cellulose issue - need help

[raph.basan]

Morning all.

I'll get straight to the point.... we use a multitude of finishes for our frames, from staining to water guilding.
We also spray cellulose for a clean "clinical" feel to the frame. the finish we get with cellulose is fanastic, with one issue.
On about 70% of the frames we spray we get cracking of the paint in the mitres, we've sanded the paint back to the wood and the frame is not cracked, just the paint. our frames get joined with wedges and biscuits. we use Titebond III ultimate wood glue... we don't have the same problem when using a stain or gesso (well, i wont go into the gesso issues now...... another time maybe ).

has anyone here had similar problems or issues ? and if so.... any hints ?

i look forward to hearing your views....

Raphael

[gesso]

Hi you may find that there is more paint towards the corner (mitres) than along the rest of the frame thus there is a greater chance that the paint hasn't dried as thoroughly as elsewhere I know that if I use acrylic paints from a can, that if I need to sand some imperfections out exposing the underlying paint then respray over it, it is here that I get cracking and not on other areas that have not been sanded.

ps make sure your well protected from cell spay as not only will it get in your system through your lungs but also your skin.

Spaying gesso is also not recommended unless your suited up like a dirty bomb cleaneruper' plus the way it effects the gesso structurally wont win you any points down the line as the layers will start to flake due to the reduced temp when the gesso mixes with compressed air coming out of your gun.....If thats what your doing?

[raph.basan]

Yea, all suited and booted for the celly, and we only spray the gesso on in very urgent circumstances, we use the good old brush applied method all the time. when spraying gesso you dont get the consistency needed for guilding....
thanks for the warning regarding the celly, we have a well ventilated area and are suited and masked for the job......

R

[framejunkie]

I don't do the cellulose finishes as i find them very plasticcy and not to my liking. However i've had similar problems with the sanded gesso and sanded plaka finishes i use instead. I have ne idea why you are getting this problem with cellulose finishes, but not others.

The old-school method used by gilders is to glue cloth across the joint before painting, but you then have a lot to do to hide the edges of the pieces of cloth.
Personally for the painted finishes i use finger joints; keyed mitres; or tongued mitres. You can get an idea of these joints(and a bunch of others) here -

http://wgafurniture.lostlagoon.com/wood ... terms.html

The downside is that you need lots of woodworking kit, and know how to use it!

[gesso]

Dont think its the mitres that are opening up.
he said they have sandedwnthe paint and the joints are closed
it sounds to me like a coating issue.

What paint are you useing befor celly?

[raph.basan]

none, we cut and join the frame with wedges and biscuits, that then gets sanded to a smooth finish. we then use a thin 1st coat undercoat, sand that back (this is done 3 or 4 times) so in essence we have 3 to 4 coats of undercoat on, we then spray the celly on, wait for it to dry, spray again, repeated 3 to 4 times again....till we get a good finish. the frames look fantastic, but then....... it all goes pear shaped, well, not on all of them...
its really frustrating...


r

[gesso]

So whats cracking the undercoat or celly you dont say which undercoat your using?

[raph.basan]

sorry, was trying to sort something out....
the undercoat used for the celly is no12 pre cat primer white high build from mylands.....
it looks like both are cracking....

r

[gesso]

Is there anychance of posting a pic of the offending crack?

sounds like there is a certain amount of stress being introduced which may be caused by a the glue you are using .How long do you let the glue dry for before applying the first coats?

Before I apply coats to my closed frames I usually have them tightly clamped for two days to ensure the mitre is sealed and glue has completely dried

[prospero]

The only thing I can think of is the wood is swelling due to absorbing moisture from the atmos after the finish is applied, causing the rails to grow slightly lengthwise. The corner bond will remain sound, but maybe the paint finish is not expanding with the wood. It the back/rebate coated with anything? Maybe sealing this area would keep the wood more stable.

[gesso]

Firstly what wood are you using?
Am I right in thinking the 12 precat is a high build water based paint in this case what prospero Is saying may be right to a degree,
with a high build there will be a lot of absorption of the moisture into the frame if you then apply a cellulose based lac over the top though your precat is dry trapped water within the wooden sub will swell then shrink depending on the strength of your joint (which may explain the occasions when there are no cracks)

[raph.basan]

hi again, pic not possible today, camera at home, phone camera not good enough.
as far as drying times for glue is concerned, the frames usually have about 1 week before we start sanding them as we usually cut and join about 2 weeks ahead.... some of the offending frames have had longer.....

i'm going to try sealing the frame first, i've had a chat to the rep from mylands, he's suggested that we put a thin coat of undercoat on, then sand it back completely, then carry on as normal, i think this would in effect seal it ? we'll see.... i need to get this sorted, its driving us all slightly mad......

[raph.basan]

90% of the time the offending wood is tulip. we don't spray any other woods as the finish is not that great.....

[prospero]

What sort of profiles are you using Raph? If you could get hold of some ready-compoed stuff in a similar shape, you may find it sprays better. I say this as at one time I used to buy the good old 1/2" black cushion and spray it with cat touch-up cans. (Thus saving having to stock lots of different colours and nice neat corners). I'm not saying it works on top of all finishes, but I think most will take spray paint very well. In fact, the cheaper and nastier the finish the better.
The thinners seems to etch the paint into the surface.

[framejunkie]

The only thing I can think of is the wood is swelling due to absorbing moisture from the atmos after the finish is applied

Tulip can be a pain with solvents. A couple of times I've sanded out a dent in tulip, then used spirit stain and found that the area where the wood fibres were compressed is now proud of the the rest of the surface. Now i don't sand the dents out until i've lifted the dent with 3 applications of meths. Given that less agressive organic solvents can swell tulip fibres, i reckon its the cellulose that's causing this - elongating the fibres after the surface of the film has dried.

Its a theory anyway

[raph.basan]

hmmmm,

this won't be the first time that tulip has caused us hassles...... it does seem to warp quite quickly as well....

i need to sit down over the weekend (over a few beers ) and think this one out.....
there seem to be a few factors worth pondering...


r

[raph.basan]

Ok, back to where we started....
I've been doing a bit of research on the net, and seem to have more answers than i had questions....
it seems that celly reacts to everything... our finishers have always blamed it on the joining... now, i'm doing the joining and have taken offence to that... it now seems that it is not a joining issue, well, i know its not as we've sanded back a few of the offending frames and have found no opening on the mitre... ok, on some of them it had been a case of the mitres opening, we sort of solved that issue by using biscuits near the top of the profile, about 3/4mm under the face of the frame, that seems to have stopped the mitres opening, but as you know we still have problems with the paint cracking... now, today, the same frame that we had an issue with yesterday has offered us another problem.... where we have the biscuits in the frame we've had to fill a few small cracks, the biscuit machine i'm using has a very slight "wobble" (technical term ) wich every now and again causes the cut to be slightly bigger than i want it to be, so, we glue the biscuit in place, once its dried we cut and then chisel it back then fill where necessary with U-POL, we only use U-POL on the frames we're going to spray with either 2 pack or celly, now, where we've used the U-POL on the corner we have swelling and cracking of the celly... i did read last night that celly can react to a bad song on the radio...and it does react badly to many chemicals... so, i'm one step further to solving this problem.... i will keep you updated as i get more info on this... thanks for all your help and suggestions so far.... I am also looking at the moisture content issue with regards to tulip.... we do have a lot of issues with our tulip, just today i unpacked and entire delivery of tulip that is all so warped i have to send it back... this seems to be happening more and more our suppliers told me last year that their wood is within the specified moisture content range.... but thats another issue for another day, warped wood..... what do you do ?

thanks so far guys...

have a great weekend.

Raph

[framejunkie]

... I am also looking at the moisture content issue with regards to tulip.... we do have a lot of issues with our tulip, just today i unpacked and entire delivery of tulip that is all so warped i have to send it back... this seems to be happening more and more our suppliers told me last year that their wood is within the specified moisture content range....

Yes tulip is cheaper than other temperate hardwoods - and there are obvious reasons why

For most painted finishes i use beech where practicable - its hard, no grain to fill, seems to behave with solvents. Takes a small bite out of my margin, but in the end i save a little time through not having to rectify tulip-related issues

What wood do others use for painted finishes? I'm interested to find out as i'm convinced that my decision not to use any tropical hardwoods is contributing to my poverty.

[raph.basan]

good question........

we primarily use tulip and have endless issues..... and we use it a lot !!!!

r

[prospero]

Raph. Just a couple of thoughts.....

Not familiar with U-POL. It's a 2-part system is it not?
Just set me thinking that some glues set quickly, but take days to fully cure and they can 'move about' while doing this. I know that Araldite can open a joint if it is not tightly clamped while curing. So while the bond may be sound, it may have moved slightly. This would account for a hairline crack in the paint.

Also, biscuits are designed to swell in the slots to give a stong joint. If they swell thicknesswise, it follows that they will also swell laterally. Having said that, I use biscuits all the time and never had a problem. I do always use PVA glue with them though.