you would not need any type of adhesive/fixative between the mounts.

As long as the bottom of the mounts are resting on the frame then gravity will take care that there is no slippage at all.

Having thought about it a bit more, I can see that by reducing the size by the width of the bottom mount reveal, you would not have to move the width stop on your (straight)mountcutter, however that would seem like a lot of trouble to go to to save having to adjust one of the three stops. And then having to, possibly, pack to prevent the back from bowing - doesn't make sense.

OK - with a manual cutter if you cut both mounts the exact same size, you have to cut the top mount aperture, replace the fallout (for use as a slip mat for the bottom mount) and then line up the bottom mount perfectly on top of the top mount and atg it in place, if it is not lined up perfectly then you cannot use start and end of cut stops accurately on the top mount - which is now your guide for the cut on the bottom mount - it can be done of course, but it's time, a slight difference in size leaves a bit of room for error and is far quicker

With a CMC cutting both boards together this isn't an issue?

John wrote:
And without a bit of packing, doesn't this differential in size give the back a tendency to bow out?

No, because the difference I use is 1/8" - so 1/16" all round - it's still within the lip of the frame.

Merlin Framers wrote:
As long as the bottom of the mounts are resting on the frame then gravity will take care that there is no slippage at all.

Really? Nothing should fit the frame so perfectly snug that you have to squeeze/force it all in. There is always SOME play in every component. Fix the mounts together and they will move together - don't and they COULD move individually.

John wrote:Having thought about it a bit more, I can see that by reducing the size by the width of the bottom mount reveal, you would not have to move the width stop on your (straight)mountcutter.

I think I know what you mean there John - are you assuming each mount is cut individually and then lined up & put together afterwards?

That's not how I do it - the method above is far more accurate and much quicker. Also how Richard Clark demonstrates.

General theory of cutting inner mount board smaller is that you always cut from the original top mount edge - thus guaranteeing that even if the board is slightly out of square - the edges are constant. However, CMCs cut all boards to same size.

I always use ATG to keep them in place - atg does like a bit of pressure to make it stick properly and I would imagine the biggest problem with mounts moving is down to poor adhesion because of bad application, rather than the adhesive flowing.

Anything self adhesive is more effective if burnished on - that's easy on say a print, where you can actually burnish the tape itself, you can't burnish DS tape directly. Plus DS tape is more sticky on the side that is applied and can give up after time. I've had many double mounts in that have slipped - a bit of PVA would have saved the customer some expense.

You apply pressure with the tape gun when applying, so that's that side taken care of, but the other, less sticky side can be the problem - you have to apply pressure through a thick mountboard.

It's PVA that does it for me - peace of mind - the DS tape is only there really to save me having to wait for the PVA to go off - oh and to prevent movement when cutting of course.

Framing Norah wrote:Is it a coincidence? We also have the rule that the short sides go to to the right.

Also, we only apply glue to the short sides.

I wonder, is this universal within the trade?

funny that, we do the same Long to the Left and glue both ends of the pile on the right

Following the comments about D/S tape between double mounts, my own experience of adhesive transfer tape has not convinced me that it is a good as we assume. As a consequence I've stopped using it completely, but I still use finger lift tape on mass production type stuff for the grockles, etc.

Having said that, I don't think finger-lift is all that fantastic either. I am fortunate to have local to me a packaging company run by a guy who really knows about adhesive tapes. We have a variety of different double sided tapes in different widths for different uses. Considering how little tape you use to fix two mounts together, the extra cost of using a really top quality/high performance tape is not worth saving, when you weigh up the benefits.

Both ATG and finger-lift a classed as medium grab. If you can't burnish it down, because it's between two sheets of mountboard, then medium grab falls well short of what's needed in my opinion. Some of my D/S tapes with tear away the surface fibres of wood if you try to remove them from wood. It worth talking to your local adhesive tape specialist/stockest.

A good objective is that the bond should be at least as strong as the materials used, should have a good specified temperature range and be possible to remove by softening the adhesive with suitable application of heat.

Most of these tapes employ an acrylic hot melt adhesive, but I also have one which employs a synthetic rubber based adhesive. This one is quite definately not conservation freindly, but I like to have something which can get you of of trouble when all else fails. Of course you can't use it for many situations, but it can help in object framing constructional problems.

we at work use a smaller back piece of mount as althought it isnt very buisness like but cost efficent, we use the left over bits of mount and stick them to the back, saves having to cut double the amount of card. Also when you go to cut mount out of a piece of large card and it only gets one large part to a sheet the smaller part can be used as the back. Bowing doesnt tend to take place much as it is very little distance.

I agree with Mark and use John’s method of a slightly smaller under mat for two reasons:

In our experience, full sheets of mat board from the factory are never exactly square (i.e. adjacent sides are not quite perpendicular), so, trimming the top and bottom mats at the same time may result in two slightly different parallelograms and, once they are attached, the reveal might be slightly off.

By using John’s method, once you PVA or ATG the smaller under mat to the top mat, you will be using the top mat against the mat cutter guide a second time. This assures that the reveal will be exactly parallel and exactly equidistant.

And, it is more forgiving to plop a smaller piece of mat board onto a larger, underlying piece than to try to align two mats of the same size.

So there!

Thanks for clearing that up.

Seems to be a perfectly cromulent method of mountcutting.

Hold on, John, time out … cromulent?

I know I don’t speak the Queen’s proper English, but that’s gotta be a pretend, made up word like brilig or lorry!

You gonna make me go back to the ultimate authority, “Alice through the Looking Glass”?

Cromulent, indeed!

Rowlbazzle!

It's pure American Bill.


Can Litchfield be that far removed from Springfield?

Bill Henry wrote:Hold on, John, time out … cromulent?

I know I don’t speak the Queen’s proper English, but that’s gotta be a pretend, made up word like brilig or lorry!

Hey Bill......what about "bespoke"? You'll find that one all over the place here and it makes me smile every time I read it. Us colonials don't use that one either!
It's one of the silliest sounding words I've heard! A picture of a part on a bicycle pops into my head! Hey that would make a great logo for a custom framer in England......a bee and a bicycle spoke in a frame!!!

Well, that's two people who have had their vocabulary embiggened!

Not your average framer wrote: but I still use finger lift tape on mass production type stuff for the grockles, etc.

I just noticed a couple more here - "finger lift tape" - what on earth is that?
"grockles" - what on earth is that?

Please "embiggen" my vocab a little more!

You guys are just going to have to stop inventing silly words or I'm just going to have to start to speak in "strine"! So there!

"Grockle" = mildly derogative term for a tourist in parts of S England.

"Finger lift tape" Is a double sided tape which has the release paper fractionally wider than the adhesive to ease separation from it.